On Sat, Oct 12, 2024 at 10:16 AM, Simon wrote:
Have a mfj 259b
I think someone mentioned? recommending the AA-55 Zoom by RigExpert.
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Unlike some of the MFJ products that may use a broadband detector, I observed that the AA-55 Zoom uses a narrow band detector that allowed the AA-55 to ignore nearby AM radio station signals that otherwise affect instruments using broadband RF detection techniques in their circuitry.
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With the AA-55 Zoom I was able to tune within 1 kHz of a radio station at 1700 kHz (just below the 160m ham band) and work without interference to measurements. When tuned TO the station frequency of 1700 kHz, I could observe obvious 'beat note' behavior as evidenced by 'bouncing values' on the AA-55 Zoom's display.
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The signal power when my large loop was tuned to 1700 kHz was around -1 dBm (just under 1 milliWatt) as measured on an HP 8591E (which passed internal Self Cal tests using its front panel CAL OUT signal source) spectrum analyzer. When the large 160m loop is tuned to 1900 kHz in the 160m band, signal power (from the 1700 kHz station) was observed to be around -20 dBm.
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I can recommend the AA-55 Zoom or similar architecture single-port S-11 style instruments without hesitation based on its ability to 'ignore'? nearby RF signal sources (at least on the 160m band and at the RF signal level I observed.)
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Note: I was unable to use a Boonton Model 260A "Q Meter" to measure the (large) loop antenna's inductance on account of it using a broadband RF detector internally.
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de AA5CT Jim
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