Long distance 23cm aircraft scatter

The result: 590km QSO on 23 cms.

The recipe: IC-9700, 150W, 28el yagi with 1.5m boom, Airscout.

Once again, when I started on 1296MHz I would never have believed this was possible. A 590km microwave contact on a flat band with an antenna just 1.5m long? No chance. And before I started on 1296MHz I doubted if I would work anyone, even in my own square. On 21 August I worked a new one four squares down and three across.

I am pretty sure that this is my longest aircraft scatter contact on 23cm. Sure, I can get further during tropo lifts, but conditions were normal that day. To make things harder, my normal 36 element 3-metre boom antenna has been dismantled while I deal with corrosion damage. So I had gone back to the 28 element WIMO given to me by Neil G4DBN - my first ever 23cm antenna.

The WIMO 28 element antenna between 70cm and 4m yagis at GM4FVM

Click to enlarge images if necessary. 

Frankly, I was not confident about reverting to the WIMO antenna. The antenna has 20 elements along the boom and eight at right-angles to the boom as a reflector. It works OK, but being half the boom length of the 36 element brings a 2dB reduction in gain, despite the reflector. However, in the 23cm UKAC on 19 August I worked six stations and that restored my faith in it to some extent.

At 11:17 on 19 August I saw EI3KD calling on 70cm FT8. My beams were still pointing in that direction as I had earlier worked EI4ACB. EI3KD and I then worked on 70cm. Mark sent a message on Tx5 that he was going to 23cm. I followed up to 23cm and I could see strong traces of Mark's signal via aircraft scatter but the Doppler shift was too strong to decode the signal on FT8. I contacted Mark via KST Chat and said that I would like to try Q65 but at that stage I did not have the time to try. I did say though that I would like to try when we had time.  

And so it was on 21 August that I saw Mark again on the Microwave section of KST Chat and I asked him if we could try Q65. I think I blundered slightly by suggesting Q65-30C as the whole thing  might have gone better on a 15 second period. Anyway, off we went and within 30 seconds of calling EI3KD I decoded Mark calling me.

I was pretty sure that we could complete because of the path as shown on Airscout. There are plenty of planes passing over the Irish Sea along the path of our contact. The problem is that not many are at the right point along the path, shown by the short pink section in Airscout.

Screenshot of Airscout along the GM4FVM/EI3KD path on 24 August 2025

Only the mid section of the path west of the Isle on Man can be useful for reflections. On the screenshot above (taken today) I can easily see that 19 planes have just crossed or will cross the path, but only one is heading for the pink section and likely to provide us with the reflections we need. So this might take some time and need a few planes.

As Aircraft Scatter paths get longer, the pink part of the path gets shorter, plus other obstructions such as hills get in the way.

Screenshot of Airscout along the GM4FVM/EI3KD path on 24 August 2025

Airscout also shows this, and the vertical diagram above shows the small pink area which planes will have to be in to help. The vertical scale is the altitude of the plane. Anything landing in Ronaldsway airport in the Isle of Man is not going to be high enough! The bottom diagram above shows obstructions on the ground along the path (on a different vertical scale!), with the Irish Sea a long gap in the middle, but the Wicklow Hills and the Pennines at each end.

Another problem is going to be Doppler shift created by the movement of the aircraft across the signal path. Doppler effects rise as the frequency goes up. Quite a few 2m and 70cm contacts on FT8 are put down to Tropo propagation when in fact they are assisted by aircraft scatter. However, the Doppler is often too strong to allow FT8 to work at 23cm. Q65 is ideal in these circumstances as it compensates well for Doppler. I did increase "Max Drift"to 30. Exactly what the "Max Drift" setting does I have no idea as the WSJT-X Guide has not yet been updated to cover it. Suffice to say that in a previous aircraft scatter test it seemed to help so I increased it again this time.

Net result of all this - only a few planes at the right height would complete the contact and Q65 will need to cope with the Doppler.

Long pause after the first decode

Airscout produced hope with small planes and possibles which altered course. Lots of hope but no results. But then, after 19 minutes two planes in opposite directions were due to pass over the right area almost together. Result:-

Aircraft scatter QSO complete - even to the 73s.

