IC9700 again

I have been busy remeasuring the reciprocal mixing dynamic range (RMDR) of the IC9700 receiver on 2m and 70cm.

Recent measurements have shown that the IC9700 has an RMDR of well over 90dB on both 2m and 70cm at close spacing (~10kHz) and even better further out.

This is a key measurement of a receiver’s dynamic range and is critically dependent on the local oscillator. Conventional superhet architecture receivers can be particularly bad. The fixed LO (clock) of an SDR receiver makes the design of ‘quiet’ local oscillators much easier than with an LOnthat must be tuneable as in VFO.

Older superhet receivers have typically given a RMDR in the 70dB range. More recent designs have improved this into the 90s and even as high as 115dB. However, this performance comes at a price. The SDR direct sampling  receiver can achieve high levels of RMDR at a much more acceptable price.

I will be presenting my measurements and those of a number of well-known experts at the RSGB Convention in October.

Sam

4m noise

4m has always been  noisy here.

Using the arrangment in the previous blog, but on my IC7300, i was able to measure the noise level around my antenna.

In the worst direction (towards the house) the noise rose 18dB over the quietest direction. Not good!

I need to investigate what is producing that noise increase.

Now to repeat the measurement on the other  bands  covered.

Sam

Measuring noise using the IC9700

No, I didn’t get on the moon on 6cm for the Apollo EME commemorative event. Chesty cold knocked me for six. Just recovering. Courtesy of our  vistors from Australia........l

It did allow me time to consider how I could make continuum noise measurements using the IC9700 (on 23cm) when it doesn’t have an IF output in the usual sense. One thought was to try and use the 12kHz IQ IF output, but I failed to find any information on this or how it could be used with existing SDR software. I know it can be done.

I had played with using my SDR-IQ at audio (it goes down to 500Hz) to measure noise power in a defined bandwidth using Spectravue running on the SDR-IQ. This worked well, but I was not happy with the amount of amplitude ‘jitter’ on the trace.

I managed to find  a working HP3400 true RMS voltmeter at Friedrishshafen, to do the same measurement with a ‘proper voltmeter’!. Again flicker, because of the nature of noise and the restricted bandwidth, made this unsatisfactory.

Finally, I set up the IC9700 as a soundcard input to Spectravue (no SDR-IQ) and selected continuum mode. With a moderate amount of FFT and smoothing the trace is as stable as it was using the SDR-IQ on the K3 8.215MHz IF output. Not only, but the results agree very well with those previous  IF measurements.

Now I CAN use the IC9700 for EME noise measurements!

Sam

Apollo commemoration - 6cm EME

Some of you may be aware Dean, VK6DSL, is working to get the 28 metre diameter dish at Gnangara, Western Australia, operational on 5.7 GHz EME to commemorate the Apollo 11 moon landings. Brian, G4NNS has been working to get Goonhilly GHY6 on air as GB6GHY as part of the celebration.

I thought it might be nice to try and get my 6cm EME system back on air to try and work them both. I haven’t used the 6cm system for about a year. As the local oscillator was not stabilised and the DB6NT MKU57 G2 transverter was located close to the dual (combined) power amplifier, if suffered badly from frequency drift due to heat. I never quite got round to modifying it for an external high stability LO source.

I viewed the new MKU57 G4 on the Kuhne Electronics stand at Friedrichshafen, last month, and decided I would buy one, especially as there was a small discount. 

To help things along I had been asked if I was prepared to sell my G2 and even my old G1. Of course!

The G4 has an external 10MHz reference input as well as a good internal TCXO. This should give me the frequency stability that I require. Doppler is bad enough to track without having to adjust for thermal drift as well.

I have decided fo locate the G4 away from the PA and LNA. That probably means at the back of the dish. That has several advantages.removing the transverter from that heat source and reducing the weight of the feedpoint equipment because I can also remove the control box and sequencer from the feedpoint.

Two low loss coaxial cables will connect the feedpoint PA/LNA/feedhorn. Both the high gain of the PA and the reasonable gain of the LNA  (a DB6NT LNA  - I don’t make one for 6cm) will enable me to run this arrangement with negligible receive system sensitivity loss and no transmit power loss.

One of the shortcomings of my previous arrangement was that the SSPA relied on simple conduction cooling to the aluminium frame at the feedpoint. Whilst this never led to any failures of the PA, a better cooling arrangement was a definite requirement.

With the transverter removed from the RF feedpoint frame I am now able to fit a 12V fan to blow air between the two PA modules that comprise the dual balanced amplifier. I found in test that I could increase airflow by cascading two identical 12v fans, one blowing into the other. In this arrangement the two fans tend to synchronise and definitely increase airflow. Whether it is twice a single fan is still unknown.....but it’s more than a single fan.

Sam

IC9700 v1.11 firmware upgrade. Updated from previous blog

First a bit of advertising.

My review of the IC9700 is in the current issue of Practical Wireless, out today, for those of us without a subscription.

