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QRP transceivers

In general, transceivers or transmitters are called "QRP" if their output power is 5 watts max.
However, in this section I will present transceivers which deliver up to 20 watts of output power.
Reason is that transceivers like the Elecraft K2 can deliver up to 15 watts output. However, I would
not call this "QRO" just because it can deliver more than 5 watts of RF power.

The motivation to go "QRP" can be two-fold:

1. the challenge and excitement of making QSOs with only little power,
2. the necessity of going "QRP" due to the lack of a strong enough PSU or batteries (for whatever
    reason) to power a 100 watt class transceiver. This is especially valid for hams going backpacking.


Index Labs QRP Plus
Juma TRX2A
Elecraft K1, K2 and K2/100
 (see comments on the K1 there, updated Dec-2011)
A low-cost 3-band QRP CW transceiver from China: HB-1A
Ten-Tec Century-22

Pick an item or just scroll down this page.

qrp plusIndex Labs' QRP Plus is a dual-mode CW & SSB transceiver. Power output is
reaching max. 5 watts on the lower HF bands.
IF frequency is at about 50 MHz, filtered by a crystal filter with SSB bandwidth.
Narrowing bandwidth happens with a SCAF filter at audio frequencies. This is
a bit of an issue if bands are wide open and very crowded. Even if the SCAF
filter bandwidth, when working in CW, is reduced to a few hundred Hertz, strong
close-in stations, if they are within the first crystal filter bandwifth, are desensing the receiver
sensitivity by driving AGC into action. I've used the rig exclusively in CW and it is fun to operate.
Discontinued since a number of years. There is quite some useful information elsewhere in the web.

Juma TRX2A all-band HF rig 

Combining "new" technology (from SDRs) with "old" technology (phasing type (de-)modulation).

Juma TRX2A front My version TRX2A of the rig is a full HF band capable SSB&CW transceiver
with 10 watts output. The RX section has general HF coverage.

It's sold as a kit from Finland, see here.

The component technology of the kit is heavily based on SMT parts. So, if
you want to build that on your own, you'll need some profound experience
with SMD soldering. Else, you may ask one of the Juma community kit builders
to build the transceiver for you at a certain (reasonable) fee.

The TRX2A is a very *special* rig. In a sense that it's font end is very much like that of SDRs, mixing
the antenna signal with a DDS VFO through a Quadrature Mixer into base band. As a result, the output
of this stage is an I/Q signal, like in SDRs. Now, as we don't use a PC plus sound card plus related
Software in order to establish the TX and RX base band stages for the various modes like SSB or CW,
this is done by a phasing type of technology (like in the old SSB times) by means of discrete phase
shifting networks.

On RX, after that a "SCAF" (Switched Capacitor Audio Filter) provides the necessary selectivity for the
various modes. There are in total 3 selectivity settings available for CW/SSB which can be adjusted from
the menue.

If you are interested in this transceiver I'd recommend downloading the documentation and read through
it carefully.

The TRX2A performs rather well. However, there are a few draw-backs. These relate to CW operation
primarily: no real QSK (relay), close-in channel AGC de-sensing action caused by strong close-in signals.

Overall impression: this is a very good little transceiver and I am using it a lot because of the clarity
of signals it produces.

For more details click here or click on the picture above.

Elecraft Transceivers K1, K2 and K2/100

The Elecraft line of transceivers are very well-made and very well-performing radios.
Detailed information on these transceivers can be found on the Elecraft website here, so I don't need to
repeat the technical data etc.

Some comments:

> These transceivers were sold as kits. If you are intending of buying one second hand you should pay
   attention to the quality of workmanship the builder was able to apply during the assembly process
   (PCB solder joints etc.).

> The K2 (first Elecraft transceiver project) has seen quite a lot of circuit updates since it's start of production.
    If you are going to purchase a second hand unit, be sure that you'll invest on a late serial number which
    already has all of the updates built-in. Or make sure that you'll get a unit which has been updated by the
    previous user to the latest revision.

    You can still purchase updates (hardware and flashed chips with the newest firmware) for older units.
    Yet, you'll need to invest quite some money for these updates plus the working hours and expertise to
    implement those updates.

> K2/100: this version of the K2 includes the 100 watts amplifier module which is mounted to the top of the
   cabinet. With this option, the K2 becomes a pretty dense package inside the box. Very little space left

> When purchasing a second hand K2 or K2/100 unit make sure that the 2 probes come with the unit.
   The probes are required for doing adjustments to the radio. They are available for purchase from Elecraft
   for 10$ each plus shipping cost.

> The K2 (and K1) have no provision for switching an external amplifier's T/R line. Elecraft doesn't offer any
   add-on kit. However, there is a third-party PCB available for the K2. You need to supply required parts.
   See Elecraft website for more details. The PCB can also be easily done by yourself.
   The switching circuit is a matter of 2 transistors plus a few passive components.

> The K1 came in 2 versions: a 2-band and a 4-band version. Bands could be selected at date of purchase.
   So, double-check which bands come with the unit.
   For the current Elecraft product portfolio they seem to offer the 4-band version only.

