[Linrad] Re: Receiving sometimes stop

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hello Isao, 

> At this moment I have another problems. One is receiving
> sometimes stops (noise level downs -5dB and receiving
> internal birdie only) for 5-20 minutes and returning. I
> guess my power supply cause a trigger and already ordered
> new one. But anyone has same problem and fixed, please
> let me know your detail.
In case your power supply becomes overheated so it switches
off or reduces the +15 or -15 DC supply (or both) you should 
see it easily with a volt meter. I am not aware of anything
else that could produce a similar effect. Maybe better
positioning could improve coolign?

> Two is a internal birdie on center frequency of each pass
> band. In problem one situation, also it is.
The center frequency corresponds to DC voltages and they
are not amplified by the Delta 44.

Near the center frequency there is 1/f noise. The normal behaviour
of the Delta44 without anything connected to it is shown here:
http://www.sm5bsz.com/linuxdsp/hware/delta44a.htm

The center spur can be slightly reduced by modifications on the
Delta 44.

During normal operation on 144 MHz when your preamplifier should 
lift the noise floor by about 15 dB the center spur should not
be visible or very weak.

73

Leif / SM5BSZ


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