Having now upgraded to V1.11 firmware, in order to improve the reference stability, here are my observations.

By now the IC9700 reference oscillator stability is a well-known problem. In fact, for most users of CW, SSB and FM, the stability is a non-issue. It is only with the narrow digital modes that the stability problem shows. It seems to be associated with poor thermal control around the 49.xMHz reference TCXO.

The cooling fan comes on on transmit only. It does not run continuously. Not only that, but it only comes on when required on transmit. When it does come on it causes a small, but noticeable drift in frequency. Without the fan coming on, drift is much less noticeable.

On 2m it is hardly noticeable, even on FT8. It is more noticeable on 70cm and definitely noticeable on 23cm, although not really a big problem using JT65C on 23cm, compared to many other rigs.

Several ‘fixes’ have been proposed, including causing the fan to run continously, albeit at half speed; full reference locking using an add-on board and the possibility of a firmware upgrade to implement a locking system in the internal FPGA.

As designed, the external reference 10MHz input is little better than a modern version of a crystal calibrator. A facility is provided to automate the calibration of the internal reference against the external reference input. Once calibrated in this way, the internal reference is once again free to ‘drift’,  controlled only by the TCXO function.

Version 1.06 firmware improved on the correction algorithm and did make a big difference. The IC9700 is able to achieve a frequency accuracy only dreamed of in rigs like the TS2000x without frequency locking mods.

With firmware v1.10 and now V1.11the reference is periodically corrected, once invoked, and now works much like the system used in, e.g. the K3.

However, the period is possibly a little long as there is still a noticeable shortbterm drift under some conditions. I can see some further work, to refine the process, may yet be forthcoming from ICOM.

So, how well does V1.11 work to stabilise the reference oscillator?

On 2m FT8 I could see no change in frequency between transmit and receive, fan operating or not. Well, maybe a Hz!

FT8 on 70cm barely showed showed any change. Certainly not enough to cause any problems.

As FT8 is not recommended on 23cm, I didn’t bother to check for change with these short, 15 second, transmit/receive periods. However, JT65 uses a 47second transmit period followed by a 1minute, 13 second receive period. This puts a much bigger strain on the thermal characteristics of the reference oscillator and drift, even with the wider spaced tones of JT65C, was previous noticed with drift exceeding 20Hz when coming back to receive after the 47 second transmit period. This is important as any difference in the tone frequency from the expected frequency leads to a small but definite degradation in sensitivity. Keeping the tones where they should be gives the highest sensitivity.

So does V1.11 improve the situation at 23cm.

Basically, yes. 

To test the drift I set up one of my signal generators to produce a very weak reference carrier signal about 2.4kHz above the dial frequency I had chosen for my JT65C tests (into a summy load). This carrier produced a nice, straight, line on Spectran. The span on Spectran was set to show just a few hundred Hz either side of the tone. A drift of 10Hz was quite noticeable at this setting.

WSJT-X was then set to give repeated CQ calls of 47 secs on followed by the receive 1minute 13 second od receive, during which the 2.4kHz tone could be seen and measured. This was done at maximum 23cm output power (100% or 10W). 

As the signal generator was GPS displine-locked the frequency of the test carrier was very stable.

On test the tone frequency was always within a few Hz of 2.4KHz when returning to receive. It would then wander up to a peak of about 10Hz HF (2.410kHz) over the first few seconds, returning close to 2.40kHz reasonably quickly. Sometimes overshooting to a few Hz below 2.40kHz.

This happened each tx/rx cycle (over) although the peak excursion didn’t always reach 10Hz and averaged about 5-8Hz.

Although not yet perfect, this is a big improvement over the v1.05, v1.06 and v1.10 firmware.

I would expect a further improvement with a refined version of the firmware.

I am quite happy with this result. It would be interesting to do this level of testing with a few of the other transceivers covering 2,70 and 23cm!

I know from experience that the TS2000x drifted about 50Hz between transmit and receive on 23cm JT65C, before doing the fan-always-on mod.

This suggests that it might be worth still doing this mod to the IC9700 to keep the fan turning all the time, as when run at low power on 23cm (1.5W) the fan rarely comes on and drift was noticeably less in these tests.

More testing to do!

Sam

QO100 portable receive system

It is our local club(s) rally on Sunday. ESWR has been running for many years and is the product of several local  clubs.

I seem to have been given the job of organising the UKuG guest interest group stand. I’m a bit surprised as I am no longer the Group Chairman and not even on the Committee this year. However..........

I have asked Jason, G7OCD, to bring his portable QO100 uplink system that he has demonstrated at several local clubs. To save effort his demos have usually used the web SDR, located at Goonhilly, for receive.

I felt it more appropriate that we demonstrate a ‘real’ portable downlink at ESWR. To that end I have been  busy.

