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UHF-uplink power problem



Hi AMSATs,


    I wondering, how is possible to reduce the output power of my UHF, by
using external device...  why that? Let me to explain you my problem :

  I've a long coaxial cable(about 100 feet) from my shack, up to UHF antenna
for AO40 UpLink.
The coaxial cable Loss is about -6 DB on 435 MHZ. My UHF rig output is 12
Watts. The -6 DB coaxial loss, giving into Dipole feeding-point only 3
Watts,
very poor feeding for the AO40 Uplink.
So, I bought a  UHF PA (Linear 15 Watts)  to place it  behind of my UHF
Yagi. This way, with 3 Watts input I have 12-14 Watts output
(PA gain =  6-7DB).
With this combination, I have not  Losses between PA and Antenna, the cable
is a pretty smal piece. And finally, I have an ERP 120-140 Watts
(PA out x 10DBd Gain of Yagi).  Ok, well done!

 But, when the AO40 is close to Earth (ie 30.000 km or less),  the  output
of
100 Watts (ERP) is high enough to activate LEILA!(it happens to me several
times).
So, now I have the other problem, to reduce my driving power from my UHF rig
to
UHF-PA .
Unfortunately, my UHF rig has not any power switch, or external pot to
adjust the
Output Power. So, I wonder how is possible that... may be by using an
external
attenuator between RIG and PA?  Yes, but this unit is difficult to construct
it,
especially on UHF !  And I can't find anything like that (commercial) to
handle
15 Watts on UHF.
Another idea is the Voltage supplying on UHF-PA. By reducing few volts (from
13.8 to 9 V), may be the output power drop down, may be not enough. (I'll
testing
that the next days).

Keep in mind, I don't like to modify my RIG for variable Power-output. It's
very
compact, without any free-place for any additional external pot on front &
rear panel.
And the Mic-gain is not the total solution.... it works on SSB but not in
CW.

Any suggestion is welcome !

73 de Mak SV1BSX



sv1bsx@yahoo.gr
http://www.qsl.net/sv1bsx





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