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Re: [Discuss-gnuradio] Quadrature demodulator update


From: John Turner
Subject: Re: [Discuss-gnuradio] Quadrature demodulator update
Date: Tue, 11 Feb 2003 15:30:36 -0800

Hi Philip,

I tend to mix AOR and ICOM, I think it's old age creeping up on me. I also
looked at the amplifier ZFL-500 and it has a gain of 20dB and P1dBm of 9dBm.

Depending on the input signal level and the gain of the unit the amplifiers
could still saturate or generate some undesired intermodulation products. In
the AOR information they quote a high level signal of 5uV, this is most
likely for a narrowband signal not broadcast FM, i.e. 20uV (-80dBm) is a
typical limit for stereo reception with 50dB quieting, and you may find that
typical signals are 20 to 30dB above this limit. As an example, we are
located quite close to some local FM transmitters and experience levels
of -47dBm, these levels are sufficient to casue overloading of commercial FM
radios.

Anyway the output impedance of the AOR is 50 Ohms by their information table
and it also looks like you have a selection of filters, wideband 6 MHz,
220kHz and 15kHz. As a quick test you might want to remove the external
ceramic filter and use the internal 220kHz filter to see if that improves
things.

A typical ceramic filter, such as a Murata SFE10.7 series, has an impedance
of 330 Ohms. The impedance can be mached to 50 Ohm with a series inductance
of 1.8uH and a capacitor to ground of 100pF. The capacitance is positioned
on the filter pins. A network is required on both the input and output of
the filter.

JT

----- Original Message -----
From: "Philip Mackenzie" <address@hidden>
To: "John Turner" <address@hidden>
Cc: <address@hidden>
Sent: Tuesday, February 11, 2003 1:06 PM
Subject: RE: [Discuss-gnuradio] Quadrature demodulator update


> 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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