AWA Teleradio 40c

This radio is all solid state AM marine tranciever, and judging from the date stamp on xtals it was probably made in the early '70s. The output power is around 10 Watts high level transformer modulation. It has a nifty variable antenna loading control on the front which basically adds more 'L' in series with the antenna. You tune for max brightness on the 'RF output lamp'. This lamp measures RF current using a current transformer and a transistor, not just a globe in series with the antenna lead. there also appears to be preset extra L that can be switched in by the Frequency control, but this was bypassed in my unit

I bought this radio at the Moorabin Hamfest in May 2005. I saw it on the table for $10 and I couldn't get my wallet out fast enough. (I know this will be a shock to anyone aware of my normal spending habits!) It was small, solid state (well I guessed it was given its size ) and clean.

Once I got it home a quick tweak got a few watts out on 1843 Khz and a poke around the final stage ( 2 x BDY90s in TO3 packages) found a high resistance bolt to the one of the transitor cases (collector) which when fixed gave a touch over 10 Watts. Success....

Checking the modulation showed a severe absence of upwards modulation. Initially I suspected that this was due to not enough drive to the PA, but in fact it was much simpler. The modulator is a pair of MJE3055s in class B driven by an audio amp that is also the Rx speaker amplifier. Checking it out put I found it was floating at around .8V , meaning any audio had no chance of swinging more negative. Once I found a ceramic bypass cap that thought it was a 500K resistor that was fixed and modulation was as good as I expected.

Moving to the reciver, I decided to use a tuned cct in place of the recieve crystal to avoid buying one (and get the rig on the air!). I figured BC band radios are quite OK tweaked to 160 so I should be OK.

I whipped up this cct and to my amazement, it worked immediatly, just requring a change of cap to get it in the right range. The 1N4004 is used as a varicap to provide fine tuning in case of a bit of drift. As it turns out I can tune from about 1825 to 1850.

The Tuning is done using what used to be the volume control for the PA (as in Public address). I have no need of this so it was obvious to use it for tuning. The log pot doesn't seem to be a problem with tuning, in fact maybe it works opposte to the non linearity of V vs C vs F of the diode. Anyway it works.

The first on air test was on the Coffee Break net on 1843, running off a 7AH gell cell in a park with a 1/4 of wire strung in the trees. Portable operation is what I bought the radio for, and apart from initial reports of low modulation, its looking good. - I just need to speak up.