Earlier this year I bought a portable ‘caravan’ satellite dish and stand. The dish is an offset 45cm steel unit and fits to the tripod stand. Instead of the original low quality, low cost, LNB, I decided to use a Gooby LNB (£5.60 each on Amazon). These are 25MHz crystal controlled PLL LNBs.

Obviously, the crystal in the PLL is of insufficient quality to provide good stability when mounted out in the open on the dish.

I decided not to use an external 25MHz reference, like I use in my home station satellite system. Instead I decided to try the beacon locking system now incorpoated in several pieces of software. I decided to use SDR Console v3.0.9

My initial attempts to run this version of SDR Console on my now elderly Sony Vaio laptop resulted in the program freezing, so I was starting to think about running unlocked after all. Sunday is getting close.

This evening I decided to try the program one last time and to my surprise and delight, it worked first time. I still don’t know what I was doing wrong previously.

With SDR Console I select ‘geostationary beacon’, then follow the instructions and the software locks on to the PSK beacon and stays there when I tune away to listen to stations. It is not foolproof and does still show some drift, although none of any consquence in the time I was listening. Some of the drift may also have been due to the reference in the RSP2Pro SDR I was using at 739MHz, also contributing to drift. Inam goingbto check that my locking the RSR2pro usingbits external reference input.

.

My laptop drives the RSP2Pro and supplies its voltage via the USB socket. The Gooby is powered from a portable 12v 12000mA/h lithium pack (Lidl) and seems quite happy. I use a protected-against-short bias tee to supply the LNB over a single coax.

Now, I hope, with Jason supplying the 2.4GHz uplink, we will have a working 10GHz downlink to complement it to show rally visitors all about QO100.

The gazebo and table and chairs are being provided by other local  club members, so I don’t need to worry about them!

73 de Sam

G3JVL

I was sorry to receive the news that Mike, G3JVL, has passed away.

I first met Mike back in the 1970s at the Crawley Court, Winchester, Microwave Round tables.

Subsequently, I joined the RSGB Microwave Committe back in the 1980s and Mike was afellow member.

We had a lot of dialogue during those years, Mike made me a 2.3GHz quad loop yagi that I used for many years and then in the 1990s I visited with him and saw his home station. From that I was loaned a small (2.5W) TWTA that I used in my home 3cm station. I had never seen a TWTA with only three (or was it 4?) connections previously. Mike showed me how to use it and I had many long distance QSOs on 3cm,  not only with Mike, but also with many of the other 10GHz narrowband home and portable stations that were around during the 1990s.

I later met Mike, again, when we were both attending the Plano, Texas, Microwave update. I think that was around 2000. Mike was visiting with his daughter who, I recall, lived local in the Plano area of Texas. 

I don’t think I ever saw Mike again. I am sure he continued active to be active on the bands,  but our paths never crossed again. Ioften wondered what he was up to.

I guess I will never know,  now.

Vale Mike.

23cm on the IC9700

I have been busy bringing my IC9700 on-line in place of my 23cm transverter based system.

It is not that straightforward. One of the problems is that the radio is on my operating desk whilst the linear is in the rack. They are either side of a door, so the cable route between them  is about 3m, at shortest. I do have coax and control cables running between the desk and rack. But, it is impractical to run large, low loss cables, so with Ecoflex cable the 10W from the IC9700 is not enough to drive my 200W SSPA to anywhere near full output. In fact just to 80W output. My answer?

I have a now rather elderly twin brick M57763 amplifier with about  30W output, when driven at 400mW. I have turned down the IC9700 to about 5 to 6W output, drive the cable to the twin brick, situated in the rack next to the 200W SSPA and then use a 12V coax relay to separate transmit and receive path. I have a 6dB/10W SMA attenuator in the twin brick input to bring the input down to about 250mW (don’t forget the cable loss). With this arrangement I can drive the main amplifier to around  150-180W output and I have some power control by turning down the IC9700 when required.

I’ve still got to tidy up the cabling, reset power levels and then connect to the dish antenna.

BTW, there’s a lovely bright, near full, moon out there this evening, but it is low in the sky.

Sam

IC9700 progress

I have been conducting more tests on the radio and talking to a number of more experienced RF engineers to get a better ‘handle’ on the transceiver’s performance. I’ve also been using it extensively on air on the three bands during contests, using satellite mode, D Star and FM on repeaters and giving FT8 a good airing on 2m.

My user review for PW is nearly complete and I’m awaiting feedback on the draft from the editor.

I will comment further on some other measurements done on the transceiver a bit later.

Regard this as a place holder!

Sam

RSGB PSC meeting

Just back from an RSGB PSC (propagation studies committee) meeting in Leicester. Just a corresponding memeber, but try to get to one meeting a year. Very enjoyable. Great committee. Serious discussions.

More IC9700 learning

I spent some time on Saturday talking to local SDR/DSP experts and as a result have a much better idea of how the IC9700 works.

I am on a steep learning curve!

I hope to publish my thoughts on this in my blog in due course.

More 9700

No measurements today. I have been reflecting in some of these numbers and measurement techniques.

