Tuesday, 15 November 2016

Post Scotex

Back from the Scottish Microwave Round Table. I spoke on the subject of my Anglian 3 transverter.
However, the social aspects of the meeting were what it was all about. This is one of the smaller Round Tables and has a limit of just 50 attendees because of limited space in the Burntisland Communications Museum in which it is held. 
The evening meal was held in the Kingswood hotel, some 1.5 miles from the Museum and around a mile from my hotel. I was able to walk from the hotel to the Kingswood in about 20 minutes in the good company of G3AAF. We were joined by G4BAO on the way back. The excellent company and interesting chat made the cold walk quite bearable!
I have to report that the food was excellent and was extremely well prepared and served.
3/4 of the 'Microwave Band' entertained us after the meal, with some interesting and unusual musical instruments. I am completely unable to remember their names (the instruments, that is) except for the accordion and that was a bit smaller than usual.......I'm sure it has a special name as well.

As for radio since returning, well I have been back on the moon, using digital modulation on 23cm and collaring several more initials (#) for my growing 23cm total. QRA64 was very effective at allowing me to QSO G4BAO off the moon for the first time. Our dishes are just 1.9 and 2.3m diameter.

I've also been preparing to launch the PGA432 preamp kit. This is a low noise, high dynamic range, preamp with effective input filtering and bandpass output filter. Gain is adjustable and powering over coax is an option. I will announce on my web page when the kits are ready for sale.

73 de Sam

Tuesday, 25 October 2016

Anglian update

Sales of the Anglian 3 144MHz transverter have been going well. I have mainly been limiting sales to the UK and Europe whilst I clear my backlog of orders.
Many of my customers have been buying the 8W PA short kit as well as the transverter.
For now I am able to hold the price of the Anglian 3 to £120 but after the noticeable increase in the cost of parts for the transverter I will have to increase the price in the New Year. The increase is mainly due to many of the parts being sourced outside the UK and priced in USD which is approximately 20% higher against the GBP than before the Referendum result caused the GBP to slide to a more realistic value. 
I will take kits to the GM Microwave Round Table next month, where I will be giving a talk on the Anglian. I also plan to take kits to the Heelweg (Dutch) meeting in January. The ferry trip is already paid for!

Sam

So how did the SDRPlay, play?

I've now got the SDRPlay connected to the Lenovo notebook and the 13cm transverter 2nd IF output. Switching the transverter LO to give 2300MHz coverage and tuning the SDRPlay to 164.830MHz I can copy several 2320MHz beacons and the local one at Martlesham, although very strong, does not cause any discernible strong signal problems. This is reverse operation of the system.
I will use it as a more conventional parallel 2300MHz receiver this evening during the UKAC/NAC 13cm and up when the main system is on 2320MHz. It should be an interesting test.
200W out to a 67 element yagi.

Sam

Sunday, 23 October 2016

Back to the SDRPlay

Today I bought one of the cheap Tesco Lenova notebook computers to use with my SDRPlay and other ham radio programs. At just £129 the notebook is good value. I was alerted to it by G4HUP and although my local store was showing 'out of stock', when they checked they found they did indeed have just one left in stock.

I downloaded antivirus software as my first programme and then downloaded the SDRPlay application together with SDRUno.

I'd already played with SDRUno previously but found it rather awkward to use and this time was no different. It really does need another GUI.  The existing one is not at all well designed. It does have some nice features that are not available in HDSDR, but I am much more familiar with that application. Maybe if I persevered with SDRUno............ 

However, after downloading the EXTIO dll, I was ready to fire up the new notebook and SDRPlay. Connected to the DG8 masthead preamp and tuned to the various beacons on 2m in turn, it acquitted itself quite well. I knew it was working on the correct frequency and had a reasonable noise figure (quoted as about 4.5dB).

My intention is to use it, tuned to 128MHz, on the second IF output of the 13cm transverter's receive converter to listen to 2304MHz EME signals after transmitting to the moon, from the UK, on 2320MHz. Alternatively it could be used tuned to 148MHz whilst the transmission is on 2300MHz. All of this is with my homebrew 13cm transverter, which although it has switchable LO frequencies for the 4 principle 13cm EME sub bands, it does not have remote switching for them, which makes it awkward to use from the operating position on the other side of the shack. Since selling the FT847 several years ago I have lost the ability to easily switch between listening on the two different allocations.The FT847 is one of the only rigs I know that has reasonable SSB receive performance at 128MHz for this type of crossband operation.

