I thought about mentioning that at the time I wrote my last message. I
included a simple variable attenuator - no need for calibrated
attenuation - so that I could reduce the signal enough to get a good
null as I got close.
73, Pete N4ZR
On 4/23/2012 12:26 PM, Dale Svetanoff wrote:
> Pete and All,
>
> I recently purchased an Icom IC-91A, a 2m/70cm dual bander, and it has air
> (and even SW band) AM capability. I plan to use it as Pete describes the
> next time I have a power line-related RFI problem.
>
> I do have a word of caution regarding use of HTs (or even mobile/base rigs)
> for tracking RFI sources: it has been my observation that the S-meters on
> many of today's rigs have limited to very limited dynamic range. Back in
> pre-historic times (the 50's and 60's), many receivers had S-meters which
> actually required 50 microvolts to = S9, and the " xxdB over 9" part of the
> meter scale were actually fairly accurate. (I can attest to the meter
> performance of my Collins S-Line receivers, as well as my Hammarlund
> HQ-110.) My modern rigs have S-meter performance all over the map. I have
> one rig that has only slightly more than 30 dB dynamic range between S1 and
> 40 over 9!!!
>
> I have not yet measured the meter's dynamic range on the '91A, but will do
> so prior to using it as an RFI tracker. Due to the limitation of dynamic
> metering range on so many rigs, it is a good idea to have an external
> attenuator available when using one of these radios as an RFI detector.
> Mine is a Kay Elemetrics attenuator, fitted with BNC connectors, and it has
> about 60 dB of insertable attenuation (available in steps via toggle
> switches). That should be enough to keep even a very strong signal within
> the range of the '91A's metering circuit. Incidentally, the IC-91A
> includes an internal attenuator to reduce front end overload. It is
> selectable via the menu system and provides "about 10 dB" of attenuation
> (according to the manual).
>
> One more caution with use of external attenuators: since HTs and most other
> rigs are transceivers, the attenuators can be damaged if you accidentally
> transmit into them. Be sure to set the rig on its lowest power setting
> before connecting the external attenuator. Yes, I know that most rigs will
> not transmit at all if you are using the radio outside of the ham bands,
> but you never know when the unexpected can happen. Toasted attenuators are
> not useful.
>
> 73, Dale
> WA9ENA
>
>
>> [Original Message]
>> From: Pete Smith<n4zr@comcast.net>
>> To:<rfi@contesting.com>
>> Date: 4/23/2012 6:38:39
>> Subject: Re: [RFI] MFJ-856
>>
>> OTOH, for less money, you can buy a shirt-pocket handi with 2-band
>> transmit capability and AM receive capability on the aircraft band. I
>> built a 136-mhz moxon (from QST} out of hardware store aluminum rods,
>> and it works fabulously well, particularly when using the narrow rear
>> null to pinpoint a source. Even if you can just isolate the source to a
>> particular pole, the power company guys will be very grateful.
>> 73, Pete N4ZR
>>
>> On 4/22/2012 8:13 PM, Dave Harmon wrote:
>>> I have both the MFJ units....with and without the yagi....they work well
>>>
>>> Dave Harmon
>>> K6XYZ[at]sbcglobal[dot]net
>>> Sperry, Ok.
>>>
>>> -----Original Message-----
>>> From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
>>> Behalf Of Patrick Dyer
>>> Sent: Sunday, April 22, 2012 12:02 PM
>>> To: RFI@contesting.com
>>> Subject: [RFI] MFJ-856
>>>
>>> Is this MFJ-856 worth a second glance for DFing RFI ?
>>>
>>> For that part of the spectrum I'm currently (since 2003) using the R,
> DE,
>>> D1, and D2 of an 11-el 144-MHz Cushcraft with an Icom IC-A4 (108-137 MHz
>>> airband xcvr). The 7-MHz difference seems to have minimal skew to the
>>> pattern (using an old Precision E-200-C signal generator as a test
> source in
>>> the yard).
>>>
>>> However, the MFJ-856 has a signal-strength meter, and the 3-el antenna
> boom
>>> length (with the rcvr on it) may be easier to manage/handle than what
> I've
>>> been using for nearly a decade.
>>>
>>> Before I got the IC-A4 (originally to track the MUF of Es events above
> the
>>> FM broadcast band using the VOR/ILS navaids) I had been using a rather
>>> decrepit (1971) Radio Shack JetStream mini (slightly retuned to
>>> 144 MHz) for RFI chasing.
>>>
>>> 73, Pat - WA5IYX
>>> _______________________________________________
>>> RFI mailing list
>>> RFI@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rfi
>>>
>>> _______________________________________________
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>>> http://lists.contesting.com/mailman/listinfo/rfi
>>>
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>
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