[OZAPRS] HF APRS Mobile

[Andrew McDade]

Gday Andy,

I use a couple of different HF antenna mobile on 10Megs. My primary mobile

10Meg antenna is a really old 5 band tapped Terlin antenna. It doesn't
have 
10Megs as a tap option ! , so I ended up using about a 700-900mm stainless

steel whip, extracted from an old CB whip antenna. I use this instead of
the 
standard 100mm adjustment whip. I set the Tap on the Terlin to the 20meter

position, and fine tune the 700-900mm whip section for best sir on
10Megs.. 
This antenna really fly's on 10megs, and I would imagine that practically 
any loaded HF mobile whip with a 20meter tapping could be made to work in 
this manner.

I also use a (heavily) loaded 27Mhz CB whip antenna on 10megs as a second 
option. I normally use this around town as it fits under the carport
without 
removal and doesn't collect as many branches as the extended Terlin. This 
also performs remarkably well considering that its not much more than a 
meter or so long. First off strip out about 10cm or so of windings out of 
roughly the middle of the CB whip. Then use about a 10cm length of 25mm
pvc 
conduit with end caps. Drill out holes in end caps to suit diameter of 
fiberglass at middle section of whip where windings have been removed.
Slide 
Conduit assembly onto whip and secure at the 10cm section of removed 
windings with silastic or similar. Wind 50 - 150 turns of enamel wire onto

the 10cm conduit section ( I cant remember how many turns ! ) ( exact
number 
of turns requires a bit of experimenting ). Solder , seal terminations of 
new winding to upper and lower sections of existing CB whip windings. This

antenna while not very long, does cover the entire band and does manage to

work quite well on 10megs but also has the added advantage of still
working 
reasonably well on 27-28 Megs without retuning. making it quite a useful 
short dual band HF mobile antenna.

One last configuration I use for a time comprised of a disused RFDS
antenna. 
It too was a tapped antenna with RFDS taps amongst a few commercial taps
as 
well. From memory I managed to get this to work on 10Megs by selecting a
tap 
as close as I could to 10 Megs, but lower in frequency. Somewhere around 
8Megs comes to mind. I then used about a 5cm width piece of allfoil ( 
kitchen variety!) , wrapped it around the antenna, from memory, around a
3rd 
or quarter away from the top of the antenna. Experimented with the
position 
by sliding this up and down the antenna, checking swr etc. Eventually I 
found a point that gave me a good swr. I then just secured the allfoil a 
little bit better by wrapping electrical tape around it. This is a bit hit

and miss with finding a suitable tap / alfoil position, But in reality its
a 
very quick antenna to put together and make work, great for getting 
something up and running for emergency use or whatever using all those 
discarded RFDS whips !!  For those that can remember, I actually used this

antenna during the Kimberly trip I did back in 2004. The beauty of this 
setup is that it was super strong and easily survived the riggers of the 
Tanami track , Gibb River Rd etc.

I hope this gives you a few starting points, If you need more exact info,
or 
photos etc etc. don't hesitate to let me know.

Regards .. Andrew .. VK5EX



----- Original Message ----- 
From: "Andrew Rich" <vk4tec at tech-software.net>
To: "ozaprs" <ozaprs at aprs.net.au>
Sent: Tuesday, April 03, 2007 6:30 AM
Subject: [OZAPRS] HF APRS Mobile


> What can I use for an antenna for 10 MHz APRS mobile ?
>
> Suggestions
> -----------------------------------------
> Andrew Rich
> Amateur radio callsign VK4TEC
> email: vk4tec at tech-software.net
> web: http://www.tech-software.net
> Brisbane AUSTRALIA
>
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