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1230Re: [at-golden-packet] "Splitter for long shots"

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  • John Huggins
    Feb 10, 2014
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      I will forever question the validity of using two opposite directional antennas with a splitter for any, but the most unusual circumstances.  A decent collinear omni approach should fulfill most situations.

      However, if you want to proceed I have some experiences...


      Splitter:
      You can avoid precise measurements of the antenna cable pair by using a traditional splitter like this one...

        http://www.minicircuits.com/pdfs/ZA2CS-600-10W.pdf

      Yes it is not cheap, but buys you great phase stability vs. frequency and keeps your cabling at 50 ohms and not tied to any specific length.

      If you go the pair of 75 ohm 1/4 wave route don't rely on anyone's stated length measurements because you can't be sure of the cable Vf and other quality controls.  Instead use a VNA or a meter like the MFJ-249 to help trim your cable to proper length.  Here is an article explaining how...

        http://www.hamradio.me/antennas/measuring-quarter-wave-coax-stubs-using-mfj-analyzer.html

      At VHF frequencies, inches and centimeters count and the connectors and dressing will play a role into the real "electrical" length of your 1/4 wave cable sections.  This will likely be a hit and miss affair.


      Antennas:
      Most Yagi-Uda designs do a pretty good job of ignoring everything behind the antenna, but this varies.  Simulating your two antennas together is the key to avoid unwelcome surprises.

      Keep in mind the mantra... you are not co-phasing two antennas... rather you are designing a single antenna array with many elements.



      Digipeating:
      Unless you are "inside" the ends of the ATGP chain, you likely shouldn't be digipeating anything for fear of causing interference.  However, one possible work around is for you to listen on 144.340 and digipeat/transmit 600 kHz up... if possible.


      John



      On Mon, Feb 10, 2014 at 1:43 PM, <dmontpe987@...> wrote:
       

      There's a picture on http://aprs.org/at-golden-packet.html of an antenna system identified as "Splitter for long shots".


      Has anyone built one and have experiences to share?

      It's a little optimistic to expect I would need one in 2014 to relay packets from Mount Carleton further north.   But I'd like to try and put one together. I was doing volunteers comms at the Canadian ski marathon last weekend and needed to monitor sweep skiers on 146.52 in 2 directions.

      My plan is to use 2 Arrow backpack yagis 5/8 wavelength apart, end-mounted on a shared boom and pointing in opposite directions.

      I plan to use RG-11 for the 75 ohm sections. Is it 12.9 inches on each side of the tee? or 12.9 total?



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