[OZAPRS] Re: Packable Tracker

Sasi Nayar sasidiver at yahoo.com.sg
Wed May 7 16:11:03 EST 2008


G'day Roger and others,
I have been trying to upload the pics when this discussion started with no luck. I have finally managed to do it a short while ago. I have two units that I made up. One is in the car with an average regulator to drive my Maxon radio from the car's cigarette lighter socket. 
The second one was designed to be portable. I assembled it late last year. I too had issues with RFI. As you found out, lots of long ferrite rods made the difference. Shortening the power leads too made a huge impact. Some pics are uploaded at
http://picasaweb.google.co.uk/sasinayar/APRSPortablePack

Yes, it is an overkill to use a 7Ah battery, but then I am doing some trials from rescue boat for the local sea rescue group. 
Would love to see what you come up with
73 and good luck
Sasi
VK5SN
http://www.findu.com/cgi-bin/find.cgi?call=vk5sn-9
 
PS : Some one handed me a copy of your Foundation Licence CD-ROM. Must say it was a brilliant piece of work!


---------------------------------------
Date: Tue, 6 May 2008 23:17:02 +1000
From: "vk7arn" <vk7arn at bigpond.com>
Subject: RE: [OZAPRS] Packable Tracker
To: "'Rob Heyer'" <vk2xic at yahoo.com.au>,    "'Australian APRS Users'"
    <ozaprs at aprs.net.au>
Message-ID: <001c01c8af7b$79109ff0$0500000a at Roger>
Content-Type: text/plain;    charset="us-ascii"

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.


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