Jack had some excellent information on a HPF that incorporated two
or three notches that made a significant difference in rejection
of specific stations in the higher portion of the AM Band. As I
recall, the difference could be going from 20-30 dB above 1200 KHz
on a simple HPF to 50 or 60 dB at the cost of flatness in the reject
region. The ability to knock down individual stations was generally
worth the trade off.
I hope I saved a copy of that information somewhere as I will certainly
need it with a couple stations between 1000 and 1400 KHz that put >
10 dBm on my 160/80 antenna (I can measure it with a sensitive wattmeter
and dummy load).
73,
... Joe, W4TV
On 2022-01-30 7:41 PM, Tim Duffy wrote:
DX Engineering makes the Clifton Labs AM receive reject filter:
https://www.dxengineering.com/parts/dxe-z10020-pm
DX Engineering also carries the excellent DLW filter:
https://www.dxengineering.com/parts/dlw-fl1718
73
Tim K3LR @ DX Engineering
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Joe
Subich, W4TV
Sent: Sunday, January 30, 2022 6:54 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Broadcast Band AM Transmiiter Intererence on 160M
On 2022-01-30 6:09 PM, Jim Brown wrote:
Unfortunately I didn't have enough cursors to put one in the AM
band, but an eyeball guestimate is that the better ones will get you
15-20 dB at 1420. That report includes measurement for a vintage ICE
BCB, which is in that range. As I understand it, Morgan took over
that line. >
> The trap that Jim Lux suggested would probably go a lot lower.
Jack at Clifton Labs had some designs that replaced the inductor(s)
in HPF designs with series tuned traps for specific 'problem"
frequencies. Unfortunately Jack is an SK and DX Engineering which
took over some of his designs seems to have dumped most of Jack's
work and all of the information on his web site.
73,
... Joe, W4TV
On 2022-01-30 6:09 PM, Jim Brown wrote:
On 1/30/2022 1:57 PM, Mike Ryan wrote:
By FAR my greatest offender is at 1420AM which is less than one
mile from my qth.
If you can kill it with a BPF or HPF, they're not the offender, the
preamp is. And with the problem station fairly high in the band, you'll
want a BPF or HPF with pretty steep skirts. Best bet is to study
published curves for stuff from DX Engineering, WX0B, and the filter
mfrs themselves. I remember looking a year or so ago and the state of
the art seemed to be in the range of 40 dB fairly high in the band.
Also, the better BPF sets made for contesting have pretty good
attenuation on the AM BC band. At the end of this report is a link to my
measured data on those that I owned or had loaned to me for measurement.
The report: http://k9yc.com/BandpassFilterSurvey.pdf
The data: http://audiosystemsgroup.com/BandpassFilterData.htm
A few years ago, I acquired a pair of used Hamation FilterMax-IV sets
that measured quite well, but I don't think I saved the data. TXBPF sets
are in my SO2R station, and the Hamation units are on the rig side of
switching for my RX antennas.
Unfortunately I didn't have enough cursors to put one in the AM band,
but an eyeball guestimate is that the better ones will get you 15-20 dB
at 1420. That report includes measurement for a vintage ICE BCB, which
is in that range. As I understand it, Morgan took over that line.
The trap that Jim Lux suggested would probably go a lot lower.
73, Jim K9YC
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