Monday, May 11, 2009

Hifer transmitter

You may have heard about "Hifers" before. The term relates to "HIgh Frequency Experimental Radio". Mostly this is concerned operating beacon-like transmitters in the legal licence-free realm of ISM. However, using QRPp transmitters, and that's what hifers are according to my understanding, is also done by licenced radio-amateurs. Here is my attempt to create a hifer-transmitter.

What you see:
  • a (smd)-crystal oscillator using a 74HCT00
  • 78L05 voltage regulator
  • ID-keyer (12F629)
  • low pass filter
Presently this transmitter is keyed by unused gates of the 74HCT00. This, however, causes a severe chirp.... diuuuuuuuu... diuuuu... Not really wanted. Thus, this experimental device will be keyed by a reed-relais, i.e. aerial vs. dummy load.

In order to be compliant with hifer-requirements, an attenuator (a.k.a. antennuator) will be required in order not to exceed the 42dBµA/m @ 10m. Alternatively one could consider to use an accordingly lossy aerial. It's all about magnetic field-strength, in a distance of 10m.

As licenced ham-radio operator I would be allowed to operate up to 400W at my present location and up to 750W at my home QTH, in band that is. Maybe both would be a tough call to be pulled out of a single 74HCT00 ;-)