A classic case of Television Interference

Anything which transmits radio frequency signals seems to have the potential to create television interference (TVI). Well, pretty much anything that I can think of, if it is positioned in the wrong place.

There are plenty of things to consider when looking into these cases. Why has the interference started? What has changed? If you can answer those questions you stand a chance of solving the problem.

Fundamentally of course the television has to be capable of dealing with RF signals on frequencies other than the ones it is intended to receive. The manufacturers claim that this is true. These days they are generally pretty good at this, but you cannot rule out this as the root of the problem. And then, even if the TV is OK in this respect, possibly some wideband distribution amplifier is not good a keeping out signals from outside the TV band. I would suggest, look for a wideband distribution amplifier as your first possible culprit.

So, when I got a report of TVI coming from a neighbour I immediately wondered what had changed. Oddly, nothing significant had changed on my side for a few years. True, I had got stuck when my knee failed at a time when I was in the middle of moving antennas about. Now though all those antennas are back where they had always been. Even my 28MHz vertical, which I use on 24MHz as well, is back where it had been several years ago.

If my antennas had not changed, and the neighbour said that her TV setup had not changed for a couple of years, then I was a bit stumped.

This seemed like an odd one, but in the end the same thing solved it as usually solves such things - a braid breaker.

Garex HPF1 HPF and braid breaker similar to the one used

I first used a braid breaker for this purpose within weeks of first being licensed all those years ago. I think I still have that one somewhere ...

Anyway, at first it did not seem too obvious what was wrong and it was too soon to jump to conclusions.

As usual, the neighbour had come to me with certainty about the interference, but no definite dates or times. This is not her fault as it is not her duty to keep a logbook. She had contacted her TV antenna installer who thought it might be due to telephone interference. This type of interference came about when part of the "Freeview" terrestrial TV frequency allocation was given over to mobile phone usage. That sounded a bit unlikely to me.

I had in my mind an incident which happened a couple of years earlier. The same neighbour had come to me as she had knocked the preset channels off the television in her bedroom. She asked me to retune the channels. This proved to be very difficult. When I checked it the signal level at the antenna socket in the bedroom was at a very low level, to the point that tarnishing of the socket was preventing any useful signal reaching the TV. By cleaning the plugs and sockets I managed to get the thing tuned, but it was marginal. At the time I suggested to the neighbour that she call her antenna installer and get him to check out why the signal was so weak.

From this visit I had gained the impression that there were three televisions in the house (bedroom, kitchen and lounge), which implied that there would be a distribution amplifier somewhere. The antenna was probably in the attic space, a common arrangement around here. The main TV was connected to a "BT box", which is an internet connected entertainment console, plus a DVD player. There were plenty of coax and internet leads around to pick up rogue signals, though over the years I have added ferrites anywhere I could, as much to keep them from radiating noise than picking it up.

TV in this area is served by an infill repeater on the nearby headland overlooking Eyemouth. The field strength from the repeater is high, but this repeater offers very few programme options. Several villagers have erected tall masts to point at the main transmitter (Selkirk). Although we are outside the Selkirk service area they still get a reasonable signal, though when I tried this some years ago it could drop out at times. Faced with this problem, most of the other villagers have installed "Freesat" satellite TV, or have subscriptions to Sky TV. We have Freesat.

Unusually, this neighbour uses the local Freeview UHF repeater, which is within sight of her antenna. It seemed odd to me back then that some time ago she was getting such a weak signal on her TVs, and indeed, was only now getting TVI.

I sought advice from Mike, GM3PPE, who kindly offered to help. It is impossible for one amateur to use their equipment and monitor TVI at the same time. Mike also agreed to come over and do some tests. We pondered over what could be happening as we went round with various pieces of test equipment, a jar full of ferrites, and a box of braid breakers. The main TV was getting a strong signal now (something had changed but at first I did not know what). We checked things out and went up to look at the antenna. In the attic space we found a mains powered distribution amplifier with four outputs. The LED light on this was on, but beside it was another Labgear amplifier, also with four outputs, which was disconnected.

TV distribution preamp similar to the one involved

Now we started the tests. I left Mike with a PMR hand portable and I took a second handie back into the shack. I then transmitted on all the frequencies I normally use, beaming in various directions and using different power levels. Mike watched the television in the lounge which had been affected by TV and reported back.

As soon as the tests started the surprises began. Having found the distribution amplifier I had guessed (correctly as it turned out) that the amp was being affected by my signals and not the television directly. I was wrong however in assuming that it was suffering from overload. I had feared that the electromagnetic field I was creating was simply overwhelming the amplifier circuit boards, as sometimes happens. Not in this case.

