> I took some measurements today with my MFJ 1025, using a General Radio
> 1001-A rf signal generator, an external calibrated attenuator and a
> 75A4 receiver. The built-in attenuator setting were compared with the
> external unit, and readings were consistent with each other. I
> measured the signal level directly to the 75A4, using the S-meter as a
> signal strength indicator, then inserted the MFJ unit and took another
> measurement. Here are the results:
Unless you use at least a 10dB 50 ohm pad on the receiver input, and
know that the source is 50 ohms, the results actually don't mean very
much.
Measurements made with a commercial 50-ohm network analyzer,
including measurements with and without filters and light bulbs, are
at:
http://www.w8ji.com/mfj-1025_1026.htm
All that aside, I'm having a problem understanding why 5dB loss or
even 20dB loss at night time would be a problem on a transmitting
antenna. Unless the receiver has a real problem with sensitivity,
almost any transmit antenna in a very quiet location would have
considerably more noise-floor headroom than even 10dB of signal
reduction could remove.
I can understand a slight reduction in noise figure when the unit is
used to phase very low sensitivity antennas together (like two
Beverages) if preamps are not placed ahead of the unit but I sure
can't fathom why a noisy transmitting antenna would suffer any
degradation even with 30dB loss.
Can anyone explain what I might be missing?73, Tom W8JI
W8JI@contesting.com
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