Topband: Bad Frequencies and Loop Pre-amps

[Greg - ZL3IX]

Hi John,

Is that harmonic generated at the Tx site, or in non-linearities close 
to the victim receivers?

Of course, the answer to that question does not affect any 
recommendation on frequencies to be avoided on TB, but we should be 
careful about blaming broadcasters for every spurious signal heard on 
the band.

73, Greg, ZL3IX

On 2018-11-14 03:44 a.m., John Farrer via Topband wrote:
> Roger
> As Lee KX4TT stated, a harmonic on 1818kHz is a problem for us in southeast England in the vicinity of the Brookmans Park transmitter for Radio 5 on 909kHz.
> 73
> John G3XHZ
>
> Sent from my iPhone
>
>> On 13 Nov 2018, at 13:24, Roger Kennedy <roger at wessexproductions.co.uk> wrote:
>>
>>
>> I have never received ANY harmonics or intermod products from any of our
>> British Medium Wave (AM) broadcast stations.  That's at several different
>> QTHs, some of which were quite near the transmitters. (and never heard of
>> anyone else having issues)
>>
>> They have to meet VERY high specs . . . but also, most are less than 1kW !
>> (one of the stations I worked for had such a good Tx site - a salt marsh -
>> they had to turn the power down to 150 watts!) Even the very big ones are
>> usually only 10kW.
>>
>> So no need to avoid the 9kHz harmonics as far as us Brits are concerned!
>>
>> What IS a problem is all the Russian Navigation Beacons in the Baltic that
>> pretty much wipe out everything between 1810 and 1820 kHz, so please try and
>> avoid that part of the band if you want to work any EU !  (they sometimes
>> turn them all off . . . but they are on most of the time.)
>>
>> The pre-amp I use on my 6ft 160m receiving loop is actually the design MFJ
>> use in their 1026 noise canceller (I have a 1025 but copied their preamp
>> design, as it uses the same pcb) . . . I get no intermod during contests,
>> even though many EU stations are 45dB over S9 !
>>
>> Roger G3YRO
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