Mobile Antenna Installation
 

"Gary Smith" wrote in
:

Thanks Owen, Yes, i know the discone is low gain, and i have (Shock,
Horror) approx 60 ft of rg58 connected to it :

Yeah, ouch. Here is the bad news, if the discone VSWR is 1.5:1 (at the
antenna) and you have 60' of RG58, you are losing 58% of your transmitter
power in the feedline. With RG213 you would lose about 30% and with LDF4-
50 you would lose around 11%. The picture is worse with increasing
frequency.

Now you can offset the loss of transmitter power with an amplifier or
another 4dB of antenna gain, but noise levels should be so low in
Casterton that you will not recover the loss of receive performance
without an LNA (preamp) at the antenna.

If you want to work some line loss solutions, try
http://www.vk1od.net/tl/tllc.php .

Before I you get you carried away with LNAs, the following article might
be a bit technical, but it has some summary graphs that might convey the
idea: http://www.vk1od.net/gt/index.htm .

Something else to keep in mind, with an FM receiver, a 1dB increase in
strength of a noisy weak signal will result in much more than 1dB
improvement in Signal/Noise ratio. Improvements to your EIRP have the
same effect at the remote receiver.

I have been playing with radio for about 20 years but only just
aquired my Ham ticket. I have read the ARRL handbook around 5 times
now i would say, cover to cover.

I am modifying an ex CFA "Polar" 163.2 MHz vertical at the moment,
there are plans on the net to modify this antenna to 146 meg. For
those wanting to view this pdf, google vk3cmc cfa. I am also going to
price tubing for a 17 element 2 Metre Yagi and later on one for 70cm.

That is a huge antenna, 17el on 2m! You are talking about a 10m boom.
Gee, that will be a challenge horizontally polarised, but a bigger
challenge if vertically polarised. Have you thought about two yagis
stacked in the H plane, and supported so that you can swing them from
horizontal to vertical polarisation?

BTW, if you are interested in DL6WU designs for a long boom yagi, and
they are probably a good place for a beginner to start, see
http://www.vk1od.net/dl6wu/index.htm .

Combined with some RG-213 i think that will be quite fine, another
station further away than i am is getting into the repeater with a 6
element. My tower will be going up soon, got a 50ft and 75ft so
debating which one to use. 75ft is narrower inner section (3 stage
tilt over crank up) so would not hold as much weight and wont take my
KR400 inside the top section (too narrow).

High towers means longer coax... you might be looking at LDF4-50 sooner
than you think, especially for 70cm and 477MHz.


I have the discone as a way to get up and running, can use the Mount
Gambier repeater with it all the time and that one is around the same
distance AND a large hill between it and me.. Most repeaters for us
are around 60-100k +. we have members all over the corner of the state
and would be stuffed without repeaters, fantastic things!!

Anyway, back to my ex CFA antenna...

That should be an intesting project. You will see first hand what is
inside the radome, and understand why poor implementations are prone to
fatigue failure.

Owen