Configuring a Codan 8528 transceiver for APRS

Information of configuring a Codan 8528 HF Transceiver for APRS using Tinytrak3.

There are a couple of modifications required to use the 8528 for APRS.

References :
http://www.aprs.net.au/
http://www.aprs.net.au/hf/hf-aprs-frequencies/

When the TT3 is set to 300 baud it uses 1600 Hz and 1800 Hz rather than 1200 Hz and 2200 Hz (as used on VHF/UHF 1200Baud)
Note that this is group C in the frequency list on the OZ APRS web site.
As such the frequency you should be transmitting packets on is 10147.60 KHz USB.

You need to select 300bd for HF operation. The TT3 tones are then set to 1600/1800Hz (mark & space frequencies).

The radio needs to be setup for a carrier frequency of 10147.600 KHz USB.
With an 8528 you can program this frequency into a "P" channel to make it easy to select.
I have setup a couple of 8528 radios for APRS via the mic socket.

So that the radio can also be used for comms with the mic, a couple of modifications are necessary.
Firstly you need to provide power to the TT3.
You need to get + supply from the Codan and put this on a pin of the mic socket.
You could use the "A" supply in the radio, it is 10V but will do fine.
Codan feed the earth return for the speaker through two pins of the mic socket
so that when you disconnect the microphone, the speaker is disconnected. I dont know why they do this.

You can ground the speaker and remove this wiring, this will free up two pins in the mic socket.

Remove the link inside the mic plug also.

Using one of the free pins connect the + supply, it would be advisable to put a low value fuse (0.5A)
in this feed in case you accidentally short the pin in the mic socket.

The audio output from the TT3 is quite a high level and will drive the radio to full power.

The radio has an audio compressor which tends to level the audio at a sensible level.

I have had a problem in a couple of these where the audio is distorted and Codan go to some trouble to
return the ground side of the mic to the mic amp and compressor.
I found that a small isolating transformer at the TT3 solved the problem of the mic earth and the power
earth being connected together. You should be able to get a transformer about the size of your fingernail to do the job.

You may want to try it without first and see how you get on. Listen to the transmitted signal and ensure it sounds clean.

You should be able to turn up the level pot in the TT3 and get around 80W of RF out.

The 8528 works well for APRS.

The TT3 also has a power on feature where you can switch the radio off when its not sending an APRS packet,
this saves a lot of power, and means you can leave the radio on always.
You will need the other spare pin in the mic socket for this if you decide to use it.
I havent done this in an 8528, but have done it successfully on other radios.

================================================================================

Measured an 8528 today on receive, and with no audio output it pulls
588mA. So this will send the car battery flat sooner than you think.

The later model Codans (after about 1985) draw about 900mA on receive.
As Owen said it wastes power if turned on all the time.
My solution is to use the tinytrak function to power the radio on and off.
The Tinytrak has all the facilities to do this, and you can specify the startup delay in seconds.
This allows you to turn the radio on and then wait, say for 10 seconds, then send the message then power down.
You can wire this into the mic socket so that the tinytrak plugs in and works.
You can then unplug it and use the mic as per usual.

from Rod VK2ZZM and Bruce VK4MQ and Owen VK2OL




  • return the VK2KFJ main page