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

[Bruce Marton]

Yes,
This is what the B&W does, it uses a transistor circuit to fire the t/r
relays.  I am assuming the Acom does the same, considering the low voltage
and current measured, but I might be wrong.  Krassy at Acom insists the amp
is set to go from the factory for virtually anything, that is:  keying,
faults, overdrive, too much reflected power, overheating, improper PA
voltages, etc, etc.   So I must assume the issue of keying voltage/current
for modern rigs has been addressed.  But I checked it anyway and only came
up with 1.6 mils.  Now I am down to the sleeping level.
73, Bruce K1XR

----- Original Message -----
From: "George, W5YR" <w5yr@att.net>
To: <icom@mailman.qth.net>
Sent: Monday, March 25, 2002 8:53 PM
Subject: Re: [Icom] Last Word on Internal Keying Relays (I hope...)


> 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
>
> All outgoing email virus-checked by Norton Anti-Virus 2002
>
> 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.
>
> ----
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