A FOOLPROOF ANTENNA SWITCH

Useful information regarding antennas for SDR products.
glovisol
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Re: A FOOLPROOF ANTENNA SWITCH

Post by glovisol » Tue Nov 20, 2018 11:04 am

It really depends if you are using (A) one antenna to feed the three Inputs of the RSP inputs, or if you are using (B) a different antenna for each input.

In case (A) only one switch is required and you could find useful information here:

https://www.sdrplay.com/community/viewt ... f=5&t=3723

In case (B) you should use one switch for each antenna input.

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Gene_50
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Re: A FOOLPROOF ANTENNA SWITCH

Post by Gene_50 » Sat Jun 08, 2019 1:00 am

I really like this...it appears someone went to the effort to mak a circuit board...is it available??

thanks, Gene
Last edited by Gene_50 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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glovisol
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Re: A FOOLPROOF ANTENNA SWITCH

Post by glovisol » Sat Jun 08, 2019 6:10 am

Gene,

I bought the relay complete with its small PC board on ebay, obviously made in China. Probably you can find one there as well!

glovisol

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Ian1951
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Re: A FOOLPROOF ANTENNA SWITCH

Post by Ian1951 » Fri Jun 28, 2019 12:03 pm

W0QE has a page devoted to tests he made on using small relays for RF.
https://www.w0qe.com/Technical_Topics/s ... at_rf.html

The "take away" is most relays and switches are designed to have current flowing through them and dry switching, with no current, often results in premature failure. We saw quite a few failures back when business band mobile transceivers used mechanical relays when well intended technical people repaired equipment and used a relay that looked OK but did not have gold plated contacts. The relays worked just long enough to cause confusion.


I tried to PM you but I haven't posted enough to have send PM privileges, such is life.
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glovisol
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Re: A FOOLPROOF ANTENNA SWITCH

Post by glovisol » Fri Jun 28, 2019 2:18 pm

I think I have hallucinations here..... one hour ago I saw a post by Ian1951 warning about dry relay contacts (not the case here) and I wished to reply and now........ZIP BANG the post has disappeared! Must be the heat playing tricks on me: I have 39 °C around me and the air out of the cooling vent of the PC must be over 60°C: better switch off!

glovisol

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glovisol
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Re: A FOOLPROOF ANTENNA SWITCH

Post by glovisol » Fri Jun 28, 2019 7:34 pm

Well, now the post by Ian1951 after misteriously disappearing, has re-appered and I can reply.

The problem of dry contacts becoming insulated in the long run is caused by oxidation. In relays switching small or negligible currents and exposed to the atmosphere, this used to be a serious problem in the fifties and sixties of last century and still is a problem if the contacts are not insulated from air.

The encapsulated relays shown and tested in the reference proved to deliver excellent and faultless service because the danger of contact oxidation is eliminated. The relay I used in my switch is of the encapsulated type, so this danger is not present.

But, apart from this, my foolprof antenna switch may handle RF current that can approach one amp when switching transmitter power, so once again there is danger of contact burnout for too much current...e.g. the other way around.

glovisol

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Ian1951
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Re: A FOOLPROOF ANTENNA SWITCH

Post by Ian1951 » Mon Jul 01, 2019 12:32 pm

I am not trying to start an argument, I am just trying to provide forum members all the information I have.

RCA was the first commercial twoway radio manufacturer to experiment with sealed relays with plastic cases that didn't use either gold or palladium plated contacts.

The "technical brief" that accompanied replacement relays said something to the effect that "volatile and aromatic hydrocarbons released from the plastic case caused contact corrosion."

I do know I worked 80 hours a week for month either repaired RCA radios that had failed or replacing the relays in RCA units before they failed.

It is interesting to note the transmit chain was unaffected, only the receive chain. I talked to a RCA "product support engineer" and he explained the RF current in the transmit chain was sufficient to keep the relay contacts clean, but the lack of appropriate current in the receive chain allowed the corrosion to build up.

It might also be useful to not there are two different type "sealed" relays, those sealed against flux, and those that are "seal" sealed. I suspect those sealed against flux are liquid tight but not air tight.

There is a third type relay that is hermetically sealed. These have metal cases with glass or ceramic "beads" where the wires leave the case. Motorola used these in some of their aviation transceivers. The units I saw looked like a transistor in a TO5 case with 8 leads. The FAA required factory training and certification for repair technicians.

I am not an engineer, much less a chemical engineer, but I suspect modern plastics still produce "volatile and aromatic hydrocarbons" that can result in contact corrosion.

