Fixing my Gemini 2 linear amplifier

EDIT. I have rewritten parts of this as it is now 6 months since I repaired it and it is working fine. I have calmed down a bit and I can see that the Gemini design is very good, but the SWR protection circuit did not work for me and several others who have e-mailed me. 

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POST SCRIPT at the start. The 300W Gemini worked for a couple of years after I got it going again. Then it blew up and needed a new PA section. I replaced it with a 500W Gemini which I kept for 9 months. They are both gone now. I am not about to try another one. 73 Jim July 2024.

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OK, I am writing this four weeks after I restored my Gemini 2 linear amplifier. By this stage, after 141 QSOs on those four weeks, I think it is working again.

Gemini 2 at GM4FVM (plus 1296 linear, PTT relay, and bent paperclip for resetting phone)

"Fixing" is the word I used in the title. Not exactly repaired, because I did not put it back the way it was, but "restored". I am using it again even though it is not as it once was.

I have had the Gemini 2 "300 watt" linear amplifier for two and half years now. For the first year it worked fine. Then it developed a fault which caused it to break down four times during the next year. And again after that.

The fault always came on the same way. The amplifier would trip with an SWR fault, even though no fault existed. I could simply restart it and then it ran for a week or two, and then tripped again. And then again after a week or so. And then every day, and then every few minutes, and then it just tripped out all the time. 

It had a two year guarantee and during that time I did not think it was right for me to try to solve the problem myself. Any meddling would just invalidate the guarantee. Various suggestions were made as to the cause such as it might be the centre pins of my N-type plugs, or my driver rig. It wasn't any of these things.

To prove that it was not something at my end I connected the linear to an entirely different set up, a hand held FM driver rig in and a 300-watt dummy load out, with different RF cables. I even changed the mains cables. It still tripped. This was clearly not a fault at my end. 

One reason I knew that it was not a fault at my end is that I was bequeathed (by David GM4JJJ) a very nice WaveNode WN-2 digital power and SWR meter which provides an almost instantaneous reading of power and SWR and it showed nothing amiss. I even took video and analysed it frame by frame. The SWR LED could be seen first glowing dimly and then getting brighter at different stages during a transmission, with the WaveNode in the same shot showing no SWR at all. I tried five different SWR meters, and none showed any problem.

WaveNode WN-2 - superb SWR/power meter (but very expensive!).

The WaveNode uses outboard sensors, and after it arrived here I added several more to cover all the bands I use. I take it to be accurate.

I returned the Gemini to the maker several times under guarantee. Sometimes it came back with no fault found but it still did not work here. 

Other times it came back with work having been done and an explanation. This was the solution that eventually got it working again for the first time, explained thus when it came with this email:- 

"I had a hunch what it was and it proved to be correct. 

The directional coupler pick-up bridge circuit feeds through two 75R 0803 SMD resistors - one for fwd and one for rev. 

The rev one was showing big swings in resistance with temperature and the thermal camera was picking up a bigger variation in temp (as it heated up the resistance was lowering to the current was increasing causing more heat and so on). 

I have replaced both these 75R resistors and the amp has been on soak test now for an hour at 150W out with no issues." 

So this was my clue as to what was wrong too. Well, it was actually exactly what was wrong. I had this clue to go on, and he sent me a photo of the resistors:-

Photo of one of the SMD resistors sent by DXShop (looks rather small, as they do ...)

Replacing the overheating resistors with more of the same solved the problem for a while ...until the Gemini started tripping again after another few months.

After another trip back under guarantee (the fifth trip back I think) I got this message:-  

"As a precaution I have replaced the directional coupler components. If it still trips then there must be some issue external to the amplifier that is failing under rf load."

That was a strange comment. If changing the components fixes the fault that suggests to me that the components are at fault, not some issue external to the amplifier. I suspect that if you change a component and if it fails again then you know where the fault lies. Suggesting something external seemed to me to be unlikely to be causing a resistor in the directional coupler to overheat.

Well anyway, I know now that there wasn't some issue external to the amplifier causing a problem. 

I felt sure that keeping on changing the resistors which keep on altering in value was just putting the problem off for a while. However, by repetition this had occupied the entire 2 year guarantee time and so it is my problem now. 

