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-Articles about LF by various authors.

Technical.

Cheap & simple 500kHz TX by GW3UEP. This design produces up to 25W and only costs a few pounds.

Bandpass RX Loops. Jim's new article on 1m squre receiving loops for 136 and 500kHz. "Band-pass" tuning means no adjustments once set up.

A 500kHz TX design by Jim Moritz, M0BMU. This 10W transmitter was designed for use under the UK research permit conditions but would be adaptable to 472kHz.

A complete DDS LF exciter. By Murray Greenman ZL1BPU. The LF Exciter described here is in use around the world, and has been heard trans-Pacific (admittedly with a PA attached!) It has a DDS synthesizer with 0.3 mHz steps, TCXO precision and stability, and a built-in programmable beacon with many specialized LF modes including JASON and Murray's new "CASTLE" mode. It includes a sweep generator for those tricky antenna and filter measurements and an incremental power control for the PA. With 1W output from 75 kHz to 300 kHz, it contains a mere 4 ICs and 2 transistors! ($10 firmware charge, $30 if you want the full source code). The DDS can now reference to a 1pps clock from a GPS receiver.

Calculator for LF loading coils By M0BMU. An Excel spreadsheet for calculating the coil and tapping point to resonate and match an LF aerial. To download it rather than display it in the browser; right-click and choose "save target as" or "save link as". There is also an explanatory PDF file.

Transmitting loop for 136kHz By G3YXM. TX loops after the design of Bill Ashlock can give a good account of themselves when supported by trees. I decided to try one at GM3YXM at Easter 2006.

The famous ON7YD LF aerials page is now hosted here as well as at the original QSL.net address.

LF Tuning meter. By Jim Moritz, M0BMU. It has 2 meters - one indicates phase, while the other can be switched between voltage and current to determine the load resistance. The circuit is slightly more complex than an SWR bridge, using 12 diodes, 3 toroid cores and a few other passive components. It does not require an external power supply, and is usable with TX power between about 20W and 1.8kW

Experiments with Argo modes. Just how much more effective is QRSS60 than QRSS10, or QRSS3 than CW, in practice, on a real band, over a real path? Dave Pick G3YXM asked Alan G3NYK to assist.

An easy LF receiving loop, tuned in the shack. © Jim Moritz M0BMU. I have used this system to great effect. Highly recommended. Also check out his article on "Band-Pass" loops. Here.

A vectorscope unit for displaying phase mod. © Jim Moritz M0BMU. A simple way of displaying phase modulation on an oscilloscope with X and Y inputs.

A simple hardware DDS for 136kHz. © Pavel Vachal OK1DX. This DDS uses 74HC series chips to produce full band coverage in 10Hz steps. Can be built in a day (if you're quick) for £20.

Jason, a slow mode for LF DX. This package was written by Alberto I2PHD and gives keyboard communication at 2.5 chrs/min in 4Hz bandwidth. Not used these days..

An Electro-Mechanical RX for VLF Inspired by the recent transmissions from SAQ, Jim Moritz has built a receiver with no active devices... not even a diode!

A 600W bridged FET PA. © Andy Talbot G4JNT. This design uses high Voltage FETs straight from the mains with no bulky / heavy transformer.

A variable phase BPSK modulator by M0BMU.Another interesting article from Jim. He has designed a modulator for BPSK which keeps bandwidth under control.

Of LF RX loops and preamps. Some thoughts by G4CNN.

The Decca TX protection system. Jim Moritz, M0BMU has written a short article on the "guard circuit" used to protect the Decca TX.

DK5PT's software-DDS for 136.Dieter Wulff has built a simple DDS for the band using a AT90S1200-12PC microcontroller chip. Diagram corrected 21/12/2000.

PA0SE's LF field strength meter. Dick Rollema has full details on how to build and calibrate the meter.

ON6ND's water analogy of antennas. Werner's LF antenna is unique. He justifies his choice of antenna with an interesting analogy.

DK5PT's compact loading coil on a ferrite core. Dieter now has this coil working with 300W and 3A antenna current.

My review of the Ropex transmitter. Written for "Radio Today" magazine and published in the June 1999 edition.

Tales.

VA7LF. The trans-Pacific tests 2006 By Steve McDonald VE7SL, one of the VA7LF team.

7S6SAJ LF operation from Karlsborg A vintage LF station fires up on 136.

The Guernsey LF DX-pedition, November 2000. A tale of rain and wind and cold and Loran.

Mike G3XDV's trip to West Wales to work GU. More rain and wind, and power-cuts.

The Isle-of-Man trip November 1999. The lighthouse strikes back.

More articles are welcome, e-mail me at