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Re: Trasmission line questions and more for a new QTH



"Adam L. Mendelson" wrote:
> 
> Well I finally have a place to operate, and best of all no HOA to deal with.
> I could use some assistance with some ideas I have for transimission lines
> and overall design of the new QTH.  This will probably be long winded so I
> appologize ahead of time.  Also if there is anyone in the DC area, I am in
> Sterling, VA by Dulles, who could act as an elmer for me?  Thanks in advance
> for any help.
> 
>Your Noise Figure is pretty much determined by your downconverter and the preamp which is installed in front of it, so the good news is that you can probably get away with using inexpensive RG-8 for runs less than 150 feet, and something like RG-8X for runs of less than 50 feet. The use of N-connectors for all of your feedthroughs and connections is a good idea, though for your downlink on 2, is probably a little overkill.

 I am using a 75 foot run of RG-59 directly from my AIDC-3733 into my
patch panel, then a short run of RG-8x for the short run to the rig. I
have an S3 noise floor with this setup, with about 4 dB of loss in the
feedline, which amounts to 1 S unit. If I ran say 7/8 Hardline instead
of the cheap stuff, I would see maybe a 1 S unit increase in my noise
floor, but the S/N ratio would be only minimally improved. 

Feedlines are another story for your uplink, which I assume will be
either on 435 Mhz or on L-Band, but a lot depends on your antenna setup.
If you are using one of the  big old 44 element KLM Cross Yagis from an
AO-10 or AO-13 class setup, or have a 100 watt brick for your uplink
signal, you can probably get away with something like RG-214 for your
uplink feedline. If you have either less antenna, less power, or a
longer feedline run, it makes sense to use better coax for your feedline
in this situation. 

If you are going to uplink on L-Band, it is critical to use the best
coax you can afford, since losses increase substantially at the higher
frequencies. 

If you are going to be using your antenna setup for AO-10 and other
satellites where you do not have a preamplified downlink at the antenna,
it is critical you use the best feedlines you can afford here. If you
want to try to work AO-10 without a mast-mounted preamp, LMR 600 isn't
overkill, and in fact you might want to investigate using something like
3/4 or 7/8 Hardline here. An economical source for Hardline is "tag
ends" of CATV hardline of less than 150 feet, which can often be
acquired for a song at a hamfest, or for the asking from your local
cable company. Sure it is 75 ohm impedance, but the slight mismatch
isn't worth worrying about. Performance of 7/8 CATV hardline is similar
to Andrew LDF-550, and the cost is right. Only problem is that you will
probably have to hunt for suitable connectors, or use your ingenuity to
adapt to a suitable connector.
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