[linrad] Re: Delta44

[<leif@xxxxxxxxxx>]

> I am working on Linrad with a new hardware I/Q 4 channels.  I
> have noticed that as soon as I connect the box external of the
> Delta44 without signal in input , appear on the screen some marks
> (spuries?).  In particular 2 many forts nearly to the beginning
> and the end of the entire band.  The Delta44 is originates
> without modifications advised from Leif. It is ground loop error?
It could be the Delta44 design error, but it could also be
an error in your new hardware.

In case you have a RX2500 you should expect some spurs if you
connect it without the +/- 15V DC supply because the RX2500
uses differential amplifiers to reference its output voltage
to the analog ground of the Delta44 and this works only when
the differential amplifiers have supply voltages. If the unit
is not powered the output will just be a resistance to the
screen of the cable and that will make the system pick up
interference easily.

To thes your Delta44 you might try to connect the four signal
pins with the analog ground but not with the screen. That is
join pins 6,7,8,13,14 and 15 on a d-sup connector.
There should be no difference when you connect it to the Delta44
regardless of whether you have the cable in between or not.
Then, with the pins still joined, hold the metal of the d-sub
at different points in contact with the computer chassis.
It should make no difference.

>  It is resolved isolating the connector of the card? .  Before
> modifying the original card I would want to be sure.
> Thanks.
If the above tests show an error you could most probably fix
it by cutting the gnd connections via the d-sub.

Your PC running Linrad is a powerful spectrum analyzer
that should help you finding the cause of the signal you see.


73

Leif


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