73 de Sam


Tuesday, 4 October 2016

Update to the Anglian 3

I have made a small update to the transmit path of the Anglian 3 transverter.
All subsequent kits will contain the new parts and those that have already gone out will be offered the alternative parts.
The update improves the transmit path gain, which gurned out to be a few dB low of what it should have been.
Slightly more IF drive was required to reach full output in the no-IF amplifier version.
More kits will be available after I get the RSGB Convention talk out of the way!!

Monday, 3 October 2016

RSGB Convention

Nearly completed my slides for my talk at the Convention 'The secret life of the transverter'.
My talk is about the principles of the transverter, interfacing it to an HF rig, and some things to look for in the transverter system. I have deliberately focused on the IC7300 interfacing as a result of recent interest in this particular rig as a transverter driver.
I understand that M1BXF has acquired an IC7300 for use in the Convention HF station. If you have wondered about this rig as your next venture in SDR technology, here is your chance go come and see one in action, and maybe go hands-on with one. Then come and listen to my talk!
I am not deliberately talking about VHF transverters (my recent speciality) but rather in more general terms about the subject.



Sunday, 25 September 2016

A break

I'm taking a short break from kitting Anglian 3 transverters. Two weeks of intensive kitting, component preparation, paperwork and shipping has taken its toll. I need a break from it. 
Started to investigate integrating the DRiACS dish controller into my existing system, beginning with an eddy current damped gravity pendalum elevation indicator. 
I was extremely disappointed with the Machine-DRO digital pendalum inclinometer. Although the reading updates very quickly ( too quickly?) it is very unstable. It seems to be similar to the well-know 'Lidl' digital inclinometer. That is also totally unsuited to moon tracking as it takes ages to settle down to a reading. The Machine-DRO is exactly the same. It is suitable for indicating elevation if hou have time (>30-45seconds) but totally unsuited to tracking, where the 'noise' masks the immediate moon (or sun) position.
So, i'm back to trying to implement the MAB25 absolute encoder solution, but with the possibility of using eddy current damping to reduce reading instability, especially during windy conditions when the dish mount will inevitably shake.
On a very positive note, the add-on GPS clock works well, even inside my garage shack. GPS lock is solid. The DRIACS indicates the actual moon ( or other celectrial object in the almanack) without worrying about clock drift.
Sam



Saturday, 17 September 2016

Crawley

All now ready to attend the Crawley Microwave Round Table tomorrow (18th September).
I'm taking a few VLNA preamp kits and PGA144 preamp kits. I'll also take some of the WA5VJB antennas and other boards.
Accompanied by Alan, G3NYK, who will take some of his boxes for sale as well as some of the HUPRF kits.
Should be a fun day.
There are some interesting talks scheduled for the afternoon. For once I'm not speaking at one of these events.


Wednesday, 14 September 2016

Disappointed

I am disappointed that apart from the usual entry in the published RSGB Convention programme, I have seen only a two-word mention in Radcom of what I think is my talk at the Convention.

This year I am scheduled to speak (The secret life of the transverter) at 16:00 on Saturday. Looking at the programme published in Radcom I see I am scheduled against some pretty good alternative talks.

Only by self-advertising am I likely to attract a few to my session, otherwise I might get overlooked!


😎

Friday, 9 September 2016

Paperwork

I've been busy preparing the documentation for the Anglian transverter. Takes as long as developing the circuitry!
Separate technical description and assembly manual for the kit
Kits only. No assembled SMD boards for now.
Should be available soon. Just waiting for some back ordered components.

Thursday, 1 September 2016

Venice and beyond

We've been back from EME2016 in Venice for one week, having stayed on a few days to have a better look at the city. For sure it was heaving with tourists and cruise ship visitors (the Cunard Queen Victoria was the only liner I recognised).
I have to congratulate the Conference organisers for a job well done. Having been one of the Cambridge 2012 organisers I know just how much work goes into the organising of a two day EME Conference, with the various dis-staff tours etc.
I thoroughly enjoyed the Conference and learnt a lot from the various talks. I was able to attend every one of the 16 talks over the 1&1/2 days.
I have been inspired to do some additional 'fettling' of my own dish and now it has additional bracing on the feed cage to overcome the cage drooping when the heavier RF horn and amplifiers are installed. Mainly the 6cm one.


