At 09:16 PM 6/23/99 +0100, you wrote:
>I just thought I would send you this message as some work I have been
>doing recently further validates the observations in one of your papers
>on High Bandwidth Primary Behaviour. It also sheds new light on the
>You may remember my posts to the list about Television interference
>many months ago. Once again, I am grateful for those who replied and
>suggested things to try, however, no definite cause for the TVI was
>found and still no solution exists for me.
>Today I ran my coil and used a Video Recorder to record a local TV
>station, so I could see how bad the interference really was.
>When I played back the video I made an interesting discovery....
>The interference consisted of 4 thin horizontal lines of white dots.
>(4 lines indicating my 200BPS rotary firing rate.)
>However, when the video was "freeze-framed" each horizontal line was
>clearly made up of exactly 23 dots with REGULAR SPACING across the
>screen. Kind of like this:-
> / \ I spoke to a friend in the TV business
>! . . . . . . . ! and he told me that one TV scan line in
>! ! the UK is 56us. Therefore, the 23 dots
>! . . . . . . .! in each line indicate that the source of
>! ! interference is pulsing every 2.43us for
>! . . . . . . . ! roughly the duration of one line (56us.)
>!. . . . . . . ! The 2.43us corresponds to a repetition
> \___________________/ rate of 411 KHz. Now for the surprise.
>The resonant frequency of my TC is 206KHz. (Half the repetition rate
>of the interference bursts !) At first I thought this was a mere
>coincidence so I removed a toroid, and retuned the TC to a higher
>frequency (280KHz). Guess what ? This time there were 31 dots per
>horizontal line !
Two things come immediately to the mind of this old TV repair guy (I have
been around :-)).
First, TV signals here in the US are "interlaced". That is, they scan the
odd lines, then the next full screen scan does the even lines. I don't
know if they do that over there but perhaps that would explain the double
Second, the TV picture is "over scanned". That is you are only seeing the
"good" parts of the TV lines and missing out on all the sync pulses and the
"black" stuff on the sides off the screen. This may mean there are more
dots that you are seeing.
Also the VCR "could" be adding to this mess with it's own frequencies,
multi-heads, and correction circuits...
I can't quite see what is going on (after a loooong day) at work at this
moment but I am sure it all works out...
I am pretty sure that you are seeing the coils fundamental but it is just a
matter if figuring out the TV's frequencies and all that. This may be a
great way for coilers without fancy test equipment to measure the frequency
of their coils!!!!
>I tried adjusting the primary tap to several new positions causing the
>TC to be out of tune, but every time, it was possible to get the
>resonant frequency of the primary from the number of dots per line !
>Even if the TC secondary was removed altogether.
>(I checked the res. freq. with a function generator and scope.)
>Eventually, I connected my HV scope across the spark gap to try
>to find out what was happening. It appears that the spark gap actually
>"turns-off" each time the ringing primary current approaches zero. At
>current zero there is a severe burst of RF noise containing many
>frequencies up to the 100MHz limit of my scope. After this burst the
>gap must "re-ignite" and the normal resonant ringing of the TC primary
>continues until the next current zero. This voltage waveform looked
>exactly like the one in your paper, and it did quench around 56us.
>In summary, if you look really closely at the primary damped current
>oscillation there are very intense bursts of very high frequency RF
>at each zero crossing. Since there are two zero crossings per cycle
>this explains why the dots on the TV appear at twice the resonant
>frequency of my TC primary circuit.
Neat!!!! This is really the first definite time anyone else has confirmed
the zero crossing bursts!! Of course, you are right! This would give
bursts at DOUBLE the Fo frequency!!!! Excellent discovery!!!!!! Very
>Also I noticed that the bursts of RF do not decay as the primary
>oscillation decays. As you stated in your paper, they stay at
>constant amplitude until they swamp the main resonant frequency, then
>the gap quenches abruptly after the last burst !
>My guess is that this effect is indeed causing the linear decay in the
>primary ringing waveform. Since the amplitude of the bursts stays
>fairly constant, an equal amount of the primary energy is radiated
>in an HF burst every time the spark gap current goes low enough for
>the gap to turn off. (In a way this effect is similar to the inductive
>kick business being discussed at the moment. Both appear to be the
>result of an inductor being open circuited whilst current is flowing.
>I guess that the resulting voltage kick is what re-ignites the gap ?)
Wow!!! You are seeing things few of use have seen!!! Nice to have someone
else see these things too! I have not studied this much further than those
papers reported but there is a LOT to still learn there!
>What I really want to know is the one thing that you omitted:-
>HOW DO I GET RID OF THESE HF BURSTS ?
>I was sceptical until I saw the evidence for myself. But now I am
>in no doubt that this peculiar behaviour of the gap is the cause of
>the very high frequencies giving the TV interference.
Yes! You have really narrowed it down very well. Unfortunately, I don't
have a magic answer that will solve the problem but now we know were it is.
First I would be sure the case of the transformer is grounded properly and
all the basic stuff like that. The HF current is probably limited to the
primary loop were all the current flows but a standard RFI filter on the
input of the transformer may do something to help. I would try putting the
gap inside a grounded metal container of any sort. Perhaps the RFI is
mostly coming from the area of the gap. A simple hand held radio may be of
use in "sniffing" out were exactly the RFI originates. It may be that the
whole primary is radiating but it also may be mostly at the gap. Perhaps
now that we know the source, some engineering would be able to stop the RFI!!
I assume you saw the part about "poor primary wiring" and how thick short
copper straps in the primary seemed to lessen the RFI effects. However
that may help but not fix the problem...
>I hope this is of interest too you. Also I would appreciate any more
>information you may have on the phenomena because I would really love
>to cure the TVI problem. Do you know if anyone else has looked into
>this type of spark gap behaviour ?
Nope. Just a few "good job Terrys" but nobody has repeated this test to my
knowledge like you have. However, Jim Lux and Gary Lau have done more with
this from a modeling stand point. Your discovery with the TV is super
interesting an important in the RFI elimination efforts!!!
>PS. You can post this to the list if you think it is of general
>interest. I didn't because the list seems to be getting all technical
>right now !
I will copy the list on this and add 500+ more brains to this problem...
Fantasitc discovery you have made here!! I probably could have guess this
from my old work but I "missed" this too. I guess I need to read my papers
more often :-))
Thanks again for great insights!