Wednesday, 20 February 2019

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



Tuesday, 19 February 2019

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




Friday, 25 January 2019

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


Wednesday, 16 January 2019

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



Wednesday, 9 January 2019

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




Wednesday, 26 December 2018

Persistent cough

Whatever the bug is, it is persistent. It just won’t clear. It seems to be very common, as well. I hear a number of people reporting a similar problem.
Hopefully, not too much longer.....three weeks is long enough.......

I have managed to do a bit more observing of the Es’Hail-2 satellite and further optimised my receiver. I still can’t get a good comparison with the beacon reception by other amateurs as each seems to have a different set up and hence way of making measurements on the 10706MHz engineering (broadcast) beacon. The problem seems to relate to making a measurement in the beacon centre carrier level in a known resolution bandwidth. Simple  you’d think? A number of levels have been given for signal level, but without resolution bandwidth these are meaningless.

This morning I decided to have another look. The engineering beacon centre frequency has always sounded ‘rough’ and showed several ‘carriers’ within the narrow passband I was looking at. This is with the LNB I had modified for external 25MHz reference input. It just didn’t ‘feel’ right. That radio engineer’s feeling for a signal? Not knowing whether the engineering beacon actually had some form of data modulation, close to the carrier, it was difficult to tell what was going on. 
As a test I set my RF Explorer signal generator to 10706/4MHz and connected it to a WA5VJB LPY antenna. The resulting forth harmonic showed quite strongly on the SDRUno display and with the same ‘data modulation. It was now clear that the external locking on the LNB was not working as intended.  As an aside, the TCXO in the RF Explorer showed within a few hundred Hz of the beacon centre frequency. 
I have a spare,  unmodified, Octagon LNB (27MHz reference version), so I substituted it for the modified one and looked again at the beacon. Now the beacon  centre frequency was clean and sounded it on the headphones. 
I’ll waterproof the system again, later, and remeasure signal levels.

I have a spare high performance 10GHz LNA and horn feed system. I am going to look carefully at using that for the satellite in preference to the LNB. Although that is a cheap approach, I am beginning to wonder if the noise figure will turn out to be too high, down at 10489MHz?
I’ll need to use my spare DB6NT transverter and the feed/LNA and an IF at 265MHz
The Minitouner will tune into the required frequency range, so no need to worry about that.

Happy New Year



Saturday, 15 December 2018

IC9700 thoughts

Apologies for no posts for a few days, but I’m recovering from a rather nasty viral infection, caught last weekend, and which is only slowly responding to doctor’s orders! I’ve not been anywhere near the shack for almost a week and the time has allowed me to reflect on what I expect of the new ICOM 9700. 

Two and a half years ago I purchased an IC7300, more in hope than expectation of a good, useable, design. I was most pleasantly surprised at how good it is, especially as a K3 with all the bells and whistles owner and user. The IC7300 turned out to be, for me as very part time HF operator, a far more user friendly rig than the K3. Undoubtedly the K3 scores well on many points, and although I know personally that it has much VHF and microwaver input to increase it’s appeal to upper bands amateurs. Its range of transverter interfaces is unmatched, with easy (too easy?) access to a wide range of  level, frequency and offset adjustments and a superb IF interface facility.  But that P3 is nothing short of useless for anything serious and although I have installed the SVGA interface, I don’t see any significant overall improvement compared to using an SDR-IQ as the ‘go to’ spectrum and waterfall display and it has the advantage of ‘Continuum Noise’ measurement when used with Spectravue which the P3 doesn’t offer. If you haven’t used this measurement you can’t be a serious radio ham!!, we won’t mention the awful encoder interface on the P3 beyond could Elecraft chosen anything worse? Yes, there are ways round all this, but I want a self contained radio that doesn’t need a PC/laptop and a 27inch monitor on my bench just to see that weak signal in the noise.
The Internal 144MHz transverter is poor. I will leave it at that. A well-known UK amateur had a far more descriptive suggestion.

No, the IC7300 is not a panacea. The German transverter interface had a major problem that was slow to be acknowledged. I’m told it’s now been sorted. I’ve not revisited it. I reverted to the good old power attenuator solution.

Given all this, why am I looking at the IC9700?

First  let me say that I have some reservations about the design and these will only be resolved once I manage to get one on my bench. 
Living as I do on the east coast, I have a few unusual conditions to contend with. On 23cm I am very close (<5km) to the GB3MHZ Martlesham 23cm beacon. When I borrowed an IC910X, some years back, and first tried it on 23cm, it was completely unusable. The phase noise from the IC910 Lo (VFO) was so poor that reciprocal mixing from the beacon was apparent 700kHz away in the usual DX frequency area of the band.
When the North Sea path opens up Belgian (in particular) radar can be rather strong. Most rigs have a noise blanker than can cope with the noise. It is not like car engine ignition or an electric fence. The radar beam sweeps past and produces multiple pulses and these are very often accompanied by forward reflections from objects out to sea (and maybe reflections from inland objects) that add together to sound like a buzz. Some rigs (like the TS2000x) can cope rather well with this, other fail miserably. This will be a severe test for the IC9700.

Another problem is likely to be on 144MHz where I have a number of well placed, adequately ‘endowed’ EME stations in the surrounding counties. The K3, with an Anglian transverter, copes quite well. The TS2000X (which always needed a masthead preamp) did not. 

So, what am I waiting for?

I’ve read (re-read) the specs, asked questions of the manufacturer’s representatives at Dayton, Friedrichshafen and in the UK and not (no surprise there then) gotten the answers I wanted. So now I have decide that the price is just about affordable to buy one and see how well it copes at this QTH.
I believe I have the experience from being the designer of many transverters for all of these bands to make sound judgement on performance and to write up my experiences on my blog.

I’ve paid my deposit and now I wait..........

Sam