[RFI] rfi problem
k8ri at rogerhalstead.com
Thu Nov 1 18:53:35 EDT 2012
On 11/1/2012 12:14 PM, Dale Svetanoff wrote:
> Jim's comments really hit home with me. I think I have said this before on
> this reflector, but it was a few years ago, so maybe worth repeating:
I'm sure I've mentioned this in the past... but many years ago, I lived
in Alma MI. I noticed that when driving through many intersections I
had problems receiving the quadrant repeater which was only about 10
miles distant. So I started tuning around, and sure enough, there on
145.25 was a very strong signal.
My daily trip was a good 40 - 50 miles so the rig was almost always on
50 watts. 160 W amps were quite popular.
I stopped at the cable company office and the signal was really strong
there. I took my HT into the office and when I showed the secretary I
could wipe out the program she had on she immediately went to get the
tech who was on duty. BTW their office was also the head end for the
whole cable system.
The tech was a bit skeptical even though I showed him that when I keyed
the HT in the office I took out *ALL* channels. Then it dawned on him
that when I did that no one in the whole town could watch cable, but he
figured it was because I was so close to the amps and dish. Of course
that was before cable had the Internet...It was 1980.
So...I went out to the car which was way on the other side of the
parking lot. I had only keyed up for a few seconds when he came flying
out the door, waving his arms. I was getting the same results from out
When I got home from work the next day I noticed things were improving.
It took several days, but I could drive around town and not hear a
peep on 145.25.
Bob is correct particularly in rural areas. You often find, even with
subscribers, instead of an A/B box they just tie their antenna with
preamp to the cable connection at the TV...or sometimes in the attic
which of course back feeds the signal into the cable and everyone down
stream from them.
> When I lived in northern IL prior to 2000, I was in a subdivision that had
> buried cable service, but I was not a subscriber. I began to have QRM on
> 145.25 and other nearby freqs, and sniffing around the cable easement area
> with a 2m HT proved that the sigs were leakage from the cable system. I
> learned this just prior to a VHF contest weekend.
> Well, I worked the contest, using both FM and SSB on 2m (at power levels of
> 50 to 150 watts). By Saturday night, the QRM on 145.25 was gone, as were
> other sigs from other CATV channels that were below or above the 2m ham
> band. A few days later, there was a CATV service truck in the neighborhood
> and a guy was going around scratching his head and looking confused. He
> did go the pedestal nearest my house and did some sort of work (probably
> tightening and/or replacing connectors). He then left. After he was gone,
> I took the HT back out to there and I could only hear faint noise on 145.25
> and the other close-by freqs. My problems at the house were gone. I
> concluded that they must have killed the system when it got hit with heavy
> RF during the contest, as I suspect that booster line amps got saturated.
> NO further issues with that system.
> Dale Svetanoff, WA9ENA
> Sr EMC Engineer
> E-N-A Systems, LLC
> Specializing in shielding applications, system grounding, and lightning
>> [Original Message]
>> From: Jim Brown <jim at audiosystemsgroup.com>
>> To: <rfi at contesting.com>
>> Date: 11/1/2012 10:29:21
>> Subject: Re: [RFI] rfi problem
>> On 11/1/2012 4:34 AM, Pete Smith N4ZR wrote:
>>> There are specific FCC requirements for signal "egress", so if you can
>>> identify the frequency with a cable TV channel, and pin it on them,
>>> then they are indeed required to fix it.
>> One reliable frequency to look for egress is around 145.25, which is the
>> frequency of the picture carrier of one the analog channels. If there's
>> egress, you'll hear a buzzy carrier here, and you can use a 2M talkie to
>> probe for the weak spots in their system. The most common causes are
>> poorly made splices, many (most?) of which are made by customers
>> installing their own illegal connections to the system.
>> 73, Jim K9YC
>> RFI mailing list
>> RFI at contesting.com
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