Some additional comments on the Elecraft K1 CW transceiver (new: Dec-2011):

When I was in a need of selecting one of my QRP transceivers in order to take it with me to a trip to some
remote place (locally or distant), I've learned from my own experience that I always selected the Elecraft K1


#1: In QRP mode I work CW mode 99% of the time. No digital modes so far (pretty boring, IMHO, sri).
#2: The K1 has a minimum footprint and weight. Everything needed for operation, except an antenna
      and keying paddle is already in the box (including the optional antenna tuner).
#3: The K1 has a very low power consumption, ca. 50mA during receive and ca. 800mA during CW transmit,
      allowing for extended operation time even when run from a small battery assembly.
#4: The K1 has a pretty capable receiver and IF filtering making CW QSOs easy even under 'heavy' band

In fact, I preferred the K1 versus my K2 for the above reasons, even as the K1 did not cover all Ham Radio
HF bands and some of the additional bells and whistles the K2 may provide.

'Lost game' for the K2 as a 'take with you' radio in my particular case.

The Elecraft K1 is one of the nicest little CW QRP radios I've seen in my more than 40 year career in
Ham Radio, predominantly experienced in CW mode.

It's just a little gem of QRP CW transceiver.

HB-1A: a low-cost 3-band transceiver from China (new: 24-Jan-2010)

A couple of months ago I purchased an HB-1A through eBay.

From it's looks, the HB-1A resembles very much an Elecraft KX-1.
After having found the schematics of the HB-1A somewhere in the Internet, it looks like it is a close
copy of the KX-1

The unit covers the 40, 30 and 20m ham bands (TX: CW only) and can receive any frequencies between
6 and 15 MHz. So, you are also able of tuning and listening to BC shortwave stations in SSB mode.

The TX section puts out about 4 watts of output. Sidetone seems to be more like a square-wave audio
side tone, as it sounds a bit "raspy".

The VFO is based on a DDS circuit, so frequency drift is not an issue.

The HB-1A manual and schematics can be found here.

Billy, M0JHA, has some more info on the HB-1A as well as for the newer Version HB-1B.

Please see here:

More details on the HB-1A and the newer HB-1B version (external link)

Ten-Tec Century-22 (29-June-2010)

After quite a long search I finally succeeded in getting a Century-22 which came through eBay US.

Over here in Europe these units seem to not having been sold in quantities during their production
life cycle.

The Century-22 is an all-semiconductor mid-power (about 20 watts RF) CW-only transceiver which
covers the "classical" HF bands plus the 10 MHz band (no 18 and 24 MHz bands).

Tech stuff:

The transceiver is a so-called "direct conversion" rig which means that there is no IF (intermediate
frequency) but the RF signal is mixed with in-band VFO directly (thus the naming) to the audio
base band. The VFO itself is of the pre-mixer type where the variable oscillator signal is mixed with
individual crystal oscillator signals per nband to achieve a resulting injection signal directly on the
target ham radio band. Hence this technique results in making audible the image signal as well
which in practise results in hearing the CW audio beat note two times: one time above the VFO
frequency, the other time below the VFO frequency.
This "specialty" of the radio requires understanding and getting used to the tuning of the VFO relative
to the carrier signal and the setting of the RX offset control (aka "RIT").

The RX bandwidth is being controlled by means of an audio filter which does it's job quite efficiently.
As the CW audio filter is inside the AGC loop the filter action does also impact the AGC action, which is

RX-TX change-over is real QSK, one of the best implementations I've seen so far (no surprise as Ten-Tec
may be also called "the QSK transceiver company" for over 3 decades!).
Change-over is noiseless and pop-free. The sidetone is smooth and relaxing to listen to.

My particular unit is stuffed with the optional electronic keyer board with the speed control located
at the rear of the radio. From todays perspective this option is rather useless as it lacks both dash and
dot memories, both features being standard in electronic keyers (including TRX internal ones) for quite
some years and where we are all dialed-in for their existence for our code-sending style at the paddles
for quite some time.

Operation, first impressions, etc.:

After getting used to the frequency tuning method and setting of the RX offset the radio is a joy to operate,
especially taking into consideration the age of it's design and manufacturing.

CW QSK operation is a blast (with external electronic keyer). It's 20 watts of CW RF output is more than
enough to work the world on almost any band.

The CW audio filter prooved to be very efficient for cutting-back adjacent QRM signals and smoothing
the AGC action at the same time (see comment above).

Sensitivity on the bands tested so far, 80 to 20m, is totally sufficient. On 30m night some BC background
"ghost" signals were observed, most likely caused by 2nd order mixing of the 2 next lower BC bands.
This still needs to be analysed more in detail.

The transceiver housing is a quite large box with ample room inside which should also make servicing
the unit an easy task.


The Ten-Tec Century-22 IMHO is definitely one of the "Classics" of the (near) QRP transceiver history.
If you are fond of such "Classics" and can get hold of one in good shape: buy it.

Yet, it would be unfair to expect the performance level of a K2 etc. kind of transceiver. That's still another
class of radio at least in some areas.

(pictures will follow soon)

to be continued...




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