Equipment used on 136kHz

In the time that UK and  European amateurs have been active on the 136kHz band, a number of different approaches to getting on the band have emerged.


Many amateur rigs these days have receive capability down to LF.  However with a few exceptions these are relatively insensitive on these frequencies and unsuitable for amateur use. Most operators therefore use some form of receive converter to a higher frequency, allowing use of the existing HF station receiver.  This also allows some gain to be included in the receive convertor. 

At G3YMC a receive converter (included in the transverter) converts to the 10MHz band.  This was selected primarily because 10MHz computer crystals are readily available.  A 3N201 dual gate mosfet mixer is used, preceded by a J310 JFET preamp.  Two tuned stages are included in the front end - good front end selectivity is essential on 136 to eliminate intermodulation products from broadcast stations.  Note that 198kHz (BBC Radio 4) - 60kHz (Rugby) = 138kHz.  If you hear a time signal on 138 you have not got enough selectivity.


Whereas receivers all seem to use similar techniques, there is great variety in transmitter techniques used on the band.  All the following techniques are in active use: 
  1. Crystal controlled, divided down from an HF crystal 
  2. Synthesised, an expansion of the above 
  3. Dividing down the output frequency of an HF rig 
  4. Transverters (as used at G3YMC) 
  5. Use of an audio signal generator as the source 
There is a similar diversity in the methods of producing output power at these frequencies: 
  1. Audio power amplifiers, including ready made power modules 
  2. Power MOSFETs (as used at G3YMC) 
  3. Bipolar transistors 
  4. Various forms of valve PAs 
It is not my intention to go into detail about each of these techniques, but to discuss their relative merits (see below).  The circuits and description of my transverter are included on this site. 

Relative merits of different transmit techniques: 

Crystal derived transmitter sources offer clear advantages for the more specialised techniques used on the band, in particular very slow CW where the transmitter must remain stable for an hour or more.  In these digital processed modes drift of 1Hz is disastrous. 

However transverters and similar techniques offer a fairly simple way to get on the band and provide adequate frequency stability for most purposes. 

There is strong feeling in the current band users as to which method is best, however it must be remembered that all the techniques currently being used allow excellent results and each amateur must be left to decide which one is best for him.

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