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Reviews of QRP Rigs

This review of the VEC 1240K transmitter was contributed by William K. Mabry, N4QA.

I leisurely built this rig in about two hours of my spare time while on vacation with the Wife in Central Florida over the Thanksgiving, 1999 Holidays. The most difficult tasks were, in my opinion, (1) installing the VXO variable capacitor.. requires nimble fingers to cut and place that double-sided tape on the board and then the cap on top of the tape... (2) winding one coil around a small toroid core... 18 turns of # 24 enamel-coated wire... and, lastly (3) the handling of those tiny multilayer capacitors... care must be taken not to flex the leads causing the bond between the leads and cap body to be damaged. You may need a magnifying glass to identify some of those tiny caps... the printing is pret-ty small! All kit parts were present and in good order and, really, the above-mentioned difficulties aren't so bad.

The rig has space on the pc board for two xtals... one is included for the popular QRP frequency of 7040 kHz, the second is optional and is up to you. A front panel switch selects one or the other. I found the VXO range with the 7040 kHz crystal to be 7038.5 to 7041.5 kHz. The power output is 1.5 watt(s) (RCA jack) as measured on a Heathkit HM-9 QRP wattmeter and using a 13.5 V, 1.5 A ac adapter, taken from a long-defunct external cdrom drive, as a power supply (The kit does not include a power supply). The power jack is the 5mm OD, 2.1mm ID coaxial type, center post positive. I have no spectrum analyzer available to give you specs on spurious emissions, harmonic content, etc.

The rig was not put on the air until our return home (Virginia) from vacationing in Florida. I have solicited several critical signal reports, from among the more than 50 contacts made to date, and have received consistently positive responses... no key-clicking nor chirping nor humming nor frequency drifting... just good keying and cw note. I use a modified MFJ Econo Keyer II and Bencher paddles for keying. Incidentally, the rig comes with a 1/8 inch (3.5mm) key jack mounted on the front side of the circuit board. Well, I didn't like the keying cable coming out the front of the rig so I added a key jack to the rear apron of the optional metal cabinet and wired it in, appropriately. I also made a simple modification to the rig in order to add a frequency "spot" function which required the addition of one 1k ohm resistor which is used in conjunction with the oscillator stage and an unused terminal on the power switch.

The rig offers a "receiver antenna" jack (RCA) on the rear apron. Diode switching reduces transmitter power reaching this jack to +7dBm according to the manufacturer. That's still a very strong signal and some receivers using this jack may suffer from front-end overload. Still, it's a nice feature.

Using this little rig and its companion receiver, the VEC-1140K, on-air results have been gratifying. To date, I have made more than fifty contacts from here in SW Virginia with stations from Ontario, Canada to Tampa, Florida to Madison, Mississippi to Vermillion, South Dakota. My antenna is an end-fed and voltage-fed longwire, approximately 250 feet in length.

The kit includes a well-written 33-page paperback manual which begins with information on: Tools and equipment required. Tips on soldering/desoldering and work habits. Parts identification. Printed circuit board parts placement (diagram). Proper orientation of diodes, transistors and electrolytic capacitors.

After the basics, it goes on with detailed parts lists, both generic and band-specific. Following that, the manual describes the step-by-step assembly which is a logically ordered process and suggests special treatment of the delicate multilayer capacitors used in the kit.

The manual next gives information on checking your assembly work, including correct parts placement and solder-joint integrity.

Once the kit is built and checked, the manual describes a modest test setup and a simple alignment procedure, then goes on to give general directions on operating the rig and even discusses antenna construction.

If you have trouble there are useful troubleshooting procedures... including a voltage chart and transistor base diagrams.

So that you know what is going on inside the rig, the manual has a good, half-page treatment of the rig's technical qualities including the requisite specs. Also a very nice full-page schematic diagram which clearly shows all component values. The optional matching metal cabinet is described in the text and shown in a drawing.

If you'd like to have a lot of QRP transmitting fun without spending a lot of money, may I suggest that you consider the Vectronics VEC-1240K.

When you are through reading this review, close this window to return to the QRP Rigs index - or - click here to go to my home page if you came here from elsewhere.

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