At 05:16 PM 8/18/2008, Patrick Domack wrote:
Between your antenna and the preamp is where you want your best coax at, cause every bit of loss you have there, is lost.
Once it's past the preamp, it will give you good gain, so then it's just how paranoid you are, as to how much loss you are willing to give up, to get it into your shack.
If your preamp has a noise level of like 1db, you should be able to safely loose 1db in coax from your preamp to your shack, and at 40feet, your talking about rg8, maybe mini8 (1.2db I believe).
I'm one of the paranoid people, and normally keep my losses <1db, and most of them are <.5 db
Quoting Michael Tondee mat_62@netcommander.com:
I need to rework my 70cm antenna system and was thinking about going with LMR 400. I have about a 40 foot run. Is there any real advantage to using the ultra flex for the entire run or can I get by with a short section of the UF between the preamp and antenna to accomodate the rotor turning? How about just using a short section of RG8U there instead of the LMR400UF? I'm trying to do this on a budget. Tnx and 73, Michael, W4HIJ
Michael,
Assuming your cable is not long from the antenna to the preamp it will not matter that much. I calculated the loss in an 8-foot run of LMR-400 vs LMR-400UF. The former shows 0.2 dB loss vs 0.3 dB loss for the flex cable.
I am running LMR-400UF from my terrestrial 432 and 222 antennas to the preamp. I then run RG-8/x or also called mini-8 from the output of the preamp to the radio. The flex is better suited for flexing around the rotator. You can use RG-8/U instead of the mini-8 equally well. But do use at least LMR-400UF in front to your preamps to get the best low-noise performance.
If you are sharing the line from the house for transmitting the run LMR-400 up to the preamps and coax relays.
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