For Leo Mobile, I started with the biggest antenna that will fit on my car and in my garage and then staring working on the coax.
I use a 2/440 splitter into 2 Mono band NMO magmounts. This way I get Taller antennas and more gain than with a Dual Bander (2/440). 2 meters is a 5/8 wave mono bander (Salesman gain = 4, Dipole gain = 1). 440 is a stacked mono band collinear 1/2 wave stacked over a 1/2 wave (Salesman gain = 6, Dipole gain = 3).
The Amp on 440 with built-in preamp was the last part I installed. Although, for the first 12 years of Leo Mobile I never used and amp. Even though I have an amp and preamp in my car, I would not recommend them to the casual user. The maintenance is usually high to keep them running. Stick with the Biggest antenna and best coax first.
Coax Tips for Low loss.
If you buy a new NMO Mag Mount, make sure you can find a way to dissect the mount and remove the magnet, etc. so you can replace the coax cable. On some Larsen, its easy to pop off the magnet to get to the screws hidden under the magnet. You will need to replace teflon pad.
Here are some number I put together on coax loss for the typical mobile installation. dB Loss dB Loss Type Freq/Length Max Freq/Length Max Center 440 440 Pwr 900 900 Pwr Size Conductor
Feet 15 100 15 100
RG-58/U 1.5 9.9 105 2.2 14.5 60 .195" .032
RG-58/A 1.5 9.9 105 2.2 14.5 60 .195" Stranded
RG-8X 1.2 8.1 250 1.8 12.1 150 .240" Stranded
LMR-240UF 0.5 3.2 380 0.7 4.7 260 .240" .059
RG-58 comes in many flavors, No letter, A, C and U U sometimes is a solid 20 AWG copper center. A and C have a stranded center conductor. The center conductor size would be similar to solid, but will have a little more loss.
Most cars will need 15 to 17 feet of coax. RG-8X and LMR-240 have the same Outside diameter (.240"), however the LMR has a foil shield and half the loss of RG-8X. The LMR-UF-240 version is the Ultra Flex flavor and can bend easier.
From this list of small car style coax, the LMR beats
them all, in lowest loss for the size and highest transmitter power loads. I was planning on installing a 440 AMP in my car, but after looking at the coax, I realized that I would fry the RG-58 coax at 100+ watts on 440mc.
I dissected an old Larsen Magmount and replaced the original RG-58U with LMR-240-UF. I have been running this configuration for over a year with good results and I have not melted any coax. There is also a nice added benefit, in the winter time during a long rag chew on 440, the 440 amp keeps the passenger seat warm.
For those of you interested in 900 mc, the benefits are even greater.
900 mc 10 watts, in, 15 feet of LMR-240, = 7.7 watts out 10 watts, in, 15 feet of RG-58/U, = 5.8 watts out
Power reference http://www.ocarc.ca/coax.htm
--- "Kent R. Frazier" [email protected] wrote:
Hi all,
I am really enjoying the satellite aspect of the hobby and have enjoyed the contacts I have made with my Icom IC-2720H with a 19" whip antenna from my vehicle. I have seen talk recently of using a preamp to improve the reception. From what I've read and understand, it appears that a "switching" preamp is needed for a setup using only one antenna for Tx and Rx such as mine. Is this correct?
It also appears that most of the preamps are mast mounted. Since this would not be an option for me can the preamp be put near the transceiver? Are there any issues that result of doing so?
Lastly, what preamp(s) would you recommend for an application such as mine?
Thanks,
Kent
-- Kent R. Frazier, K5KNT _______________________________________________ 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
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