136 kHz Transverter
The 'transverter' (transmit & receive
converter) was designed to work with a Yaesu FT707 transceiver, operating at 10 MHz.
All of my best DX QSOs were made using this set up. More recently, I have
modified the transverter to interface with my IC756PRO.
|Click on thumbnail
receive, the antenna is link-coupled to a tuned 'longwave' coil having a ferrite rod core.
The signal then passes through a bandpass filter (two top-coupled tuned circuits) to gate
1 of a BF981 dual-gate FET, where the signal frequency is mixed with 10 MHz to produce the
10.136 MHz output to the transceiver.
On transmit, I use another BF981 FET mixer driven by the low-level RF signal (about 100
mV) available on the back panel of the FT707 and IC756PRO. Incidentally, the level
of the RF signal is continuously variable on the FT707 using the CARrier level control on
the front panel. But the RF POWER control on the IC756PRO provides only a
limited range. The 10.136 MHz from the transverter is mixed with the 10 MHz local
oscillator to produce the required 136 kHz. The signal is then amplified to drive
three bipolar transistors (Sanyo 2SD325D) connected in parallel. Bifilar-wound, dust-iron
cored toroidal transformers match the low-impedance collectors to 50 ohms. Finally,
the output passes through a single section low pass filter and directional power meter.
Many of the components were found in my junk box, so I'm sorry that I haven't
been able to include any manufacturer's part numbers! Please contact me if you
have trouble finding suitable components, and I'll try and suggest some
L1 is a 'long wave' coil slid over a short section of ferrite rod and resonated to 136
kHz. A couple of nice slug-tuned coils of about 3.5 mH were used for L2 and
L3 (salvaged from an old tape cassette player). L4 and L5 are 10 MHz IF
L6 is another slug-tuned coil salvaged from an old tape cassette player.
L7 and L8 are ex-equipment coils (about 60 turns), wound on EMC grade ring cores coloured
yellow & white; 21 x 12 x 6 mm.
|Driver and Power
L9 and L10: same as L7/L8.
L11 and L12 are each 25 turns, bifilar-wound on ex-equipment, EMC grade ring cores
coloured yellow & white; 33 x 20 x 11 mm. I never did understand why the 0.22uF
coupling capacitor between L11 and L12 works so well: it seems that 2.2uF would be a
better choice! Also, the use of 25 mm OD 3C85
ring cores for L11 and L12 (instead of EMC grade material) will provide
greater PA efficiency.
Each PA transistor will draw about 1.2 A. Select a device that will be happy at
1.5 A at 10 W dissipation. Use a heat sink! My PA delivers about 18 W output
for 40 W input - you must be able to do better than this!
LPF; and Power Meter
L13 is wound on a piece of ferrite rod.
L14 and L15 were made using the same type of coil as used for L7/L8/L9/L10 (see above),
with a two-turn link winding added. 25 mm OD 3C85 ring cores would be more suitable.
Suggested improvements would be most welcome!
Des M0AYF has based his transverter on the above design. Click on the thumbnails
below to see the completed unit.