[OZAPRS] Packable Tracker

Tue May 6 23:17:02 EST 2008

Hi Rob
It's good to know I'm not the only one with an RF feedback problem!  I've
changed my concept and now have the Puxing PX777 and TT3+ in a "rehydration"
back pack with bladder removed - and it's working on low power.  Initially I
used the plastic lunch box approach and overcame some of the RF problem by
lining the box with aluminium foil, but found I still had to put the GPS at
least a metre away from the radio antenna.  The purpose of the set up is to use
pedestrian or horseback mobile and the lunch box needed a backpack to carry it
anyway.  Opening specials of a new Anaconda store in Hobart included
"rehydration" packs for $20 which seemed to lend themselves to the purpose,
given outlets for drinking tubes and filling etc.  After much sewing to make an
insert with appropriate pockets, the result was an RF disaster.  Double lots of
ferrite on every lead (GPS, Tx, Rx and power) and it now works fine on low
power. (The power lead ferrite seemed to have greatest effect). I have read that
a similar problem was solved by placing the TT in a metal box inside a second
metal box and providing a common ground to all.  I'm hoping to achieve the same
with aluminium foil.  Shopping for heavy duty foil tomorrow.  Also have a
problem with the Byonics supplied TT to Kenwood HH lead which sticks out at a
right angle to the radio and therefore takes up space and is vulnerable.
Waiting for delivery of a right angle plug from Argent Data Systems.  The foil
lining will hopefully also assist the antenna.  I've made up an aluminium
bracket with a BNC connector which, together with the coax, fits through the
drinking tube outlet to sit on one shoulder (ear fryer).  The bracket extends
inside and across the top the back pack.  The aluminium foil will be in close
contact with the bracket, hopefully to form a ground plain of sorts.  The
antenna is a Nagoya  NA-702 BNC dual bander approx 300mm long.  The Byonics GPS
is Velcro'd to the other shoulder strap, with the lead passing through the
second drinking tube outlet on that side.

The set up (VK7ARN-8) as is has been heard consistently by digis about 8 and
20kms distant.

I know a picture or three is worth a thousand words and I've probably used up my
quota of those.  Give me another couple of days to complete refinements and I'll
put some pics up on http://tas.wicen.org.au and put a note on Aus APRS Users.

You might find VK7ARN-8 on Wednesday when I give it a go round the clubrooms on
Hobart's Queens Domain, but you'll have to zoom in close to see the track.  I
ain't going far on two legs!  I prefer wheels or somebody else on four legs.
(The jogger icon is the closest I could get until it goes horseback).

Best of luck with yours.  Lots of ferrite and screening!

Roger VK7ARN

PS I've probably gone overboard with power, using a Jaycar 1.3Ah SLA battery
which sits nicely in the bottom of the pack.  The radio uses its own battery
(with a spare).  I'll worry about that side of things when I get the whole set
up working free of feedback on the full 4W.

-----Original Message-----
From: Rob Heyer [mailto:vk2xic at yahoo.com.au] 
Sent: Tuesday, 6 May 2008 22:01
To: vk7arn at bigpond.com; Australian APRS Users
Subject: Re: [OZAPRS] Packable Tracker

Rodger,
Hi, I'm Rob VK2XIC.
I have been doing some work with APRS portable / bicycle. I have been trying to
put every thing a lage lunch box, but have run into RF feed back etc.

http://aprs.fi/?call=VK2XIC-4&mt=m&z=11&timerange=3600

I like the http://aprs.fi site (URL).

I have found that a rubber duck with 5 Watt H/H is not enough to deliver a good
signal to the digipeter. In fact 1/4 Wave has not been much good either.....

How have you got on with what you have done? I would be interested in seein g
what you are doing, on the net....

I have planned to make some changes to my equipment, I would let you know when I
have things up and would be pleased if you could see if you could see me.

Rob VK2XIC

vk7arn <vk7arn at bigpond.com> wrote:
I'm building a "Track in a box" for use on foot or horseback, TinyTracker 3
Plus (bundled with Byonics GPS) and a Puxing PX777 in a sandwich box which I
picked up today rather than a much more expensive Pelican type case. The box is
ABS, weather sealed etc. I also have a BNC rubber ducky antenna supplied by the
Puxing supplier recommended in an earlier dialogue. What I'm after are ideas on
mounting the GPS and the radio antenna. I envisage the box being in a backpack
(on foot or horseback) with leads from it to somewhere. Any ideas appreciated.
The trackee may not be an APRS enthusiast so the rig needs to be user friendly
and light weight.

Cheers

Roger VK7ARN

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73's 

Rob Heyer 

IRLP VK2RMP Node No. 6018 (146.850 MHz) 
EchoLink Node No. 114630 
WIA 

Eat Australian lamb a 1,000,000 Dingos can't be wrong !

Get the name you always wanted with the new y7mail email address. 

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