Author Topic: signal relays (1khz - 1Mhz)  (Read 3491 times)

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Offline thefatmoop

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signal relays (1khz - 1Mhz)
« on: May 16, 2013, 07:18:01 pm »
I'm a bit at a loss on what relay to buy from digikey. I need a relay that will pass a 1kHz to 1MHz sine wave with low esr (no real design requirements, just lower is better). There's only about 100mA tops going throught it, and there arent any high speed switching requirements. The relay doesnt need to have an extremely long lifetime either. I would like something in a fairly small package.

Can someone point me to a good family of relays? I say family because i may need Single Pole Single Throw (spst), spdt, dpst, and dpdt
 

Offline KJDS

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Re: signal relays (1khz - 1Mhz)
« Reply #1 on: May 16, 2013, 07:36:56 pm »
I'd use the AGN series from Panasonic EW. They've only got the DPDT but there's no need to use all the poles, only need to buy one part type and they're a sensible price.

Offline mikes

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Re: signal relays (1khz - 1Mhz)
« Reply #2 on: May 16, 2013, 07:43:40 pm »
1 MHz doesn't need anything special. Something like the Omron G2RL or G6K would be fine.
 

alm

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Re: signal relays (1khz - 1Mhz)
« Reply #3 on: May 16, 2013, 09:04:12 pm »
Note that not all relays are designed for dry circuit (very low current) switching, as might be required for signal applications. Standard relays (with silver contacts) rely on arcing to remove oxide, and specify a minimum current for reliable operation. Gold contacts don't have this problem, but can only switch tiny currents (up to 10 mA or so). There are gold over silver relays, which can be used for both, but once they're used to switch larger currents, the gold is gone and they're no longer suitable for dry circuit switching.
 

Offline KJDS

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Re: signal relays (1khz - 1Mhz)
« Reply #4 on: May 16, 2013, 09:08:03 pm »
Note that not all relays are designed for dry circuit (very low current) switching, as might be required for signal applications. Standard relays (with silver contacts) rely on arcing to remove oxide, and specify a minimum current for reliable operation. Gold contacts don't have this problem, but can only switch tiny currents (up to 10 mA or so). There are gold over silver relays, which can be used for both, but once they're used to switch larger currents, the gold is gone and they're no longer suitable for dry circuit switching.

...and the expensive stuff has rhodium, titanium, tungsten and gold in many and various combinations.

Offline ejeffrey

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Re: signal relays (1khz - 1Mhz)
« Reply #5 on: May 16, 2013, 09:27:18 pm »
Reed relays are often used for signal switching.  They are hermetically sealed with an inert gas filler so the contacts don't oxidize.   I have used reed relays from hamlin and coto.  By far the most common are SPST-NO, but -NC and changeover contacts are also available.  I haven't seen DPDT reed relays, but digikey lists some from coto. Alternately you could just use two with the coils in parallel...
 

Offline thefatmoop

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Re: signal relays (1khz - 1Mhz)
« Reply #6 on: May 16, 2013, 10:38:27 pm »
thanks everyone! especially for the contact corrosion reminder.

I'm hoping to use a DDS to generate the sine wave. There are a bunch of libraries/sample code floating around for the AD9850 for Arduino. Noob question, but it can generate the range of frequencies i need without an issue right?

http://www.ebay.com/itm/New-AD9850-DDS-Signal-Generator-Module-0-40MHz-Test-Equipment-/170783661135?pt=LH_DefaultDomain_0&hash=item27c37fdc4f

http://www.ebay.com/itm/AD9850-DDS-Signal-Generator-Module-0-40MHz-IC-Test-Equipment-/400336533737?pt=LH_DefaultDomain_0&hash=item5d35eab8e9
« Last Edit: May 16, 2013, 10:41:16 pm by thefatmoop »
 

Offline lewis

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Re: signal relays (1khz - 1Mhz)
« Reply #7 on: May 16, 2013, 10:58:04 pm »
Matsushita/Nais TQ2 series is good too...
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Offline JackOfVA

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Re: signal relays (1khz - 1Mhz)
« Reply #8 on: May 17, 2013, 01:57:20 am »
I have several hundred NEC EB2-12NU (12 is the operating voltage, also available in other voltages) in customers hands where the relay dry switches microvolt level RF and have not had a single failure to date. Many of my preampifier products use it, as does my active antenna. And yes, I know they are rated at 10mV minimum DC voltage, but all I can say is they have proven to be extremely reliable switching radio signals.

These are inexpensive parts, available in surface mount and through hole, designed for the wire-line telephone industry. The through hole parts are the EA series and I have not checked recently to see if  they are still available.

The main problem with relays not specifically designed for RF is leakage through the open contacts - a good RF relay will have some internal shielding to minimize leakage.

But at the frequency range you are interested in, a pF or two leakage may not be important.

Plots below show the performance I measured of the EB2-12NU relay when used in the Z10080A RF switching board I sell. The first three plots show isolation of various contact configurations (the contacts are open) and the fourth plot shows the through loss when installed on a Z10080A board. The data is taken in a 50 ohm environment, so if you are switching high impedance circuits, the effect of a couple pF leakage capacitance will become more important. http://www.cliftonlaboratories.com/z10080a_bypass_relay.htm for more information on the switching board.

 


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