Ok, I just took a look at this and see where the problem is.
With a resolution bandwidth of 3kHz the 3 order IMD products are masked by
the real signal. For example if you should have a 14.2815 MHz signal and a
14.282 Signal producing 14.2825, you will not see the 14.2825 MHz signal
because it will be a tiny bit added to the 14.282 signal in the spectrum
analyzer's detector. What you need to do is to reduce the RBW to say 500
Hz or a bit less and sample longer (a lot of talking)until you get the full
spectrum filled in as you did before. And you should see a difference. In
fact since the bandwidth of the SSB signal is only 2.5kHz or so wide to
start with you will most likely not see any IMD products using a 3kHz
resolution bandwidth. A 2 tone test is good because it is easier to compare
results but there is nothing wrong with what you are doing. You in fact
could do a infinite tone test (random noise source) and perhaps get results
that would be easier to compare to others if they should try it.
73
Bill wa4lav
At 10:01 AM 3/23/2005 +0000, Mark Marsden wrote:
>Hi Randall
>
>Have a look at
>http://granta.digital-crocus.com/Linear_Design_notes/Spectral_regrowth.jpg
>
>That's a screenshot of the transmit spectrum of my 4CX1000A linear, (Va
>2750V, Vs 350V, ZSAC 250mA). It was made by speaking into the microphone
>normally for a minute and accumulating the trace with the spectrum
>analyser on peak hold. The lower trace is a barefoot FT1000MP, the upper
>trace is the output of the linear.
>
>73, Mark, G4AXX
>
>
> >>> "ad5gb" <ad5gb@myway.com> 18/03/05 20:33:36 >>>
>
>I just found a chart that listed the distortion characteristics of varioius
>tubes. I was really disappointed to see how poorly the 4CX1000A ranked
>amongst
>the competitors. IIRC, I think it was the absolute worst in the bunch.
>
>I got a couple of these things (with sockets) very cheaply a little while ago
>(well maybe longer than that ) and hoped to build something nice for HF out of
>them. I planned to try a grid-driven AB1 configuration at max anode potential
>with the best screen/bias regulation I could come up with but based on that
>chart.... it doesn't look like the most wonderful of things to try to do.
>
>Anyway to make these run more satisfactorially? Cathode drive /w
>NFB? Grounded
>screen (float the cathode below ground) Anyone with any experience and
>distortion figures better than in that Eimac chart I found?
>
>Thanks
>
>
>--
>Randall D. DuCharme (Radio AD5GB)
>
>
>
>
>
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