[OZAPRS] Antenna for HF-APRS...

vk2ycj at bravo.net.au vk2ycj at bravo.net.au
Sun Mar 1 21:35:59 EST 2015


What a great story.  Thanks for sharing it with us.


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>     Strange that I should writing about this - I've probably made my
>     last transmission on HF APRS.   The good old ute has been sold,
>     something new and complicated is coming in its place (Pajero), with
>     no clear options for mounting antennas of any sort (That's still to
>     be confirmed, but the outlook is not good). <br>
>     <br>
>     So what did I use?   A couple of different antennas - both home brew
>     - as much as I could.  I have more or less standardised on the
>     Terlin base / mounting spring combination using 1/2" UNC threaded
>     antennas.<br>
>     <br>
>     In the early days I used a system of home brew top loaded antennas
>     with resonators / loading coils based on the Scalar system.  <a
>       href="http://www.users.on.net/%7Etfneumann/Amateur/Magna/Magna.html">Here</a>
>     is an example from the  past concentrating on the antenna base
>     rather than the antenna itself, but perhaps you can get the idea.  I
>     have a full set of loading coils from 160 through to 10 metres
>     including some of the RFDS frequencies.    Top load is good from the
>     RF side, but there can be mechanical complications.<br>
>     <br>
>     More recently I had used a DSE / Mobile One no compromise, high end
>     helical antenna originally intended for 27Mhz.  I scored two of
>     these at a ridiculous price at a time when DSE was quitting stock. 
>     Happily they both used 1/2" UNC bases and indeed came with the bases
>     as well.  A further enhancement was that they had adjustable tuning
>     tips at the pointy end  - top quality antennas at a bargain price.  
>     I stripped the heatshrink and the windings, and rewound one for 40
>     metres and another for 20.   They  have both performed in a very
>     satisfactory manner on the bullbar of the ute, and generally I've
>     enjoyed excellent results on APRS  using a Tiny Track with an IC-706
>     running around 50 watts.<br>
>     <br>
>     I've also made up a HF helical using a commercial fibreglass
>     electric fence space about 1.5 metres long -  in this instance for
>     40 metres.   I  incorporated an adjustable tuning tip in this one as
>     well.   Originally made for tractor usage, it's also been tested on
>     the ute with good results both radio wise and in the mechanical
>     integrity aspect.<br>
>     <br>
>     All of this assumes that one has access to a lathe and supplies of
>     hexagonal brass - and you like doing this sort of thing (I do).   
>     Otherwise it's something commercial.<br>
>     <br>
>     Apart from the RF considerations it's extremely important that the
>     mechanical integrity of the entire antenna installation is 100% at
>     likely highway speeds.  The wind forces on the antenna are
>     impressive, and keep in mind that if you are driving into the wind,
>     the force becomes the sum of ground and wind speeds (110 kph vehicle
>     speed + 40 kph head wind = 150 kph force on the antenna).   There is
>     an obligation not to start shedding bits of antenna at following
>     traffic, or at yourself if it's mounted at the front of the
> vehicle.<br>
>     <br>
>     HF APRS is good fun.   Too bad I don't see myself doing much of it
>     in the future  <span class="moz-smiley-s2"><span> :-(  </span></span>
>     <br>
>     <br>
>     Mind you it wouldn't work at all if it wasn't for dedicated amateurs
>     who offer their stations as Igates for the rest of us to enjoy.  
>     Thanks everyone whose facilities I enjoyed over the years; it was
>     greatly appreciated.      <br>
>     <br>
>     73<br>
>     Terry<br>
>     VK5ATN<br>
>     <br>
>     <br>
>     <br>
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