[TowerTalk] Broadcast Band AM Transmitter Interference on 160M

[Joe Subich, W4TV]

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 at contesting.com] On Behalf Of Joe Subich, W4TV
> Sent: Sunday, January 30, 2022 6:54 PM
> To: towertalk at 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