The diagonal braces are of substantial gauge aluminium alloy and secured with M5 screws.
Laying one of my laser levels on the mount, I have checked the 'true ' of the cage and where its red dot appears on the fence. This enables me to reset the SPID RAS at intervals to overcome the inevitable SPID pulse count errors!

Monday, 15 August 2016

EME2016

This last few weeks have really all been about getting ready for EME2016, later this week.
The International moonbounce Conference is held biannually. The last one was in France and the previous one in Cambridge, UK. This year's Conference is being held near Venice.
As has become usual for me, I am offering a selection of my EME VLNA preamps, both kits and semi assembled  kits. It has been the preparation of these preamps that has been occupying my time. In addition to the VLNA preamps I have been building a number of PGA432 70cm preamps for evaluation by a number of other amateurs as well as taking one or two to EME2016 to be independently measured.
And.....the new Anglian3 transverter boards arrived last week and so I've been busy building up some of these for testing. I'm pleasd to say that they work as well as the Anglian 3 that they replace, and with some added features. Unfortunately I hve not had time to get Anglian 3 kits redy for EME2016, although I will have the first ones on show.
I've also been finishing off my presentation on failures in LNAs (too much RF - they don't like it up 'em)
The nub of the presentation is just how much abuse a HEMT LNA can take before it fails, and what happens along the way! I'm scheduld tobe the second talk. It will be nice to get mine out of the way early on, although as an ex-lecturer I don't mind standing up in front of such a bunch of established academics, enthusiasts and EME  experts.....much!
As well as all these preparations I have been trying out the new digital mode of QRA64. This is in alpha release for testing and will form part of the new release of WSJT-X. Possibly after EME2016. Joe Taylor, K1JT, and Nico Palermo are presenting at the Conference.
My testing has been with a well-known EME op, but on HF. Honestly!
QRA64 is a weak signal mode, well suited to EME, and usable at HF. It answers many of those critisisms of digital, aimed at how some of the computer processing has been considered 'cheating'. Troglodites..........
QRA64 and the new fast mode of MSK144 could quickly supplant some of the existing digital modes like JT65 and FSK441. We will see what happens over the next few years.

Sam



Sunday, 24 July 2016

Anglian 3 update

For those of you who don't subscribe to Twitter you will not have seen my progress with the Anglian 3 transverter. I have been tweeting regular updates (for anyone interested!)
The second set of Prototype PCBs were deliver last week and a second unit built up to prove the design works as it should. I'm pleased to report it all worked as planned, although there were still a few very small errors on the PCB. Version 3.1 PCBs have now been ordered and are expected in a few weeks. 
The new Anglian 3 is designed as a direct replacement for the Anglian 2, but with a few small improvements. These include transmit enable delay, better transmit amplifier gain distribution, programmable transmit IF gain (for use with ICOM rigs, with their low transverter output level), better transmit IMD, but retaining the same excellent receive performance, lockable local oscillator, separate IF receive and transmit connections and all SMD construction as the 2.
Unlike the Anglian 2 I have no plans to offer the Anglian 3 as a fully assembled PCB, as this has proven to be uneconomic for small production runs of boards with specialist RF parts.
However, I may offer partially assembled boards, depending on demand.
Also, depending on how Brexit affects component purchase (many parts are sourced from overseas), I anticipate the cost being lower than the Anglian 2.

Sam



Sunday, 17 July 2016

70cm low noise preamp for Contesting and Satellite mode J


I have had a 432MHz version of my PGA144 preamp on the stocks for some time. I never bothered toadvertise  it because I knew it needed more development. I took the time over the last few days to look at the filters again and then put one together. As always some tweaking of values was required compared to what the design software said, die to stray capacity of pads etc.
The results are quire pleasing.
I've not yet measured the input two tone third order (IIP3), but it ought to be pretty good.
Of particular interest is the deep notch I have been able to place on 144-146MHz to suppress signals in this range. Similarly the frequency response is well down in the Upper digital TV band, GSM band and at 23cm.
The noise figure measures under 1dB ( 0.8 to 0.85dB on the prototype) on an open board, which is not the ideal way to measure noise figure due to 433MHz SRD interference.
As the accompanying plots show, the input match is exceptionally good, so that a filter could be placed at the input if required and its frequency response would not be badly affected. try that with many common 432MHz designs!
Noise figure and gain (can be varied if required) at 435MHz

Yes, I know that attenuators is spelt wrong......