It ran for a further three months before the same fault happened yet again. As nothing had changed, just keeping on doing the same thing (changing the resistors for more of the same) will not bring a different outcome.

Another way I knew the fault was not at my end was that during the periods the Gemini was away I was using the excellent Microset SR200 linear amplifier. No SWR fault there. When the Gemini came back I sold the Microset (mistake). When the Gemini failed again I acquired an RM Italy VL-250. The Microset SR200 was good, the RM Italy VL-250 was excellent. The VL-250 has a very fine protection suite including SWR protection - and no fault showed up there either. There was no fault at my end to find.

Three months after it came back for the last time from repair under guarantee, it failed again. I just put the Gemini 2 on the shelf and plugged in the RM VL-250 and tried to ignore it. 

There, sitting on a shelf, was a nice piece of kit which I could not use. Obviously I was going to do something eventually, but just then I was really fed up with it. 

A couple of months later I calmed down and started to think that the Gemini needed to be restored. 

I read back over everything that had happened. I decided to assume that it was true that the two resistors in the directional coupler were overheating and varying in value. One thing that seemed to be supporting that idea was that the output meter on the Gemini had started to work erratically - and it is powered by the directional coupler too, albeit by the forward power circuit. If changing the resistors worked for a while each time then perhaps that is the only fault, and the power meter is affected in the same way.

I poured over the Gemini circuit diagrams and read the manual backwards and forwards. I opened it up and examined all the things I thought I could do. It seemed that I had four options:- 

1) Turn off the protection by turning down the potentiometer on the control board (which would stop over-drive and over-temperature protection too) 

2) Replace the SMD resistors in the directional coupler with devices which could withstand the heat/current 

3) Simply disconnect the directional coupler and run without any SWR protection, leaving the other protections in place 

4) Do (3), but add some outboard SWR protection of my own. 

 I rejected option (1) as being too risky. 

Option (2) appealed. I may do this later and restore the Gemini to more-or-less original condition but for now I will not being doing that. Too many imponderable possibilities.

Option (3) was possibly an immediate solution to see if that solved the problem. Although I have used lots of linears over the years with no SWR protection, I felt sure that Murphy's law would step in and blow this one up if I ran it permanently without any protection. I had no strong reason not to do it, and I think it should be safe enough. 

BUT, option (4) looked the easiest way of getting the Gemini working again and having some SWR peace of mind. 

I should perhaps say that the Gemini 2 has NEVER tripped due to high SWR when there really was an SWR fault. It has tripped dozens and dozens of times, but only as a result of this false trip issue. Despite this I though I should do SOMETHING to protect against high SWR, simply to put my mind at rest. 

When David JJJ became silent key he left me his WaveNode, as mentioned above. David and I had talked about my false SWR-trip fault and he was as worried about it as I was (he had two Gemini linears himself). Now, whether he had thought about the possibility of neutralising the SWR circuit and using the WaveNode for protection I do not know. After all, when we spoke about this fault it was still under guarantee. Anyway, the WaveNode he left me has an SWR protection circuit. There is a trend here - everything David left me has been useful, even if I could not work out why he left them to me when they arrived.

So we had two fairly simple tasks:- 

First complete Option 3) - disconnect the connection between the directional coupler and the control board (then test everything works) 

The complete Option 4) - rig up SWR protection from the WaveNode. 

First: cutting off the on-board SWR protection 

This is pretty simple, or it should be. The wire from the directional coupler uses the multi-pin header plug on the W6PQL control board. Despite this being fairly simple to disconnect I managed to disconnect the wrong wire three times. 

Getting them back in once removed was tricky. Use a commonly available crimp tool "under $30 on Amazon" says W6PQL. Anyway, none of the crimping tools I had worked and eventually a home brew method using a screwdriver and extreme force did the job. 

Did I ever mention that I am colour blind? I am not the right man to send on a job to a 20-pin plug to find any particular wire. I am bound to pick the wrong one. Not that I actually needed to do that, as I could have just counted the pins (bet you would have started counting at the wrong end Jim).

The 20-pin header plug on the W6PQL control board (colourful, eh? I would not know)

I did not disconnect the forward power line to the power meter on the front panel, which perhaps I could have done at the same time. 