NPR would be a much better way to test the SDR architecture, but the appropriate filters are not available to me. I used to do NPR measurements on microwave link equipment, so I am familiar with the technique.

I had a first contact using the IC9700 this evening.  Admittedly it was ising the 9700 only on receive on the QO100 satellite. As much as I would have loved to use the transmit side for the uplink, I could not find an 8 pin DIN to connect up the SEND output to drive the transverter and PA, so I had to connect up the FT847 for transmit.

My contact was with G7OCD. Jason was using a Lime  Mini for transmit and receive.

IC9700 part 2. Some numbers

I spent all afternoon re-testing and confirming measurements on the receiver sections of the IC9700.

 My measurement of noise figure are based on the Y factor method, using HP noise heads with known and well characterised ENR.

Noise power measurement at the receiver output used Moetronics Spectravue Continuum mode running on a Lenova desktop PC and SDR-IQ.

This Y factor technique is well known, although the use of the SDR-IQ to measure the resulting noise output is possibly a little unusual.

Like all these measurements, there are uncertainties in the measured values due to assumptions, rounding and the tolerance of out-of-cal test gear. The values given here are best efforts to get it right, but no guarantee is given as to accuracy.

Noise figure

Noise figure at 292k ambient.

144MHz 

Preamp on   preamp off

4.2dB          17.3db

432MHz

Preamp on   Preamp off

4.8dB          15.9dB

1296MHz

Preamp on   Preamp off

4.8dB          8.7dB

A low ENR HP346A was used for the preamp on and an HP346C for the preamp off  (higher ENR required for 144 and 432MHz)

High noise figure is expected with the direct sampling technique, without preamplification, as used in the IC9700 

The 1296MHz down conversion arrangement loses some of the direct sampling advantage but does allow a lower noise figure. The preamp is still worth switching in, however, but does not have such a profound effect as on the lower two bands.

On-air listening tests and signal generator tests seem to confirm that these numbers are not far out. 144MHz, without the preamp switched in, is particularly deaf, but quite acceptable with preamp on.

Spurious free dynamic range

144MHz only so far

Two tone dynamic range

Using two very low phase noise test oscillators

The two oscillators are combined in a high isolation combiner and then well attenuated.

Applied at the receiver input, the levels were adjusted to give a third order product at the receiver noise floor.

The test was done with the preamp on and repeated with it off.

The IP+ was then used to test its effect.

Preamp on

89dB at 20kHz tone spacing. I don’t have any low phase noise oscillators at 2kHz spacing

Frequencies 144.100 and 144.120MHz 

Preamp off

91.7dB at 20kHz tone spacing. Same test frequencies. 

I found that IP+ was only effective with preamp on. The dynamic range was not changed, only shifted upwards. However, the noise floor increased by 3dB. This was as expected.

This form of dynamic range test, with a direct sampling SDR receiver, can give misleading results as an SDR does not follow the usual rules for third order intermodulation. It is possible that the third order product may approach the noise floor level at some lower levels of two tome input, dropping away again as the tone levels are increased. The quoted levels were found without difficulty but I cannot be sure that one or more lower levels may have been missed. IP+ helps to overcome this problem by introducing noise as a ‘dither’ signal. As I don’t have the IC9700 service manual and schematics I cannot be sure this is the technique that ICOM used. The 3dB shift of dynamic range (only a shift of position, not an increase in dynamic range) when IP+ is on suggests that the  -89dB figure is not that far off.

S meter calibration

As you would expect of an SDR based receiver the S meter calibration is fairly good. 

Each S point is 3dB and above S9 each 10dB measures 10dB!

Preamp on 

S9 = -95dBm

Preamp off

S9 = -84dBm

If  an 11dB (approximate) gain preamp is used on 144MHz then  if the noise figure of that preamp was about 0.8dB, the overall preamp on and off noise figures are about right.

I still need to test on 432MHz and 1296MHz

These measurements are my copyright. If you want to quote them, please acknowledge this blog.

I offer no guarantee as to the accuracy of the measurements. They are best effort and may be amended following further testing.

IC9700 noise figures part 1

Now I am a little more familiar with the rig and have updated to v1.06 firmware I have at last started to make measurements on this much-anticipated transceiver.

The first measurements made are the receiver noise figure. Unlike preamps and transverters, transceivers don't usually have an RF out from their receiver, so that noise figure/gain analysers like the HP8970 can’t be used to measure sensitivity. The analyser receiver section doesn’t usually go down to audio.

The more usual way to measure receiver sensitivity is to measure MDS (minimum discernible signal  or minimum detectable signal). This can be a very misleading name as when measured, as MDS is defined, the signal is usually most definitely still discernible!

The accepted definition for MDS is when an applied signal power equals the receiver noise floor in whatever bandwidth is selected  (usually 2.7kHz for SSB and 500Hz for CW).  There are two problems here.

