[hpsdr] Kenwood TS-940S as a power amp for HPSDR

[Joe Martin K5SO]

All,

Following the lead of the earlier mention of using an SB-104 with  
HPSDR, here is an example of how to modify another older HF  
transceiver to achieve an inexpensive and easy solution to obtain 100w  
or more output power with the HPSDR Penelope/Mercury board set if you  
happen to have such a transceiver available.   I promise we won't put  
so much detail in other postings of this nature but I thought it might  
be useful to others if we post the modification details for one radio  
at least, as a representative example of what might be involved!

We have modified a Kenwood TS-940S HF transceiver to use the HPSDR  
boards as an exciter for the TS-940S solid state amplifier and Rx.   
The HPSDR/TS-940S combination provides enough output power to run 125W  
(250W PEP) out barefoot or to drive a linear amplifier to full legal  
output power on the HF bands using Penelope on transmit and Mercury on  
receive using the T/R relay, Tx bandpass filtering, and output power  
monitoring of the TS-940S.  We elected to give up the original rear- 
panel RTTY arrangement of the TS-940S  to avoid drilling  a hole in  
the TS-940S chassis to mount a new connector.  The TS-940S  
modifications and HPSDR interconnections that we used are:

Tx:
1) Remove the bypass capacitor and shielded wire connection from the  
RTTY phono jack on the rear panel of the TS-940S and tape the ends for  
storage (in case you want to restore the xcvr to its original config  
later).

2) Unplug the coaxial cable at the DRV jack on the RF UNIT board  
(bottom side of the transceiver) and reroute the cable to the RTTY  
jack  on the rear panel.  Solder the center conductor and shield of  
the cable to the RTTY phono jack.

3) Connect a 6 dB BNC pad on the Penelope BNC output connector (to  
lower the drive level out of Penelope suitably).  It takes only 90 mW  
to drive the TS-940S to 125W output power (Penelope has 500 mW  
available, of course) and connect a BNC cable from the 6 dB pad to the  
RTTY phono jack on the TS-940S using a phono-to-BNC adapter (available  
at Radio Shack) for the cable end at the TS-940S.

4) Connect the PTT open collector output pin 13 (PPT OUT) and pin 17  
(ref) of the DB-25 connector on Penelope to pin 13 (PTT) on ACC2 plug  
on the TS-940S.

To key the transmitter we use PTT on the DB-9 connector on Ozy but any  
alternative PTT key point in the HPDSR board set should work just as  
well.

Rx:
1)  Connect a phono-to-BNC adapter to the RX ANT SWITCH phono plug,  
move the slide switch at the phono plug to OUT, connect a BNC cable  
from the phono-to-BNC adapter to the BNC input jack on Mercury.

If you are already pleased with using either your PC audio or taking  
audio from a Mercury jack to an external audio amp system, you're done  
with the modifications at this point.

We, however, wanted to be able to use the volume control, audio amp,  
and speaker/phone jack of the TS-940S instead of using the PC audio so  
we continued on with the following Rx mods:

2)  Insert a mini-mono audio plug into the Mercury line output port  
(the TS-940S audio is mono) and connect to unused pin 10 and pin 12  
(ref/ground) of the ACC2 jack on the TS-940S.

3) Unplug  the shielded cable from pins 1 (AV1) and 2 (AV0, ref) from  
the 4-pin plug at jack 23 of the IF UNIT board (bottom side of the  
transceiver) and solder a 510-ohm and an 82-ohm resistor in series  
across the shielded cable (82-ohm to shield wire) to form a resistor  
divider which will lower the audio level from Mercury to approximately  
0.3V p-p across the 82-ohm resistor.  Connect a new piece of shielded  
audio cable across the 82 ohm resistor and solder it to pins 10 & 12  
(ref) of the ACC2 jack at the rear panel of the TS-940S.

Now the HPSDR set has a 125W solid-state amp, transmitter bandpass  
filtering , and T/R relay switching.  The power meter and band  
switching (and AF volume control too, if you performed Rx 2 & 3 above)  
should work as usual on the TS-940S.  Output power level is set/ 
adjusted in PowerSDR by the PC.

Be sure to remember to the change band selection on the TS-940S when  
you change bands in PowerSDR so that you will be using the proper Tx  
bandpass filter in the TS-940S transmit line!

Have fun and good DX!

73,  Joe K5SO