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Re: UHF-uplink power problem



Makis,

You did not say what your rig model number was, but there may be more 
possible solutions.

You can find 25Watt 10db Bird attenuators around fairly cheaply these days   
You could use a gang switch, a transfer relay, or 2 separate RF switches or 
relays and switch in the attenuator when needed.   A 3 or 6DB attenuator 
might be better choice if you can find them.   Another trick I sometime use 
in a pinch is to place a T fitting and hook up a dummy load for a little 
attenuation.

You might find your rig has an ALC jack or pin.  I have used that approach 
to lower my power for most every rig I have so far (except my FT-100 which 
seems to be all or nothing).  You connect a adjustable supply of -0 to maybe 
-8VDC.  I perer to use a 10 turn pot witha vernier dial to finely adjust the 
power output level.  I use this for transverters to drop the power to 
50-200mw level.

Another option is to open the cover and find the power adjustment, many have 
an internal drive level adjustment somewhere.  This is likely last resort, 
but maybe you can find a level that works for all conditions.


73,

Mike
K7MDL

>From: "Makis" <sv1bsx@yahoo.gr>
>To: "Amsat-BULL" <amsat-bb@AMSAT.Org>
>Subject: [amsat-bb] UHF-uplink power problem
>Date: Thu, 8 May 2003 01:21:27 +0300
>
>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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