Thursday, 13 June 2019

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






Thursday, 6 June 2019

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



Sunday, 19 May 2019

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.








Saturday, 18 May 2019

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

Friday, 10 May 2019

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

Saturday, 4 May 2019

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.


Sunday, 28 April 2019

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.