[Elecraft] Re: MFJ259

[Jim Miller]

is this an application where a direct conversion (QSD) might work better? 
certainly easy to hit a narrow bandwidth.

jim ab3cv

----- Original Message ----- 
From: "Jack Smith" <Jack.Smith at cliftonlaboratories.com>
To: <w3fpr at arrl.net>
Cc: "Elecraft reflector" <elecraft at mailman.qth.net>
Sent: Wednesday, March 14, 2007 6:14 PM
Subject: Re: [Elecraft] Re: MFJ259


Don:

I have little or no problem putting an HP8752B VNA on my antenna
feedline, or my N2PK VNA. Both have narrow band receive (adjustable down
to 10 Hz in the 8752B) and hit the antenna with a reasonably hefty
signal, 0 dBm or so. Consequently, unless you have a very strong signal
inbound, measurements can be made without much trouble.

The subject needs further though and library research, on the theory
that an hour in the library can be worth a month in the lab.

Jack

Don Wilhelm wrote:
> Jack,
>
> Yes, connecting a measureing instrument directly to an antenna can be
> troublesome if there are strong broadcast stations in the area or other
> sources of signals that can fool the instrument.
>
> Zack Lau addressed that situation in a Technical Correspondence article in
> QST a while ago - his answer was to measure the antenna indirectly with an 
> L
> network - the L network provides selectivity - adjust the L network to
> provide a 50 ohm match, then remove it from the antenna, terminate what 
> was
> the measurement side with 50 ohms and measure the side previously 
> connected
> to the antenna.
>
> Sounds like a sane way to approach it to me.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>> From: Jack Smith [mailto:jack.smith at cliftonlaboratories.com]
>> Sent: Wednesday, March 14, 2007 4:38 PM
>> To: w3fpr at arrl.net
>> Cc: Elecraft reflector
>> Subject: Re: [Elecraft] Re: MFJ259
>>
>>
>> After thinking on it more, 30 KHz bandwidth is too wide to be useful for
>> a noise bridge detector, as it will not provide enough frequency
>> resolution for the lower bands. 7-7.3 MHz would only have 10 discrete
>> measurement points, for example.
>>
>> If the device were to be used only to measure components, and not
>> connected to an antenna, lots of circuit simplification is possible in a
>> bridge  generator / detector approach, i.e., a knock off of the classic
>> GR916 RF bridge with an integrated source and detector. Like Boonton did
>> with the 250A RX Meter, for example.
>>
>> However, as soon as you connect the unknown port to an antenna, simple
>> detectors are out as the null will be submerged in trash unless the
>> detector receiver has excellent selectivity and that means frequency
>> stability as well.
>>
>> Jack
>>
>>
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No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.446 / Virus Database: 268.18.11/721 - Release Date: 3/13/2007 
4:51 PM