Input match (in yellow) marker 1 at 435MHz and 145MHz with frequency response in blue withe same markers

Tuesday, 12 July 2016

Anglian 3 update

As I have run out of the current Anglian 144MHz transverter kits I decided that rather than order more boards to the current design, for reasons that will become obvious as you read the following, I needed to design a replacement. The replacement is the Anglian 3.
It is the same size as the Anglian 2. 

The redesign gave me the opportunity to make improvements, especially on the transmit side. The original Anglian 2 was designed to work with HF rigs like the K3/S or TS590 that have typically 0dBm 28MHz  transvert output. I found that I could get it to work with the typical -20dBm output from some ICOM HF rigs by slightly modifying the transmit IF input attenuator. Whilst the output would not quite reach 100mW (+20dBm) when driven at this level, it has proven adequate to drive a Mitsubishi module to full output. However, I never quite felt comfortable driving the mixer that far below its nominal IF input level where the full IF to RF isolation was achieved. At this drive level the transmit amplifier chain needs the full gain of the two transmit amplifier stages.

Some users have reported a short burst of transmit output when switching from receive to transmit. This appeared from my tests to be dependent on what was connected to the receiver input or transmitter output. The gain from receiver input to Anglian 2 transmitter output could momentarily be 70dB! It didn't take much additional gain in a masthead preamp or PA and an RF burst could appear. The changeover from receive to transmit originally had a small overlap of a few ms where both were on. Reducing regulator reservoir capacitor values speeded up switching since  there was then less charge to keep the receive amplifier working for those few ms.
However, the proper solution was two-fold. Decrease transmit amplifier gain and introduce a delay between the receiver switching off and the transmitter switching on (sequencing).

An improved output amplifier, with lower gain and better IMD, has solved the first problem. A MOSFET switch instead of a bipolar switch improves switching speed and allows the introduction of a simple but effective sequencing delay to solve the second problem.

Of course the reduction in transmit gain now meant that a low IF transmit input could become a real problem. This was solved by the introduction of an IF transmit (28MHz) amplifier stage. If not required it can simply be left out or a link arrangement allows it to be bypassed.
With the new TX IF amplifier the Anglian 3 now easily produces more than 100mW output at 144MHz for less than -20dBm input at 28MHz. Harmonics are less that -60dBc at 100mW output.

I had also been asked if it was possible to include a 28MHz band pass filter in the 28MHz transmit IF input, which I have now done. The TX IF input now passes through a single stage bandpass filter centred on 29MHz.

The LO chain is largely unchanged except that it now works entirely on 5V and runs from a single 5V board voltage regulator. The Anglian 2 had three voltage regulators! The LO still produces +20dBm output and can be locked to an external 116MHz input, if higher stability is required.

I have not changed the receive converter side as it already has about optimum performance for the design and components used.

My plan is for kits to be available later this year. I need to check the revised PCB and if satisfactory, will order a batch of production boards in August. I will probably initially revert fo full kit version with assembled SMD boards coming later. Small runs of assembled RF boards are not economically efficient! 

The aim is to keep the price (component costs permitting) similar to the Anglian 2, or maybe a bit less. We'll see how the pound fairs later this year.

Sam





Tuesday, 28 June 2016

Yet more IC7300

I have taken delivery of an Alpha Delta 4 way coax switch to direct the output from the 7300 to the 4/6m antenna, HF antenna, dummy load or to the Anglian 2m transverter.
I have opted for the simple approach go interfacing to the Anglian and Gemini 2 PA.
I use just a 20dB power attenuator after the switch into the Anglian. I have the 7300 28MHz band power set to 8W. The reasoning is that if I was to accidently forget to turn the 28MHz power down (it is set per band) then the max that would hit the Anglian would be 1W and transverters tend to be more tolerant of overlod due to the usual input attenuator before the mixer. The 20dB attenuator is a25W unit which will stand a degree of overload before burn out.
My tests using the spectrum analyser on max hold etc indicated no significant spiking of output power when set to low power. I have seen some reports of ALC overshoot on SSB and CW. I have not seen this.

