Re: [Discuss-gnuradio] AR5000 and downconversion

[Joshua Lackey]

When I get back from this business trip I'll post a FFT screen shot from
my PCR1000.  It doesn't appear to me that there is any adjacent channel
interference but I'd like others to look at it.

Quoting Joseph DiVerdi (address@hidden):
> 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
> ><snip>
> >
> >The ar5000 has a bandwidth of 10mhz
> >http://www.aorja.com/ar5000e.html
> >http://www.aoruk.com/5000bull.htm
> >
> >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
> 
> -- 
> Joseph A. DiVerdi, Ph.D., M.B.A.          
> http://xtrsystems.com/           970.980.5868 (voice) 
> PGP Key ID: 0xD50A9E33
> 
> 
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-- 
Joshua Lackey, PhD. -- address@hidden