Hi Guys! Chalk up another satisfied TVI-complaining neighbor!
This neighbor lives in the house next door. We share a common 300 ft
driveway and their house is about 200 ft from my big tower (the one with all
of the RF eminating from it). They had complained about TVI and PHONEI a few
months ago and I made an unsuccessful attempt to clear the TVI/PHONEI at that
time.
Here's the situation:
Phone interference was prevalant when I transmitted on 160 - 10 M SSB. HF
generated TVI was present primarily on VHF TV channels 4 and 5.
VHF generated TVI was present on channel 4 when either my 2M packet node was
on the air OR when my 220 MHz backbone link packet station was on ther air.
The telephone they used most, and the one with the interference that they
were complaining about, was a wall-mounted, speaker-phone equipped Panasonic
telephone with integrated autodialer and 25 ft coiled handset cord.
The TV is a 40 inch floor console model with a preamplified, TV top mounted,
"rabbit ears" antenna! Since the preamp was built into the rabbit ears, I
could not insert a filter between the antenna and the pre-amplifier.
I tried a highpass filter in line at the TV...no help.
I then installed a 20dB attenuator in the antenna line at the TV. That
stopped part of the VHF interference. At that point, the TV got TVI only
when BOTH the 145 and 220 MHz packet transmitters were on simultaneously.
This was still a problem, though, especially when we're rapidly putting out
those putouts!
I then went to the phone, hoping for better luck. No such luck! I tried the
K-COM filters, no good, still had HF SSB interference.
I went home to ponder the problems.
For sure, none of these "problems" is officially my fault. We all know that.
But, sure enough, on Superbowl Sunday I received a call from this neighbor
complaining about channel 4 TVI. (You guessed it, Channel 4 = NBC in the DC
area!) They hadn't had PHONEI because I worked no SSB contests since they
first complained during the SSB Sweepstakes. Anyway, I went over to their
house in the middle of the game and tried another 20dB pad in the antenna
line. No good, so I removed it.
I left, telling them that the cause is their antenna and its built in
preamplifier and recommended they install on outdoor antenna like I have,
with no interference. They didn't like to hear that.
I then ran some tests on two of my own TVs, using rabbit ears (unamplified)
and coordinating on the LL with Frank, W3LPL, who initiated packets so that
my 145 and 220 MHz transmitters were on simultaneously, while I verified that
I got no interference on my two TVs, tuned to channel 4. [BY the way, the
difference between my 220 MHz and 145 MHz frequency falls right in the middle
of over-the-air TV channel 4, hense the TVI at my neighbor's house]. This
experiment verified our hypothesis that the intermod was caused at the
neighbor's pre amp, since neither of my two TVs had the problem.
With this knowledge in hand, I went to Radio Shack and bought a TV top
VHF/UHF rabbit ears antenna (no preamp) and the associated cables, etc to
hook it up to their TV. I had previously bought a bullet-proof wall phone of
the color of my neighbor's Panasonic. I bought it from PRO Distributors in
Texas, one of the sources of TVI proof phones per the FCC 1992 report.
Tonight I went to their house, plugged in my portable TV with one rabbit ear
and set it within inches of their TV and we all saw their TV get interference
while mine did not, both tuned to channel 4! (Pretty convincing evidence, by
the way.)
I then told them that their preamplified antenna was the problem. They left
the room for a moment and brought in their old, non-preamplified,
rabbit ears! I installed it, removed my 20 dB pad which was still there,
added a high pass filter at the TV set, and volla! No interference.
{I didn't even have to tell them I had a new antenna in the black bag I
brought in, hi, hi.}
Next I went to the phone. I had previously set up the K3GEG special test
setup using two HTs and the VOX on my rig tuned to 28.500 MHz. So, I talked
into my HT and heard the 10 Meter SSB on the phone. After trying
unsuccessfully, again, to eliminate the problem with K-COM filters,
one on the line cord and one at the handset cord, I went into my black bag.
(The K-COMs minimized the interference, but the 25 ft coiled cord was just
picking up too much of the SSB)
I brought out the "phone" and installed it. Volla! No interference!
I explained that this was a special phone manufactured specifically to
eliminate interference and that it cost me $80. I also explained that the
amplifiers/transistors in the Panasonic phone were the problem, not my equipment
for which I was licensed to use. I told them that I was giving them the phone
so that they could make calls anytime. They told me that they considered the
phone a "loan" and that they were just borrowing it and that when they move,
they will give it back to me! I agreed to consider it a loan.
We thanked each other and I went home to get on the air!
One more "satisfied" neighbor! Three down and one (known) to go.
More later on the continuing saga of the N3RR allband TVI contest!
73!
Bill, N3RR
By the way, Pro Distributors number is: 1-800-658-2027. I have absolutely
NO affilliation with them. I got their number/name from the FCC FOB
Information Bulletin No. 10, Published 1987, REVISED EDITION, June 1992.
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