The best decode at my end was -13dB which did look rather faint and Doppler shifted. The 73 afterwards was very difficult to see, but Q65 decoded it OK:-

Final decodes in Q65

So although nearly 600km is almost right at the end of the radius of aircraft scatter QSOs, it did prove practical even with a less than brilliant set-up. I now have 41 squares worked on 23cm. Who would have thought it?

Even if you find all this daunting I would still urge anyone to try 23cm aircraft scatter. There are lots of IC-9700s out there which, like mine initially, have never strayed on to 23cm DX. All you need is a decent antenna and coax. Or, in my case, a simple antenna and some coax I used to use on 432MHz. It is perfectly possible to make good aircraft scatter SSB QSOs during the contests using simple equipment. At other times many QSOs are arranged using KST microwave chat. Airscout helps, but you can just rely on the DX stations to tell you when a plane is approaching the path. Let them use Airscout!

Nothing here implies any greatness from GM4FVM or his equipment, which was largely donated by others. GM4JJJ (sadly SK), G4DBN, and G8SFA each helped me no end. Most local amateurs will help if you ask. 

There is still more for me to do on 23cm. It is not the weird place I used to think it was.

Perhaps later I will explain a bit more about Airscout. 

73 Jim

GM4FVM 

FT8 etc, weak audio, try unticking audio enhancements in Windows

A fellow ham was having problems with the audio stream on data modes after he switched to a new Windows 11 laptop. It emerged eventually that a box marked "Enable audio enhancements" was checked and this was altering (mostly reducing) his audio level. He uses WSJT-X but I expect that the same thing would apply to MSHV and all the rest of digital radio software.

This was in Windows 11 but it may apply to earlier versions of Windows too. 

In the end what we needed to do was untick the box, but finding it was a long operation.

Untick this box in the Advanced section of the Microphone Properties tab

What are Audio Enhancements? 

Audio enhancements depend on the hardware installed or connected to your PC. Therefore, on my basic gaming computers and laptop they were absent. I found this on a Windows help site :- 

================================

Audio enhancement packages are designed to enhance your specific audio hardware performance and quality.

Available audio enhancements will vary depending on the manufacturer.

Sometimes these audio enhancements can cause problems with audio and sound. If you encounter an audio or sound problem, you can try disabling audio enhancements to see if it may solve the problem. 

================================== 

So the basic answer is that these enhancements could be anything, and they could alter the audio between your rig and your WSJT-X software in any way you can think of, and probably in some ways you cannot imagine.

The solution is to find the rig's entry in the Microphone Properties tab and turn them off. 

The problem here was variable and often very low level audio stream. Solving it turned out to be tricky as I had no idea what I was looking for. My laptop does not have this box so I was at a loss. I took my IC-7300 and my laptop over and compared it with the other setup. His rig worked perfectly with my computer, my rig worked perfectly with his old computer, my rig showed the same problem as his with his new computer. Clearly the problem was in his laptop.

After a lot of pondering, we went through the Sound settings (you find them in Control Panel). Mysteriously, Windows calls the audio input section "Recording" so click that (the output is called "Playback"). Then you click the tab for your rig input, probably "Audio Codec" or "Audio Device". Microphone Properties appears and you click "Advanced".

Untick the "Enable audio enhancements" box

If you are wondering why my example says "Headset Properties" at the top, I just used this illustration to show where the culprit lies. My PCs do not normally show this box and therefore I was totally unaware of its existence. However, I found that by linking my JBL headset, which has a microphone, to the computer via Bluetooth, I could make the box appear. That is why the audio stream is only tape recorder quality; for radio purposes I use DVD quality at 48000 Hz.

So if your existing PC does not have this box you can ignore all this completely. But if you buy a new machine or something is updated or added, you might find that it suddenly appears. And your audio stream level could suddenly take a huge dive.

In any case, I do not like pre-ticked boxes in any circumstances. Windows updates have a habit of including new pre-ticked boxes for features I never requested and don't want. This is just another one. 

If a pre-ticked box suddenly signs me up to a credit agreement I never asked for I could probably live with the annoyance. But when pre-ticked boxes affect the audio stream for FT8, well that is just outrageous.

