Pa Power Amplifier

SSB Electronics of Iserlohn. Germany, Is an up-and-coming manufacturer of many quality products for VHF and UHF enthusiasts. The company also offers a full complement of receive converters, transmit converters, transverters, and amplifiers for microwave enthusiasts. The PA2310 is a solid-state amplifier for the range of 150-1300 MHz, which operates from 13.8 volts and allows SSB, FM, or ATV operation*

Ordinarily, a low-power monoband UHF ampler might not warrant much attention; however, there are very few available in the medium-power range for 23 centimeters. There are several trans« verters on the market for this band, but most of them are limited to 1 to 3 Watts output. The PA2310 complements those transverters, especially since it requires only 500' to 750 mW of power to attain full output.

Another reason it's handy to have 10 Watts of power here is that most outboard high-power 23 cm amplifiers utilize 2C39/ 7289/3CX100 type tubes, operating in grounded grid configuration. These amplifiers are usually good for 10 dB of gain in this mode, so 10 Watts of drive will usually yiefd 100 Watts or so of output. Use two of these tubes and you'll see close to 200 Watts output. The PA2310 fills the gap nicely as an intermediate driver stage, so you will see 100 Watts or more of output instead of 10 to 15 Watts using just the transverter.

The photo shows the unit with its cover off. The circuit is simple and employs three type BLU90's —one as a driver and two as finals. The output circuit is the usual etched microstrip type Bias is set by the pot in the upper left corner Note that there is no provision for standby operation, although you could incorporate it if needed. The amplifier operates in grounded-emitter mode and gain is typically on the order of 6-7 dB per stage.

SSB Electronics rates its amplifiers at 14.5 V dc, which is apparently common practice in Europe. How did this model do? With a Bird Model 43 Wattmeter and 25G slug (25 Watt, 1.1-1*8 GHz), I measured exactly 10 Watts output across a Termaline 50-Qhm dummy load. The driving source was a Microwave Modules MMT 1296/ 144, which was throttled back to about 500 mW output; the source voltage was 13,8 volts. Raising that voltage to 14.5 volts resulted in about 12 Watts of output power Lowering the voltage to 12.5 volts dropped the output to 8 Watts.

In actual operation, I used this amplifier on Slide Mountain in June of 1985 with the MMT 1296/ 144, Our power source was a motorcycle battery, which started out at almost 14 volts and dropped to about 13 volts when we concluded our operation. The amplifier ran cool at all times- The heat sink should be adequate for 1296 ATV operation; however. I'd recommend reducing the drive and keeping the output power at 8 Watts or so in this mode. Note that the BLU90 transistors aren't swr protected, and there is no ALC circuit in the output. You must take caution not to load them into an swr of 2:1 or greater—otherwise, you might be waiting a bit for replacements from Germany. (At this time, there are no sources for this device in the United States.)

In my home station, I mounted a Dow-Key 12-volt coaxial relay atop the amplifier chassis. This amplifier switches the antenna lead from amplifier to transverter antenna input and also turns the dc power on and off to the PA2310. Again, some sort of switchable bias could be used and would accomplish the same thing.

All in all, the PA2310 is an excel-ient medium-power, reasonably priced amplifier for 23 cm. Price: $300; U.S> distributor: The VHF Shopr 16 S. Mountain Blvd., Mountaintop PA 18707.

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