I found it easier to take the W6PQL control board out each time while working on it. It is screwed to the right hand side of the Gemini case and hemmed in by other components.

Having carefully insulated everything which had been disconnected, I put the linear back in its case and tested everything with no SWR protection. Unlike before, when it tripped immediately, it all worked perfectly. It worked fine for three days before I set up the SWR protection. 

Then setting up the outboard SWR protection. 

Pretty simple too. The WaveNode has an on-board relay which trips at a pre-determined SWR level which you can set in software. 

The WaveNode monitors four power and SWR levels at once (in my case, 6m, 4m, 2m and 23cms). However, it can only do SWR protection on one band at a time as it only has one physical relay. For the sake of simplicity and to avoid any confusion later (hopefully) I moved 2m to monitor One, and set the SWR trip level at 2:1. This is in fact a tighter trip level than the Gemini had initially.

WaveNode monitoring 2m (band 1), set for SWR2:1 (actually it is 1.132:1 in this setting).

 The physical wiring looks complex but is pretty basic really. 

Using the WaveNode to monitor the Gemini SWR

For the sake of clarity the diagram leaves out the 24 volt relay which switches the IC-9700 PTT line between the 2m and 23cms linears. That is the relay you can see in the first photo. Well, not just for clarity: it is wired in the wrong place. It too cuts off the 23cm linear should the 2m SWR trip work. Far too much wiring to get that right so I left it the way it is. This place is like a spider's web already without adding more wires.

The WaveNode has a three pin PC board socket on the back of the main module. Being the sort of person who never throws anything out I had a matching plug in my "computer parts" box. It was simply a matter of attaching phono plugs to that so that it matched my PTT line standards. 

If the SWR on 2m exceeds 2:1 the relay will trip and de-activate the PTT from the Gemini. That leaves the rig facing the high SWR, but it is well protected and that was always the case with the on-board protection anyway. 

I suppose that there is some risk of a cable failure between the Gemini and the WaveNode sensor, but then there is a risk of cable failures inside the Gemini too. And in any case such a fault would probably trip the SWR circuit anyway (I am not about to test this to find out).

I tested it with a high SWR at the antenna and the trip worked immediately and also gave a loud audio warning "HIGH SWR TRIP ACTIVATED" over my PC speakers.  

You could do this with much simpler and cheaper SWR meters than the WaveNode, but that was the one I had.

So finally ... 

The Gemini is restored. 

Maybe one day I will delve in and replace the two resistors in the directional coupler with high wattage and high stability alternatives. On the other hand, maybe not. 

For the first few days there was a "hot electrical" smell which suggested that the resistors were still overheating. Gradually the output power meter got more and more erratic. Then the smell stopped, the output power meter stopped working, and normality was resumed. 

I can read the output power and SWR from the WaveNode, which displays this information for all bands conveniently on my PC screen. It also shows one band directly on the readout on the WaveNode module itself.

I am left with various issues to ponder over. One reason I did not replace the resistors (again) was that I am not sure why they were so hot in the first place. This Gemini 2 is very quiet, compared with my 4m and 6m Gemini linears. Could it be that the fans are running too slow?

I have tinkered with the pot on the control board and poked about at the secondary fan control board, but the airflow seems OK. There is plenty of hot air coming out over the PA heatsink, and the fans do accelerate as you might expect. So is it just the SMD resistors cannot handle the current? Why not? Or is it heat leaking from the PA?

Never mind it works, for four weeks so far anyway (EDIT six months now). 

I have now sold the splendid RM VLA-250, a fine 200W linear. 

I have since bought a new 70cm linear - a Tajfun 1000. The Gemini design is good and the price not unreasonable. It is a pity that those two resistors could not stick the pace in my amplifier..

Thanks again David.

I do not know how you knew, but you knew.

73 

Jim 

GM4FVM

Using the IC-9700 as a dual band FT8 decoder plus heaps more tropo.

 OK, TROPO - loads and loads. New squares, new countries, but more of that later.

Stations worked at GM4FVM 15 to 21 September 2020. Red pins for 2m, purple for 70cm, light blue for 23cms. It is only a week's activity you know.