This should be made illegal and the perpetrators locked up.

Or something. 

73 Jim

GM4FVM

What to do at the end of the current solar cycle - 432MHz?

What, is it over? Well, no, but I have been thinking about what to do when it is. The answer appears to be that I should "do more of the things that I like doing". Such as ... working a ton of stuff on 432MHz.

I suspect that an HF operator might go lower in frequency bands, and I will probably go higher. No great breakthrough involved in that idea, but it would involve readjusting the direction of my efforts and maybe some equipment.

For a couple of weeks I have been dithering about what to do when (if?) the intercontinental DX fades away. Should I switch my emphasis away from 6m and 4m? To what ends? Go back to more EME (moonbounce)? What result am I striving for? What will I end up enjoying most?

And then, without bidding, up popped a tropo opening on 70cm. Wow! I was aware of a high pressure system approaching, but it did not look as if the timing was right for the two 70cm contests in August. The first contest is the RSGB UKAC on 12 August using SSB and CW and I do not often participate in that one. Usually I turn my beam East on the same evening and give away points in the Nordic contest going on at the same time. I usually do quite well across the North Sea, and I work a few stations quite easily. The second contest on 13 August is the 70cm FT8 UKAC.

On 12 August I managed to work PA3CWS at 08:36 but nothing further until DK6JU at 16:02 and DR0X at 17:25. DR0X was a huge signal calling CQ for quite a time but he got very few contacts, which indicated a duct forming over the North Sea. Once the contest started could only I allocate it about 45 minutes due to domestic duties. Between 19:15 and  19:57 I contacted 4 x PA, 4 x OZ and GM8JBJ. Total for the day was 12, not bad for a 70cm operating session.

13 August dawned bright with haze over the North Sea. The air was still and with high pressure it all looked great. Sadly I was to be out of the house for most of the day. Between 06:26 and 08:48 I worked 6 x PA, 4 x DL plus OZ1DGN,  F5APQ and G4RQI - a good two hour spell. I was then QRT until 17:56. After that I was busy and could just look in for five minutes at a time. In a series of five separate five minutes spells, 6 x PA, 3 x GM, 5 x OZ, plus DL5EBS, EI3KD and LA6P 

This contest work plus a few worked later produced this result:-

432MHz contacts at GM4FVM on 12 and 13 August 2025

Total operating time was probably around 4 hours but this is hard to judge given that I was in and out of the shack. It brought a total of 38 QSOs in 8 DXCC including 16 squares. Best DX was to DG0KW in JO64 at 978km, there were nine QSOs over 700km, and nearly all the rest were between 600 and 700km. 

After this I went on to 50MHz and worked PY5EW in GG46 at 9940km.

Now this made things very plain to me. I was much happier reaching 38 stations on 70cm than I was working the the far more distant one on 6m. Whether this PY contact will be possible outside this sunspot peak I am not sure because I worked PYs at the bottom of the cycle too (but not that far away). But if 6m DX declines I can still enjoy a blast on 70cm.

I also get some pleasure by doing things like this without a kilowatt linear and a vast stacked array of antennas. Just 150W and 16 elements - modest by 70cm standards. 

Everybody will have their own place to go when the DX declines. Top band? Construction projects? Building ships in bottles? Anyway, for me, a good blast on the higher bands when conditions are good is hard to beat.

Conclusion: do what you enjoy and don't fret over what the sunspot cycle has given and then taken away. 

I will now reflect on the fact that outside a contest I often struggle to work anyone on 70cm. Lack of activity is a big problem, and also the narrow antenna beamwidths can make life difficult. But being very busy during a contest brings its own joy so I think I will migrate back up the spectrum when there are poorer harvests on the lower bands. 

 73 Jim 

 GM4FVM

VHF propagation changes like the weather

I think of the Solar Cycle as being like the annual climate chart, changing over a longer period of 11 years, but vaguely predictable in the long term. VHF propagation is more like the weather, seemingly changing at random week by week and day by day. Here in IO85, also like weather, VHF propagation can change minute by minute. (I will avoid the Doobie Brothers reference which would have been Minute by Minute - I keep holding on).