First, the signal level must be measured for its true noise power. This requires a true RMS voltmeter. This should preferably be an analogue (moving coil) meter rather than a digital meter, since the nature of noise is such that when measured in these relatively small bandwidths the digital display will be flickering all over the place, unless well damped, and this can lead to other errors. You are measuring a sine wave signal against band limited noise. Never an easy thing to do when the signal is close in level to the noise.

The second problem is that the signal generator must be well screened and preferably a very low minimum output level. It is usual to operate the signal generator a little above its minimum level to improve screening, however, in order to minimise poor screening effects. As the required signal levels will most likely be in the range -130 to -140dBm, the generator is often set at about -90dBm and then an additional 40dB of in-line fixed attenuators plus  an 11dB step attenuator used to reach the low level required. The step attenuator is used to exactly set the signal generator signal into the receiver so that the meter shows a rise in level, over no signal, of exactly 3dB, indicating that the signal power is at the same level as the receiver noise floor. The definition of MDS.

This method can be quite accurate and repeatable, but often is not so due to less than perfect screening in the signal generator, uncertainty in the fixed and step attenuator calibration and coax cable leakage. Double screened coaxial leads are most definitely required.

For these reasons I am a little sceptical about some published MDS results and decided I wanted a better way to measure the sensitivity of the IC9700 receivers on each of its three bands.

Since I have an HP346A (5dB ENR) noise head I thought it would be interesting to use the Y factor method of measurement.

The well specified, low level, noise output from an HP346A noise head can be used instead of a signal generator to measure the complete receiver noise figure from RF input to audio output.  

Just one problem. How to measure the audio power and overcome the noise flicker?

My solution is to use my SDR-IQ, as it can be used down to 500Hz, to effectively replace the receiver section of the HP8970 noise figure meter, and then measure both the noise power from the receiver with no input and with the noise head switched on and producing the excess noise. The ratio of these two noise powers is the Y factor and it is easily converted to indicate the noise figure of the receiver.  The switching on and off of the noise head is done manually as described below.

 It is important to ensure that the SDR-IQ range is set a bit bigher than the bandwidth selected in the receiver. I used 4kHz with a  centre frequency of  2kHz 

The SDR-IQ, in Continuum mode, can be set to give a great deal of smoothing and increase the FFT. Since the noise source is manually switched on and off, the amount of time in each state is effectively unlimited, leading to improved resolution of the Y factor.

The SDR-IQ, when running Spectravue in Continuum mode, shows the noise power as a dB difference (Y factor when converted) between noise on and noise off. The HP8970 driving the noise head can be switched between these two states with the 14.1 and 14.2 Special Function and the actual ENR used in the measuring band can also be shown using the 5.x Special Function.

To be continued..

At last!

I collected my IC9700 from ML&S on Easter Saturday. Braving the A12/M25 Easter traffic I was able to arrive mid morning and pick up the new rig, a dust cover and an SP38 external speaker (to complement my IC7300).

I spent Easter Sunday sorting out my 2m and 70cm antennas. They had been plumbed into linear amplifier and masthead preamp systems. For my evaluation of the IC9700 I wanted to bypass these items. That turned out to be a little less easy than I expected.

So far I have a 9 element 2m yagi and a 23 element 70cm yagi directly connected to the shack cable frame, with the 2x44 element 23cm still to be re-connected after removing (temporarily) the masthead preamp.

Initial impressions are quite favourable. I’ve only used the rig to listen to 2m and 70cm beacons and some data signals, so far. The thing you notice is how ‘clean and clear’ the signals sound compared to several of my other rigs like the FT847 and the K3 with 2m transverter. This is something I also noted with the IC7300 on 6 and 4m.

Once I’ve sorted out the transmit parameters and installed firmware v1.06 i’ll see if I can find a few local stations to test with.

I will be posting some of my measurements on the IC9700 in due course. 

I will be publishing a user review in PW, if all goes well.

Sam

No IC9700

Sadly, it looks like I missed the first cut for an IC9700.

What is particularly galling is that I chose to place a deposit with one of the large dealers in the belief they would have the early stocks. The irony is that some smaller dealers seem to have received stock at about the sme time, and because they didn’t have so many pre-sale deposits, some had uncommitted stock.  These wre quickly sold. The result is a longer wait to receive one from my chosen dealer.

I had been asked to submit a user review to one of the UK ham radio magazines. That is now delayed.

Packed the test gear away again!

New cable

I spent some time pulling-in a new coaxial cable to use on transmit between my PA and the QO100 tx antenna. The existing cable seems to be a bit unpredictable. The new LMR600  cable still needs to be terminated. A job for tomorrow.....

I know fairly reliably the gain of the antenna. I can measure the loss of the LMR600 at 2.4GHz and I  can measure my transmit power.

By transmitting a carrier to equal the lower beacon level, I  can compare my system against the published parameters for the narrowband transponder. As the transponder parameters were changed this last weekend It will be interesting to see how far the transponder parameters now varies from those original figures.