That might be an image that needs to be clicked for a larger version ... not to mention the others.

Yes, it is true, I monitor several bands at once. As someone asked how I do it I hope to cover this in a later posting. I cannot listen on several bands at once because few humans can do that. However, I can have various displays on my computer screens, and I can monitor multiple bands that way. This allows me to jump up and down the spectrum and sometimes "do the treble" by working into a country on three bands in quick succession.

The object of this posting is to explain how I am using the IC-9700's dual band capability to monitor data modes (and not just FT8) on two bands at once using the IC-9700. There is nothing very startling about this - you can listen to SSB or CW on the loudspeaker on both bands. On data most people will connect the IC-9700 to a computer using the USB socket. That is fine for one band. I use the other audio output from the back of the 9700 and feed that into the computer to cover the second band.

For this purpose I picked 144MHz and 1296MHz, because I use an IC-7100 for 70cms. You can use any two of the three bands on the IC-9700. I also decided to use MSHV to decode the second audio stream, simply because it looks different and I am less likely to get confused. Getting confused is not unlikely - the IC-9700 has a complex system of VFO A/B and band and sub-band which can be very hard to fathom.

So I went for simplicity (?!). As the sub-band cannot be used for transmit, I reserved the second audio stream for decoding (listening) only. The second display is just for reading, it does not report reception to PSK Reporter. This is because I will be switching between bands and the second stream does not have CAT information. If I enabled reporting on the sub-band it would keep reporting the wrong band if I switched between bands. 

And anyway, I need to be able to get my head round it. Everything recorded on the sub-band, whatever frequency, turns up on the secondary MSHV screen. I work on the current WSJT-X screen - always. I switch between bands by pressing the upper multi-function button ("M/S") which swaps the main and sub band frequencies. The WSJT-X software I use for the main working area keeps up with the working frequency, but the secondary one doesn't. I know I can only "listen" (watch?) on the other sub-band one. When the working band is 23cms (on my left), the monitored one is always 2m (on my right), and pressing M/S swaps them over. Simples.

Main-band reception of 23cms GB3NGI beacon on JT4G at GM4FVM

Simultaneous sub-band reception of 2m GB3NGI beacon on JT65B at GM4FVM

To show me receiving both of these at once I had to use a beacon. I would rather have done it with FT8 and active amateurs but I forgot during the recent tropo lift and now everybody has gone off the air. But obviously both bands can be heard and therefore decoded simultaneously. If you wanted to transmit in the secondary frequency you just press the M/S button to bring the required band into use.

It really could hardly be simpler. To add the second decoding software you can add another "app". In my case download the latest version of MSHV, install and run it in a new folder, and connect the audio to it. For that you need  ... an audio cable with a 3.5mm plug on each end.

EDIT - I did not know it at the time because the IC-9700 manual doesn't mention it, but I could have used a second channel on the USB audio output instead of a analogue line. Thanks to Greggor for pointing this out. See here for an explanation. The analogue system described below will work, but the two steams via USB will have less noise and save some wiring. 

If your computer has a spare audio input socket, just plug the cable between the sub-band socket on the IC-9700 and the computer. In my case I did a lash-up first with a USB audio card from eBay (cost £3). That worked, though the signal/noise on the sub-band was quite poor. I added an audio attenuator (also a small sum from eBay) as that device only had a microphone-level input. It wasn't great but it proved everything worked.

Next step for me was to add a better outboard sound card - one I bought a few years ago in the days before USB audio input direct from commercial rigs. This is better quality and it has a line-level input, but it still cost less than £10. The S/N on the screen was better, the reports higher and I have stuck with that.

Cheap USB audio card with attenuator

 

As I say, there is nothing special about this. We used to connect our audio output from our radios to our computers in the early days of PC based data modes. Just as in those days, once you plug the lead into the IC-9700 sub-band output you will not be able to listen to the radio on that speaker (but you can turn on "listen" to the audio stream in the computer). You have to set the sub-band volume control for the correct reading on the software, in my case made easier thanks to the attenuator. But strictly you do not need to attenuator if you can balance the volume controls on the radio and in the computer (and MSHV gives you a volume control too).

