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[TenTec] Narrow FM

To: <tentec@contesting.com>
Subject: [TenTec] Narrow FM
From: w8au@sssnet.com (w8au@sssnet.com)
Date: Mon, 04 Oct 1999 11:40:10 -0400

Yes, they are correct.   NBFM was established as +/- 3kHz deviation (total
BW=6kHz), so as to be compatible with existing AM transmissions on any
band.  It's not very effective (for noise reduction) at that low deviation,
but it can be copied on any AM receiver by tuning off to the side of the
signal, thereby allowing the FM signal to slide up and down one side of the
receiver selectivity curve, causing amplitude variations which are copied
as AM in your receiver.  This is called, "slope detection."

The FM restrictions you see in the rules (only above 29.0 mHz) apply to the
standard commercial deviation of +/- 5kHz.  (or greater)  Copying 5 kHz
(total BW=10kHz) deviation signals on ten meters with your OMNI-V 2.4 kHz
filter will cause distortion as the sidebands move out beyond the filter
skirts.  If you have the optional 15 kHz filter installed you will have no

A few years back I excercised my old Hallicrafters HT-19 on 75 meters by
running NBFM on the AM spot freqs.  (The HT-19 did not have AM, only NFM)
Some caught on, some did not.  I had to set my frequency slightly high or
low so they would all be copying via "slope detection."

Now you know how to make more use of your NBFM....if you want to!


Perry    w8au

At 10:58 AM 10/4/99 -0400, you wrote:
>Although I find the FM mode in an Omni-V quite poor with its narrow
>receive bandwidth and audio squelch.  I have had fun with it on 10 meters
>as well as great reports on the transmit audio. One thing that I've
>wondered about is the use of "narrow band FM", in Ten Tec instructions
>they state that narrow band FM is a legal bandwidth to use anywhere ssb
>can be used and on any band. Why don't I ever hear about this being used?
> I'd like to give it a try on 40 or something but just have never heard
>anyone doing this. Nor can I find any info to support or disprove Ten
>Tecs claim in a hand book or anything.  
>Any thoughts?           73 Jeff  AA8VE
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