[AMPS] Re: 4-1000A Impedance Variations

[Rich Measures]

>>You are talking about measuring swr with a tuned circuit/flywheel at the 
>>cathode.  Cathode impedance, this is not.  You must measure direct into 
>>the cathode? .  .  One problem with a noise bridge is that the power is 
>>in the microwatt range.  .  
>>........
>
>Rich,
>
>One thing I want to point out is that I got the idea of using the RX 
>noise bridge from the paper that Jim Thomson sent to me.  Again that was 
>an article by Irvin M. Hoff, W6FFC that was published in the January 1973 
>issue of Ham Radio.  This article was re-run in the March 1978 issue 
>which is where Jim got it from.  
>
>To quote:
>
>"The easiest and quickest method of measuring input impedance would be to 
>use a variable impdeance bridge such as the RX noise bridge."

Easiest and quickest is not to waste your time measuring.  
>....
>"When making the impedance measurement the high voltage must be on the 
>amplifier, and the meter hooked as close as possible to the place the 
>network will be added."
>
I don't think I would be inclined to connect a Rx noise bridge to the 
cathode of 4-1000A with six or seven kV on the anode.  

>The article also references some another article:
>
>"RX Noise Bridge for Accurate Impedance Measurements."  by Frank Dotting, 
>W6KNU and Robert Hubbs, W6BXI.  Ham Radio, February 1977 page 10.
>
>We shall see how it works!
>
To save time,  build a 40m or 20m pi network with a 25 ohm Xc at the 
input.  Adjust L1 and C2 for the best match..  Measure the values, scale 
them up and down as needed for the other bands.  .  If the scientific 
measurements, do not agree with what makes my exciter happy, "frankly, my 
dear, I don't give a damn".  . 


cheers
Rich...

R. L. Measures, 805-386-3734, AG6K   


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