And it works! I often leave the rigs running while I am out of the shack. Normally that means monitoring 2m, but now of course both 2m and 23cms on the IC-9700. I was passing the shack with my coat on about to leave when I spotted something on the MSHV screen. It turned out to be DF5VAE on 23cms - I just pressed a button and I was ready to try to work Charly. It took a few moments. His linear amplifier had failed but he was stronger barefoot. We quickly completed a contact for my longest DX on 23cms, with a new square and DXCC into the bargain. Without a second monitor I would never have been able to do it.

The same thing happened several times during the past week, and in both directions. I was on 23cms when I saw something interesting on 2m too. Why not? The IC-9700 has two receivers, so why not use them to monitor two bands at once?

Of course anyone else doing this will probably not follow my idea of using two different bits of software to decode each stream. I do this to make it clear to me what is happening - MSHV for sub-band (right hand of screen), WSJT-X for main-band (left hand of screen). I like to know where I am. 

If you are adding multiple instances of WSJT-X you need to follow the guidance on the WSJT-X website (link on the side bar of this blog). Basically you need to give each rig a separate name (I have four instances!). Maybe I will cover this in the later posting. Anyway, it is very easy just to use MSHV for this purpose. Easy, Jim, your mother never liked you doing easy. But it is, and it works for most things (but not JT4 from GB3NGI beacon as MSHV doesn't have that mode).

 Right, time for some tropo reports.

On 13 September I worked DJ8MS on 2m. That is not so unusual, but what happened after that was unusual. For the week 15 September to 21 September there was tropo every day. A large high pressure system moved in over the North Sea, and although that faded after a few days, another high from the Atlantic merged with it. Hepburn predicted it very accurately of course.

By 17 September the PSK Reporter page for 70cms was beginning to look more like the normal one for 2m.

432MHz as shown on PSK Reporter on 17 September 2020

 

At different times propagation moved around covering France, Belgium, Netherlands, Denmark, Norway, Sweden, Northern Germany, Czechia (!), Poland (!!) and Estonia (!!!). And while 2m was like a bear pit, 70cm was busy and even 23cms was a bit busy. 70MHz, a band which can produce some good tropo openings, was also affected. Just goes to prove it is worth monitoring as much as I can. 

Busy is not the only way to judge it, so how did I do for DX? Well, as is so often the case, things got better just before the opening ended. And then, just when you think this is going to get even better, it is over.

In 7 days I was actually operating for 21 hours and 33 minutes to work 65 squares in 15 countries. Best DX was, perhaps appropriately the last of 170 QSOs, to ES8TJM in KO18 at 1575km. Wow.

The highlights were ... everything ... , but to look at each band in turn (except 4m which had 5 tropo QSOs and 6m one on Es):-

144MHz contacts at GM4FVM 15 to 21 September 2020

 

Hard to know what to say about that.

97 QSOs to 49 squares in 12 countries.

I look back at the log and, quite frankly, I cannot recall some of the entries. I am reeling. I need to look more carefully at it to appreciate the individual detail as well as the whole thing.

Thanks to ES8TJM for my first 2m tropo contact to Estonia. Thanks also to HF0BW who would have got the award for best DX to Poland had ES8TJM not won it by 19km. And thanks to the rest who were making it a very memorable week.

432MHz contacts at GM4FVM 15 to 21 September 2020

 

56 QSOs to 31 squares in 12 countries. Loads of new squares. Thanks to SM1FMT for my best ever tropo DX on 70cm for 1359km to JO96 in Sweden. Surprised would be the word about that one. 65watts and 2.5m boom yagi. Eh? And as I keep saying, two years ago I didn't even have a 70cm antenna because I thought I would not work anyone. And thanks to OK1VVT for my first contact on 70cm with Czechia.

Let us get this straight. Unlike some (those who regard themselves as part of the Senior Service of amateur radio) I do not sit on the sidelines and wait to pounce on the choice DX like some radio-spider. I know that other operators need GM as a country, or IO85 as a square, and I like to do my bit. 