The nice thing about the LMR600 is that it is rigid enough to be forced through the now-congested duct into my shack!

My 738 to 144MHz downconverter is now GPS locked so I can see, with the upconverter and LNB also being locked, that the FT847 has about a 350Hz offset between 144 and 432MHz. That is getting a bit much and needs to be corrected.

QO100 transmit (uplink) antenna

Sam

LNBs for QO-100

Although I have an Octagon with 25MHz reference, injected externally, my second Octagon has a 27MHz reference. It seems to be difficult to obtain a consistent supply of the same type of Octagon

I was keen to try another brand of LNB and having seen that the Goobay 67269 sells on Amazon for £5.43 and uses the NXP chip (guaranteed 25MHz ) TFF1017, I ordered one. On opening it I confirmed it has a 25MHz crystal reference. I haven’t tried it on air yet, but I plan to try it on my smaller, portable ‘Sky’ dish. If successful I will modify it for an external 25MHz (or other frequency) reference input, or maybe one of the SMD TCXOs I bought a while ago!.

The NXP LNB chip should be amenable to a range of reference input frequencies (within reason) opening up the possibility of a 2m or 70cm IF.

Having had success with one Goobay LNB I ordered two more to check out whether it was a repeatable source. The two arrived and were duly opened and checked as both 25MHz reference. They were.

Unfortunately, the Goobay 67269 only has one F socket port, so the possibility of having simultaneous horizontal and vertical polarisation is not possible. Nor can a second port be used for an external reference input. However, the large cavity under the  board, currently used to accommodate the 25MHz crystal, is ideal for mounting a second socket for this purpose.

Sam

QO-100 developments

I have been using a number of different antennas for the uplink on 2.4GHz.

As I am unable to achieve much more that 1.2W output from my SG Labs transverter, my tests have nearly all been done with 1W or less.

1W into the cable out to the 17.5dBi gain Huber Suhner flat plate antenna results in a signal that most QSO partners report as a just a bit too weak for comfortable copy (<10dB SNR in 2.5kHz?). Using my 2.3m EME dish with 13cm band septum polariser feed requires that I turn the power down to around 100 -150mW to reach beacon level. The septum polariser feed is probably not working so well at 2.4GHz. It was designed for 2320MHz. QSOs are easy with this set up, though. No PA required.

I have built a 4 turn helix to the W1GHZ online antenna book details. The match is as shown below. Excellent!

This shows almost 40dB return loss at 2.4GHz, although in practice keeping the spacing of the matching strip to the reflector is difficult and when set up for more testing, 20dB was about the practical limit. Once Dow Corning sealant was added to hold the helix in place, the RL had dropped to about 17dB. I judged this adequate for testing and with the helix temporarily taped above the LNB in the 1.1m offset dish, it was hard to get much a over 10dB below the beacon level, even at 1W into the feeder. The estimated (not measured)  cable loss to the feed was about 4dB. It was obvious from results that a bit better optimising was required.

With this set up I called and worked 3B8FA on the satellite. He was clearly having trouble copying me, so I completed the QSO using the EME dish!

Due to the kindness of one of my local amateurs I will be taking delivery of  a set of metalwork for one of the G0MJW dual band patch, dielectric lens feeds to try in the (near?) future.

One of the joys of this satellite is that I have already had QSOs with friends I haven’t worked on the radio for some time. Everyone seems to be having a go at working the satellite.

I worked Per, DC3ZB earlier today. The last time I saw Per was at Friedrichshafen a few years ago. Lots of time to chat and compare systems and news.

Sam

Video on QO-100

I had a lot of problems decoding the video beacon from the satellite. Decoding was intermittent and variable. I tried a number of solutions and concluded that the Channel Master 90cm dish had lost gain, possibly due to degradation of the fibreglass surface or the underlaying mesh.

I decided to buy a new dish. The Triax TD110 was available at a good price from a big dealership (Eurosat East) in nearby Ipswich. I also looked at the non-penetrating roof mount (sometimes called a pallet mount) that is just over 4 foot square and held down by 4 x 1 foot paving slabs.

Having got the dish on the mount I found it a bit flimsy compared to my CM on its 3inch ground mounted pole. Adjustment was a bit hit and miss as tightening bolts was enough to move the dish far enough to point away from the satellite position.

Eventually this was sorted by ensuring all bolts were adequately tightened, the truly awful elevation arrangement well lubricated and the mount held down firmly by more paving slabs.

After this was done the dish and mount became much more acceptable. I guess a professional installer would have already known and attended to all this. 

What has proved disappointing is that signal levels are about on a par with the CM, suggesting this dish was not seriously degraded after all! Oh well, it’s only money......

With the help of G4BAO and G8BHC it became possible to receive the video beacon and also at least one RBW signal.

What became clear is that I really had not taken enough care to align the dish well enough and with G4BAO’s experience the dish was successfully aligned. Expect to take a few hours to get this right.

