[AMPS] Low Output on 10 meters

John / NS1Z ns1z@agate.net
Wed, 26 Aug 1998 21:36:43 +0000


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

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