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Re: UHF-uplink power problem



Makis, Mike:

That is a good suggestion Mike.  I did that many years ago on 432.  

If you use RG-58 the loss at 450 MHz* is 10.6 dB/100-foot so using 10 dB
should be close enough number.  So a 20-foot length should provide you a 3
dB attentuator, and two 20-footers 6 dB.  That will give you the ability to
operate 120, 60, and 30w ERP.  The last is equal to what you had barefoot
using your existing coax.  The coax can be coiled so it makes a small package.

Now a caution on these numbers.  Often amplifier gain is not constant as
drive drops off so at some lower point you may see rapid power drop.
Hopefully, you have power meter to measure what output your amp gives with
lower drive.

BTW I use the same approach for my UHF uplink.  I have a 50-60w linear that
is under my antennas on the roof and fed with RG-58.  Fortunately my FT-847
has a power control so I just raise lower using it.  I get 12w max to the
amp this way for 60w out.  Very rarely need that kind of power with my 16.5
dB yagi.  There is a 20-foot RG-213 run to the yagi from the amp.

GL - Ed
*per Times Microwave tables

At 06:42 PM 5/7/2003 -0400, Mike73@aol.com wrote:
>In a message dated 5/7/03 6:28:56 PM Eastern Daylight Time, sv1bsx@yahoo.gr 
>writes:
>
>> 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?
>
>Why not use a length of lossy coax @ 435 like RG-58 or smaller to build an 
>inline attenuator. Cut the cable length for amount of attenuation needed.
>
>73,
>Mike, N1JEZ
>AMSAT #29649
>Local Area Coordinator
>"A closed mouth gathers no feet."
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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> 

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