Tune Doubler Here

FROM FiRST CONVERSION LJ3 (L3Ï O

(OR MORE FOR COUPLING TO GRID OF 7984*

FROM FiRST CONVERSION LJ3 (L3Ï O

Fig, 5. Second conversion of the two meter transmitter. An input of 23 MHz from the first section

[he grid circuit is simplicity itself but does warrant some discussion. The input capacitance land some usually unmentioned inductance) reduces the size of any ordinary lumped inductance you might wish to put in as a "grid circuit." The choice for now is a quarter wave fixed tuned lank as shown in Fig. 6. A full wave circuit was tried but so far was not any great improvement, other than to allow link coupling, which you cannot use with the quarter wave circuit shown. It tuned nicely but showed signs of self-oscillation. If you remember, neutralization had to be used in the six meter unit. Note that tile amplifier must be next to the exciter,

By simple cut and try the grid coil was worked out. I his puts the grid on 144 MHz, fairly broadbanded, and works like a charm,

Through the 25 kLI grid resistor, there is about lis mA of grid current Try for 2 mA

A real good plate dip is obtained along with a zippy noisy arc from a pencil test on the plate while dipped from 200 mA to 50 mA or so. This not quite the roaring flame you get w ith the switching six and two 200 watt final with the 4X250 (see 73, April 66) but it does light a 50 watt bulb to dazzling brilliance.

And reports on the air are all good. Modulation was provided by the old standby with a pair of 6L6GCY See June 73, page 20.

Reports were "At least 100^ modulation", ''Clear", "Excellent", etc. Stability was checked with a number of QSO\s, one with a receiver (with 2 kHz bandwidth) receiver 40 miles away. Anyway, on selective receivers it comes right on at the same frequency every time. And last night I had the opportunity of checking with a Collins 75SI and over some ten minutes he had not touched the receiver dial

No FM either. This can be nastv« Some-

gives output on two meters. The crystal used is 60.75 MHz. Output is about half a watt.

times YFO's can get some final rf on their grids. The result is a slight amount of FM which shows up as unsymmetrical modulation, That is? the modulation is not the same on each side of the carrier, and maybe the middle is mushy. If you get this condition (you wont with this rig).,you're in for trouble as it is real hard to get rid of, unless you build a new and different rig.

So, what more do you want from $1 per watt?

Conclusions

11' you build this rig as shown you will get a real I eel for a genuine ^professional type" transmitter.

l ake the time to tune up the various coils and frequencies and you will be rewarded with a rock-stable fully modulated 80 watt \ O rig for two meters. You'll enjoy building and using it,

0 0

Post a comment