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RE: [Discuss-gnuradio] Quadrature demodulator update


From: Philip Mackenzie
Subject: RE: [Discuss-gnuradio] Quadrature demodulator update
Date: Tue, 11 Feb 2003 21:06:27 -0000

John,

We are actually using an AR8600 not an ICOM. When I was doing this about a
year ago I tried to get more information from AOR about the 10.7MHz output
(see response below). They didn't have exact details for the 8600 but I
suspect that the A5000 they mention is similar. I don't see any numbers for
the IF output impedance...but maybe this is usually a standard value?

The exact amplifier we are using is the ZFL-500 at this (different) URL
http://www.mini-circuits.com/dg03-174.pdf. We have the amps connected to a
standard bench power supply at 15V.

If you can post a circuit that would be great. I can try it out and post my
results. Thanks,

Philip.


>From AOR:
It is usual for the 10.7MHz IF output to typically provide a positive
output in the range of +10dB to +40dB above RF input at the aerial
socket.

In other words, a relatively strong signal of 5uV (-93dBm) at the aerial
socket of the receiver would produce an IF output of 500uV (-53dBm),
this is 0.0005V (very small).

It may be worth looking at the AR5000 IF output table which provides
actual figures:

http://www.aoruk.com/5000bull.htm#if_out_level

Usually, secondary receivers are connected to the IF out for monitoring
or a spectrum display unit used to provide display, information relating
to the AOR SDU5500 display unit is available on the AOR UK web site:

http://www.aoruk.com/sdu5500.htm

A file relating to the activation of IF out of the AR8600 is available
from the AOR UK web site but does not quantify levels:

http://www.aoruk.com/pdf/8600_if.pdf



-----Original Message-----
From: address@hidden
[mailto:address@hidden Behalf Of
John Turner
Sent: 11 February 2003 20:06
To: Philip Mackenzie; Eric Blossom
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Quadrature demodulator update


Hi Folks,

Some comments:

The ZFL amplifiers have reasonably high gain, ie. 50dB when cascaded, but
not the greatest power handling. The data sheets gives the gain compression
point as 5dBm at the device output. This translates to an input of
around -45dBm. The effect of the amplifier going in to saturation will be
lower gain and intermodulation which could be causing some of your spurious
responses especially if the ICOM radio has a relatively wide IF.

It's also possible that there is interference from the sampling clock on the
DAQ board getting into the from end of the radio. The additional high gain
may make matters worse. You could try moving the antenna and receiver away
from the DAQ board.

You also might try placing the filter before or between the amplifiers.
There will be an increase in broadband noise hitting the ADC but you will
restrict the signal range to the bandwidth of the IF filter and hopefully
reduce any intermodulation products.

If the filters or the output of the ICOM is high impedance, i.e. 300 Ohms,
the loss when connected to 50Ohm amplifiers will be considerable. Smith
charts are a great method of graphically looking at impedances and would
really help in matching the filters or if the filters are high impedance and
you want to post a model number I can give you a suggested matching circuit.

All Best,

JT
----- Original Message -----
From: Philip Mackenzie <address@hidden>
To: Eric Blossom <address@hidden>
Cc: <address@hidden>
Sent: Tuesday, February 11, 2003 11:16 AM
Subject: RE: [Discuss-gnuradio] Quadrature demodulator update


> Yes we did. I keep 2 channels at 50. I've tried it at both impedances and
I
> experience the same interference. I have a feeling the answer lies in the
> realm of smith charts...
>
> Philip.
>
>
> -----Original Message-----
> From: Eric Blossom [mailto:address@hidden
> Sent: 11 February 2003 18:57
> To: Philip Mackenzie
> Cc: address@hidden; Maitland Bottoms
> Subject: Re: [Discuss-gnuradio] Quadrature demodulator update
>
>
> On Tue, Feb 11, 2003 at 06:42:09PM -0000, Philip Mackenzie wrote:
>
> > Actually if anyone can explain the noise then I'd be interested to know
> what
> > was causing it (I'm sure its some kind of impedance problem).
>
> Shot in the dark: Did you get out your soldering iron and "configure"
> the 4020 for 50 Ohm termination?
>
> Eric
>
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://mail.gnu.org/mailman/listinfo/discuss-gnuradio
>



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