[OZAPRS] HF Gateways

Jamie Campbell - VK2YCJ vk2ycj at bravo.net.au
Thu Jun 25 13:23:06 EST 2009


Thanks for the update and suggestion on Codan units.  That's a good idea, 
and with the extra power it's likely to make it a bit easier for the mobile 
station with noise and interference in the mobile environment.

A group of us here in the Hunter Valley (near Newcastle) were inspired by a 
recent article in the WIA AR Magazine which discussed magnetic loop antennas 
for HF.  We are building a unit to test that will work well on 40m and good 
on 80m.  Fixed frequency operation on a magnetic loop is a good thing 
because they tend to be very narrow in bandwidth and thus require a slightly 
complicated tuning method (split stator capacitor, motors, insulated shafts 

The one we're building is 10m in circumference and is made of 75mm copper 
pipe.  Indeed a bit of an overkill in pipe diameter, but that was the pipe 
we had on hand.  The magnetic loop modelling software suggests a maximum of 
about 1/3 of a wavelength circumference for optimum results.  That's about 
13.3m on 40m and the model gives very good efficiencies and a sensible value 
tuning capacitor.

Our understanding is that having a sharply tuned antenna will give us 
significant benefits on receive - less noise, more selective, better 
lightning noise immunity etc.

There is a mobile version available too which is a half-loop design mounted 
on a car roof rack.  It boasts NVIS radiation characteristics (near vertical 
incident scattering) which could be a heap more useful in a car than a low 
angle of radiation whip.

Anyway, the antenna is almost ready for testing and we should have it under 
test in the next few weeks.  Once that is done and we know it's 
characteristics we can do some more thinking about APRS.

Thanks for your input ...

Jamie Campbell
vk2ycj at bravo.net.au

You'll never reach your greatest potential if you walk
past the dishwasher without emptying it or leave your
costume on the bathroom floor.

(Nancy-Bird Walton, Australian Aviatrix, 1915-2009)

----- Original Message ----- 
From: "Phillip" <zl2tze at yahoo.com.au>
To: "Australian APRS Users" <ozaprs at aprs.net.au>
Sent: Thursday, June 25, 2009 11:23 AM
Subject: Re: [OZAPRS] HF Gateways

Hi  Jamie,

40 is a bit sluggish at the moment ,but I have been copying VK5, VK2, VK7s 
around 07.00 to about 11.00 in the mornings here in NZ..

I haven't seen much else about not even on 30 / 20 but lets face it the sun 
spots are not helping it appears that good DX can be had if you are scanning 
the bands for it but you must be johnny on the spot.

APRS is on a fixed freq so its either there or not  can't chase it :-(

Look for Codans they  work well and there is a heap of them out there and 
plenty of info on them as well.

73 Phillip


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