October 2017 51
OPEN COMMUNICATION ; BY LOU FRENZEL W5LEF
Generally speaking, the higher the power, the
stronger the signal and the farther it can travel. However,
many other factors are involved such as antenna types,
propagation conditions, frequency of operation, and
receiver sensitivity. On the high frequency bands ( 3 MHz
to 30 MHz), propagation is such that even a low power
signal can travel around the world.
What makes the QRP idea so attractive is the
challenge of making contacts with low power. It is usually
easy with a 100 watt transmitter, but with one watt or less
you have to take special steps to make it happen.
I have been a ham for many years, but just recently
got the QRP bug. Here is a summary of some of my
adventures and experiments.
One early choice I made was to buy a complete QRP
transceiver. I discovered the MFJ-9340 Cub QRP unit. I
paid just under $100 for the kit (see Figure 1). This is a
sophisticated little rig crammed into a single PCB (printed
circuit board) with about three inches per side. It features
a superhet receiver with a crystal filter and a multistage
transmitter with a 2N5109 final stage that puts out one
to two watts; that is adjustable. The unit operates with an
external DC supply of 12-14 volts.
The PCB comes pre-populated with the surface-mount ICs and many of the resistors and capacitors. The
kit builder installs more resistors, capacitors, inductors,
crystals, and connectors. While the manual and instructions
are clear, the installation is a real challenge given the small
spaces involved. This is no beginner kit, for sure.
Unfortunately, once I finished, the end result was a
dead transceiver. It did not power up and I could not get
it to work. I did some troubleshooting, but the small size
made it difficult. I finally sent it back for repair and MFJ
sent me a new one. Thanks MFJ! The new one works great.
Despite my difficulty, others have had good results
with this transceiver. Overall, the reviews of the MFJ-9340
on several QRP websites are very positive. If you have the
time and equipment to do the proper soldering, alignment,
and troubleshooting, give it a try.
Cheap Transmitter Kits
My other QRP adventures involved testing low cost
transmitter kits. There are literally dozens of cheap versions
you can buy from the Internet. One of these is the Ramsey
QRP- 30 (see Figure 2). Ramsey no longer makes these kits
but you can still find them online.
My unit operates on 30 meters in the 10. 15 MHz
range. It is crystal based, but uses a pair of diodes as a
varactor to pull the crystal for tuning over a narrow range.
It uses a 2N3053 final amplifier that can put out about one
RP is the amateur radio Q code for Reduce Power. It is also a clear
niche or specialty of ham radio that focuses on radio communications
using low power transmitters. There does not seem to be a firm
definition of what low power is, but five watts maximum is the usually
stated limit. Some say 10 watts. In any case, it is a lot less than the capability
of the common ham transmitter. The typical transceiver today is usually
capable of 100 watts of power, and many hams use auxiliary power amplifiers
to boost power to the 1,500 watts peak allowed.
Going All The Way With QRP
Low power operation, better than you think.
Figure 1. The MFJ-9340 Cub transceiver. It’s a cool
product, but I could not make it work initially.