The 11 years Solar Cycle may bring F-layer propagation, increase TEP, or decrease aurora as it passes along, but its influence over Sporadic E is debatable. In fact, what causes Es to vary like the weather is a mystery. Take the last two weeks. Two weeks ago on 70MHz I managed eight QSOs, not much to report for a seven day period in late July. Of course I blamed everything from my station to some of the more kooky theories about Es. Eight QSOs to seven squares in five DXCC in a week. Best DX was not bad at 1859km to EA6SX but for this time of year those were slim pickings.

I was comforted by the old saying "what goes around comes around". According to this, things balance out in the end. A more scientific approach might be the statistical concept of "reversion to the mean" which states that if things are unusual then they usually go back to normal soon. So maybe next week would produce a bumper catch of stations to compensate for a thin netting the week before. What are the chances of that happening?

"Patience dear boy" as someone might have said. Me? Patience?

Last week the next seven days duly delivered. It reverted to the mean. I had 59 QSOs to 15 DXCC in 43 squares. Even the DX was better - EA4L at 2122km. 

WEEK ONE - 70MHz contacts at GM4FVM - 22 to 28 July 2025

WEEK TWO - 70MHz contacts at GM4FVM - 29 July to 4 August 2025

As usual, click on the images to enlarge them if necessary

So one week's Es is different from another. What does this prove? Well, whatever the figures say for me it is mostly about things which are all in the mind, more than about things to do with the propagation. There are lots of random factors at play with things like this. For example, was I at home, in the shack, waiting for a contact when an opening occurred. Was there anybody else at the other end in a similar state of readiness. Were we both likely to use the same mode? What about the time difference (like me doing my post-22:00 round up when it is after midnight in Finland)? Was there an opening to the West where only the cold grey Atlantic lies to swallow up my radio signal?

The thing is, after the first poor week I might be tempted to give up. I might think that 14MHz or digital voice could certainly be easier (perish those thoughts). Perhaps it is all in the mind, but that first week could have put me right off trying again.

Things got better later. With such a random set of factors set against a pretty chaotic propagation background, OF COURSE there will be weeks when less happens. There will also be weeks when lots of things happen. I have to take the rough with the smooth.

The sunspot numbers change, the weather changes and tropo propagation comes and goes just as Es does. It helps to have several bands to use.  I worked V51WW on what was probably Es-linked 6m TEP. Also, two PY stations probably on multi-hop Es. 

Things often get better if you keep trying. They would get better anyway whether you try or not, but if you are still trying at least you will be there to witness it.

73 Jim

GM4FVM

Scotland to China opening on 50MHz

Did I get this wrong? In my last post I suggested:-

As I write this on 23 July I am assuming that these propagation modes have closed for this year ... maybe not!

"... maybe not!" And so it proved.

On 30 July I could see that some stations south of me were working into Japan though there was nothing from Japan heard here. I reckoned that something might happen so I beamed at about 30 degrees and started calling CQ. I worked OH5KNL, SM0GNS and OH1EEZ, all in the right direction. It seems to be the case that Es towards the Nordic region is necessary for propagation to opening towards East Asia.

Then I was called by BG3OJZ at 08:48 and completed that contact. This was followed by working three more stations in China, including BA4SI at +01dB. Shortly afterwards BA4SI peaked at +06dB. I topped it off by working JE6WOQ at +00 at 09:16. I also called but did not complete with two more stations in China and two in Japan.

50MHz contacts over 7900km at GM4FVM on 30 July 2025

The distance increased at the start of the opening from 7963 to 8423 and then 8928km. The propagation then shifted slightly to the East at 8382 and finally 9096km. Not bad dx for me.

Someone suggested that I should explain why this happened so late in the year when this type of propagation is usually associated with the end of June equinox. I have no idea about why this happened.

I heard at least six other GM stations take part in this event, plus two GIs. This suggests that there is nothing special about my station or my location.  

Despite several failed attempts I had only contacted one station on 6m in China before, and that was BA4SI on 27 June 2024. The problem with this later opening is that I cannot lower my vigilance as July comes to an end. If this can happen at the end of July, then can any propagation happen at any time?

73 Jim

GM4FVM