[Icom] More on isolation relay with non-ICOM amps

Adam Farson [email protected]
Thu, 26 Dec 2002 00:33:01 -0800


Hi Larry,

If you can e-mail me a scan of the interface schematic you mentioned, I
shall be able to create a Webpage for it, and upload it to the Icom FAQ site
as a subsidiary page to "On External Keying Relays".

I worked in the telephone-switching industry for many years prior to
retiring 3 years ago.  We used various types of reed relays as impulsing
("A") relays in trunk interface circuits for telephone exchanges. The most
arduous application was dial-pulse sending at 10 pps (600 ops/min,
equivalent to 20 wpm QSK CW.) Typical contact-load parameters were 50 ~ 100
mA at 50V DC. I do not recall one impulsing relay ever failing in our lab;
relay damage in customer installations was generally attributable to
lightning surges or power crosses on the line facilities.

I recall our component guys testing reed relays at 20 pulses/sec for an
application in Japan, which uses both 10 and 20 pps dialling. 20 pps equates
to 1200 ops/min, or 4 times the OMR-109 spec. They observed some pulse
distortion at the higher impulsing speed, but accelerated life tests did not
indicate any significant increase in contact degradation over time, as
compared to 10 pps testing. (pps = pulses/sec).

From a perusal of the reed-relay literature, I have noted that many of the
vendors state expected-life figures as minimum values. For the case of the
OMR-109F, the stated no-load value of 100 million ops equates to 5555 hours
of QSK CW keying at 10 wpm. Even if the life "number" is not a minimum, 5555
hours adds up to a lot of on-air time! Per the OMR-109 data sheet, this
figure is reduced by 50% at 5 ~ 10mA/12V (still a pretty respectable number
of operating hours.) Higher load voltage/current will reduce the expected
life even further, as can be seen from the data sheet.

Our experience with these relays in telephony applications, as described
above, suggests that the expected-life spec is indeed a minimum. Thus, I
believe that projected reed-relay life will probably not be an issue with a
light load (e.g. 5mA/12V.)  A simple transistor buffer circuit between the
exciter relay and the amplifier keying line will accomplish this, whilst
eliminating the latency associated with an auxiliary relay.

It seems improbable to me that the product planners, designers and component
engineers at Icom would have expended precious R&D resources to provide QSK
CW in their higher-end HF transceivers, only to knowingly compromise this
feature by specifying a relay which would, in effect, put an expiry date on
it.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Icom FAQ Site:
http://www.qsl.net/icom/



-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of W3UIO
Sent: Wednesday, December 25, 2002 14:30
To: [email protected]
Subject: [Icom] More on isolation relay with non-ICOM amps


The following references the Alpha Power web site
which in turn references another site posted on this
list recently. Apparently the problem with the ICOM
send relay is not related to voltage/current but to
the number of operations per minute that it will
sustain. This url indicates that CW operation above 10
wpm will exceed the relay specs.

This also explains why some have used non-ICOM amps
without a buffer or isolation relay and have not
experienced problems.

http://www.alpha-amps.com/html/icom.htm

"IC-756 and IC-746 family:
The Alpha 99 / 91B has 25vdc @ 7ma at the RELAY jack.
This is within the specs of
the OMR-109 relay in the Icom radios (60v/500ma),
although Icom says it is rated for 16v/500ma.
The problem is not the voltage rating, but the spec of
the relay for operations per minute.
With NO electrical load on the contacts, it is rated
for 300 operations per minute,
or about 10 wpm QSK CW. Faster than this will cause it
to fail prematurely." -- Alpha Power

A simple schematic which does not require its own
power source will be posted here either by me or by
Dave (AA6YQ) as soon as I get it scanned or get a copy
to Dave for scanning. The circuit is from ICOM
Technical Service and contains one transistor, one 1 K
resistor, and one 1N4002 diode. This transistor will
key the amp.

Larry, W3UIO