>
>>>>At 08:01 AM 7/19/02 -0700, Richard Measures wrote:
>>>>...
>>>>>Yes. Please tell us about the results.........one 5408,
>>>>>or? Previously, when I asked you for test data on your recommended
>>>>>diode biasing , your response was that I "didn't need no stinkin'
>>>>>data." Why now?
I knew that the story about 6v bias variation was unsliced bologna, so I
measured the result of Si junction Vf with a 0.1A to 1.2A current
variation.
>>>>>
>>>>> >I've done it with a Henry 3-K Classic X, using and 8877,
>>>>> >and the bias soared about 6V from zero to full signal.
>>>>>
>>>>>V sounded a bit high, You bet it was high and you can't compare a
>>>>>Semtech assembly with a sample of one 5408. BTW, the early Henry 2-Ks
>>>>>used a 50W, 6V Zener.
And Henry Radio went to the more rugged fwd-biased diodes ckt.
>>>>
>>>>>so this morning I tested a 1n5408/3A diode for fwd
>>>>>V-drop using 8877-sized currents, assuming a ZSAC of 0.1A and a signal
>>>>>max Ik of c. 1.2A. At 0.1A, the V-drop was 0.734v. At 1.2A, the V-drop
>>>>>was 0.813V. Thus, with a 10-diode string, the change in bias V for an
>>>>>8877 would be 0.79V from zero-sig to max-sig. For improved IMD, and
>>>>>less chance of overdrive with more than 78w drive, add a few ohms in
>>>>>series with the diode-string to increase V-drop at max sig.
>>>>>
>>>>> >Read that power limiting that must result in additional distortion
>>>>> products.
>>>>>
>>>>A diode has more V-drop as current increases. A resistor has even more
>>>>V-drop as current increases. A resistor can be added in series with the
>>>>cathode to create RF-NFB. (which I read in Svetlana, Eimac, and RCA
>>>>pubs).
>>>>
>>>- Marv - Does more RF-NFB increase or decrease IMD?
>We all know the
>answer to that one but you have to know the net effect of the ratio of
>the biasing distortion to the negative feedback afforded by the resistor.
>>>>>
I already know that RF-NFB works from on the air checks using humanoid
mod.
>>>>> > I couldn't wait to dump Henry's Semtech diode pack and put in a
>>>>> 50W,12V Zener. IMHO,
>>>>>
>>>>>Humble ? Yes, humble and it is not obvious that you know much about that.
>>>>
I have eaten enough humble pie to know what it tastes like. I know what
bologna smells like. Bologna salesmen cause Amateur Radio operators to
waste money. I am not the friend of such salesmen.
>>>>> there is nothing worse than diode strings as a biasing element.
>>>>> > Further, just ask the G-land 6M ops what they think of the bricks
>>>>> >that find their way into cluttering up the band with relatively high
>>>>>levels of splatter resulting from diode bias. Ian et al, are you
listening?
>>>>>
>>The red herring.
> Now, don't tell me that you've gotten into fishing?
>>>>
I fish for red herrings.
cheers, Marv
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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