29 September 2013

Transmitting on 23 cm (thinking of)

After one year of SWL'ing on 23 cm I feel I would like to have a QSO up there. Besides buying a transceiver for that band, another option is a transverter. Current DB6NT catalog lists a 144 to 1296 transverter for 425€ built, or 199€ in kit (SMD). But how about a simpler solution? I came up with:
  • a Si570 generator/kit, at 60€ or so, and it requires a power amplifying chain
  • a frequency multiplier
While checking if any of my XTALs or canned oscillators would fall within 1296 MHz, it occured to me that 1296 is an integer multiple of 144 and 432 MHz. This observation led me to explore the almost forgotten world of multipliers and I met the varactor component.

A varactor is a sort of high power varicap diode which is able to return a signal tripled in frequency with a 35% efficiency, all with passive components. FM or CW only. Since I own a 30W UHF transceiver, I potentially have a 10W CW 1296 MHz transmitting chain. I think this technology has been almost forgotten, while today it would allow many amateurs to give 23 cm a try.

A quadriband transceiver will transmit on 70 cm (or at least 2m if using a 5x multiplier), and they are very popular => no additional cost.
An RTLSDR stick will provice wideband 23 cm coverage for 20 USD.
A computer is then needed as part of the receiver, but I would say most HAMs own one => no additional cost.

So, for the cost of a RTLSDR and a varactor multiplier you can be active on 23 cm (CW/WBFM). Not bad.