I had an interesting problem when set up. The Gemini 2 would fail to SWR when driving bove 100W output. This was eventually traced to the bulkhead lightning arrester on the antenna feed starting to trigger at this

level. The arrester has been replaced by an N bulkhead adapter. All is well now.

This evening saw several new locators added to my 6m total in the NAC contest. Now to try and leave  the system as it is now instead of yet another rearrangement.........
WTS

Sam






Saturday, 18 June 2016

More IC7300 tests

Since I want to try my 2m system with the IC7300 I was interested to know how well the power control on the new Icom works. In particular, does it spike on switching between receive and transmit?
I set the rig to 28.2MHz and (carefully) connected it through a 150W/40dB attenuator to my HP8592 spectrum analyser. The analyser was set to 20mS sweep and 5MHz span. With the IC7300 set for full output, the reference level was set to 0dB on screen. The mode was SSB. The analyser was then set to Max Hold in order to capture any spikes. The IC7300 mike gain was set to zero.
Keying the IC7300 transmitter on and off produced a small spike, caught by the Max Hold on the analyser. The level of the spike was around -55dBc
The IC7300 was keyed in different modes with similar results.
Winding the power down to '0%' resulted in the spike amplitude being similarly reduced.
Power output at 0% was 22dB down on maximum output, or about 700mW. This is below the  2W claimed.

It would appear that the IC7300 does not power spike to any significant level.

Connecting the IC7300 to my 2m Anglian transverter with DG8 mast head preamp, though the 40dB attenuator, produced a barely audible increase in noise.  No surprise there!
Reducing the in-line attenuator value to 20dB result in a greatly increased noise output and lots of beacons appearing on the 7300 spectrm display.
16dB is about optimum for my system and so it was with an MCL 15dB 2W attenuator that the system seems to work well and achieve about as good a dynamic range as I could expect with this set up.

Using a 15/20dB power attenuator is required to further reduce the power into my Anglian. I don't like to dissipate more 28MHz power in the transverter than absolutely necessary.

Although the IC7300 does not appear to spike, this is still not proof against forgetting to turn the power down.............

A 20dB, several watt, IF attenuator will give some protection and then fuse if severely overdriven. Hopefully you will have noticed a problem by then and there could even be time for an overdrive protection circuit to operate. I do not advocate this approach in order to drive an LDMOS SSPA as it would probably fail a whole lot faster than any protection circuit unless carefully designed to prevent any drive reaching the PA before checking its level.

Sam



Monday, 30 May 2016

Cold Bank Holiday

So far it has been a very dull and chilly Bank Holiday Monday, so I've been using the time to catch up on some writing. I have two Conference papers to write with both of their deadlines looming in the next week.

In addition to those I have an equipment review to write for Radcom, so what am I doing writing this blog as well?  Good question, but whilst the words were flowing seemed like a good time to put something onto the blog about the new rig.

The new IC7300 has been working out well, with a number of new locators and DXCC worked on both 6 amd 4m since Saturday. I've also been thinking about how to add a sutable transverter interface to the 7300 so that I can use it to access other bands.

The touch screen spectrum display is a pleasure to use. That doesn't mean it's perfect, by any means, but it is a big improvement over some other implementations and I think in ICOM's next SDR transceiver it will be even better.

One of the shortcomings of the touch display is that when you select the signal you want to listen to it brings up a static, magnified, view of the spectrum around the signal. You then need to touch the screen again to select the signal. I find I cannot touch the right spot to tune accurately to the signal without then having to use the tuning knob to tune it in accurately. I am sure that with the power of modern DSP processors it should be possible to do this automatically. Of course you would then probably need a 'defeat' facility in the event you wanted to select a weak signal next to a strong one!
One other observation is that there is no 70MHz band 'button' necessitating a frequency input, which means several button presss to go to, e.g. 70.2 input
You quickly get used to this, but a 4m band button would be nice, please, Mr ICOM
More anon.
Sam


Sunday, 29 May 2016

IC7300

I was able to pick up my new IC7300 at yesterday's Waters and Stanton open day. I have been in two minds about the wisdom of buying one, but Dayton finally decided me. I already have a several rigs, but I had several reasons for going ahead with the 7300. Not least is the desire to develop a suitable interface to an external transverter for 2m and/or 70cm. With all those 7300s out there, just asking for use on higher bands, I just need to do this.  A complement to the Anglian transverter, maybe?

