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80 MFJ Cub 40m QRP CW Transceiver circuit walk thru and review, plus bandsweep, ham radio MFJ 9340

From - Posted: Feb 17, 2013 - 10,233 views
Cooking | 80 MFJ Cub 40m QRP CW Transceiver circuit walk thru and review, plus bandsweep, ham radio MFJ 9340 | 80 MFJ Cub 40m QRP CW Transceiver circuit walk thru and review, plus bandsweep, ham radio MFJ 9340
80 MFJ Cub 40m QRP CW Transceiver circuit walk thru and review, plus bandsweep, ham radio MFJ 9340
80 MFJ Cub 40m QRP CW Transceiver circuit walk thru and review, plus bandsweep, ham radio MFJ 9340
Duration: 16 minute 36 seconds 
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I assembled this MFJ-9340 Cub QRP CW transceiver for 40m for my friend Gerry - N2GJ. It's a very pleasant kit to build. All surface mount components are already mounted on the board. Assembly involves soldering the through hole components, and winding two toroidal coils. For me, the assembly took one evening, and the alignment took another evening. The video goes through the block diagram of the transceiver, then walks through the schematic, describing the function of each circuit. The transceiver tunes from about 7005kHz to about 7.070kHz. At the end of the video, I sweep through the band, listening to the various CW signals that can be heard on the 18" antenna I have connected in the basement. Pretty sensitive for a simple receiver.
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MFJ CUB 40m QRP Kit ARRL Package

Here on YouTube.comNG9D we spend a lot of time fiddling around with low power (QRP) radio transmitters, simple receivers, home-made wire antennas and various little gadget kits, celebrating perhaps the best hobby in the world - Ham Radio! In this video we look at a 40 meter QRP transceiver, kit. ARRL sells this radio kit together with an informative book on Low Power Communications. All the Surface Mount Devices (SMD) are factory installed, which makes it very compact and easy to assemble. To align the kit, there are several ways to do it but the only sophisticated piece of test gear needed is a ham transceiver with accurate frequency display! The only other gear you will need is a dummy load (can make from two 100 ohm 1W resistors), a QRP power meter (can make from a 5mm LED), a telegraph key, a 12 volt power supply, and earphones. ... Alignment is simple - it is all done by adjusting the trimcaps and slug tuned coils with a plastic screwdriver. This might sound complicated, but it is really not at all. The manual gives VERY good instructions. I will give you the complete method I used:1. BFO Frequency Spot it by listening to your receiver and Adjust: Trimcap C27 product detector operating frequency to 11.996 MHz. 2. VFO Calibrate: Slug-tuned coil L3 sets the VFO tuning range. Adjust by listening for Cub's VFO signal on receiver. Set for 4.940 to 5.000 MHz. 3. Receiver Bandpass Filter: L1 and L2 peak the receiver's front-end for best weak-signal sensitivity. I did not use a signal generator, I adjusted for maximum noise. Easy. 4. BFO C27 is touched-up for correct sideband LSB, I used signal from my ham transceiver into a dummy load. 5. VFO touch-up, L3 adjusted with Cub into dummy load, and frequency set within ham band. 6. Transmit Carrier Offset: Trimcap C40 sets CW-offset frequency for the desired pitch (say 600 Hz or so). 7. Transmitter Bandpass: L6 and L7 select the desired mixer product and peak the transmitter for maximum RF-output. I used a QRP power meter kit from Ten Tec, but you can also adjust for maximum brilliance of the LED homebrew power meter (LED connected across dummy load terminals). 8. Power Output: Trimpot R19 (mixer drive) sets RF-level from zero to full output Adjust up to the point of max power, but no further (to keep signal clean).Use plastic tool! Metal detunes circuit. I had a plastic tool from a Ramsey kit. You may have one already, if not buy or make one. They are inexpensive and save a lot of grief.This is a good kit for QRP builders, and works very well. By the way, I counted ten of the thru hole caps as type NP0. Temperature compensation of VFO in the completed unit seemed very good. The other video (wire loop with Cub) was made from cold start. I found that the rig exhibits very good stability on 40m.The kit is well manufactured and the instructions are clear. Assembled and tested Saturday, 18 Oct 2014 1445 hrs local with coax fed one wavelength doublet antenna 25 ft high. The book that comes in the ARRL package, "Low Power Communication - The Art and Science of QRP", 4th ed. 2012, included in ARRL kit package is written by Rich Arland, K7SZ. It contains a huge amount of entertaining and useful info. Appendix C contains the complete MFJ step-by-step assembly and alignment procedure for the CUB transceiver. Rich writes well and discusses equipment, antennas, operating, propagation, accessories, modes, etc. ... He covers many popular QRP rigs, but I was a bit surprised he didn't mention a couple of my favorites, the Ten Tec T13xx series and the Hendricks PFR-3A -- or any Hendricks kits for that matter. But this is explained also, there is only so much room in a 299 page book! There are even a few small antenna projects outlined. It's a fun read for QRPer,So, for about $110 including shipping, this is a very fun and educational ham radio project!73, Lynn - NG9D
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