Ramsey Electronics QAMP20 manual

Ideally, you have a small RF wattmeter, already inserted in the antenna line, capable of accurately measuring low output power in watts. And it cost you less than what you paid for the transmitter kit. Right? In the words of Wayne from "Wayne's World"... Not! So here are a few other ideas for you to try.

Saying the same thing another way, we assume you know that accurate, commercially built RF wattmeters cost much more than what you paid for this Ramsey amplifier kit. Since this solid-state amplifier does not require lots of critical tuning or adjustments, a periodic power output check-up should suffice. If you don’t own or have access to a low-level RF power meter, use a trick that is decades old - the common flashlight or panel bulb. All you need to know is the basic difference between bright, superbright, dim, unlit and burned out! Using a light bulb to check power output is also a satisfying way to put Ohm's Law to work. Your Radio Shack catalog specifies operating voltage and current in milliamperes for a variety of small replacement lamps and a local automobile parts store is a treasure trove of various other lamps. It may be worth your while to make up a simple plug-in "output tester" for your amplifier - a male RCA plug connected to a socket for the bulb of your choice or even soldered directly to the bulb.

RF voltage levels in this amplifier can vary from 2 to 25 volts RMS depending on various factors. Typically, 1 watt power levels are achieved in the 5 to 7 volts RMS range, 5 watts at 12 to 15 volts, and 10 watts at 20 to 25 volts. A good test bulb for this amplifier is the #93 automobile lamp bulb or the #1156 type bulb. Both are 12.8 volt rated, with the #93 being specified at 1 amp and the #1156 being 2 amps for normal brilliance. Using some Ohm's law calculations shows that the #93 is a 12 watt lamp and the #1156 is a 24 watt lamp. We can conclude that 10 watts or so of RF should light a #93 bulb reasonably well, while 20 watts should be about right for a #1156. Try it out!

Please remember, though, that a flashlight bulb does NOT present the proper load impedance to the amplifier output, so theoretical calculations based on the bulb`s rating can only be approximate. For example, the #93 at full brilliance presents a 12 ohm load to the amplifier. Because of this, the amplifier may act "flakey" when tuning up into a light bulb, and by all means you should not consider a light bulb an accurate indicator of the QAMP-20's performance! If ANY light bulb lights up when connected to the antenna jack of this amplifier, you can be satisfied that you have RF output power at least equal to the DC power rating of the bulb you are using. If you burn out your bulb, rejoice and put your rig on the air!

Amateur radio magazines and handbooks provide a variety of circuits for RF wattmeters and relative field-strength indicators, including methods of using your VOM as an indicating device. CQ magazine for March 1990 offers an article by

QAMP20 • 14