Topband: Transmit High Pass Filters for BCB Interference

[Grant Saviers]

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

Having the filter between rig and amp worked fine for me.  200w rating 
for the Heros.

My power line had ~1v of RF, so ebay Sprague 20 amp line filters were on 
the shack 120v supply and 240v amp also.  Plus 240-31 ferrites on the 
green wires.

It will take some proper ferrite chokes to kill the RF on the coax 
shields and any other control cables.  Plus a good ground system.

IMO, Dunestars have poor reliability for their HF bandpass filters when 
on DXpeditions.

I always like to see the VNA sweep in the ad and then use my VNWA to 
test whatever I buy since the tuning is hand optimized.  A couple went 
back for retuning.

K9YC has some comments re BCB rejection for 6 band filter sets.  That is 
another alternative.
http://audiosystemsgroup.com/BandpassFilterSurvey.pdf

Grant KZ1W

On 7/29/2019 9:29 AM, Mark K3MSB wrote:
> A friend of mine in our local radio club sent me the following email
> 
> "I'm 6/10's of a mile from an AM 910 KHz. transmitter. They operate with 5k
> daytime and 2k at night.
> 
> They're S9+45db on 160 meters with clear audio and S9+35db on 80 meters.
> have an inverted "V" resonant at 3.715 MHz. orientated east-west, towards
> their reflector tower."
> 
> The station is willing to pay for a filter for my friends station,  and he
> has looked at notch and band pass filters but has concerns.
> 
> I recommended he look at transmit high pass filters to knock out signals
> below 1.8 Mhz and provided him with various links:
> 
> https://www.dunestar.com/store/160-Meter-Highpass-Filter-pid-8.html
> 
> http://www.kf7p.com/KF7P/Morgan_Filters.html
> 
> https://www.dxengineering.com/search/part-type/transmit-high-pass-filters/product-line/dlw-associates-am-broadcast-band-brick-wall-high-pass-filters?autoview=SKU&sortby=Default&sortorder=Default
> 
> I have no practical experience with any of these filters and was wondering
> what the TB Gang thought.
> 
> He would prefer one that handled 1.5 KW but I told him he may have to
> settle for 200W.
> 
> He prefers an "out of the box" solution.
> 
> Thanks
> 
> Mark K3MSB
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