There are some choice bits in there which I would have missed had I not got involved with the masses. F6DBI is a nice bit of DX for me on 70cms. I have worked him a few times on 2m, but this was only the second on 70cms. I have not heard so much of ON4POO lately but a first contact on 70cms was a pleasure. I still reckon 70cms is very interesting. Working GM0HBK is a treat, and working DF5VAE or DL7APV is a joy. And that bag full of OZs are always interesting.

If they want to contact me, I will try to work them. How do I know - I might be the best bit of DX they have worked all year. And, frankly, these contacts are all equal value to me whatever record they may break, or not break, as the case may be. I only go on about the records because they keep surprising me.

23cms was great fun. Now I can monitor it without taking my eye off 2m.

1296MHz contacts at GM4FVM 15 to 21 September 2020

 

12 QSOs to 10 squares in 6 DXCC. But what QSOs! Thanks to GI6ATZ, F5APQ and PA0O for my first contacts on 23cm into Northern Ireland, France and Netherlands respectively. And thanks to DF5VAE for my first contact on 23cm to Germany and my best DX on that band at 1001km to JO64.

I had several requests to try to contact stations in Poland on 23cm and Czechia on 70cm on CW amongst other things, but none of it worked. Still, perhaps that saved them listening to my crappy morse, so it was not all bad. Plus I still have some goals in my radio life.

Sorry this article has been so long but how do you describe the last week in any other way? Now that I can monitor three bands at once and hop between them I have been able to range across the frequencies as conditions changed.

Towards the end of the opening, on 21 September, the conditions went into overdrive. There were whistlers moving up and down the band. Stations had signals which were dissolving into dust rather than forming FT8 traces. I sat and watched superstations working Finland and Latvia and just monitored them off the back of my beam. No need for me to get involved because I have neither the station nor the drive to try. Maybe I am what a certain President would call a "loser" for not wanting to plaster myself over the clouds. But how can I not be content with what I did this last week?

If you were there, I hope you had a good time too.

And if you have a log periodic ready for that IC-9700, what is stopping you getting back on?

A radio-spider? What is that? Have you gone totally bonkers Jim?

73

Jim

GM4FVM

Some more tropo and having delusions of competence.

Sometimes I get carried away. I allow myself to be deluded into thinking that I know what I am talking about.

Maybe I am not the only ham who suffers from this.

Anyway, sometimes I believe I can actually out-think the experts. In this case the expert is the very reliable William R Hepburn, whose superb tropo ducting predictions are linked to the sidebar list on this blog.

Hepburn suggested that tropo conditions would be good here on 7 and 8 September. I looked at the weather outside, felt my bunions (always reliable in the past) and concluded that tropo conditions would not be good. (Does anyone remember the Bunnion strip cartoon in the evening newspapers? Not the same as my bunions though).

I related this unwise prediction of mine to Jeremy M0XVF as follows:-

It is blowing a hoolie here now so I cannot imagine tomorrow will be very good. Maybe further south. I live in hope though. 

I was, of course, talking total nonsense. Yes it was windy here. Also, the Reporting Scotland weather forecast looked pretty poor.

Hepburn knows best.

I do not need to know anything else about tropo, just that Hepburn knows best. I can look it up, and not go off on fantasies of my own. In this case my predictions were wrong, and his were right. Who'd 'ave thought it?

Jeremy sent me a reply that the Angus beacon was loud with him, the GB3NGI beacons in Northern Ireland "v loud indeed" and that he held hopes for conditions into Europe. He was right. There is nothing like the facts to upset my imagination.

If I do get on my high horse and think I know more than I do, I hope I can accept it when somebody else knows better. I decided to accept that Jeremy knows what he is on about and have a listen. 

I left Mrs FVM to watch some gruesome TV programme about people who suffer from unidentified dread diseases, and turned on the radio instead. Tough choice, but someone has to swerve the morbid images of pus and sores to check out the radio. Did any of them have bunions? I will never know.

Result:-

 Above: VHF contacts at GM4FVM on 7 September. Red pins = 2m, blue pins= 70cm. 

Click the images to enlarge (seems to be working again).

The thing about all of these QSOs were the very strong signal reports. G3NSM in IO91 was +12dB here and gave me +07, GW8ASD was +09 and he gave me +16. Even though the 70cms contact with G4RRA took a while to complete, he gave me +08 from my piddly 65W.

