I have no affiliation with this company, but I was very surprised by their prices, and very happy with their coax: http://www.jefatech.com/product/ll400

Even if you do go with the 'real' LMR400, I think you'll have better luck than with RG8U.

73 de W4AS Sebastian

On Aug 18, 2008, at 7:05 PM, Michael Tondee wrote:

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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

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 [email protected]:

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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

----- Original Message ----- From: "Michael Tondee" [email protected] To: [email protected] Sent: Tuesday, August 19, 2008 1:05 AM Subject: [amsat-bb] LMR400 or 400UF?

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 _______________________________________________

Hi Michael, W4HIJ

The attenuation in dB of any transmission line connected between the antenna and the preamplifier add directly to the Noise Figure NF of the preamplifier and the power of the signal lost between the antenna and the preamplifier cannot be recovered.

The attenuation of RG8U at 420 MHz is 4.8 dB /100 ft while the attenuation of LMR400UF at 400 MHz is 3 dB / 100 ft

You don't mention how many ft of cable you plan to use between the antenna and the preamplifier wich is antenna mounted by the way it is obvious that the LMR400UF has less losses in comparison of the RG8U and it is preferred.

Suppose that the run of cable between the antenna and the preamplifier is only 10 ft and the Noise Figure of your 70 cm preamplifier is NF= 0.5 dB

Using RG8U the NF of your preamplifier is like to be 0.98 dB while using LMR400UF the NF is like to be 0.8 dB

About the real advantage of using the ultra flex LMR400UF instead of LMR400 for the entire run of 40 ft between the output of the preamplifier and the RX input from the receiving point of view there is not any advantage because the loss for 40 ft of LMR400UF is 1.2 dB while the loss of 40 ft of LMR 400 is 1.08 dB

By the way the gain of any good preamplifier for 70 is in the order of 20 dB minimum so that the loss of 1.2 dB for the entire run of LMR400UF versus 1.08 dB for the entire run of LMR400 subtracts directly to the gain of the preamplifier but the loss of gain is so low in both situations that the overall Noise Figure of the receiving system is not deteriorated using one cable or the other one as calculation shows.

From the transmission point of view thinks are much different because the

full run of 40 ft is used as well for TXing so that the LMR400 with only 1.08 dB attenuation versus 1.2 dB for the LMR400UF is preferred.

In conclusion all considering for RX/TX conditions I would use:

LMR400UF between the antenna and the preamplifier and LMR400 between the preamplifier and RX/TX

For detailed information on this matter and how to perform calculations I suggest to read the article:

"Receiver Noise Figure Sensitivity and Dinamic Range ,what the Numbar mean" by James R. Fisk, W1DTY Ham Radio Magazine october 1975

Since the above article is very old and difficult to find I cand send a zipped copy of it to everyone is interested.

Best 73" de

i8CVS Domenico