[Fwd: LF: LF receive performance]

[André Kesteloot]

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
evenings?
André N4ICK
********************************
G0MRF wrote:

> 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.
>
> IC756.
>
> 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