NOTE TO SELF:- must do something about that 70cm power level, apart from just complaining about it.

OK, so I was wrong. What was Hepburn saying now?

  Above:- Hepburn tropo prediction for 8 September 2020.

I was beginning to think that I needed to take this a bit more seriously. The weather forecast on the TV was still showing nothing really interesting, with moderate pressure and a meandering front passing from west to east. But Hepburn also considers other factors such as the relative humidity of the air which is a crucial factor. So I guess he knows better than me.

Of course he knows better than me. He has been doing this for decades.

I needed to get up the next morning and spend some time trying to work someone. Oh dear. I am not at my best in the morning.

Next morning produced this:-

Above: VHF contacts at GM4FVM on 8 September. Yellow pins = 6m, blue = 70cm, red = 2m.

Best DX was, of course, as so often, DF5VAE in JO64 on 2m at 1001km. Even that one was +06/+13dB signal reports. Best on 70cms was with F6HMQ in JN18 at 888km. I do not wish to take away from any of the contacts, and I was especially pleased with the others on 70cms as we shall see later.

I am not sure if I like using different coloured pins on the map to show up different bands. Apart from anything else, there is no coloured pin for 70MHz. There were two contacts on 4m during the tropo opening, one with ON4IQ and the other with DL6BF. Tropo contacts of 702 and 730km are good stuff on any band, and maybe my best tropo contacts on 4m (I did work ON on 4m tropo many years ago but that was on CW and my CW is never nice for the other station).

So on 7 and 8 September 2020 I worked 33 stations in 23 squares and 7 DXCC. I concede that Mr Hepburn was correct in his predictions.

I might mention that the RSGB UKAC 70cm contest was held later on 8 September but I seemed to have done better by not waiting for the contest. I was finished at lunchtime, and the TV viewing that evening was much better than the day before (Tour de France, England getting beaten at cricket and Eat Well for Less!). I would rather watch Gregg Wallace make an omelette than listen to a flat band at contest time.

Before I leave the subject of 70cms and tropo, I want to mention that tropo also happens when there is no ducting. Combining both days when there was ducting with the other eight from the last ten days produces this:-

Above: 432MHz contacts at GM4FVM from 31 August to 9 September 2020

These are in succession, MM1FEO 484km, G4YTL 429, GM0HBK 269, G4RRA 578, PE1NMM 681, F5APQ 606, F4HRD 606, F6HMQ 888, and G4VQZ 563km. Only in the case of MM1FEO did we move up from 2m, all the rest were "random" - in other words - CQ calls answered. 70cms has certainly surprised me. For a band which I did not have an antenna for two years ago, I seem to be making progress.

Is this event over? Probably but there are usually more high pressure systems on the weather chart somewhere, even if they are still days away from reaching me. I need to watch Hepburn more carefully.

What is left of this event seems to be producing very good conditions further south and east of me. Here normality has returned for now.

This opening gave me a good chance to give a work out to my disgraced Gemini 2m linear amplifier. I have given it some surgery to get it working again. It has been out of operation for four months and it needs a good soak test before I am willing to claim it is now ready to go solo. I did use it for all the 2m contacts listed here and so far so good. I will write it up if and when I am happy it is working again. After six breakdowns I can hardly be blamed for not trusting it. Now that it is out of guarantee I feel able to do some work on it myself - at last.

I have also been poking at my TE Systems 175W 432MHz linear which seems to be terminally silent key. It needs money spent on it and I doubt if it is worth it. With such wonderful high power devices now available I an unsure whether I should be spending my cash on old-style replacement Motorola transistors. If I do get it working, it will still be an old-school linear as opposed to the latest high gain amplifiers like those from Freescale. And then there is the little matter of changing 5 transistors with surface mount components on their fingers. With my shaky old hands? New the devices, even un-matched ones, would cost more than the linear cost me in the first place, and that leaves second hand ones. Hmmm.

I hate abandoning something that needs to be fixed. Maybe it should be a project on the shelf for days when there is no tropo,

Never mind, if I can do all that on 70cms with 65 Watts I cannot be too unhappy.

73

Jim

GM4FVM