My first impressions of the 7300 on 6m and 4m are very positive. The multiview touch screen is easy to use and a very much easier to use implementation of a spectrum display than the P3 I use with my K3.

On 40m I initially thought I had a problem. It appeared that the receiver was deaf. But it turned out that the receiver was just very quiet. Signals really stand out from the noise when you tune to one.
Selecting signals to listen to is very easy using the touch screen spectrum scope. It's certainly better than winding an encoder knob to bring a marker onto a signal and then pressing the encoder knob to select (in the process pushing the P3 backwards!).

It is also nice to have up to a full 1MHz display. You rarely need more than this as the resolution is likely to be poor on most screens. The display was especially nice on 4m where it was possible to see the many OIRT FM broadcast signals, at once, as they popped up and disappeared.
I have been sold on the future of SDR architecture for both receivers and transmitters for some time. This is one of the best implementations I have seen yet. 
I have already increased my 4m and 6m locator and DXCC scores with the 7300.

More as I get to know the rig better. And maybe something about the rather nice IC31E D Star handheld I won in the raffle at W&S. Thank you W&S and thank you ICOM!

Sam




Sunday, 15 May 2016

A bit more 13cm EME and Upcoming Dayton visit

I set up again today to check out some changes I had made in the shack. I've repaired my MFJ memory keyer and can now run either a keyboard or straight key. I may buy a decent paddle at Dayton. My 'peers' keep telling me I need to use CW more if I want to get my speed back up!
Anyway, whilst testing I noticed that although the moon is currently at apogee and therefore the degradation is high, I could occasionally hear as well as see my own echoes with the 200W PA in the shack and with an unacceptable amount of transmit cable loss. My plan is to move the PA out to the dish. The 27V PSU is already out there in a weatherproof case with 110V AC supply and all ready to go.

Dayton
I am off to Dayton on Thursday and back early the following week. Whilst in Dayton I will be attending the new VHF/UHF weak signal dinner in Miamisburg, Dayton on Friday evening. This new event replaces the excellent event previously run by Tony Emmanuel, WA8RJF, but sadly no longer organised by him.

I will be in the Dayton fleamarket much of the time, on stands 2766-2769 with WA5VJB.
It looks like it will rain (nothing new there, then!) Friday afternoon through Saturday, so I'll need to take the wayerproofs!
I'll report back on Dayton on my return.

Sam



Friday, 13 May 2016

2320MHz EME

Today I replaced the 6cm EME feed with the 13cm feed and hooked up the transverter and PA in the shack.
It is no where as critical to track the small 2.3m dish on the lower band as the beamwidth is so much greater.
Although I didn't see any trace of a JT65C signal from D44TVD I was asked on the HB9Q logger by UA3PTW for a sked. His -15dB signal was easy to find and he gve me -16dB. When we had completed I was called by an enormous signal that turned out to be HB9Q. His -11dB was one of the largest signals I have seen on 13cm EME. He gave me -13dB. IK3COJ then askd for a sked and we swapped -15/-20dB
This has brought me up to a logged 21DXCC on the band with 18 of these on EME. I know I have worked many more terrestrial DXCC than the 3 it looks like but these have not been transferred from my paper logs yet.


Thursday, 12 May 2016

5760 EME

I have set up the 6cm EME system to try with the D44TVD dxpedition. He is trying to be QRV at 14:00Z today.
6cm is not my best band due to low transmit power (25W) but sun noise is good and I can see moon noise. JT Echo mode is showing lots of libration and a very weak return. Degradation is high at present.
I may have to change bands to try with him on another day. His 1m dish will make it difficult on any band when I only have the 2.3m dish at this end. But hey, don't try, don't know if it will work!