However, not being happy with someone else showing me how it should be done and thinking I could do better.......I re-aligned the dish using the narrowband beacon as my reference level source.  This was better (sorry John and Martin....).

Another problem then became apparent and confirmed by G8AGN.

My Octagon OTSLO 25MHz is externally locked to a high quality OCXO. This works extremely well on the narrowband transponder.

When using this LNB,  video decoding was still a bit ‘iffy’. Substituting a similar OTSLO that had not been externally locked and running with a 27MHz crystal instead of 25MHz, video decoding was a lot better. Even with an Inverto DRO LNB, weaker RB amateur transponded signals were decoded better.

I decided to explore the level of 25MHz required to lock the original LNB. I found that the +1.5dBm was JUST sufficient to obtain lock and that at 6dBm it was far more solid. Not only that but the video now started to decode far more reliably. I did have to change the MMIC in the 25MHz  source for a higher gain one in order to get more output, but then had to attenuate the too-high 25MHz down to +6dBm to feed the RG58 going to the LNB.

With this change I was able to see and decode a lot of amateur video signals, at various symbol rates and levels, using the locked LNB and the SSB, CW and beacons on the narrowband transponder were being received extremely well on the 1.1m dish.

Barry, G8AGN, confirmed that he got better decodes with his non-externally locked LNB. I don’t know how much further he got with his.

My video beacon decode shows a steady MER of 6 whilst the amateur signals average a MER of 4.

Enough for now.

Sam

Update on yesterday’s blog

I finished the case but on test found that the SMPSU was providing far too much noise on the 25MHz reference output, so I have decided to change out the SMPSU for a linear one rather than try to filter the big one. That will mean a external PSU again, but will free some room in the case for some extra parts, to be decided.

I also found a problem with the LNB PSU to RSPPro2 (crimped) power connector lead into the bias tee. I’ve never seen this PowerPole intermittent problem previously, but will ensure I look for it next time!

A further update

I found that the original SMPSU, that fitted into the rear of this case, was completely RF quiet and spike free. In preference to using an external linear PSU I have grafted this SMPSU back into the case and am using it to power the reference OCXO/multiplier reference. Since  this PSU  is  rated at 50W (with small fan) I am going to try and use it to power the transverter as well, even though the overall 12V rating is marginal. As long as the OCXO is warmed up the total current draw is just about manageable. As the 5v/8A output is not being used, and neither is the slightly lower current rated SB 12v output, then the main 12V output should be comfortable at or slightly beyond that 12v output rating.  We’ll see what happen!

Sam

My Es-Hail update

Having now had several QSOs on the satellite narrowband transponder with parts of the system scattered around my shack and cable everywhere, I decided I really  ought  to rationalise the system in light of what I’d learnt.

The 5MHz OCXO based reference works well, so that is being retained. More on that in another blog.

Instead of combining the transverter and 25W PA in one large, weatherproof, Storno CQM case, initial tests have shown that with the antenna I am  currently using 1W is enought to exceed the level of the beacons, so the transverter goes in an internal 1U rack case with the 5>25MHz reference and a substantial 12V PSU.

A considerable number of bulkhead connectors on the rear of the 1U case bring in the 10MHz reference for the transverter (SGLabs), all the RF interconnectors for the transverter, including IF and RF input and output & PTT from the IF. Other connectors route the LNB IF coax through an internal link and back out, for later expansion facilities.

Also the 25MHz output to the LNB appears on yet another SMA connector.

The PSU is left on all the time, to power the 25MHz reference, whilst a substantial toggle switch is used to switch power on and off to the transverter and external 25W PA (via another switch to enable the PA, when required). See next day update on this PSU.

The LNB IF is routed to the operating desk where the 12v/18V polarisation switch PSU is located, together with a three way splitter for the Minitiouner, RSP2 Pro and the 738>144MHz downconverter.

I have done away with the separates (K3 and 144MHz transverter for receive IF and FT817 for transmit).

Whilst I wait for the IC9700 to arrive (it may have been delayed, from rumours about FCC acceptance problems around the recent US government financial shut down) I acquired a rather nice FT847 satellite transceiver at a very good price. This radio does full duplex satellite (it has separate IFs for transmit and receive) with normal or reverse tracking. This means just tune to the wanted downlink signal and as long as it is set up properly, the transmit is right on frequency. Nice!  It makes life so much easier. The IC9700 has the same facility.

I’ll cover the DATV side in another blog.

I started by using a HS 17.5dBi  flat plate antenna with the barefoot transverter and about 3dB of feeder loss. In other words, about 17-18dBW EIRP. My SSB signal was about 6dB SNR in 2.5kHz. This is a solutely marginal for comfortable SSB copy. I later discovered my transverter output was a bit lower than I thought.

However, I am going to provide the 25W PA as a switchable option in case it’s needed and to use with a few other antennas I want to try.

