Projected Life of Reed Relays in High-Speed QSK-CW Service

by Adam Farson, VA7OJ/AB4OJ

First published December 26, 2002 on the Icom Reflector

Fig. 1: Typical DID (direct-inward-dialling) trunk.
Fig. 1: Typical DID (direct-inward-dialling) trunk.

Concerns have been expressed that prolonged QSK-CW operation of an Icom HF transceiver fitted with the OMR-109F amplifier keying relay in excess of 10 wpm will seriously shorten relay life.

I worked in the telephone-switching industry for many years prior to retiring at the end of 1999. We used various types of reed relays as impulsing ("A") relays in trunk interface circuits for telephone exchanges. (An example is the "A" relay contact in the left block of Fig. 1.) 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 50~100mA 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 worked with our component engineers 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-109F 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.

I am not aware of any OMR-109F relay failure due to extensive CW operation. Had this been an issue, Icom would have specified a different relay many years ago.

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.

Copyright 2003-2008 A. Farson VA7OJ/AB4OJ. All rights reserved.

Last updated: 10/19/2008

Click for Microsoft FrontPage site.