[hpsdr] Norton Amps

[Bob McGwier N4HY]

Francis:

That is a good answer.  Thanks very much.  It has the answers I needed. 
The Norton amplifier stuff looks very interesting indeed.  Thanks Ulrich 
and others for filling this hole in my knowledge.

Bob
N4HY


FRANCIS CARCIA wrote:
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> Bob,
> I suffer from a pair of 8640Bs, an HP141 and an RMS volt meter. It gets 
> pretty hard to measure dynamic range above 100 db close in. I seem 
> to remember the third order spur showing up with the input signals 
> around -27 dBM. I was pretty sure the crystal filter after the amplifier 
> was generating the spur.  I hate to quote this kind of performance 
> without the right test equipment.  Also I was seeing a MDS of better 
> than -140 dBM. This was with my homebrew second mixer into the Racal 
> RA6830 IF using a 300 Hz filter at 455 KHz. The stock SD5000 first 
> mixer / filter module is passive with an active limiter ahead of that. 
> This means there is 10 dB of loss before there is any gain stage. The 
> stock Racal has a U310 as the first gain stage and it also has an MDS 
> (3db) of better than -140 dBM at 40.455 MHz. Yes I could say -143 to 145 
> but who knows how good the leakage is around the output attenuators. I 
> had a 10 dB pad on the generator.
> The RA6830 has an (3dB MDS) of -130 to -134 DBM out to 30 MHz with this 
> configuration. It does not need an RF amplifier when using a good 
> antenna. The nice thing about the Norton is the low gain. This allows 
> maximum dynamic range without saturating.
> Ulrich mentioned CATV amplifiers. The performance is great but what do 
> you do with all the extra gain. I have never been able to find a way to 
> take advantage of the performance due to the high gain. I never found a 
> way to get gain distribution right.
> They do look like a great LO amplifier for a high level DBM.
> I can say the push pull Norton easily outperformed the 40.455 MHz Racal 
> crystal filter for dynamic range. Many filters are rated 30 dBM IP3 so 
> the amplifier beat that.
> Dallas Lankford did a lot of testing in his article and he quotes IP3 
> performance above 40 dBM. I trust his numbers and know he is careful 
> about the way he measures this kind of performance.  I can send you a 
> copy of his article later if you don't have it. 
> Also around -25 dBM out of my combiner is about the point there seems to 
> be some interaction between my generators. I use a pair of 6 dB pads at 
> the output of the generators but the isolation does not seem good 
> enough. I'm pushing the test system limits around the performance limit 
> of the stuff I'm testing.   Frank
> 
> 
> 

-- 
Robert W. McGwier, Ph.D.
Center for Communications Research
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