[Premium-Rx] Nice piece of test gear for RX intermod testing on HF bands

[Calvinf15]

Hi folks,
 
With all the recent talk regarding the measurement of high level
intermod, I thought it appropriate to put a plug in for a really nice
piece of test gear I am parting with on ebay.  It is a precision
arbitrary waveform generation system made by HP (HP8770A based system)
that runs the R4 system software by Rapid Systems as well as Labview 6.
The wonderful thing about it is its ability to generate very clean, low
phase noise signals, with the capability to produce arbitrarily spaced
multi-tone signals necessary for 2-tone intermod testing across the HF
band to a nyquist frequency of better than 60 MHz.  Better yet, it has
the realtime bandwidth to create the noise-power ratio (NPR) signal
generation with brick wall filter slopes.  
 
I experimented with the NPR technique (well described here:
http://cp.literature.agilent.com/litweb/pdf/5965-8533E.pdf ) and found
it to be an outstanding measure of RX front-end performance.  The basic
technique is this:  generate a broadband noise waveform that has a
"notch" of several KHz in the band of interest, perhaps 3 or 5 KHz.
Then, feed the signal to your receiver and monitor the IF on a spectrum
analyzer.  The perfect receiver will not "fill in" the notch with noise.
The less than perfect receiver will tend to fill the notch with varying
levels of noise products, representing front-end intermod or overload.
The test yields surprising results and in many ways is superior to
t-tone testing.  The problem with NPR testing when attempted without a
digital generator is that one needs a set of very steep and well
characterized/calibrated notch filters for each test frequency of
interest.  Of course, digital filter design programs allow extremely
sharp filters for this type of test.
 
Of course, t-tone testing is a fast and simple means of accomplishing
similar performance measure, but fails to realistically represent actual
operating conditions, especially on our noisy HF bands.
 
Please contact me off list if you have any questions regarding these
techniques or other applications of this system.  Here is the link to
item # 5751715613
 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=5751715613>
&rd=1&item=5751715613
 
Regards,
 
Adam, N1GX
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