Mods to use Omni 6 with Acom 2000A

Soon after the Acom 2000A amplifier was introduced, problems were reported with “RF Power Detected at the Wrong Time” errors occurring with Ten-Tec transceivers (Paragon and Omni 6). Acom initially recommended a mod for the transceiver (this won't completely resolve the problem). Later, Acom updated production units and recommended Ten-Tec users do the update to their amps. I installed all the mods - I still get errors in SSB using the TX EN/TX OUT keying loop. This information is provided for historical purposes only. The updated recommendation can be found on Mod to use Omni 6 with non Ten-Tec QSK amplifiers


Transceiver Mod

Two different ways of using QSK CW with Ten-Tec transceivers plus ACOM2000A amplifier are described below.

1. The simpliest way is to use a phono (RCA) T-adaptor in order to connect the TX OUT to the TX EN connectors of the Ten-Tec and connect its third branch to the KEY IN connector of ACOM2000A. Left free the KEY OUT connector of ACOM2000A. This way you can use QSK mode safely since the amplifier does look after its relays.

2. A total solution of the problem is to make a simple improvement inside the transceiver. A MOSFET and a resistor are only needed. Add them to the original control board. A schematic diagram for Ten-Tec Omni 6 transceiver is shown below, but a similar modification could be made to other models. Any low- power N-Channel insulated gate MOSFET transistor of VN10-series (VN10LP, VN10LM, VN10KM, VN2222L, VN2700 etc) is suitable for Qa. The resistor Ra is 10kOhms 1/4W and its value (5-15k) is not critical.

txenoutmod.jpg

The problem in the original wiring is that when you pull the TX_EN input to the ground, the transceiver unconditionally changes to transmit mode, regardless you may have not pressed a PTT or CW KEY at all. Also, you cannot return to RX after releasing the PTT or KEY until the TX_EN is grounded.

The addition above takes care about real PTT or KEY condition. It uses the TX_ACK command issued by the LOGIC BOARD. The transistor Qa disables the base current of Q15 when the LOGIC BOARD says “RX mode” (TX_ACK is low), thus ignoring the TX_EN input during RX. No functions are modified in TX mode.

The resistor Ra does not concern the logic functions. It is added to eliminate another problem existing in the original schematic. If Ra is not present, the base of Q15 is floating during RX mode, so any (even insignificant) residual emitter-collector current of Q14, as well as any reverse collector-base current of Q15, both would lead to uncontrolled transmit mode of the transceiver. Adding Ra makes the schematic virtually immune to the Q14- and Q15 normal reverse currents.


Amplifier Mod

Please check these modifications have been done on your INTERFACE PCB. They concern Ten-Tec PARAGON and OMNI compatibility and have been introduced in the current production as follows:

- D30 added in September 2000;

- D31 added in April 2002;

- R92A added and C82 removed in July 2004.

(note that the changes to the Ten-Tec transceiver described in a previous document TenTec.doc may not be necessary once these changes are made to the 2000A)

INTS_D30_D31.jpg
INTV4_R92A_C82.jpg

(based on info provided to N1EU by Acom Bulgaria)