Mike quickly reported that I was indeed causing TVI on some bands (4m and 2m, which surprised me), but lowering the output power by 3dB stopped it entirely. Likewise, moving the beam antennas 10 degrees or so away from the TV antenna also stopped the interference. Rather than totally swamping the amp this looked like there were simply unwanted frequencies getting into it and being amplified, probably arriving down the antenna coax. 

With swamping, where the signal is getting directly onto the boards, quite small signals can cause big problems by desensitising the amplifier, and there tends to be a "cliff edge" effect whereby only by reducing the signal to a very low point does the interference stop. I was still thinking about the time in the past when I found low signal levels, and I thought any desensitisation would cause problems. Here, though, the interference weakened very quickly, and seemed to be stopped entirely at about -3dB lower signal at my end. This should be fixed fairly easily, I thought.

Next stage was to try a filter in the antenna lead between the antenna and the amplifier. I had various devices in my box, including 50, 70 and 432MHz notch filers, and several general purpose braid breakers. At this stage Mike's wise approach came into play. He studied the data sheets for the various braid breakers to check which would introduce the minimum attenuation to the wanted TV signal. My approach was a bit gung-ho, so I would have just tried something. Mike rightly wanted to select the best one for the purpose. The best one of the bunch turned out to claim an insertion loss of better than 2dB "at UHF". Other details were rejection on the inner of better than 60dB at 30MHz and below, and better than 25dB at 30MHz and below on the outer. Given that 3dB seemed likely to do the trick we tried this. 

The choice was made on the basis that although the HPF1 filter I brought had greater rejection of the unwanted signal, it did not quote a insertion loss, whereas the HPFS had a quoted figure for loss at TV frequencies. Based on the tests we felt that we did not need more rejection of lower frequencies. Of course, I use frequencies up to 432MHz (I doubt if 1296 is an issue) so the attenuation will be less as the frequency rises, but it seemed like a useful first step before trying the notch filters. In the end we did not need to try anything else.

I fitted the braid breaker (the HPFS, not the similar HPF1 in the photo above) and returned to the shack to do the tests again. Mike reported no TVI. Not on any band, at any power, beaming in any direction. Mike then moved on to the television on the bedroom and achieved a similar result. So what had happened to suddenly cause this TVI?

The homeowner told us that the antenna installer had installed the current distribution amplifier a couple of years ago. The old one, which I guess had failed and was the cause of the weak signals I had noted back then, was a neat Labgear. Like most Labgear amps, no doubt it was well screened. The new one produced a stronger signal for her but was wide open to interference. So why did this not prove to be a problem immediately when the amp was replaced? Well, probably because this was when I had my antennas moved while I was recovering from my knee operation. At that time they were displaced, but lately I have put them all back where they had been originally.

When the TVI was reported I could not work out why, when everything was where it always had been, there was suddenly a problem. But the new preamp had been there for a while and it could not have coped with my original layout as the old preamp could.

Incidentally, we never did see the TV antenna involved. Once we found the preamp there was no need to climb any further. We simply connected the braid breaker into the input of the amplifier. Checking the antenna would have involved a lot of attic crawling which was not needed. Clearly there was enough signal getting down the coax, wherever it was coming from.

Also, there turned out to be a fourth output from the preamp, feeding a TV in another bedroom. We just did not know what we were going to find that day. As it turned out, there was a proper preamp, and it worked quite well once it had a filter added to the input. I attached a label to the filter "Do not remove" - we can but hope.

Initially I had feared that, as in some other houses, we would find a non-amplified "aerial splitter". These "dumb" splitters introduce 3dB loss per output. Some antenna installers fit them to avoid installing mains wiring and possibly later to rule out the possibility of preamp circuit failures. It is true that the earlier preamp had failed, so perhaps the point is arguable, but for me a properly installed preamp should always produce the best results.

So that seems to be that. It is impossible to check every outcome at different power levels and beam directions but several weeks have now passed and no further complaints have been received. I have checked and the neighbour seems quite happy with things as they are now.

I could not have solved this problem without the help of GM3PPE. His advice was very valuable, and he carried out the tests at the other end. He tactfully discussed the issue with the neighbour and provided a very useful expert for her to rely on. Thanks Mike.

Now, what is next?

73 Jim

GM4FVM

A tropo opening at last.

Perhaps the strangest thing about this latest tropo opening is that it is so long since the last one. My most recent posting here on this subject was in early June, 3 months ago.

I think of Summer in this part of the UK as not being particularly hot but often having long settled sunny spells associated with high atmospheric pressure which brings tropospheric enhancement. Not this Summer. After a promising start, July and August were grey and miserable with low pressure for weeks on end. Of course the low pressure does not last for ever, just like the high pressure never did.

