EMRFD Message Archive 4271
Message Date From Subject 4271 2010-02-17 09:01:34 david_c_partridge Newbie question on RF relays, attenuators and substrates I have an application that requires two 20dB attenuators in conjunction with a couple of RF magnetic latching relays to switch them in or out of circuit.
The intent is to achieve no attenuation, 10x or 100x. Input signal level (50 ohm impedance) to the attenuators is between -2dBm (0.5Vp-p) to about +19dBm (5.5V p-p) maximum. So the attenuators don't need to handle much over 0.6W
The initial frequency range I'm concerned with is DC to at least 500MHz, but flat to >2GHz (or better) would be preferable.
The system it will be used in supplies a short pulse of about 7mS of either (I think) +12V or -12V to select which way the relay switches. The relays in the unit I'm trying to replicate are twin coil types, but I don't think that's crucial. There is no other non-signal voltage available.
I'm looking for recommendations for the best choice of (probably) surface mount relays and attenuators. Price is a concern as some RF relays seem to be extremely expensive.
I'm also concerned about choice of substrate - I've heard conflicting views on whether 0.8mm FR4 is OK once you get above 1GHz.
4272 2010-02-17 09:07:28 Matt Palmer Re: Newbie question on RF relays, attenuators and substrates If you want flat to 2GHz you better let price go as a concern.
sent from my VIC-20
4273 2010-02-17 09:28:31 David C. Partridg... Re: Newbie question on RF relays, attenuators and substrates Fair comment, so let me set some boundaries:
USD20 expensive I can handle, USD300 expensive I can't.
4274 2010-02-17 09:46:12 Matt Palmer Re: Newbie question on RF relays, attenuators and substrates The attenuators are easy pie, you can make your own, or at least you should,
if you want a cots part minicircuits should have you covered. For the
relays, I usually go with that microwave outfit in korea (name is escaping
me at the moment). $20 for relays is going to be tricky.. especially if you
are buying in low quantities. For such low power you really want the mercury
sent from my VIC-20
4280 2010-02-18 05:55:36 David C. Partridg... Re: Newbie question on RF relays, attenuators and substrates >The attenuators are easy pie, you can make your own, or at least you shouldWell, maybe, but you end up with the following oddball resistor values (yes
I do understand
4287 2010-02-18 13:22:36 Tim Re: Newbie question on RF relays, attenuators and substrates 4288 2010-02-18 14:31:54 David C. Partridg... Re: Newbie question on RF relays, attenuators and substrates >You're gonna have to explain what accuracy "high accuracy" is.Plus/minus 1% would be good given the error budget in other items. Overall
output level error should be [+1.5%, -3%] across the entire system including
the levelling circuit which I believe to be good for [0%, -2%] up to at
So if I'm getting 5Vp-p out of the output side of the levelling detector
(just before the attenuators) and both attenuators are switched in, the
output had better be be 50mVp-p as near as can be measured. 1dBm variation
just doesn't cut it.
Sorry this isn't strictly "EMRFD" - I was pointed here as a location where
I'd likely find the RF gurus.
The application isn't quite your normal transmitter, it's an amplitude
calibration system for 'scopes, hence the tight error budget on the
4290 2010-02-18 20:21:49 Pat Villani Re: Newbie question on RF relays, attenuators and substrates Would these meet your needs:
They are available from Digikey.
4292 2010-02-19 03:01:46 David C. Partridg... Re: Newbie question on RF relays, attenuators and substrates Pat
Thanks for the pointer, the 0.3dB tolerance is a little wide, but they might
do the job. 5.5Vp-p = 1.94Vrms so we're talking about less than 0.1W, so
the power rating of shouldn't be a problem for the PAT1220 or larger parts.
Digikey don't actually seem to stock the PAT3042S 20dB parts, only the
PAT0510 and PAT1220 parts which go to a maximum of 10dB, but 2 10dB parts in
series would probably do the job.
The price is good too at about 70 pence (about USD1.15) each after tax.