[CQ-Contest] CB QRM in 10m test (opposite)

Leigh S. Jones kr6x at kr6x.com
Wed Dec 17 22:17:41 EST 2003

Though it's not very common these days, in the old days of radio most
receivers had a 455 KHz first IF frequency.  For the 27.155 channel
that would require a 27.610 local oscillator frequency.  Can you see
where I am going with this?  Subtract 28.066 - 27.610.

Now of course, the question I'd have to ask for you would be whether
your transmitter uses a mixing scheme that could generate a signal on
27.156 or whether his receiver has a 27.610 LO?  This translates to
a question of whether your transmitter is sufficiently old enough to
a 455 KHz IF.  Transmitters haven't done this for a very long time,
because of the difficulty of filtering the potential spurious 27.156
signal sufficiently to satisfy regulators.  On the other hand, cheap
radios that use crystal oscillators and multipliers to generate the AM
transmitter signal but cheap receivers with poor image rejection can
get regulatory acceptance.

----- Original Message ----- 
From: "BlakeM" <n4gi at tampabay.rr.com>
To: <cq-contest at contesting.com>
Sent: Wednesday, December 19, 2029 6:22 PM
Subject: Re: [CQ-Contest] CB QRM in 10m test (opposite)

> I had exactly the opposite happen.  While CQing on 28.066 in the 10m
> last weekend, I got an e-mail from a ham in Canada (rates were
slow...) (a
> VE1) who said he had his CB on CH16 and could hear me calling there
479.  I
> think he said that 16 is around 27.155.  I took my handheld R-10
> and couldn't hear myself xmitting anything down there, .  I've got a
> filter in line before the amp (titan425 ~1.2kw).   He was using a
long wire
> for an antenna.  Pretty strange, but we just let it pass as overload
on his
> end?  Any other ideas?
> I hate to be out there spewing crap, so if anyone has any comment on
how I
> sounded, I'd appreciate a report-
> 73,
> Blake N4GI
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