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Re: [Discuss-gnuradio] AR5000 and downconversion

From: Joseph DiVerdi
Subject: Re: [Discuss-gnuradio] AR5000 and downconversion
Date: Thu, 15 May 2003 00:04:08 -0600

At 11:58 PM -0400 5/14/2003, Krzysztof Kamieniecki wrote:
>John R. Ackermann N8UR wrote:
>> Hi Alan --
>> I doubt you'll find many radios that support a 6-7MHz bandwidth around a 
>> 10.7MHz IF.  That's way too great a percentage of the center frequency for 
>> traditional radio design to work with.  I suspect the 10.7 IF in the AR5000 
>> is not going to be able to handle more than NBFM, or at most WBFM (eg, 
>> 200kHz or so) bandwidth without major surgery that would likely render the 
>> radio useless for normal tasks.  A radio that supports TV bandwidths is 
>> likely to have a much higher IF, anywhere from 45 to 70MHz or higher.
>> John
>The ar5000 has a bandwidth of 10mhz
>AOR claims there is a NTSC demodulator for the ar5000 it's called TV5000
>Rumors says ar8600 has either 2 or 4 mhz bandwidth (i've seen both mentioned)

>Krzysztof Kamieniecki

Couldn't help adding my two cents here. 

I must agree with John's original comments - based on "conventional RF design 
wisdom" the bandwidth of a 10.7MHz IF is generally much less than +/- a few 
hundreds of kHz. Unless something unusual is going on there will likely be real 
problems with adjacent channel interference. 

A snippet of the ar5000e.html URL cited above by Krzysztof follows:

"The receive circuitry is a triple conversion superheterodyne with IFs of 
622MHz, 10.7MHz & 455kHz. Multiple switchable IF bandwidth are available in 
both the 10.7MHz and 455kHz IF stages: 3kHz, 6kHz, 15kHz, 30kHz, 110kHz, & 
220kHz with provision for an optional 500Hz Collins mechanical filter."

These values make sense for a communications receiver. There are three 
sequential IFs (good design technique but can be a bit pricey) and the 
bandwidth specified for the second and third IFs is quoted in the tens and 
hundreds of kHz. Again, it is unlikely that the hundreds of kHz bandwidth 
values are available at the third IF (455kHz) but more likely available from 
the a tap of the second IF (10.7MHz).

As Krzysztof also notes there is a quote on the page referenced by the same URL 
which follows:

"The AR5000 is ready to plug straight into the optional SDU5500 spectrum 
display unit for "real time" band occupancy evaluation and measurements in both 
frequency and dBm signal level. The 10.7MHz I.F. output of the AR5000 has a 
suitable 10MHz bandwidth ideally matched to the SDU5500."

Now this is really curious. I would not be surprised to see a 10MHz bandwidth 
available from the *first* IF (622MHz) but am dubious of the claim as written. 
It *is* possible but would be highly unusual.

Need to look into this a bit more but getting sleepy, sleepy, sleepy...

Best regards,

Joseph A. DiVerdi, Ph.D., M.B.A.          
http://xtrsystems.com/           970.980.5868 (voice) 
PGP Key ID: 0xD50A9E33

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