Topband: Transmit High Pass Filters for BCB Interference

[Don Kirk]

Had a similar problem at Field Day a few years ago with WJR (50,000 watt
station).  Noticed the problem was not present when antenna tuner was
inline.  Many modern rigs have broadband front ends which provide very
little attenuation to out of band signals, and just the addition of an
antenna tuner solved our problem (the tuner provided very good out of band
filtering).

Don (wd8dsb)

On Mon, Jul 29, 2019 at 1:34 PM Grant Saviers <grants2 at pacbell.net> 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
>
> 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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> Reflector
> >
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