Re: [Discuss-gnuradio] Quadrature demodulator update

[John Turner]

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
>
>
>
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