[Fwd: LF: LF receive performance]
Sun, 03 May 1998 17:50:56 -0400
Who in AMRAD has already made similar tests? Mark N4TPY probably has the required
test equipment, and each of us could bring his receiver to Mark's lab one of these
> Commercial amateur radio transceivers usually feature extended receive
> performance, or general coverage receive, as part of their specification. But
> how good is the performance outside of the traditional 1.8 to 30MHz ?
> My Icom has General Coverage receive from 30 kHz to 60 MHz. In the absence of
> a large enough set off attenuators to test Minimum discernible signal, I used
> the internal S meter to provide a guide to sensitivity.
> RF gain full on.
> Pre Amplifiers - off.
> Mode CW.
> Bandwidth 500 Hz
> DSP, NB, tuner and Noise reduction - off.
> Frequency. Signal for S9. Relative level.
> kHz micro Volts dB
> 10,000 14.1 0
> 2,500 12.6 -1
> 1,000 39.8 +9
> 500 50.1 +11
> 250 89.1 +16
> 200 125.9 +19
> 136 199.5 +23
> 72 562 +32
> The circuit for the transceiver shows a fixed 10dB attenuator permanently in
> circuit on frequencies below 1.8 MHz. This can be seen in the results. The
> reason for the rapid fall off in response below 500 kHz is not so clear, but
> it may be the transformers used in the preamp and mixers becoming inefficient
> at LF.
> It would be interesting to see how the LF response of other transceivers
> compare. Perhaps an LF review?
> 73 David G0MRF