[amsat-bb] Question on 23cm WiMo Helix
73 Bob W7LRD
w7lrd at comcast.net
Thu Apr 2 17:08:38 UTC 2020
Hi Tom et al-- Back in the days of AO-40 (sob sob) I built a 16 turn RHCP helix. Several of which I sold around the country. Currently I am using a 24 el looper. I am planning to put my helix back up there (20" tilt over tower) with a relay to switch between the two antennas just of fun.
I use 70 feet of LMR600 I could have gotten by with LMR 400 which I use on U & V. I use a IC-910 at 10W. I have a 70W amp that's waiting for my ambition to catch up. The book Antennas by Krauss has a ton of valuable helix info. Here in W. Washington there is some local L band activity. With mountains all around L band presents some interesting bouncing propagation. We only have one satellite (AO-92) with L band capability, and that's only once a week. I would like to see a linear bird with L band, maybe even S band down like the aforementioned AO-40 (sob sob). I'm sure others will chime in with information. On Ebay there are a few antennas available https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=1.2+ghz+yagi&_sacat=0
I have one I have yet to try out. ABout $50 it's cheap enough to try. I don't know if any of us are using one of these. At this time we all have the time to play radio <grin>. Lots of options Tom.
73 and stay safe out there
> On April 2, 2020 at 8:14 AM Thomas Schaefer via AMSAT-BB <amsat-bb at amsat.org> wrote:
> Reading the prior posts about the counterbalance, made me think again about adding the 23 cm helix antenna to my sat beams before they go up, but I wanted to check my thinking on this…
> There appears to be only one L band satellite, AO-92. That is an uplink. Given that, I obviously have no need for a preamp. But I also believe that I need not worry too much about using anything better than LMR-400. In checking the Times Microwave loss calculator, using LMR400 over a 50 foot run would lose 2.6 dB. Using LMR-600, would lose 1.7 dB. 7/8” hardline would be .8 dB. But given that the Helix has 13 dBd, that is over 100 watts at the antenna. Plenty AO-92.
> So while cable loss seems academic, are there any satellites in the works accessible from the US with an L band downlink? If not, it appears LMR-400 is just fine (even with a short loop of LMR-400 UF at the top for the rotor).
> Tom Schaefer, NY4I
> Blog: www.ny4i.com
> Madeira Beach, FL (Grid: EL87ot)
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