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Dual Band (2m-70cm) Mobile Antenna Recommendations,coax loss




Hi Kent:
Do not forget about coax loss.
On 2-meters is not a huge issue, but in a car
440 coax losess can be 1.3-1.5 db for 13-15 feet of
coax.

The comet CM-5m mag mout is using 13 feet of RG-58A/U
coax. Loss at 435 will be near 1.3db, just of for the
coax.

for satellelite work in the car, i use 2 mag mounts
and a splitter.
on 2 meter mono band 5/8 wave fill size vert.
on 440 a mono band colinear stacked 1/2 verts.

45 degree passes on ISS 145.800 are no problem.
FM birds are ok too, when the band is empty.





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


73 Miles WF1F



--- "Kent R. Frazier" <k5knt@amsat.org> wrote:

> I have been unsuccessfully trying to hear AO51 over
> the last week with my
> mobile rig (Icom IC2720 with a Comet C767 dual band
> antenna mounted to the
> rear hatchback with a Comet CP-5M mount).
> 
> Since I am able to transmit and receive on our local
> repeaters, I'm guessing
> that the issue is with my antenna. I've been using
> the online AMSAT
> satellite pass predictions to predict passes I try
> to listen to.
> 
> Can anyone recommend an antenna I could use with the
> above mount to improve
> my satellite reception? I'll settle for reception at
> the moment. I have a 2m
> handheld (Icom T-22A) that I've been thinking of
> using for transmit. I'm
> thinking of adding a Arrow antenna for this.
> 
> I'm not that knowledgeable with regard to antennas
> currently, so specific
> models would be helpful.
> 
> Thanks,
> 
> Kent
> 
> -- 
> Kent R. Frazier, K5KNT
> _______________________________________________
> Sent via AMSAT-BB@amsat.org. Opinions expressed are
> those of the author.
> Not an AMSAT-NA member? Join now to support the
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> 



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