22 Jan 2013

137kHz E-field probe mag-mount

Tiny E-field probe on the car roof on mag-mount
This is the schematic of my simple mag-mount based E-field probe for 137kHz reception in the car. I use a low cost MPF102 FET and a low cost 2N3904 transistor. Performance seems to be totally adequate, detecting my very low ERP QRSS3 beacon as I drive around the local area up to around 10km (yet to test at greater range) from home. The whole unit is attached at the base of a 15cm whip on a mag-mount stuck on the centre of the car roof. The coax from the EFP connects into an FT817 with the IPO button ON - this makes the sensitivity better on 137kHz, a tip worth knowing.

1 comment:

John said...

The E-field probe sounds like the answer to a QRN-sufferers noise-induced headache!
I'm going to knock up a PA0RDT circuit today (if I can get away from this damned HMRC thing that needs doing) and hang it in the garden.
QRN from next-door's telly makes 160m & 80m all but useless until they all go to bed.
Good luck with 137khz!
John
G4WQD
GQRP 2725