On moving to Thailand we subscribed to the UBC Corporation of Thailand satellite reception system, that uses a small satellite dish. This provides about 30 TV channels, and a few sound channels. I had carried out routine checks to confirm that I did not cause any interference to our own TV reception, and thought no more about the matter. Following the neighbors visit, I inserted my best TVi filter, an old Drake 1 kW low passes filter, and cautiously kept off 10 and 15 meters. Preferring to keep a low key, on 40 meters and occasionally using 20 meters late of a night time.
It was shortly after breakfast on Sunday morning after a good session on 40 meters, and a very brief spell, long path to USA on 20 meters that my wife Carol reported a strange vehicle parked outside the front gate, with a large random antenna on top. They were the men from the radio frequency and monitoring bureau, looking up complaints.
This was serious stuff and after being satisfied that I was in fact a licensed amateur operator, licensed to own a tower and equipment, (both requiring a license from Bangkok), offered to undertake local testing. I was required to change bands and antenna directions etc. This was conducted via mobile telephone. The tests were brief and I concluded by offering to take my LPF and several others on hand to their office in the morning for testing.
I now started to analyze my position, and what was wrong. I soon realized that 99% of all neighbors watch Thai TV on band one, although 605 lines are used in Thailand, the bad old days of transmitter harmful third and fourth harmonic radiation, was back again.
The following chapters describe ways I devised to combat TVi. The process whilst still not complete, has taken almost two years effort in cleaning up the station, in a quest to remove interference. A broad outline follows, and section details are listed below.
Grounding, Screening, Filtering, and Rusty Bolts Effects. Unfortunately there is no short cut once TVi occurs, identification and eradication is a case of covering each category. Perhaps it is possible to mathematical devise a formulae that would allow a short cut of one or two items, but complacency is no guarantee of eliminating TVi. Here are the steps, that I selected to undertake, and every step must be recorded for reference.
Have a TV set conveniently located, say across the room, for monitoring purposes, whilst operating. Identify which of the amateurs bands, interference's occurs with which TV station, and very important at what power level interference occurs. Turn the antenna and record the result as a plot. More about this later.
Likely you will have filled up several pages of data and not seen any pattern. I have provided a spread sheet for ready reference, and doubt if your circumstances are that much different from mine.
If you are serious about curing your TVi, you have a lot of work ahead. The object of the clean up is to eliminate earth loops, RF pickup, electromagnetic radiation between objects to objects, object to wires, and wires to wires. At this early stage we are not clear as to why we have TVi so the order is to establish some basic ground work. This includes data recording of channel interfered with, transmitter level at which interference starts, and very important how you perceive your reception, is it very quiet, not a problem, can hear all the DX on 40 meters, (I don't thing so) or, very noisy, to, can't hear anything.
There are two ways of evaluating this situation. One is to operate the receiver off batteries and switch everything off, preferable at the house mains. The other and very important put a dummy load on the end of a long piece of coaxial cable, say 10 meters or more, out into the garden, and do the same test with the mains off. The dummy load, on the end of coaxial cable, must be connected to the normal antenna port. Equipment including cables must not be bypassed, for convenience sake. The test is to check the integrity of the whole system for leakage, in and out of our systems.
We now subdivide this interference that you hear on the receiver even if only an S1 as mains born electrical noise or interference at RF from outside. In both cases they would appear to be the same, but they are not. The principle to grasp, it that a two way system is in operation, if mains noise is coming up the domestic supply then the transmitter interference to the TV is carries back the same way. If on dummy load it is noisy then there is a RF leakage somewhere.
The object is to make everything RF proof, the receiver should sound dead, and I mean dead on all bands. Lets talk about proofing the transmission RF path threw to the antenna. Most transceivers will have air vents on the top cover, have you placed your antenna rotator on top of the rig, can the control cable see the air vents? If so relocate the rotator controller. Remember that we are talking about RF getting out and radiating a signal causing TVi.
Until this is eliminated we can expect it to happen in reversed and those +60 DB signal to block out reception. My rule of thumb was that no equipment wires should see the transceiver. This includes coaxial cable, control cable, speaker wires mains wires. Get rid of the rats nest.
Mains Born Interference and Peculiar Effects
When touched on any equipment the led was very bright. When on the neutral incoming wire it was bright, when placed the supposedly mains earth, it was bright. In effect the neutral was hot at most sockets outlets. The antenna guy wires were also showing bright, when supposed to be at zero potential. Even the earth around the house appeared hot. At first it was thought that RF was being picked up, especially on the guy wires.
