The AM Forum

I live close to an AM station on 1350 KHz. My Kenwood TS-570 can handle it WITH the attenuator turned on, but my old Kenwood R-599 is severely overloaded even with the RF gain turned down.  I think a notch filter tuned to 1350 KHz would be just what I need. Are there any commercially available units that would fit the bill?

Bobby Dipole ND9B

I have a run of the mill "T" antenna tuner inline with my xcvr. It's the MFJ-901B and not only works as an antenna tuner but, by virtue of being of the T configuration it is inherently a high pass filter. I just checked and when tuned for 75 meters it provides 45dB of attenuation at 1330khz and 60dB at 810kHz (both local BC stations here). You can think of it as a high pass filter with a free antenna tuner built in! Such a deal.

our club used to op field day near an am bc station with open wire fed ants .... the only ant tunas that would completely block the am bc stn were Johnson kw boxes

http://www.morganmfg.us/radio-products/bcb-interference-filters/

Here are two High Pass BCB band filters.  These were previously sold by ICE, International Communications Engineering.  At the owners death death several years ago the family took a long time to sort out the business.  It was posted that a brother or brother-in-law, owner of Morgan Manufacturing was the actual fabricator of ICE products and would be selling the line directly.

They have not been high profile in advertising and I can't vouch for them.  I do own an ICE 1.8Mhz BCB filter.

I have never seen any commercial notch filters.  Another approach is to build your own notch or 'wave trap' filter.  For receiving purposes it requires only 1 resistor, 1 capacitor and a metal enclosure.  There a many examples available on the web.

****EDIT****
Here is a nice little paper
http://www.dxing.com/tnotes/tnote06.pdf

Bob, I built a homebrew filter one time that consisted of a series L/C network from the antenna input of a susceptible receiver to ground.  Can't remember the values now, but I adjusted it to minimize the cross modulation caused by the BC station.  Actually the interference didn't "minimize" it totally cleared up.  Since you are using separate Tx and RX, a network like this could be installed in the line feeding the receiver, and the transmitter wouldn't know it was there.

Many years ago I had a Hammarlund HQ-145 and I recall (its been a while) that it had an L/C network as a notch filter on the antenna input that you could adjust to knock down one specific frequency on the AM BCB.  If you can find some old (or new) parts, a 365 pf variable cap, and a slug tuned coil like the stuff in those 100 in 1 electronic kits, you could slap together a notch circuit in a couple of minutes and place it across the antenna terminals.

73
Ted W8IXY

I had to put homebrew tuned traps on the antenna input of two of my Hallicrafters receivers because a station in Iowa on 1650 Khz. would roll right into the Halli first IF when I operate on 160 meters.   I wound a small coil based upon a formula in the handbook, used an air variable in series to tune it, then measured the air variable value and replaced the large air variable with a small  fixed mica and ceramic trimmer cap in parallel which are much more compact. 

You hope the antenna tuner will bring down that fundamental overload possibility and you do not have to buy Bcast filters. Expensive!!
Fred

Save a ton of money. Build your own.

http://www.ok1rr.com/index.php/technical-topics/40-an-efficient-mw-band-stop-filter

http://hackedgadgets.com/2011/07/26/am-broadcast-band-rejection-filter-for-shortwave-reception/

Here is (http://www.tonnesoftware.com/svcfilter.html) a handy filter program, I used it to build a BCB reject filter, and I'm really pleased with the results.   It is also on the CD that comes with the '13 ARRL handbook.   

A quarter wave open stub of any impedance coax will give a good notch, cheap if you have any RG-6 around. About 173' times velocity factor.

Carl

Can twinlead, like 300 ohm TV lead be used for stubs?

Sure, that was done by hams way back to notch out their harmonics for TV sets but I doubt you could easily make a well balanced version for the BCB.

Carl

The use I had in mind is the church FM station across the street from me.

Thanks, bill

One problem with building a 1/4 wave stub for your receiver to notch 1350kHz is that it will also have notches at:
3/4 wave 4050kHz,
5/4 wave 6750kHz,
7/4 wave 9450kHz,
etc,
etc.
As long as you're willing to live with that, it will work great for receiving.

Don

Click On/Off = problem gone.