During the period 4 to 9 September a series of high pressures passed from West to East. For a time there was a low pressure system to the North West of me (as there often is) which brought winds and shut down the propagation, but generally conditions remained up for most of that period.

Things seemed to be best on 144MHz, with 432 not bad and 1296 pretty poor.

144MHz contacts at GM4FVM 4to 9 September 2023

39 QSOs into 30 different squares was a very agreeable outcome.

Those of you who have clicked on the image to give a better view of the map may have noticed that F6ASP appears to have his station located in the middle of the English Channel. If that was true the UK Border Agency would be out to try to send him back to France. In fact what has happened here is that because I only have a four character locator for that station the map assumes that he is in the middle of the JO00 square. This happens a lot, and I have to look up six character locators for some stations who do not list them on QRZ.com, or for which VQlog does not have the full details. In this case F6ASP does not have a more precise locator anywhere that I can find it, so he will have to remain in a watery position for now. 

Queue the tune "Sailing By" written by Ronald Binge, which is played by the BBC before the Shipping Forecast. This is now used by anyone too lazy to find anything more relevant to the sea. I am as lazy as the next man. I know Claude Debussy's La Mer and Benjamin Britten's Sea Interludes might be better but perhaps I will just stick to what I always do. This "don't blame the lazy" theme will return at the end of this posting, but by then it might have some amateur radio relevance [about time Jim, this is not a music blog].

On 5 September I had the chance to operate for a short period during the NAC contest. I switched to using the EU contest mode in WSJT-X and worked SM7VUK, DG1BHA, SB7A, SK7OL and SM7SPG in 33 minutes. I could have worked more but had to go to attend to domestic duties. Contests have their uses but I am not about to become a slave to them.

Things seemed to be going pretty well on 5 September so I decided to try coming on to 2m at 05:00 local time on 6 September. This was to see if the supposed good conditions early in the day would pan out. I was pretty pleased then to work EU3AI in KO22, a distance of 1757km, at 05:40 UTC. Of course I have worked him before (!), but this time it was tropo which is definitely the hardest way to work Belarus. 

Having worked Belarus on 2m both of the easy ways, by meteor scatter and Sporadic E, doing it on tropo seemed to complete the set somehow. Just as people say that if the Jumbo Visma cycling team win the Vuelta a España this week, resulting in a clean sweep of winning all three Grand tours this year, somehow doing it three times in different circumstances makes them invincible. It doesn't mean that of course, and nor does me working Belarus three different ways mean anything very significant other than that I was in the right place three times over.

Still, I am claiming that my early arrival on the band that morning was the result of superior planning on my part and shows how knowledgeable, dedicated and devoted I am to my hobby. It doesn't mean that of course. Ever heard on insomnia? What else do you do at that time of the morning other than listen to the radio?

I also heard two Russian stations in the Saint Petersburg region and one Ukrainian station, but did not work any of those. I cannot complain though as 15 countries worked on 2m is five days is still pretty good.

OH1ND in KP00 is 1493km, still a good trip on 2m, and LY2WR in KO24 is 1681km, barely 70km short of EU3AI. So there was plenty of action short of the ODX.

Moving on to 70cm

432MHz contacts at GM4FVM 4 to 9 September 2023

35 QSOs on 70cm is only four less than the 2m total and shows how well we can do on that band during reasonable lift in conditions. SM0DJW in JO88 is a pretty good contact on this band at 1242km. There were more contacts into PA on 70cm and there is no doubt that the path from me into Benelux on 70cm can often be better than 2m. Once again the DXCC total is pretty good - nine countries worked on 70cm would have been a good lifetime haul for me when I started out on this band. 

Meanwhile on 23cm...

1296MHz contacts at GM4FVM 4 to 9 September 2023

On the face of it, 23cm looks like a bit of a washout compared with the other bands. It did not feel like that at all. The QSO with  G4YTL was particularly interesting. We were in contact via KST chat and after setting up the initial details, it took 20 transmissions from me on FT8 for David to decode the two that he needed to complete the contact. That is over a distance of just 427km during elevated conditions. We then switched to Q65 and competed a second QSO in just over a minute. In FT8 David could not decode 18 of my 20 transmissions, while on Q65 he decoded all of them (just three needed to complete).

There is nothing very starling about this. I have worked David on Q65 on 23cm before. What surprised me was seeing the comparison in modes play out. Q65 is simply a superior mode to FT8. The difference may not matter much on HF or during favourable conditions on other bands. However, once we reach marginal conditions or bring into play scatter propagation as with aircraft scatter or EME, then Q65 shows how good it always has been.

