Relay stuff

Relays for RF use.

Duty factor and number of operations

If all you're doing is switching antennas, then you won't rack up all that many operations. Say 10 years at 1 changes/hour, and you're looking at around 90k operations.

If you're running an antenna tuner, you're probably looking at more operations, particularly when you retune. Maybe 10-100 times as many operations. Figure there's 10-15 relay operations for each tune cycle.

If the relay changes every time you hit the mike button, there's a lot more operations. Let's take some numbers from contesting on field day. There may be 1000 or so QSOs, each one of which might require 2 presses of the switch (4 relay operations). If you did that 50 times a year, it's around 200k operations/year, or 2 million in 10 years.

The Matsushita JW1FSN type mentioned below have a rated life of 5Mops at 180 closures/min. (see http://www.naisweb.com/e/relaye/mech_eng/pdf/mech_eng_jw.pdf ) The expected life at 6 cpm with a resistive load is 100,000. The life curves on page 4 show also that if you don't hot switch (not the case with an antenna tuner application), or, at least you limit the current to 2 A (as opposed to the rated 10A), the life is 10x greater (1M)

The P&B RKS-5DW (Potter and Brumfield is now part of Siemens, or maybe Tyco, by the way) gives an expected mechanical life of 10 million operations. I note that Siemens recommends using the RT series instead of the RKS series. http://relays.tycoelectronics.com/datasheets/RT_DS.pdf gives contact life based on the Breaking capacity in terms of kVA with a resistive load. In any case, it looks like 100,000 operations at 4.0 kVA, rising to a million ops at 0.4 kVA.

Tyco points you to an interesting datasheet on Relay Contact Life http://relays.tycoelectronics.com/app_pdfs/13c3236.pdf

" The electrical life expectancy of general purpose and power relays is generally rated to be 100,000 opeartions minimum, while mechancial life expectancy may be one million, 10, or even 100 million operations."

 

Info gleaned from some lists at contesting.com.

Tom Rauch W8JI@contesting.com
Fri, 12 May 2000 08:22:15 -0400


Does anyone have wisdom to share on selecting relays for home-brew legal limit remote antenna switches? In particular, can anyone explain to me what an RF Relay is, as opposed to the common Power Relay?

Three things combine to cause SWR problems, the AMOUNT of impedance bump, how that impedance changes along the length of the bump, and the overall LENGTH of that bump.

The best relays either use short wide leads, or are a constant impedance that matches the transmission line.

Of course current rating and voltage rating are important, and the dc or low frequency AC current contact rating printed on the relay has little to do with the non-switched RF current capability of the relay. Some 15 ampere rated relays will overheat at radio frequencies with 5 amperes, while other 5 ampere relays will handle 15 amperes or more of steady RF current!

In general the best relays have wide armatures with thick leads using non-woven strands, or better yet pull a shorting bar between two stationary contacts (like the RCS-8 relays do).

To give you an example, an RCS-8 style relay using the same contacts but with wire leads is good for about 2 kW ICAS to 30 MHz, but that same relay as configured with the shorting bar (called a "form X" contact) will handle 10 kW ICAS at 30 MHz and work up to 250 MHz with reduced power!

Bottom line is look for a relay with good insulation and very thick leads, or better yet use a form X contact with big contacts.

Is there any reason that I can't use an off-the-shelf 30 amp power relay to switch RF?

Some will work, some won't. The low frequency AC rating is almost meaningless.

73, Tom W8JI w8ji@contesting.com

George, W2VJN w2vjn@rosenet.net
Fri, 12 May 2000 11:46:07 -0700


Does anyone have wisdom to share on selecting relays for home-brew legal limit remote antenna switches? In particular, can anyone explain to me what an RF Relay is, as opposed to the common Power Relay?

Is there any reason that I can't use an off-the-shelf 30 amp power relay to switch RF?

Thanks!
***dan, N6BZA

The relays which we use in the Top Ten Devices boxes are 10 amp, sealed power relays. They are very small and have very low inductance. The contacts are connected to the base pins with wide conductors. I have run many power tests on these relays and the pc boards they are mounted on with temperature monitors and they will take full amateur power (+) to over 30 MHz. We rate our boxes conservatively at 1.5 KW. The part number is JW1FSN-DC12V. They come with several different brand names on them. Similar relays are being used by other manufactures of amateur boxes and they rate them variously at 3 KW and 5 KW.

George, W2VJN

Don Moman ve6jy@freenet.edmonton.ab.ca
Tue, 25 Jan 2000 17:36:33 -0700 (MST)


On Tue, 25 Jan 2000 K3SV@aol.com wrote:

> I am looking at some Potter Brumfield relays/switches to remotely switch in > loading at various antennas. At a KW output, what should the rating of the > contacts be on the PB relays? Will 5 amps be adequate? >

Maybe... but more is better. I have used the P&B type RKS-5DW-12 which are 16 amps at 277 vac. These are the exact same as used in the DX Engineering remote ant switch. I have homebrewed many antenns relays with these and zero problems. I also have used the much cheaper ($3 vs $9) Omron (I think) JS1-12v which are 10 amps at 125 vac. Again zero problems in heavy multi op contesting over several years.

73 Don
VE6JY


radio/relay.htm - 6 Dec 2004 - Jim Lux
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