[RFI] Re: QRM from AM broadcast

[Tom Cox]

Thanks to all who responded to my request for info. All replies were 
helpful, and I'm sure I'll get something done before long. I may make 
use of two or more different approaches suggested, just to reduce the 
QRM from varioius directions -- probably a combination of an ICE filter 
and one or more notch filters in several places.

Thanks again, and Happy New Year to everyone on the list.

73,
Tom, KT9OM

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>Today's Topics:
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>   1. RE: RFI FROM nearby AM station (Patrick A. Thompson Sr.)
>
>
>----------------------------------------------------------------------
>
>Date: Tue, 30 Dec 2003 20:47:08 -0500
>From: "Patrick A. Thompson Sr." <wa4tukhr at comcast.net>
>To: "Tom Cox" <tomcox at iquest.net>, <rfi at contesting.com>
>Subject: RE: [RFI] RFI FROM nearby AM station
>Message-ID: <NJEBIJHBJAHPKFLOIMGBKEDCCEAA.wa4tukhr at comcast.net>
>In-Reply-To: <20031230164720.5AB55319A95 at dayton.akorn.net>
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>I live about 3 miles from a 10kw station on 990khz.  I also have an IC-746.
>
>I've got enough RF coupled into my 256ft horizontal loop, used against
>ground on 160, to cause an old fashioned SWR bridge into its field strength
>port read up scale with noticeable modulation!
>
>I had broadcast overload on 160 until I started using an external matching
>unit (tee match style MFJ-969). I still get interference at the 2nt harmonic
>but the overload is gone and 160 is usable. In this mode I don't use the
>746's internal tuner. This might be the most satisfactory solution. Maybe
>you could borrow a tuning unit for evaluation.
>
>I built, years ago, a high pass filter into a Radio Shack variable
>attenuator originally made for CATV use. That helped a DX-440 (consumer
>quality SWL receiver) perform well. I had video sweep gear available and was
>delighted to see a nice knee at 1600khz and 28 db or so rejection.  The
>design was right out of the ARRL handbook. It was not designed for transmit
>power.
>
>If you go the homemade filter route, check your junk box for discarded audio
>cassette recorders.  I found a useful adjustable coil from the bias
>oscillator section.
>
>You might also consider a pair of bypass relays for transmitting.
>
>Pat
>wa4tuk
>
>-----Original Message-----
>From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com]On
>Behalf Of Tom Cox
>Sent: Tuesday, December 30, 2003 11:47 AM
>To: rfi at contesting.com
>Subject: [RFI] RFI FROM nearby AM station
>
>
>Happy Holidays, Everyone!
>
>I am looking for a practical, reasonable-cost way to keep RF from a nearby
>AM broadcast station out of the receiver of my IC746 when I have a 160M
>half-sloper connected to it. The station is three miles away, transmitting
>1 KW on 1340 KHz.
>
>I would like to notch the station out, if possible, so I
>can listen to other BCB and LF stations on the half-sloper when I am not
>using it for transmitting. If that's not possible, I would guess a
>high-pass filter is my next alternative, but I will entertain all
>approaches.
>
>The IC746 doesn't have a separate RX port, so I need a filter with 50-Ohm
>ports that is capable of handling 100 Watts in transceive service.
>
>I welcome your input.
>
>73,
>Tom, KT9OM
>
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>End of RFI Digest, Vol 12, Issue 22
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