The Panasonic Relay technical sheet at https://www.panasonic-electric-works.co ... mation.pdf
has several cautions about dry circuits

The IEEE has a nice paper on relay case outgassing and the effect on relay contacts, unfortunately you either have to be a member or have access to a good library, https://ieeexplore.ieee.org/document/113015

I have seen sealed relays fail in an audio switching matrix. Our church has a custom designed and built audio distribution system that uses about two dozen sealed Panasonic relays.

To be fair I don't know if they were truly sealed or only sealed against flux, since they were plug in, I suspect they were fully sealed, but I don't know.

The warranty lasted a year and a few months after the warranty ran out the relays started acting odd. Sometimes they'd carry line level audio, sometimes they wouldn't, you could switch back and forth betweens sources and generally get the relay to pass audio.

I was asked to take a look and I made a jig that exercised the relay, a NE555 and transistor switched the relay on and off ~once a second and feed about 100mA through the contacts, 12V supply with a 120 ohm resistor feeding the common with the NC and NO both grounded. I let each relay run for about 5 minutes, and this "cleaning" restored the ability to switch line level audio and bought me enough time to convince the business manager to replace the relays with units from the same manufacturer, Panasonic, with relays that had the same form factor, but had gold plated contacts.

We were very lucky the relays were plug in. The idea of desoldering 24 relays in a tight electrical case gives me nightmares.
I will add the sockets the relays plugged into were gold plated and the replacement relays with gold plated contacts also had gold plated plug in contacts.

I've concentrated on gold, but platinum, palladium and other members of the platinum family are also used because the entire platinum family is chemically inert like gold.

To be fair, the relay matrix is in a non climate controlled utility room. The temperatures here in Western Kentucky vary from -20F to +110F [-29C to 43C]with a relative humidity of 90%. It's 95F with a relative humidity of 87% right now and it's only 11:30AM.

The news is running stories on how hot it is in France and Italy, sort of once a lifetime event. We routinely hit 100F every summer for several days in a row from mid July through the first of September. Then we have 3 months of sane weather and the cold rushes in.

I'm certainly no saying "Don't use relays with gold plated contacts in dry circuits." I am saying "You might want to keep relay failure in mind just in case your receiver suddenly goes deaf."

The W0QE relay page addresses some concerns when using non-RF relays for transmit purposes that might be worth a read.
Last edited by Ian1951 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Mike2459
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Re: A FOOLPROOF ANTENNA SWITCH

Post by Mike2459 » Mon Jul 15, 2019 4:48 am

After reading the reference material provide by Ian1951, IMO the title of this post should be changed to 'A Fool's Antenna Switch'. And yikes, hanging this switch from the SMA connector of the radio's plastic case sends chills up my spine.

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glovisol
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Re: A FOOLPROOF ANTENNA SWITCH

Post by glovisol » Mon Jul 15, 2019 6:52 am

After reading the reference material provide by Ian1951, IMO the title of this post should be changed to 'A Fool's Antenna Switch'. And yikes, hanging this switch from the SMA connector of the radio's plastic case sends chills up my spine.
Mike,

I do not know why one should hang the switch directly from the RSP SMA connector. Coaxial cables are readily available. Or why hanging it anyway should provoke chills up the spines of the beholders (a new type of air conditioner, maybe?). The reference material by "departed" Ian1951 has no bearing at all on the matter at hand, as I have explained already and is on par with the now self-eliminated, torrential posts about lightning dangers on USB cables by another "departed" guy, namely Nullouser00. In fact if you carefully read the referenced page by W0QE, you realise that indeed encapsulated relays are immune from the dreaded effects described by Ian1951.

Apart from this, it is evident that, declaring that several participants of this thread, who contributed to its development and the undersigned are "fools", is just the way to try and provoke another unnecessary and damaging crisis thread based on nothing.

Please stop this, nobody is hating you and as Tech_Support has reiterated many times, we are here to share and help each other, not to fight....

Gianfranco

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vk7jj
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Re: A FOOLPROOF ANTENNA SWITCH

Post by vk7jj » Mon Jul 15, 2019 9:47 am

Mike2459 wrote:
"General Purpose relays are just that general purpose."
Hi Mike, making generalisations tells us nothing at all about any particular relay.

The relay pictured is not an unbranded unkown it is branded "Songle" and is said to be sealed.

Have you had a go at finding the specs of that relay and telling us whether or not it is suitable in your view?

There are very many Songles about, I use them for a range of purposes as they are widely available with various on-board low level drivers suitable for the Raspberry Pi control systems I build, they are outdoor systems so I was happy to see know they were sealed but I to what degree I don't know.

And as Ian hinted, it appears gold contacts are not necessarily as worthwhile as they might sound, eg. I found a few comments in this article interesting:

https://www.findernet.com/en/unitedstat ... -it-matter

Regards, Phil

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