[amsat-bb] Re: LMR400 or 400UF?

Edward Cole kl7uw at acsalaska.net
Mon Aug 18 23:18:48 PDT 2008

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 at 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


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.

73, Ed - KL7UW              BP40iq, 6m - 3cm
144-EME: FT-847, mgf-1801, 4x-xp20, 185w
http://www.kl7uw.com     AK VHF-Up Group
NA Rep. for DUBUS: dubususa at hotmail.com

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