Re: [amsat-bb] AO40 Downlink, RG213 verses 1/2 inch

[Bruce Nolte N3LSY <brucenol@xxxxxxx>]

zs6y@metroweb.co.za wrote:

>Hello List,
>I am running RG213 from my DEM downconverter to the shack,it is 
>25 Meters long..I have the DEM 2401/144 at the dish feed point.
>Is it worth the effort in laying down 1/2 inch Andrew hard line to my 
>144Mhz rx. Will I notice a big jump in signals?
>
>Hope one of the experts out there can help..
>Thanks in advance.
>Etienne 
>ZS6Y
>
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>
>  
>
RG-213 has about  3 dB of loss per 100 feet (30 meters) so  you are 
losing a little over 2.5 dB in your feedline. Hardline such as LDF4-50 
will reduce this to about .8 dB, but there is a catch. You will need to 
terminate the hardline with an adapter so you can run flexible cable for 
the last few feet to the downconverter, assuming your dish is set up 
with an AZ-EL rotor system, and you operate over a large part of the 
range. The extra connectors will add a bit of loss to the setup, 
depending on the quality of connector used, but figure about 1/2 dB. 
 This should result in an increase of slightly over 1 dB of signal at 
your receiver.

Another factor is the gain of the downconverter, as well as its noise 
figure. MMDS downconverters with excess gain, such as my AIDC 3733 
provide a noise floor at my FT-736  of  about S 1.5 with the dish 
pointing away from the satellite, and using about a 30 meter run of 
 (gasp) RG-59, which eats up about 4 dB of signal or more.  MMDS 
downconverters were deisigned less in mind for a good noise figure than 
providing a satisfactory signal down lossy cheap coax.  I checked on 
DEM's website and they recommend getting the gain module if there is to 
be more than 6 dB of attentuation in the feedline, which you already are 
beating by 3.5 dB.

If it were my money, I would put it into a larger dish, or a receive 
preamp rather than spend it on the 144 Mhz downlink coax. If in the 
future you have to make a much longer coax run (say 100 meters or so) it 
might be worthwhile to upgrade the coax.

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