This brings me back to the question I often ask myself. Why, when Q65 is better, do VHF and above operators still not use it? It seems to me to be absurd that many EME operators on 2m still use JT65. If we could bring Q65 to bear during ionoscatter or troposcatter it might well make the difference between completing a contact and failing totally.

Sure, if you are on a chat room like KST (argh, how I dislike that but needs must) you can set up a Q65 contact. But what about the generality of contacts which happen randomly? Could VHF operators not decide as a group to use Q65 instead of FT8? This is a bit like asking why some people still use FSK441 or RTTY. They use outdated protocols because they do not want to change. They have every right to use old modes, and I do not deny them that right. But that is like saying that they have the right to miss all the QSOs. Sure they do. Knock yourself out with that idea, mate.

In conclusion ... this opening was a test for me to check out the two band with two feeds DUAL 2m/70cm antenna. I doubt that it can be quite as good as the I0JXX for 2m and the Wimo for 70cm because they are single band antennas and are designed for that one job. However, it went pretty well and I think I should be content enough about that.

Now, the 23cm antenna might now come into the reckoning for change in some way. Elevation? Time to think again about 23cm EME?

73

Jim GM4FVM

A long term milestone reached at last - and TEP or multi-hop Es in September?

It is sixteen years now since GM4FVM returned to Scotland and took up this callsign again. After a busy few years of moving from GM to GI to G, finally we came back to Scotland. Finally (I think). Mind you, having done G to GI to GM before that, you never know.

It took a while to get established here, and I had my first 50MHz contact as GM4FVM on 23 February 2010, over thirteen years ago. That was to GM8BDX in Birgham, less than 30km away, but it produced DXCC number one on 50MHz. 

So that was the start. It was three months before S53CC gave me DXCC number two.

By March 2017 (only seven years later!) I had reached 55 DXCC on 6m, over half way towards that magical DXCC itself. DXCC on one band still seemed a bit of a stretch for me. However, by March 2018 the total was 63 and by the end of 2018 it had reached 71.

I think you can see where this is going.

By July this year the total had reached 93, and a month ago 99. Almost there. However, that seemed to be it for 6m Es in 2023. This year's Es season appeared to be over and certainly as far as multi-hop Es was concerned.

However I still keep an eye on the space weather via Solarham (link in the sidebar). There was a disturbance on 3 September. The data on DXMaps.com stated "SWX=Moderate Storm" which was enough to get me interested.

I had been checking in at the shack at various times just in case something happened. Otherwise I was watching an excellent episode of that reliable Kiwi detective drama "Brokenwood Mysteries". This one surrounded a murder amongst a female motorcycle gang and I got quite involved in the plot. I do think that the arrival on the scene of Detective Chalmers has definitely brought a slightly more gritty angle to this series - and it needed it. Anyway, I devoured the whole thing.

When I strolled into the shack again at 20:59 UTC I was surprised to see that there was a lot of traffic on 6m from the direction of South America. In fact, I saw Gordon GI6ATZ working a CE station and David GI4SNA working an LU7. Time for action.

By 21:06 I had worked PU4JOE, and then CE3VRT by 21:09. And that was it. CE3VRT was my first 50MHz contact into CE from here, and also CE was my 100th DXCC worked on the band. Job done.

Contacting PY5EW completed activities for the night, at 21:13.

50MHz contacts recorded on DXMaps on 3 September 2023.

DX Maps tells the tale but maybe does not answer all the questions. All of those contacts into South America are shown as Trans Equatorial Propagation (TEP). Yet, when similar contacts were made a week or so earlier they were all recorded at Multi-hop Es. There certainly was Es about as can be seen by the red lines within Europe.

Was this TEP at 21:13 in September, or multi-hop Es, or a combination of the two? I do not know.

Moving on from that question, I had to check Clublog just to see that they had acknowledged my 100 score. You never know you know, someone near to me might have sabotaged me sending Clublog the details. You do not need to be paranoid to write this blog but it makes it a lot easier to fit in if you are.

Clublog personal DXCC chart page for GM4FVM

Well, I can move on from that too. 

The achievement moves me to 1523rd place in the Clublog 6m DXCC list. I would not describe that as having achieved greatness. I am 1523 steps down the ladder from the top, but rising to the top has never been my ambition. I only do this to measure how my station is operating.

Who cares about places on that DXCC list? Not me.

These little milestones just serve to motivate us and to check if things are getting better. They might spur us on to improve the antenna or something similar. After that the next thing happens.

I am more interested in the mode of propagation which got my 50MHz signal to CE3VRT than the achievement of working 100 countries. Even more intriguing was reading CE3VRT's QRZ page about his efforts at 23cm moonbounce using a 1.8m dish.

Hmmm. Most interesting.

73 Jim 

GM4FVM