Using SMA transfer relays?

23cm, 2.4/3.4/5.7/10/24/47 GHz and above - antennas, propagation, operating, etc. Includes Optical communications, with light,
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Using SMA transfer relays?

Postby VK4GHZ » Thu Dec 27, 2012 12:42 pm

Hi all

I'm looking at using an SMA transfer relay to handle some 1296 MHz masthead switching.
It will switch a masthead PA in the path during transmit, and be "straight-through" in the idle NC state (ie; during RX).

I note that W6PQL uses a transfer relay in his 150W 23cm amp project.
Image

It appears that the PA input and output are connected together in the idle state.

Image

It necessitates removing power to actual amplifier, so as not to form an oscillator!
I am missing something here, or is this just the way it's done?

The alternative of course is to have two separate change over SMA relays... but I'm left wondering why W6PQL chose the transfer relay method.
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Re: Using SMA transfer relays?

Postby ZL1RS » Thu Dec 27, 2012 12:54 pm

... the bias would be off the PA during the RX condition?

... no bias, no gain, no oscillation?

Another nice Job Adam.

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Re: Using SMA transfer relays?

Postby VK3QI » Thu Dec 27, 2012 2:15 pm

Adam,

How much power are you running with your 1296 amp?

If it is in excess of 150watts, then you should consider using N type relays (either a DPDT (Transfer) or two SPDT N relays.

The SMA relays are reaching their limits on 1296 at 150 watts.

The query you have about oscillations does not come into it, as your PTT line that runs the relays will, no doubt, be switching the bias and/or the + supply voltage to the preamp or power amp.

For an idea about power ratings for the various types of relays, the following graphs are useful.

http://www.relcommtech.com and choose "typical characteristics"

and

http://www.dowkey.com/dowkey-catalog/00 ... ection.pdf page 8 Power Chart


Cheers

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Re: Using SMA transfer relays?

Postby VK3ALB » Thu Dec 27, 2012 4:11 pm

Adam,

Don't forget your RX preamp and consider the contact isolation of the relay you choose. For what it's worth I used a Tohtsu CX-520D which grounds the unused contact and offers around 40dB isolation at 1500Mhz. As long as you don't hot switch I reckon it's a good choice.

http://www.rfparts.com/coaxial/cx520d.html
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Re: Using SMA transfer relays?

Postby VK3AMZ » Thu Dec 27, 2012 5:22 pm

HI Adam

I'm not much of a forum user...... I noted the W6PQL approach to the transfer relay. Don't get too embroiled in it's function. He uses the transfer relay simply because it eliminates the use of two relays, one input the other output switching. I have a couple of type N style transfer relays I plan to use in a similar project to yours. Transfer relays have been shunned by the amateur populous simply because they usually operate of 24V and/or are latching type. If you look about you can find some very cheap units that are certainly up for the job. My relays came from a Radar unit which had a peak pulse power of 500 kW so they're are up for the job. SMA...they're a bit of a stretch.....you can use them but you can not hot switch, they'll fuse for sure. W6PQL has used them but only with a sequencer....

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Re: Using SMA transfer relays?

Postby VK3AMZ » Thu Dec 27, 2012 5:27 pm

Sorry typo 50KW peak impulse power

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Re: Using SMA transfer relays?

Postby ZL2BKC » Fri Mar 01, 2013 6:59 pm

Adam,

I have been meaning to add to this thread and have finally gotten around to taking some photos and capturing measurements to share.
At present I am partway thru the construction phase of a 150W W6PQL 23cm amp based on the XRF286 FET, and have been closely following some of the threads on the subject as there appears to be a number of people with similar plans afoot.

My ultimate plan is to parallel 2 boards together to achieve 300W and for obvious reasons I am not comftable using SMA relays for that power level which forced me to investigate options using type-N relays. I settled on a Type-N transfer relay model ARS-BPR-01N which is available on eBay.

At first I thought the relay was faulty as 2 of the connections could not be activated, but thinking more about the configuration it could actually be used to my advantage.
A picture is worth a thousand words:
Relay.JPG


As can be seen from the pictue ports J1 and J3 are never connected as per a classic transfer relay. The relay is labeled with "Opt: Non." which I suspect relates to this feature.
Using this specific realy if you connect the power amplifier stage across J1 and J3 you will not get the situation of connecting the PA output to the input as per the original concern. Yay!!!

Taking measurements on loss and isolation, this is a very good quality relay. Firstly the N connectors have gold contacts, and more importantly 6 point contacts for better contact. Isolation is better than 80dB (actually 90dB at 1296), with insertion loss better than 0.05dB - Note this was relative to my N-N thru adapter which I could not calibrate out of the network anayzer so the values should be considered closer to 0.1dB

ARS-BPR-01N Relay J2-J4 Open.gif
Isolation

ARS-BPR-01N Relay J2-J4 Closed.gif
ARS-BPR-01N Relay J2-J4 Closed.gif (10.17 KiB) Viewed 1169 times


For reference this is a picture from the outside:
DSC_9022.JPG


Ebay item #300618827064

73,
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Re: Using SMA transfer relays?

Postby VK3QI » Fri Mar 01, 2013 10:05 pm

Wayne,

I have a swag of those relays that I use in my masthead preamps for 1.2 and 2.4Ghz. As you say, they have excellent isolation. I usually use an adjustable 12 volt stepup voltage board and run them at about 23 volts.

To connect the preamps in circuit, I use N to sma adaptors (the preamps have SMA connectors) and the transmit connections are the normal N plugs.

Every so often, you will find one of those relays with a slighty different configuration with the J1 thru J4 switching , so it pays to test them before you use.

Thoroughly recommended for 1.2 and 2.4 Ghz. My preamp is switching 400watts on 1.2 Ghz and 200watts on 2.4Ghz (naturally with proper sequencers!)

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