Ramsey Electronics QRP30 Instruction Manual - page 18
QRP30
• 18
YOUR POWER SUPPLY AND RF OUTPUT POWER :
For optimum performance, one or two volts of extra DC supply power can
make quite a difference for this transmitter. For example, two lantern batteries
in series, or 8 "D cells" obviously provide "about 12 volts" with sufficient
current capability for casual operating. For maximum RF output power, use a
supply of 14 to 15 volts DC. The easiest method is to place two fresh "D cells"
in series with your power source, if a full 13.6-15 volts DC is not available.
If your supply voltage is in the 11-12 volt range, you can expect a 200 to 250
ma current flow and about one-half watt of the RF output power. With a solid
14 to 15 volt supply, you can expect about 400 ma current draw and up to one
watt of RF output power.
VERIFYING TRANSMITTER RF OUTPUT:
The most important thing to know is whether your transmitter is delivering
some measurable and reassuring level of RF power to the antenna. The sound
of the transmitter's keying in a receiver is of some help, but even the simplest
crystal oscillator can send a fine signal into your neighbor's receiver, as we
have already discussed.
Ideally, you have an small RF wattmeter, already inserted in the antenna line,
capable of accurately measuring low output power in watts and even
milliwatts! And it cost you less than what you paid for the transmitter kit. Right?
If not, we have a few other ideas for you, OK?
Saying the same thing one more way, we assume you already know that
accurate, commercially built RF wattmeters cost much more than what you
paid for this Ramsey transmitter kit.
Since this solid-state transmitter does not require tuning or adjustments, a
periodic power output check-up should suffice. If you do not 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 differences
between bright, superbright, dim, unlit and burned out! Using such a 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. It could be worth your time to make
up a simple plug-in "output tester" for your transmitter, 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 transmitter can vary from 2 to 10 volts RMS depending
on various factors. Typically, 1 watt power levels are achieved in 5-7 volts
RMS volts range. A good test bulb for this level is the PR-4 flange-style