The transverter used by G3YMC for use on 136kHz transverts to and from the 10MHz amateur band.  This band was chosen primarily because 10MHz computer crystals are cheap and readily available, and the performance of many amateur transceivers is rather better on this band than on the more commonly used 28MHz band.  It is used in conjunction with my FT101ZD which has given me stirling service over many years, both as an HF rig and as a transverter source to 6 and 4 metres.

No originality is claimed for the design.  It was built up using published circuits in the ARRL handbook and elsewhere, modified ad hoc for the application.  It has been used for several years now, although with anything which is experimental it has seen various changes and repairs.  The receive side has been in use rather longer as a 73kHz converter, although I never got round to getting a transmit NOV permit for that band.

The circuit is described in blocks, with all components shown but no details is given on the inductors and transformers except for general guidelines.  It is intended as an experimenter's unit rather than something available off the shelf, although it has been suggested that it could be made into a kit.

See my Equipment Practices page for a discussion of the relative merits of transverters over other equipment for 136.

Crystal Oscillator

Crystal Oscillator Circuit A 10MHz JFET crystal oscillator is used. This is a conventional circuit and outputs a reference to the receive and transmit mixers. A trimmer capacitor can be used to set the frequency accurately. 

The oscillator is powered from a stabilised 5V rail provided by a 7805 regulator to ensure stability. 

The two output capacitors may be adjusted in value to obtain the correct injection levels.

Receive Converter

The receive converter uses a dual gate MOSFET mixer preceded by an FET preamp.

Receiver Circuit
Input from the antenna is applied to a fixed tuned stage, T1.  This transformer uses a cut down long wave ferrite rod from a scrap radio and resonates in the 136 band with a parallel capacitor of around 300pF.    This is top capacitive coupled to a second tuned stage (using a pot core) which can be tuned from 65-180kHz with a dual 500pF variable capacitor.  An input is provided here for a wideband reception antenna, eg for 73kHz, but at lower intermodulation performance.  The preamp which I used to use has been removed as it tended to overload when fed from my vertical antenna.

A 3N201 dual gate MOSFET is used as the receive mixer, with the oscillator injection applied to G2.  This is conventional with the drain resonated to 10MHz by T3, wound on a quarter inch former.

Details of the transmit stages are given on the next page.
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