Sorry Roger, but I was not around in 1952. Not that old. I'm not at all
familiar with the problems you're describing but I have heard of them.
I was talking about TV sets before cable TV and before external stereo
speakers that required addition of high pass filters to keep the ham signals
from interfering with the TV sets video & audio.. We used them on my
neighbors TV sets in late 70s with good results. Of course a Low pass on
the ham station was (and still is) necessary.
So it is a similar interference problem but in reverse.
73, de ed -K0iL
-----Original Message-----
From: RFI <rfi-bounces@contesting.com> On Behalf Of Roger D Johnson
Sent: Sunday, July 8, 2018 12:13
To: rfi@contesting.com
Subject: Re: [RFI] FCC Compliance and Enforcement
You're talking about two different problems. Many of the early TV sets had
an IF frequency near 21 MHz. This was fine until hams were allowed to use
the 15m band in 1952. The 15m ham signals got into the TV IF section due to
inadequate filtering and/or shielding. This was the fault of the TV design
and not the ham operators although it caused much grief and aggravation to
the hams.
Also, back in those days, ham transmitters used class C biased final
amplifiers.
These were prolific generators of harmonics. If the ham transmitter was not
properly filtered and shielded and used a low pass filter on the output,
these harmonics could cause TVI if they fell on a local channel. This WAS
the fault of the ham's equipment.
Two completely separate issues.
73, Roger
On 7/7/2018 7:44 PM, Ed K0iL wrote:
> Remember the old days when the old TV sets had no filtering and the
> ham causing the interference had to cease operations during prime time
> TV hours until the problem was resolved? Ever wonder why the FCC
> didn't force all TVs to be properly filtered to not be susceptible to
out-of-band RF signals?
> Simple. It's money.
>
> The cost to properly redesign and filtering all the TV sets would've
> cost much more than adding individual high-pass filters only where
> needed making that a much lower costs because not every TV set sits next
to a ham station.
>
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|