[OZAPRS] Antenna for HF-APRS...
vk2ycj at bravo.net.au
vk2ycj at bravo.net.au
Sun Mar 1 21:35:59 EST 2015
Terry,
What a great story. Thanks for sharing it with us.
Jamie
VK2YCJ
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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 Originally made for tractor usage, it's also been tested on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>
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>
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