When Chrisitne got her new truck (4wd) I was keen to install some HF radio gear into it, i realised a codan 9350 auto tune antenna would be a nice addition, I had previously used a terlin tapped whip, and while this was a good performer, it was a pain to change bands when mobile! You had to choose your band and stay with it.
The new car allowed easy mounting of the 9350 on a rear bracket, so i started looking for one. I ended up with a second hand but relatively new codan 9350 and NGT SRx radio! and its worked well for a couple of years.
UNTIL… the other week, the radio started to refuse to tune the antenna. I checked and changed the connections, and it made no difference 🙁 she wouldn’t work. Below 10Mhz, it instantly returned a tune failed message, above 10Mhz it would attempt to tune, running the motor for ~15 seconds looking for a tune until it would stop and tell me the tune failed 🙁
A call to Dr Antenna and a time organised, I made the trip to visit the doctor the other day and the diagnosis wasn’t good.
The codan 9350 consists of 3 parts basically, the outer waterproof black shell, the internal electronics/controller/motor drive and the tuning coil and tuning mechanism.
We first connected the antenna up to a test set on the bench and confirmed the tuning issues, the instant failure below 10Mhz and hunting above this frequency.
Next we cracked open the antenna case, opening up the bottom screws and found the main problem, out came around 30ml of water.
Why was it wet? the case should be fully sealed. they don’t leak! but I had sprung a leak. The next test was to check the electronics, the PCB had moisture all over it, but it was clean water and hadn’t caused too much damage, no component corrosion or tracks lifted, it seemed in tack, so we repeated the test on the bench and it had the same failures, at least the electronics appeared to be ok.
So, why had it got wet, the bottom seal looked good. We then connected up a base that is used to pressurise the antenna outer and see if it had a crack. Into a water bath, and the top srcew connector was leaking lots of air. This is where the water was getting in. I was shown a cut away of this seal, and its amazing that mine had broken, the seals and screw are built into the outer cover at construction and it would take a lot to break it. My antenna has never had a hit or other damage that I know, but it was second hand when I got it, so who knows.
Next we turned to the tuning coil mechanism. This showed signs of getting very hot, of mechanical damage and wasn’t in very good shape. We removed my tuning could and installed a known working one onto my electronics and connected this to the test setup, it worked, tuned as expected and worked well. So the issue was my cracked outer case, and damaged tuning coil. This was starting to look expensive.
The below pics show the discoloured / heat damaged brown band ⅔rds down and the deformed tuning rod that runs inside the coil, the black marks on the top machined steel piece
The theory on the tuning coil failure appears to be, the moisture had caused some shorting of the antenna coil, which has lead to arcing that damaged the enamel coating, leading to more arcing, damage and heating until its finally really got hot, deformed the tuning coil and mechanism and stopped. The damage is the black ring 5 turns down.
The fix, Dr Antenna had a second hand coil/case that had a damaged electronics unit, I needed a case/coil, but my electronics appeared to be OK.. so it was expensive , but not a completely new antenna. Yay.
We loaded my electronics into the new case and coil, and.. Nothing.. My electronics hadn’t really survived the water bath. The fact it failed almost instantly wasn’t good enough for what (as a land mobile RFDS radio phone device) may need to save my life one day in the outback. So, a new electronics unit was got and now I have a second hand but essentially new antenna.
On the upside, the new antenna is a much newer version, with a G serial number, this incorporates a number of improved features, one of which is a one way pressure/moisture release valve to minimise this water issue! On the downside, I’m a bit lighter having had to buy a new antenna. but i have HF working from the car again, and it is often my radio shack! All installed and working again! And to prove its working, I successfully worked the VK9NT Norfolk Island DxPedition on 18Mhz on the Geelong freeway coming home from the repair!
Pressure release valve on new G model antenna circled
Thanks DR Antenna! Thank you Dennis and Peter from Lara Electronics for your help/repairs.