Friday, 22 April 2016

A little news

I volunteered to act as Chairman of the UK Microwave Group, following the Martlesham Microwave Round Table AGM. I've just heard from one of the current Committee members that my offer has been accepted
No one on the Committee wanted the role, which to be honest can be a bit stressful at times, so I made the offer to act as Chairman for the next year, at which time a prospective, new, Chairman may be willing to take over. 
I have previously been Chairman, taking that role for the first 3 years of the then new UK Microwave Group. 
As one of the original 'Gang of Three' who set up the group when it appeared that the RSGB spectrum committees were probably going to be disbanded, I was extremely pleased to be appointed as the first Chairman and saw the Group through the first, sometimes difficult, few years of its life.
The UKMicrowave Group quickly became the recognised elected voice of UK microwavers. That is a role it has performed well for nearly 17 years. 
OFCOM recognises the Group and has been known to seek our help in matters relating to amateur microwave operation, allocations and even technical help. 
I am pleased my offer to act as Chairman for the year has been accepted and I will do my best to live up to the role.










Sunday, 10 April 2016

Mast maintenance

With the help of G8BHC (Scatterpoint editor) I did some maintenance on my antennas this afternoon. My intention was to replace my failed (coax relay) 2m masthead preamp with a DG8 premp and return to single cable working ( leaving a free coax for 6/4m).
In the event we ended up removing one of my two 23cm 44 element yagis and moving the 67element 13cm yagi into the space vacated. The 3cm dish was moved up the mast (slightly). All of this in addition to fitting the DG8. However, we ran out of time before I could run in the new length of LMR600   coax between the preamp and the shack. I did manage to measure out the run and the new coax was was just long enough.
Listening on 23cm, using the single antenna, didn't reveal any great loss of system performance but time will tell. I have been suspicious of the 23cm antenna combiner and the removal of one antenna seems not to have resulted in a 2-3dB drop in performance, as best I can tell. Similarly the 3cm system was checked out and reception of GB3SEE at -13dB on JT4G was a bit above normal, but probably due more to conditions than the marginal move of the dish to its 'higher' location on the stub mast.
All in all a useful afternoon!


Saturday, 19 March 2016

Anglian transverter

Some of the readers of my blog will be familiar with my Anglian 144MHz transverter kit.
Around 200 of these have been sold with the majority being of the form of an assembled SMD PCB. The builder is then left to install the board in the supplied case, solder in the leaded tunable inductors and the crystal. 
This has worked well and although there has been the occasional dry joint problem, most seem to work first time and provide the builder with a transverter that is high in performance and low in cost whilst allowing the builder to boast that they built it themselves.
I am now coming to the end of the current batch of assembled boards, helped by a recent 'sale'. This has been more successful than expected and the boards have quickly depleted.
My dilemma is what to do next. Having boards assembled has not been without its problems and is by no means an economical way to go with relatively small production runs.
I am not inclined to have any further boards made this way.
Unfortunately the PCBs are designed for reflow solding and therefore have small SMD pads. These are awkward to solder to when using hand soldering.
As the Anglian has been so successful I am reluctant to stop production. Maybe the best way forward is to re-design the board, changing a few aspects of the circuit for even better performance and selling this as a kit where the builder has to solder around 120 SMD and leaded parts onto the board?
With about 12 boards left I am going to have to decide soon!
73 de Sam



Life on 23cm EME

Last weekend I got the 23cm EME system back on line. A careful check of my log shows I had worked 62 'initials' ( first contact with a new station or #) up to May 2012, when I last operated on 2cm EME.
Since last weekend I have brought the initial score up to 74
It is quite clear that a lot of new stations have appeared in the last few years. I recognise a lot of the callsigns as those belonging to customers who have bought an VLNA23 from me. I find that very gratifying!  I think it should be possible to raise the number of # to 100 by the end of the year. At least it gives me a target to aim for and means I will have to keep the 23cm preamp and feed on the dish.
The majority of new contacts have been worked on JT65C and running MAP65 has allowed me to see who is on without sitting in front of the PC laptop all the time.
I can see that not withstanding last weekend's 23cm DUBUS CW EME contest, when up to 16 stations at a time were visible on the spectrum display ( P3 and SVGA card to 23 inch monitor), the move to digital on the band is seriously underway. I realise this will unsettle a good few of the old CW stalwarts, but King Catute showed the fallacy of trying to hold back 'nature'. In this case human nature.
I'm not a good CW operator and am always relieved when a CW contact has finished and in the log, wheras I actually enjoy the surety of digital contacts. It's not fashionable to say this, but I still can't see the attraction of CW when digital allows so much greater reliability of contact exchange information. And for me personally, far less anguish about not copying callsigns correctly or dealing with 'off sequence' information.
Sorry guys!

