[OZAPRS] 30m mobile antenna

Mon Apr 12 09:28:36 EST 2010

Hi Stuart,

Ive played about a fair bit with various antenna combinations on 30m APRS mobile. I use a modified 5ft CB whip on 30m when driving around town. ( I can leave it on the bull bar of the landcruiser when parking under the carport ! ) .. Basically its a trial and error thing. Start with a CB whip 5ft or whatever length suits .. Get a 20 or 25mm piece of PVC pipe say about 100mm long. About half way along the CB whip cut into the plastic coating and remove about 100mm , then cut away about the same amount of antenna braid leave an inch or so of braid to use as the solder connection point for each end of the loading coil. .. Slide the tube over the whip and secure in place with silastic. Wind between 30 - 40 turns of  wire around the pcv tube and solder ends to braid. You will need to play around with the number of turns and the spacing between the turns etc. By a bit of extra fiddling Ive managed to get mine to work on 30m and 10m at the same time, with less than 1.3 to 1 swr on both bands. Because I made mine adhoc so to speak, I never really measured anything while I was making it, but I could send you a photo of it if you like as a starting point. It does work suprisingly well though. Always seem to get into a HF gate without any problems. 

I also use an old modified multi tapped Flying Doctor terlin type antenna, for when Im out in the sticks .. Its a bit longer .. probably about 6ft or so. ( and doesnt fit under the carport ! ) I had an old one here that happened to have a 9660 tap. I chopped ( hacksawed ) about an inch off the top and now its perfectly resonant on 10.146 .. swr 1.1 to 1 .. This makes for a very robust antenna . Mine has survived some very rough trips .. banging through trees etc .. and still works extremely well on 30m APRS .  

Another antenna that works excedingly well is to use a normal 5 band amateur band terlin type tapped antenna. Ive had one of these antennas for many years, In fact I think it was my first mobile antenna covering 80-40-20-15-10. The trick with these antennas is to replace the ~100mm tuning stub on top of the whip with a stainless whip. roughly 1 to 1.5m long, scrounged from from the top section of an old CB whip. Then while using the 20m tapping on the terlin, trim the  ( extended stub ) whip and surprisingly enough you will be able to obtain  perfect resonance on 30m.  This configuration works very very well, probably the best 30m antenna configuration for mobile use.  Trick is to find the ~1m stainless whip to go on the top, with the same diameter as the original tuning stub, where it slides into the retaining nut. The main advantage is that you can replace the original tuning stub and still use the antenna on its original bands as well. Bascially making it a 6 band antenna. 

If you want any more info , let me know ..

Regards .. Andrew .. VK5EX

  ----- Original Message ----- 
  From: Stuart Cameron 
  To: ozaprs at aprs.net.au 
  Sent: Thursday, April 08, 2010 2:09 PM
  Subject: [OZAPRS] 30m mobile antenna

  Hello all, I would like to find out if there is any recommended HF 30m mobile antenna as I am currently using a Codan 7350 which I would like to use for general HF.

  Regards, 

  Stuart Vk5ade

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