[Icom] 706 MKII keying & using amp???

Tue, 31 Dec 2002 19:09:41 -0800

Hi Larry,

The HSEND and VSEND lines are bi-directional. When you key the IC-706
transmitter via the mic or key, the line extends a ground. When you apply an
external ground to the line, the IC-706 switches from receive to transmit.

Is it possible that when the amp SEND key is depressed, the amp extends a
ground on its keying line with sufficiently low source resistance to key the
IC-706? This would account for the loss of receive. If this is the case, you
should be able to block the sneak path with a diode in the keying line
(cathode towards IC-706).

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of W3UIO
Sent: Tuesday, December 31, 2002 18:38
To: [email protected]
Subject: RE: [Icom] 706 MKII keying & using amp???

--- Adam Farson <[email protected]> wrote:
> The IC-706 has a solid-state keying circuit; the
> specs follow.
>
> Pin 2 GND Connects to ground. (red)
>
> Pin 3 HSEND Input/output pin (HF/50 MHz). Goes to
> ground when transmitting.
> When grounded, transmits (connected to 8V line thru
> 2.2 k? resistance/144
> MHz operation). Ground level :-0.5 V to 0.8 V.
> Input current : Less than 20
> mA (HF/50 MHz bands) (orange)
>
> You should be able to build up a simple 2-transistor
> buffer circuit to
> safely key the Alpha 76CA. from the HSEND line.
>
The Alpha 99 amps manufactured after Dec. 15, 2002,
have 12 vdc@ 7 ma. on the relay jack.

Since the 706 has no relay, I can't damage it. I built
the one transistor circuit provided by ICOM for radios
with the reed relay. That circuit will be posted here
when scanning has been done.

The circuit does key the amp, but when the amp send
button is depressed (as it is for operation to begin),
the effect on receive is as if the antenna has been
disconnected. Something in that circuit is messing
things up when in receive position.

I guess either no buffer should be used, or some other
circuit such as has been posted here tonight. The only
problem I had heard about from not using a buffer was
regarding the red relay.

Anyway, thanks for the help.

=====
Larry, W3UIO

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