Thanks for the info. As I said to Jon in a private e-mail there is an
education here for those who are willing to learn. I, myself, spent 4 good
years in Wild and Wonderful, in Preston County. Thanks Pete.
At 10:46 AM 8/26/98 -0400, Pete Smith wrote:
>
>At 09:26 AM 8/26/98 -0500, Jon Ogden wrote:
>>
>>>INPUT TUNING: What I found to be the hot ticket has been the MFJ 259B
>>>antenna analyzer. Remove drive cable from your amp and connect it to the
>>>259, key the amp and adjust the slugs. Just watch the meters as you crank
>>>the slug into resonance.
>>>
>>>Others, more astute than myself, will provide the answer to the 10 meter
>>>problem...
>>
>>There is a problem using this analyzer to do input tuning:
>>
>>The input impedance of a tube varies wildly over the drive cycle and
>>drive level. So in other words to really match it properly, you need to
>>apply full drive to the amp and then tune it. The MFJ analyzer really
>>puts out micro watts or so and that is not enough to drive the tube from
>>its cutoff region to active region. Yes, it may get you "close" but
>>"close" is not necessarily a good match at high power. Large signal
>>impedances are different from small signal impedances.
>>
>>I didn't believe this at first when people told me, but I read about it
>>and then I watched it in real life. I watched as my SWR literally varied
>>significantly as I increased or decreased drive to the PA.
>
>Jon's right about this. I sometimes use my SB-220 on 12 meters, and for
>maximum output I need to use my TS-930's internal tuner to match it. The
>only problem is that as the transferred power changes, the "target" moves.
>I often have to abort the tuning process by switching out of "SEND" when
>it's close enough.
>
>Why not approximate with the antenna analyzer, and then connect the
>transceiver for final tuning? Use either the internal SWR meter or an
>external unit between them.
>
>73, Pete Smith N4ZR
>In wild, wonderful, fairly rare WEST Virginia
>
>
>
>--
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>
>
>
John Wilcox NS1Z
FN44rn
ns1z@agate.net
fon: 207-364-2246
871 Route 120
Rumford, ME 04276-3836
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
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Administrative requests: amps-REQUEST@contesting.com
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Search: http://www.contesting.com/km9p/search.htm
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