When Elecraft introduced the KH1 a year ago, I was immediately enthusiastic about the concept. A small and lightweight shortwave radio with an integrated telescopic antenna.
This means that, weighing less than 400g, it can be used in any suitable location on shortwave. So I wanted to build something myself.
I immediately began my own experiments with telescopic antennas for 7-30 MHz. This confirmed that a counterweight is absolutely necessary. This wire, which is a quarter of the wavelength long, contributes significantly to the radiated energy.
So the idea arose to forgo the telescopic antenna and experiment with end-fed wires twice the length. Of course, it makes sense to stretch the wire as high as possible.
But I also got respectable reports with EFHW lying on the ground or in bushes. In this place the antenna may detunes itself, so a tuner is necessary, as well as the standard 1:64 transformer (Unun). The tried-and-tested resonance circuit (Fuchs Kreis) performs both tasks.
Once the antenna issue was resolved, QRP Labs brought out the QMX. The ideal TRX for my projects, and now even capable of SSB.
Now all that was missing was a suitable housing with an integrated battery and a speaker with an amplifier. Then a paddle for CW as a contactless touch key directly on the device.
And the QMX Carrot was finished. But it wasn’t that simple, because everything had to be as small and light as possible. It now weighs 340g and measures 15x8.5x3.0 cm.
Today I successfully tested the QMX Carrot for the first time at a summit. Despite the low power of 3W and the poor conditions, I managed in CW and SSB 12 QSOS with six S2S.
73 Chris
I watch this forum couple of year, without registration, but your project brought me to registration, because I have some question.
I am facinating concept KH1, but it is expensive. Your idea and project is brilliant. I have same idea with my Venus SW-3B, too couple of months, but I dont start customing yet…Now I choise velcro, for hang external battery and SWR meter. In video (below) I testing external speaker from desktop pc with apmlifier. In future I want get speaker and amplifiler into TRX case. I want use smal switch, for disable power for amplifier, if I want use headphones. Do you have posibility use headpones in QMX Carrot? If yes, do you switch off amplifier, if using headsphones?
Jan, thank you for registering here, and welcome to Sota Reflector.
A few words about your question. The switch contacts of the headphone and paddle jacks are accessible on the board. This means that when not plugged in, the internal connections are forwarded to my audio amplifier and touch paddle.
By the way, this option and other interesting options for further development are also available on the QMX+. Compliments, Hans!
The QMX Carrot has completed its first activations. I initially had some difficulty using the tune mode (“Read That F. Manual” ). Since I tune the EFHW with a resonant circuit, an internal SWR measurement is essential.
And the QMX delivers this perfectly. Now I can work with the 20-meter-long EFHW on 40, 30, and 20 meters. For 20, 17, and 15 meters, the EFHW must be 10 meters long.
73 Chris
Because of my own experience, I respect the saying “experience teaches one” I always preset the ATU to maximum noise in the receiver before keying the transmitter (even with the QMX with Tune SWR).
I do the same thing. I even marked the sweet spots on the knob. By connecting the antenna to a tap on the resonant circuit coil, the Q is very high. And the tuning is very fine.
Your set looks very good, Heinz.
How did you get the labeling so professional?
73 Chris
When developing the QMX Carrot, I was initially concerned about whether the internal 1500mAh LiPo battery was sufficiently dimensioned. After all, the amplifier for the speaker still needs power.
Today I activated it for 1.5 hours and had 22 qsos, of which were 13 S2S with 61 points, and consumed only 386mAh at an average of 7.9V. Theoretically power for 4h more.
The QMX is a power-saving miracle with maximum of 3W out at 8V!
). Since I tune the EFHW with a resonant circuit, an internal SWR measurement is essential.
