[amsat-bb] Re: Questions on practical aspects of coax and preamps.
gzook at yahoo.com
Sat Oct 25 08:04:56 PDT 2008
I use RG213/U for the flexible connections around the rotor and in the shack and have no qualms about this. However, I do not use LMR-400. All of my feedlines are either 1/2 inch Heliax or 7/8th inch Heliax except for my 40 meter phased verticals which do use RG213/U. That is, all of my antennas from 1.8 MHz to 432 MHz.
Frankly, I obtained a large number of Heliax runs with connectors on both ends, most of which were 100 feet long (100 feet just makes it from the top of my main tower - 54 feet above ground - down into my shack) for absolutely nothing. As such, I would have to actually spend money to get poorer feedlines.
The losses using RG8/X (or Radio Shack RG8/mini) start adding up above 30 MHz. Primarily I only use RG8/X for jumpers or for temporary antennas below 30 MHz. Now RG8/X is definitely better than RG58/U but not as good as RG213/U and LMR-400 is slightly better than RG213/U. However, 1/2 inch and 7/8th inch Heliax are better than LMR-400.
--- On Sat, 10/25/08, Curt Nixon <cptcurt at flash.net> wrote:
From: Curt Nixon <cptcurt at flash.net>
So, after this last week of ISS fun, I have the bug to upgrade into some simple satellite work. I will be confined to simple FM untill I can upgrade to all-mode rigs. My question is on coax and preamps.
I will use a pair of vertically polarized yagis to begin with. One for 144MHz and one on 70cm. I have some LMR 400 I got for the ISS project on 144 but it is so stiff, I didn't use it.
1. If you use LMR 400, do you add flexible sections at the antenna end and in the shack, using LMR400UF? Or, should I just use all UF and forget the additional connections? The cost of the additional connectors (N) both in loss and $$ is probably advantage $ for UF. Not sure about the loss potential for adding two sets of interface connections.
2. With a 5-7 element yagi on 144, is it really necessary to use low loss coax as a opposed to 8x or 8x mini. Runs here are 35' if munted at 12' and 60' if mounted to roof tower at about 20'
3. On 70cm, I plan to add a mast preamp, but will use the yagi "barefoot" to begin with. With a preamp at the antenna, is low loss coax still required or can the cost increment be put to better use in the preamp to begin with? The preamp of course also gives a convenient place for a connector interface from stiff to flexible if desired.
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