Thursday, 25 February 2016

Initial results of LNA destructive testing

I've repaired a few VLNA preamps for customers where the noise figure has gone up noticeably whilst the gain remains at the original level.  Because the gain remains normal it can be difficult to diagnose without noise measurement, as everything appears nornal except signals are weaker.
As part of my tests of failure levels in VLNA preamps at 23cm I have now managed to duplicate this problem. This, with other test results, will appear in the proceedings of the EME2016 Conference, later this year.
The problem is due, not surprisingly, to RF overload, probably causing increased gate current to flow.
The signal level it took to cause the problem is the big surprise!


SDRPlay

CHaving read the review of the SDRPlay in Radcom I thought that I'd buy one. Now it has arrived I needed to connect it to my TS2000X in order to monitor 23cm. I am able to do this already via my SDR-IQ and a PAT board connected to the 10.695MHz second IF.  However, I find this most unsatisfactory as the 'span' is limited to about 30kHz and it reverse tunes (LO is high).
Connecting an SDR to the TS2000X first IF (135.495MHz) turned out to be surprisingly easy as there are a number of MMCX connector test points on the 23cm module board. CN8 is a light tap (1pF) between two 135MHz tuned circuits and after the first mixer (dual gate fet). CN7 is after the 135MHz monolithic filter and first IF AGC controlled stage. I really didn't want to have the SDR connected after an AGC controlled stage as it meant high level signal level measurements would likely be wrong as the AGC activated. I was not sure whether the IF at CN8 would be clean enough. It was.

I had a short UF/L to SMA cable end jack available, purchased originally to use with a small GPS module. The cable is about 15cm long and very thing, but as this is 135MHz it doesn't really matter.
This cable turned out to be long enough and thin enough to loop around the 23cm antenna flying lead as it emerges from the TS2000x. By carefully drilling a 7mm hole in the removeable (2 screws) cable clamp plate I was able to fit the SMA bulkhead jack in place next to the cable lead. There is not quite enough room to do up the SMA nut, but a dab of superglue soon fixed that!

With this IF tap cable in place I was able to do some tests through the front end. Previously ARRL Lab had measured the TS2000X noise figure as 6dB as quoted in a QST review. From 23cm RF cable input to CN8 cable IF output I measured a very acceptable 4.1dB, consistent across the whole 1240 to 1300MHz range with a centre band gain of 14dB falling by about 1dB at either end of the range. I felt this was adequate for connecting the SDRPlay without using one of the G4HUP PAT boards, although this might be fitted at a later date. 

Checking with my spectrum analyser there were no spurious mixing signals within the 135MHz IF range down to at least 70dB below my -40dBm 1296MHz input test signal.
Using HDSDR I was able to see noise from the SDRPlay up to about 3.5MHz either side of centre band (IF) and able to zoom right into signals such as the Martlesham 23cm beacon. There is no centre (DC) spike even using the zero IF option!

If ever the SDR application teams ever get round to adding Continuum mode to this or any of the other SDR programes they will become really useful for measurements rather than just looking at signal spectrum (Spectravue does have Continuum but doesn't run on the SDRplay!)

Back to destroying 23cm preamps in the name of determining safe input levels......

Sam


Thursday, 4 February 2016

G3PYB -SK

I am off to Havant in Hampshire tomorrow. Peter's funeral is on Saturday morning and to avoid an early start from over here in Suffolk I thought I would stay over Friday night at the hotel where the post funeral reception was to be held.  It turns out that a number of other microwavers and ATV enthusiasts had the same idea. I only just managed to get a room!
There will be, among memorial items, a QSL board where we will be able to place our QSL cards. 
This seems to be a popular idea and has been seen at several memorial receptions over the last few years. 

I haven't been in the Havant area for many years and I'm looking forward to seeing it again, albeit in somewhat sad circumstances.