BEAR-2 Cross-Band Repeater

James, VE6SRV, gave me his ICOM 24AT dual-band radio to use for a cross-band repeater for BEAR-2, but noted it didn't work and would have to be repaired first (What a sneaky way to get his radio fixed for free!).

And below is the radio after it was repaired and modified for use as a cross-band repeater for BEAR-2.

Ready to fly
cross-band repeater

Interior of IC24-AT

Components removed to save weight and/or reduce power consumption.

(Sorry James - I couldn't help myself! But don't worry. Believe it, or not, when your radio is no
longer required for balloon flights it will be able to be put back together the way that it was.... Really!)

After about 30 hours of work I had James's radio operational. A lot of time was spent cleaning up previous repairs and damage done by someone without the proper tools, supplies or technique. The radio also required a lot of TLC (tender-loving-care) work as, like most handheld radios, it had received a lot of use. Then, as I was doing final testing, the micro-processor failed with a shorted protection diode on the PTT switch input pin which caused the radio to constantly transmit. It's a mystery as to what may have caused the failure. Was it simply old age and the diodes time to die or did a static charge cause it to fail as it tryed to do what it was there to do? Anyway, a new micro was ordered, installed, and all is now well.

The 24AT is a very nice radio. I have repaired 3 of these radios which all had super receive sensitivity. I like the hardware design as it makes the radio easy to modify for special applications and why I couldn't resist modifying the radio to reduce the squelch tail that was too long for my liking while in cross-band mode. I also eliminated the constant band switching and the delay introduced while the radio alternately checked both bands for a signal as we only required UHF to VHF cross-band operation. This also eliminated any chance of a problem due to APRS VHF transmissions not being rejected or otherwise getting into the radio.

For a future flight I plan to program and use a PIC micro-processor to replace the one in the 24AT. This will allow the front half of the case, keypad, LCD, the 24AT control board and the weight associated with these items to be removed. This will also make it possible to provide remote control operation of the radio as well as other things, like cameras, and to do much more with the radio.

Bear-2 Cross-band Repeater Performance
Repeater current with
receiver squelched
54 mA ----
Cross-Band Repeater
VHF transmit power
and current drain
vs battery voltage.
9.0 1.03 A 3.30 W
8.5 0.99 A 2.95 W
8.0 0.94 A 2.65 W
7.5 0.90 A 2.34 W
7.0 0.85 A 2.10 W
6.5 0.80 A 1.78 W
6.0 0.74 A 1.50 W
5.5 0.69 A 1.24 W
5.0 0.61 A 1.00 W
4.5 0.53 A 0.77 W
4.0 0.45 A 0.59 W

Bear-2 ended up in the middle of the Battle River and a photo of the damage done
to the cross-band repeater radio by the rivers very alkaline water is HERE.










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