[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Linrad] Re: A/D Margin 0.00

Hello Leif,

Thanks for the ideas. I suspect it is wideband. I see the horizontal lines in the waterfall but looking 2 mhz wide from 27-30 I could find no narrow spikes. I think the noise blanker eliminates it good. I will probably be on a holiday until spring and won't be able to put the cavity in front of the preamp. I have used the cavity but it needs looser coupling as the response is too narrow.

Thanks again for the great program, Linrad.

73, Stan

-----Original Message-----

From: Leif Asbrink <leif@xxxxxxxxxx>

To: linrad@xxxxxxxxxxxxxxxxxxxx style='visibility:hidden'>
Sent: Mon, Oct 19, 2009 5:18 pm

Subject: [Linrad] Re: A/D Margin 0.00

Hello Stan,

> I am using Linrad-03.08 with Perseus. I have a 144 to 28

> converter in front of the Perseus. I have discovered something

> that surprises me. When pointing my antenna in 1 direction

> the A/D amplitude margin starts in the 60's but in a short

> period of time, (less than a minute) it drops to 0.00.

> All of the other Amplitude margins remain good and I see

> no trace on the waterfall display indicating a strong signal

> had appeared and caused the A?D to drop to zero. Everything

> appears to be working fine. Hitting the "Z" key rerstors the

> A?D margin but in less than a minute it drops to 0.00.

> This is directional. When pointing mu antenna in other

> directions the A?D does not drop..

The Perseus is saturated occasionally. Every time the A/D

converter saturates the Perseus will set a flag and Linrad will

tell you it happened by setting the A/D margin to zero.

I suggest you disable the second FFT and set the sampling rate

to 2 MHz with no waterfall averaging. You would then have no

noise blanker and you would see wideband pulses as white horizontal

lineas. Change the frequency in steps of 1.5 MHz or so and see

if you can locate a pulsed narrowband signal.

Occasional saturation of the A/D is not necessarily harmful.

Every strong signal in the passband will get an incorrect

amplitude value and therefore produce large wideband "keying

clicks" The Linrad noise blanker might remove them completely.

In case saturation lasts a little longer you might find false

responses and it could be a good idea to reduce the total gain.

In case your amplifier chain is already optimized for gain

(the preamplifier dominates and increases the noise floor by

about 17 dB) the only improvement you can add is in the form

of filters.

In case saturation is caused by wideband pulses there is no reason

to worry about it. You could get rid of the problem by reducing

the bandwidth into the Perseus. If there is a pulsed transmitter

somewhere outside the band you should reduce it with a suitable

filter. Maybe a cavity filter on 144 because the signal level

required to saturate the Perseus is pretty high and probably not

within the linear range of your 144 to 28 converter.


Leif / SM5BSZ

You received this message because you are subscribed to the Google Groups "Linrad" group.
To post to this group, send email to linrad@xxxxxxxxxxxxxxxx
To unsubscribe from this group, send email to linrad+unsubscribe@xxxxxxxxxxxxxxxx
For more options, visit this group at http://groups.google.com/group/linrad?hl=en