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TopBand: Re: 1830 noise

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Subject: TopBand: Re: 1830 noise
From: (w8ji.tom)
Date: Sun, 10 Jan 1999 12:45:44 -0500
> W8JI wrote:
> >I've gotten some input but I'm still asking for help from anyone who
> >hears BC hash around 1830, in particular if they hear it really strong.
> Hi, what I understand this is an example of RX-overload.
> The programs are transmitted on 1310 & 1140 kHz.
> Of this mix we have the difference of 170 kHz.

This signal is a real signal from one source, not mixing in a RX. It might
be useful to explain how you can tell...

Two ways to tell are:

1.) Add attenuation, and watch signal levels for a linear progressive drop.
Receiver IMD falls out faster than the amount of attenuation added. Just
remember virtually ALL  S meters are not 6 dB per S unit, and those that
are generally only behave properly near mid-scale. (My FT1000 is about 2 dB
per S unit below S6 or so but pretty good at S-9 plus or minus)

2.) With mixing, you always hear the modulation of both stations when they
are both modulated. One may have less recovered audio, but they are always
both there.

> 5th mixing product.  This is due to some ARCING OVER between radial wires
> OR direct radiation from one TX to the other. This is easily detected on
> spectrum analyzer at the TX site.  Fortunately this takes place OUTSIDE
> the HAM bands (in Eu). The site is located in Russia and transmits on
> the BC 40mb. Only on rare occations we can hear traces of this on 7070

We have that type of problem in the USA on 1820, 1830, 1840, and 1855 kHz
on 160 meters. Please remember that when working USA!! Many Eu (and other
DX) transmit on 1830, right in a strong spurious signal from AM BCB mixing
and harmonics (generated in transmitters, so there is NO receiver end fix).

The signal on 1830 is gone now, but was spikes at audio peaks and about 5
kHz or more wide. It occurred only during audio peaks, and  was not easily
identified. If a person did not know what it was, he might think it was a
power line arc or something since it only occurred at peaks of modulation.
It was S9 plus here, from a north direction. The noise matched audio peaks
of a syndicated program also audible on WDOD AM, but it might have been
another station carrying the same program.

Thanks for all the help. If this comes back, I'd like to find the culprit
BEFORE it wipes out a special DX event. Someone in the USA will hear it
locally, with a booming signal.

73 Tom

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