Codan HF Tx troubles...

Submitted: Monday, Jun 07, 2010 at 21:34
ThreadID: 79162 Views:3747 Replies:5 FollowUps:1
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I've had a Codan 8525 in the Nissan for about 2 years - and "always" had problems contacting VKS737 Base stations... Hit and Miss (usually Miss...)
I wondered if the RF earthing was adequate cos the Antenna Bracket supplied with the Codan looked older than the Codan itself - so I took the bracket off last week in Litchfield NP and cleaned it up - and got an improvement...
I'm now in Katherine and tried to contact Alice on Ch 2 - 8022) - could hear him perfectly - and got through but sked operator said very poor signal from me - but then another VKS member came online and said I was 5:5 - and he was in Broome.
So... If my Codan can Tx A-OK to Broome, but not to Alice... Is that due to Atmospherics..?? Or is there something I can or should be doing..??
Thanks if you can help to educate me.
Jedo
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Reply By: Grungle229 - Tuesday, Jun 08, 2010 at 07:14

Tuesday, Jun 08, 2010 at 07:14
Are you relying on the attachment of the antenna to the bullbar as the earth or do you run a braided earth strap from the antenna mounting stud to a part of the body that has been taken back to bare metal and then bolted?

Should be the later.

Cheers
David
AnswerID: 420004

Reply By: Robin Miller - Tuesday, Jun 08, 2010 at 08:02

Tuesday, Jun 08, 2010 at 08:02
The signals are usually pretty weak from a car mobile antenna Jedo , and they do vary which makes it hard to see how yours is going.

If you get a chance try your when someone's nearby can try there's and compare.

The antenna is critical - and you need to know its ok , so get the tuning checked.

Beyond that there are two things you can do.

1/ use an earth strap from base of antenna backet to ground - long tent peg and a bit of coax outer braid will do.

2/ Use a 1/2 wave dipole - this makes a big difference - it can be done better or brought but can be as simple as a few meters of of coax from your radio , each side of the coax goes to 30 ft of wire stretched out roughly in a line (30ft for 8022) , the ends of the wire can even lay on the ground , but put the centre part a few feet of ground.
I use a velcro strap to attached the centre part of mine to the top of mobile aerial to get it off the ground.
Robin Miller

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AnswerID: 420013

Reply By: MEMBER - Darian, SA - Tuesday, Jun 08, 2010 at 09:59

Tuesday, Jun 08, 2010 at 09:59
What type of antenna are you using ? Re contacting bases (I'm a VKS operator) - the pattern of success is always variable - in recent times it's been very good overall - it's quite normal though to find in certain locations, at certain times, natural conditions will boost some comms and reduce others. The thing of it is that you should always be able to get one of the bases really well from any location (but selcalling / beacon calling may be necessary off sked) ... keeping in mind that early or later in the day is best, and usually while stopped.
Agreed re the above about comparing your performance with someone else in the same place, after checking all of your connections - I don't know the 8525 but maybe it has some facility to display diagnostics on screen re power consumption ? That is not TX performance of course but might be a factor. Oh.... and don't forget the 'long wire' - hung off the antenna to a nearby tree - more wire is better :-o)..........8.8m suits 8022khz quite well.
AnswerID: 420030

Reply By: anglepole - Tuesday, Jun 08, 2010 at 10:00

Tuesday, Jun 08, 2010 at 10:00
Hi Jedo,

Firstly there was a model of a Codan auto tune Antenna that had some problems with tuning. As I recall, it would only tune at the lower frequencies. If you have any doubts about that have it checked out.

The earthing is most important, braid to the body and chassis from the antenna, and braid from the RADIO to body and chassis. Bare metal and spring washers.

If you have access to the internet you can find the best frequency via IPS

http://www.ips.gov.au/HF_Systems/1/1/1 (Hourly HAP charts.)

Codan Barrett type tunable antennae are very inefficient. A Barrett mounted on the back of a Patrol has between 5 and 10db loss at 8mhz. This means in the worst case; that although your Tx is giving 100 watts only 10 watts gets to air.

The Alice Base has 2 antennae if you try and access the base using the North South set up it is better than when using East West antenna.

Cheers
AnswerID: 420033

Reply By: Jedo_03 - Tuesday, Jun 08, 2010 at 21:24

Tuesday, Jun 08, 2010 at 21:24
Thanks very much to all for your informative replies.
I don't have any braided earth wire running from the bracket stud to the nissan body - so I'll do that - and braided earth from the radio unit too...
I like the idea of the coax and tent peg too...
Darian - yes, I think it was you running the sked on the evening I alluded too when Alice could hardly hear me but the member from Broome said I was reading a 5:5 to him...
The 30ft / 8.8m wire solutions are good recommendations too.
Thanks - let you know how I go.
Oops - nearly forgot to mention: I have a Tap Aerial
Is there anyone in Alice who could check the tuning on the Aerial..??
Jedo
AnswerID: 420098

Follow Up By: MEMBER - Darian, SA - Wednesday, Jun 09, 2010 at 14:06

Wednesday, Jun 09, 2010 at 14:06
Using a good tap may well be the best mobile solution (mine was very good on an old Tracker Scout) - purely re effectiveness, I understand they are superior to autotunes. Agreed re a technician having a run over your installation - should be able to tell you exactly what you are putting out, using a meter.
I haven't been round there, but this is the only radio tech mob I know of in the Alice. Central Comms
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