Most likely to be some form of overload in your receivers or preamps. If
adding a plain resistive pad reduces the product by more than the amount of
the pad, its in the receiver. - (you have to use a pad big enough to show a
material difference to resolve with ordinary measurements)
A real band pass filter in front of the first active stage will probably
help enormously. In Most- but not all - cases the offending products are
not radiated by the AM station but are generated locally, either by the
rusty joints Tree mentions, or in your own hardware. The fact that you see
several products, not one specific one leads me to conclude the issue is
locally generated.
This is one of the reasons that the exact round 10 KHz frequencies are on
the bad frequencies list. Everyone suffers from the problem to one degree
or another, unless you live well away from any AM station, AND have
excellent front end filtering. A 50 KW AM station 500-1000 miles away can
generate HUGE signal levels in a 160M receive array - or in your transmit
array, and be re-radiated, or direct coupled into your receivers.
Use a band filter, many are available commercially, and I expect the
designs for even more effective filters are available in several places,
notably the W8JI site.
Only place I can think of where the problem was unlikely to occur is in the
beverage array at VP6DX... too many miles, and K3 receivers.
Robin, WA6CDR
----- Original Message -----
From: "Tree" <tree@kkn.net>
To: "Mike Waters W0BTU" <mrscience65704@yahoo.com>
Cc: <topband@contesting.com>
Sent: Sunday, February 21, 2010 05:47
Subject: Re: Topband: What are these weak birdies every 10.0000 KHz?
> On Sat, Feb 20, 2010 at 07:28:33PM -0800, Mike Waters W0BTU wrote:
>
>> I have these constant weak carriers on 1810.000, 1820.000, 1830.000,
>> 1840.000, 1850.000 ... on both my R-4C and IC-751A.
>>
>> A crystal-controlled wall-wart running at 10.00000 KHz? ;-)
>>
>> I've heard of others that had these problems. Any ideas what they might
>> be? TIA.
>
> Those are birdies of your local AM broadcast stations. Likely there
> isn't much
> you can do about them. However, if you do have some wires around (like
> wire fences
> or guy wires that are not broken up by insulators) - you might find that
> by doing
> some work making sure you don't have bad connections - you can clean them
> up some.
>
> When you have a bad connection, it will act like a mixing diode and make
> these
> birdies a lot worse.
>
> Often, the mixing is being done near where the AM station is transmitting
> and is
> very hard to track down.
>
> 73 Tree N6TR
> tree@kkn.net
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|