[amsat-bb] Re: loop yagis

[Edward Cole]

Greg,

At 10:40 PM 5/7/2007, Edward Cole wrote:
>Greg,
>
>My experience was with my 144/1268 15w DEMI Tx-converter mounted on 
>the elevation crossboom with 7-foot of 1/2-inch hardline to a single 
>45-element loop-yagi.  I measured 9.5w at the feed with a Bird meter.

After reading what I wrote, I realized this was not an accurate 
description of what I used on AO-40.  This is what I built after my 
on-air experience to lessen losses.  This setup resulted in about 14w 
to the antenna.  I never got the chance to test this on AO-40 as it 
shutdown by then.

What I ran on AO-40 was about 20-feet of LMR-400 from the antenna to 
the ground below my short roof-top tripod.  That resulted in the 15w 
being attenuated to 9.5w at the antenna.  This does show how little 
it takes in coax loss to reduce 1.2 GHz power delivered to the 
antenna and the uplink.  I bought Ser. No. 102 of DEMI 144/1268 15w 
AO-40 transmitting converters.  My order was placed a year in advance 
of launch so I got nearly the first production unit.  Its a nice 
piece of equipment but DEMI discontinued it shortly after the demise 
of AO-40.  The 18w PA chip used in it is no longer available.  I have 
a DEMI 1296 15w PA that uses that same device.  Hope they hold up as 
when they fail the equipment will not be reparable.




73,
Ed - KL7UW
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