[RFI] tracking RFI with a marine direction finder

[Lee STRAHAN]

  Hi Guys,
     The Ray Jefferson I have has both the sense antenna and amplitude control. The sense antenna simply gives it a quite deep null in a single direction of the rod antenna. I Can't recall the model number at the moment. But the ferrite rod antenna itself is motor driven or manual and it finds the null direction automatically at least on a Broadcast carrier.  It is totally fascinating to watch it work. It will null the power line noise source as well but has a hard time zeroing direction automatically. It also has the Low Beacon Band and 88 to 108 FM Band. No DF capability on the FM band.
Lee  K7TJR  OR

-----Original Message-----
From: RFI <rfi-bounces+k7tjr=msn.com at contesting.com> On Behalf Of AA5CT via RFI
Sent: Wednesday, January 27, 2021 8:47 PM
To: nm8rmedic <nm8rmedic at rocketmail.com>; Dennis Monticelli <dennis.monticelli at gmail.com>
Cc: rfi at contesting.com
Subject: Re: [RFI] tracking RFI with a marine direction finder


Do not under-sell the usefulness the cardioid (unidirectional) antenna pattern adds (via the "Sense" antenna function) when DFing noise or other signals when using a Coastal Navigator/NAV 101 receiver.

Riding a bicycle and continually 'rotating' the cardioid antenna I can practically 'drive up to' any interfering signal on the 160 or 80 meter bands when DFing same.Using a loopstick alone (with only nulls to go by) is a little trickier.
Nowadays I feel quite confident when taking compass bearing readings for later plotting when using the Coastal Navigator/NAV 101 DF receivers, first confirming the direction of the source using Sense and then refining with a null (if sufficient signal strength allows). ALSO NOTE the ferrite rod antennas in these units employ internal shields to eliminate E-field response and/or interactions with the operator's hands when in proximity with the rotatable ferrite bar antenna..

About the Pilot - The Pilot lacks the Sense antenna feature that the Coastal Navigator/NAV 101 DF receivers have. I have a couple of these too, but be CAREFUL when putting the batteries into the holder. There are markings for Mercury batteries which in the day had little 'posts' on the opposite of what we expect today (polarity is reversed) and the marking on the batt holder can be confusing. Incorrect insertion of the batts can kill the receiver.

Also, I have found that the Coastal Navigator is the ONLY Marine DF receiver that has a functioning Sense antenna feature. The Benmar/Bendix series model 555 Sense function does not operate, and neither does the Sense function on the one model (6140) Ray Jefferson I have. A couple of us here locally have owned the Bendix/Benmar model 555's and the Sense feature did not work on any of them.

Additionally, the so-called "BFO" on the NAV 101/Coastal Navigator modulates the final IF amplifier with a 400 Hz tone so a CARRIER ends up with a tone on it; this does NOT aid on SSB reception.

de AA5CT/Jim







On Wednesday, January 27, 2021, 8:12:13 PM GMT-6, Dennis Monticelli <dennis.monticelli at gmail.com> wrote: 





Scott,

Yes, the Pilot series is good and easy to lug around too.  Like the others, they are inexpensive.  I have one awaiting restoration.

Dennis AE6C

On Wed, Jan 27, 2021 at 5:56 PM nm8rmedic <nm8rmedic at rocketmail.com> wrote:

> Another good portable RDF is the Pilot Pal series, with its long 
> rotateable ferrite rod antenna and S-meter.  Same NDB/MW/Marine Band 
> coverage.  The model I have, Pilot II, also has a DF level potentiometer.
> Scott.
>
>
>
> Sent via the Samsung Galaxy S8+, an AT&T 5G Evolution capable 
> smartphone
>
>
> -------- Original message --------
> From: Dennis Monticelli <dennis.monticelli at gmail.com>
> Date: 1/27/21 18:18 (GMT-05:00)
> To: rfi at contesting.com
> Subject: [RFI] tracking RFI with a marine direction finder
>
> All,
>
> Another useful and inexpensive tracking tool is a vintage marine 
> direction finder.  My particular model (Newmar NAV 101, but sold under 
> many a private
> label) is battery powered and has three bands: Beacon, BCB, and Marine 
> (1.6 to 4MHz).  It has an RF gain control, sig strength meter, a BFO 
> of sorts, and of course a big lovely azimuth calibrated rod antenna 
> that is capable of nice nulls.  I found mine on the local CraigsList 
> but there is always eBay.  Many different makes and models were made.
>
> Dennis AE6C
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> RFI at contesting.com
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