I was very unhappy with the house mains distribution box, which with a volt meter showed a few volts difference across each phase input wires. Whilst we have a single phase supply distribution to the house, three cable wire enter the house, with 30 meters of cable running up the drive way, which is then joined together and tapped off a single phase power grid outside. The solution was to joint together all three incoming cables with a large strap in the house distribution box. This entirely cured the potential difference with respect to earth at all electrical outlets.
Unfortunately, the distribution box was still hot when switched off, so a separated earth was provided to ground. Then breakers were then switched on, one by one, checking for live earth returns. It was found that every air conditioner whether on or off, required a separate earth, this applied to the fridge freezers and all fixed electrical appliances. After carrying out extensive grounding, the above test were carried out again.
With all radio room equipment unplugged, the neon was dead, on the neutral wire and earth's. This included the antenna tower guy wires and ground. It is assumed that the neon can pick up 50 cycle leakage. The radio equipment was now switched on, and the difference in background noise was amazingly quiet. All sorts of odd noises had disappeared. Unfortunately it was found that with the radio equipment switched back on that the ground was once alive.
These measurements have never been consistent, strangely different when measuring standing in front of the rig, to those measurements when standing behind. Also reversing meter leads or even holding one end, produced some sort of reading.This was never understood, despite using outer coaxial braiding as earth straps, that should have bonded each piece of equipment together. AC measurements, DC measurements, and ohmic resistance were all inconsistent.
I contemplated using a copper strap as a main buzz bar, but copper strapping is not readily available in Thailand, nor is it a thing of beauty after a few years, when oxidized. I opted for a piece of aluminium 2 by 2 by ¼. Bolting this to the back of the operating bench as per photos. I next double bolted each and every piece of equipment to the buzz bar with a short aluminium strap 1x1x.8 this included the computer, speaker, transceiver, remote VSWR meter, remote coaxial switch, and antenna rotator controller, and station monitor.
I mounted the low pass filter along the aluminium buzz bar. I used a crimped and solder lug with a half inch nut and bolt at the end of 10mm cable to bridge the equipment buzz bar, to the outside tower base. This is a completely separate earth called the station earth.
Again the results are amazing, all voltage and ohmic testing showed a solid zero between all equipment's.The neon was out when used at the front of the operating desk, but not when standing around back. How could this be, I was standing on several mains wires and several were resting on the antenna coaxial cables.
Following the installation guide lines set out as before, that no cables should see any other cable. I re roughed them all, making a single point distribution block, instead of mains leads running all over the place. I undertook the mammoth job of screening all mains cables, all supply cables, all speaker cables, cables etc. This included 220 Volts ac and 12 volts equipment cables, and all signal cables. Testing after completion, the neon was dead, when holding or standing on the single point 240 AC cable.It is worth mentioning that along the way, that a source of interference was attributed to the computer. Hash coming from the computer was so bad, that chasing DX on 40 meters, I had to turn the computer off to be able to copy.
Here are the things I did, to eliminate switch mode power supply problems. Scrape all edges of the cabinet enclosure and case frame with sand paper until all the coating has gone, and the metal is bright, so that the lids, sides back and front, are solidly bonded. I fitted an approved mains input socket filter. There is a place on the PSU board for one, but was not fitted. In my case a little filing was necessary in order for it to fit snugly.
The main noise source, now came from the 5 volt supply. Fortunately, whilst there are many wires, the 5 volt leads are long enough to wind several turns around split ferrite cores. It is handy to listen on a portable radio in AM mode, to test how the filtering is progressing. I added about four ferrites on the five volt supply. For good measure I change the 240 AC mains input supply lead to screened type, between the computer and monitor.
Looking objectively, how else could any harmonic signals, escape the radio shack. It dawned on me that the antenna remote cable, and rotator cables, where a prime candidates. The remote Ameritron had bypass capacitor fitted, but the CDE rotator controller did not. I fitted inside, a 0.01 micro farad bypass capacitor, to each of the eight cable pin. Final testing, I was very pleased, having spent a few bob on screened cables, and lots of accessory parts, many hours of labor, and off air time to cure the interference.
Now checking with the neon tester, all equipment is now dead, receiver on dummy load dead, reception better, able to operate on 40 meter whilst the computer was on. Repeating our TVi test now showed a positive improvement. In my case, before the modification, it only required a few watts to cause television interference. After modification at 100 watts, nothing.
However this is not the end of the story, wishing to operate at higher power levels, it was necessary to do additional work. This is described under the subject of "TVi Filtering"