After the flat plate antenna QSOs I connected the transverter over about 1dB feeder loss to my 2.3m diameter EME dish with septum polariser 13cm feed for circular polarisation. I had to turn the power right down to stay below the satellite beacons!

Photo of the reverence/transverter case to follow.

Also the 25W PA on its separate heatsink.

Sam

Es’Hail -2 on 2m

I’m currently working on a 739MHz to 145MHz down converter so that I will be able to hear downlink signals on my 2m band transceiver.

432MHz will  be used to drive the 2.4GHz uplink transverter/PA/antenna. A dual band, ‘satellite’ transceiver can then be used on Es’Hail-2 in full duplex mode.  The propagation delay will make sending CW and voice difficult, but at least you will know you are getting in and not qrm’ing someone else.

As PA5Y has pointed out, the latency of the typical SDR would make this even worse, suggesting an analogue receiver might just be preferable!

The downconverter is based on my Iceni transverter board, receive section and LO, with 99MHz (lockable) crystal oscillator. I’m using a up mspare (redundant) Iceni V1.0 PCB.

The first problem is that the original LO could not be persuaded to generate any worthwhile power on 594MHz (739-145MHz). Instead I opted to tune it up to half frequency (297MHz) and try using  sub-harmonic mixing. After a lot of work I am achieving a conversion loss of about 20dB through the mixer in this mode.

With a 735MHz Toko helical filter (tuned to 739MHz) on the RF input and suitable filtering/ mismatching on the IF to try  and ensure that the mixer was seeing unwanted frequencies reflected back in the correct phase to minimise conversion loss, i was able to add a post mixer amplifier and filter to achieve  an overall insertion gain of -10dB. As the LNB has massive gain, the downconverter noise figure is not critical.

I have more work to do on the converter before I am happy with it. More anon.

I subsequently found that the level of noise from the LNB, down at 739MHz, was considerably down compared to at 1GHz. Consequently my plan to add a passive three way splitter after the bias tee feeding the LNB resulted in a poor overall system noise figure when feeding the downconverter. I may have to add the PSA4-5043 RF stage back into the Iceni-based downconverter....

Sam

More on Es’Hail-2 sat.

After seeing today’s excellent test signals in the satellite amateur transponder passband I was motivated to dig out my 13cm SG Labs transvreter and fire it up. It hasn’t been touched in two years and never previously fired up on 2400.050MHz. That’s the start of the 250kHz narrowband uplink range, extending to 2400.300MHz.

After initial tests, using my FT817 on 432MHz, and checking all was well on my spectrum analyser I thought it might be interesting to see just what 432MHz drive levels I could use and still get useful output from the transverter. The reasoning being I wanted to use an Iceni 70cm transverter with my K3 as the drive source. I wanted, if possible, to use the Iceni barefoot i.e. no add on 70cm linear amplifier. The SG Labs transverter can stand several watts of 70cm drive, but the barefoot Iceni only generates 50mW.

I first tested with various levels with my SMG Signal generator set to 0dBm, transverter input attenuator set to minimum loss. The transverter gave +7.5dBm output. The RF Vox did not operate. As I don’t require this facility, no problem. Increasing the drive to +10dBm gave +18dBm transverter output. Finally, with +16dBm drive, the SG Labs gave +25dBm output. RF Vox worked from +10dBm upwards.

The transverter will be mounted in the shack and a coax cable will connect to the 25W output GaAs FET PA out by the transmit antenna.  The  power amplifier requires about +10dBm at 2401MHz (wideband PA) for full (saturated) output and that gives lots of room for both coax loss and an attenuator at the PA input!

It looks feasible to use the Iceni barefoot  in this application.

Of course, underdriving the transverter will result in the spurious outputs (image and any Residual LO) as well as the transmitted composite noise being effectively 10dB below spec. However with a 432MHz IF these are a long way down.

Now to box the transverter and arrange for somewhere for it to mount in the rack.

Sam

Transverters

Yesterday I announced on my web page, and in a couple of reflector messages, that I would no longer be producing transverter kits. These have proven to be very time consuming to produce, to the detriment of my involvement in the hobby. Added to that the stock handling and holding is a pain, although the whole excercise has been interesting and shown there is still a demand for this type of radio equipment. VHF and up SDR radios have not taken over entirely!

I am in discussion with a well known and established company to take over producing the transverter kits, but it is early days and no guarantee it will happen. The economics may well rule it out.

I still have stocks of many transverter parts, but I will not be putting these into full kits; instead I will make them available as parts only to anyone wanting to build an  Iceni or Anglian transverter, prior to having a new supplier. After that it will depend on my agreement with the new owner.

I am no longer arranging to hold new stocks of the WA5VJB PCB antennas. Again, I still have existing stocks of these antennas to sell. Although not a particularly time consuming part of my kit business, arranging to acquire adequate stock of some antennas can sometimes be frustrating.

I will continue to produce my VLNA and PGA low noise preamp kits. These are far less time consuming to produce!

Sam