Topband: Transmit High Pass Filters for BCB Interference

[Larry]

There is a 50KW AM broadcast station line of sight to my top band antennas. Caused huge problems at greyline because they are dawn to dusk transmitting.I built the HPF in the ON4UN handbook. As designed the rejection below 1.8 mhz was 60 db. With careful tuning of the coils and the use of a spectrum analyzer the rejection is now 72db.Problem solved.It's a simple project and cost me less than $20.Good luck.n7dd

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 On Tuesday, July 30, 2019, Richard (Rick) Karlquist <richard at karlquist.com> wrote:

On 7/29/2019 10:33 AM, Grant Saviers wrote:
> Here is what I used when I had the same problem 50kw line of sight 4 
> miles 1MHz.  Expensive, but worked very well.
> http://herostechnology.co.uk/pages/RF_Filters.html
> 

Yes, at 1 MHz, this would work well.  Other hams would be
advised that it is ineffective for QTH's with stations
high in the BCB.  The data sheet goes to a lot of trouble to
obfuscate this.  At my QTH, I have a strong BCB station
right at 1.7 MHz.  This fact rules out a large number
of filters.  You can see in the photo in the data sheet that
only 3 toroids are used.  This explains the poor performance
at 1.7 MHz.  As always, YMMV.

Rick N6RK
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