[Icom] Last Word on Internal Keying Relays (I hope...)

[George, W5YR]

There *is* one additional factor to take into consideration regarding the
capability of the SEND relay and that is the nature of the load it is
switching.

In most cases it is *probably* a relay coil, although that may not be a
"given." If it is, however, it is imperative that a snubber diode be
included across the relay coil to limit the voltage transient that develops
when the coil current is removed to deenergize the relay. 

The old L di/dt thing gets into the act and some very large voltages can be
developed which could arc and even weld closed the contacts of a small reed
relay.

Fortunately, it is almost unthinkable that any competent amplifier designer
would fail to properly implement his relay circuitry by omitting the diode,
but it could happen. Hence, the most prudent thing to do would be to
observe the voltage across the keyed relay line with a scope as the coil is
activated and deactivated. In that manner, the peak transient voltage can
be determined and compared with the radio relay's voltage rating.

The "probably" above is included to cover the situation wherein the amp
manufacturer has removed the possibility of damaging the transceiver amp
switching relay by building solid-state switching circuitry into the
amplifier which in turn activates the actual switching relays, if used.

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437

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Bruce Marton wrote:
> 
> Steve and everyone else,
> Why not just measure your voltage and current at the back of your amp and
> see if it fits the specs of the transceiver?
> I just put an Acom 2000A on line, which is very similar to the Alpha 91B,
> only fully automatic and computer controlled, and I was very worried about
> what would happen with direct connection to the IC 781.  I measured the amp,
> it displayed 12 vdc at 1.6 mils and no problems.  I connected it directly to
> the 781 and I am good to go.
> I would not loose sleep over this issue if you measure it with a good Fluke
> or similar meter.
> 73, Bruce K1XR
> P.S.
> Adam has always given me very sound advice over the years, he knows his
> stuff.