Hi All,
I'm giving my new hafler audio amp set up a try out on 137 WSPR.
IC706mk2G as an exciter (puts out about 100uW on 137), feeding into 1.5W broadband amp off ebay as per Dave Pick's article in Radcom. New chokes fitted 600nH.
This then feeds into the unbalanced input of the the Hafler P4000.
The output is a 4:1 step up txfrmr wound as per the plans on the W1VD webpage. 2 lots of 16uF caps feeding into two 7 turn coils of coax wound on 77 material
ferrite toroids (I didn't have the cores to hand).
The coax cores then connect to a balun assembly made using 77 material cores and this goes to the antenna.
The whole assembly steps up the impedance from the speaker terminals from 12ohm to 50ohm. The impedance was measured as 195ohm vs a 50ohm dummy load (4:1) and
is broadband from 50khz up to 1mhz. DC resistance is 2 ohm.
The amp is rated at 500W for audio and de-rated by 3dB @ 137khz.
I'm currently WSPRing on 137.5.
Any spots most welcome IO92ub Biggleswade
With best regards
Jim
Dr. Jim Cowburn G7NKS
