BATC Forum

I'm following the 5.8GHz builds in the magazine and have acquired a couple of parts myself: a transmitter capable of 750mW, a receiver, and soon to be an antenna to use on both systems. I may also add an amplifier to get up to 3-4w in the future. Goal is to try some wideband FM and digital ATV while chasing some grids. The builds often discuss using panel antennas, but I'm opting for higher gain to try mountaintopping.

But because the transmitter and receiver are separate, all they have right now is the rubber duckie vertical antennas that both came with. I'd like to changes these to a panel for experimentation, but eventually go to a dish feed. But rather than buy 2 dishes just for one station, I'd like to feed it to run both the transmitter and receiver off the same dish.

I've been nudged to look at SMA coax relays and these seem great. But I have no familiarity with these.

As I understand it, some relays switch back and forth when a certain voltage is applied (say, 28V, but there are many other voltage ones I see also). And others use some other type of technology to toggle between the transmitter and receiver.

So, not familiar with relays, I see some that go as high as 10GHz, 20GHz, etc.

A couple of questions:

1) How do I know which one to get
2) How do I get it to switch back and forth between the units (turn off the transmitter and turn on the receiver? apply 28V to get it to switch over? something else? does it stay on this feed until I hit it with 28V again to switch it over? Do I need to continuously supply 28V to keep it on 'this one' and the lack of 28V kicks it back over to the other?)
3) What is the typical current draw of these coax relays?

My thought was to put batteries in series to get to the right working voltage. But not sure if batteries would give enough current to be able to run the relay, switch it over, etc.

In the meantime I may get some panel antennas since they aren't overly expensive--but the gain is 'only' 14dB. Better yagis aren't hard to find around 20dB and dishes (but usually with N-connectors) are around 27-30dB.

I'll end up building two stations ultimately, so I can operate it mobile and have someone with a working setup to also work mobile. So really don't want to buy 4 dishes or run low gain panel antennas if I don't have to.

Thanks, K3RW

K3RW wrote: ↑

Sat Feb 03, 2018 8:19 am

A couple of questions:

1) How do I know which one to get
2) How do I get it to switch back and forth between the units (turn off the transmitter and turn on the receiver? apply 28V to get it to switch over? something else? does it stay on this feed until I hit it with 28V again to switch it over? Do I need to continuously supply 28V to keep it on 'this one' and the lack of 28V kicks it back over to the other?)
3) What is the typical current draw of these coax relays?

That's more than a couple of questions.

I suggest you make contact with your local microwave club. Google tells me you are in Vancouver, WA which means you are not that far from Seaside Oregon where there is a very good hamfest coming up. I mention this because I have purchased the sort of relays you are looking for from there in the past.

The ones to get are ones like these https://www.surplussales.com/Images/Rel ... a-b_lg.jpg and they ought to be $20-$30. There are many similar ones available. Often on Ebay e.g. Item 183051710508 appeared just now and is a 12V SMA relay for $30. The guy has 7 and at that price he won't have for long. Don't be put off by it being a latching Relay, W6PQL does a PCB kit to deal with that. You will need logic to do the switching anyway unless you just use a toggle switch.

Normally, the non latching ones are just like a 12V DC relay with normally open and normally closed ports. Latching relays have the same ports but are bistable and don't need power once switched. If its a conventional relay and 28V don't worry, GM3SEK has a little PCB that will allow you to use them from 12V.

Current varies with coil voltage but a few 100mA.

Mike

As above, the relays shouldn't be too difficult to source. I got this 18GHz one from a Rally last weekend for £20. (about $25), nearly all the ones I saw were 28V, that seems to be the standard (odd voltage.. anyone?).
I haven't had time to play just yet so I'll find out what voltage will be needed to throw it over and I'll probably cheat and simply add an extra small battery (or two) trickled into a Capacitor which can be used to provide a -16V supply (to the common pin) while 12V is applied to the switching pin.

The way the changeover contacts work is shown on the side, It seemed sensible to add a tiny 2W 50R SMA dummy load to the empty pin, which will be connected to the Txmtr during Receive and to the Rxcvr during Transmit.

On this one there are also some extra contacts which will indicate the actual position of the relay contacts, 1 side might also be used to trigger the power to the Txmtr which will add a small mechanical delay after the RF contacts change to Tx.[/color

In case anyone wasn't aware, the style of relay pictured above in Wolfie's post is known as a transfer relay.
It's probably worth keeping an eye on eBay for these, and for 3-port 'changeover' relays as they do often appear in voltages other than 28V. I managed to pick up a handful of 8V ones - which are great as you only need a series resistor for 12V operation - and I have seen both 12V and 6V ones over the last 12 months.
There are various designs for generating '28V' from a 12V supply, so that isn't a problem, and as for pulse driven (latching) relays, probably any pulse width between 10ms and 100ms will do the job.

Thanks everyone for the replies. I'm getting quite an education on relays and sequencers. A lot of it is beyond my current level but I'll get there.

Ultimately I'll may use a switch to prevent problems. There may be a possibility that running a 3-4w amp next to the receiver could overload it since I'll be trying to keep the kit relatively compact. Future goal is to run a big gain dish for it, and I'll have to double everything in the station kit to have one as a fixed kit, and a rover, for chasing 5 grids on 5.6GHz. The terrain makes in manageable here but its still a challenge.

g0mjw wrote: ↑

Sat Feb 03, 2018 8:57 am

K3RW wrote: ↑

Sat Feb 03, 2018 8:19 am

A couple of questions:

1) How do I know which one to get
2) How do I get it to switch back and forth between the units (turn off the transmitter and turn on the receiver? apply 28V to get it to switch over? something else? does it stay on this feed until I hit it with 28V again to switch it over? Do I need to continuously supply 28V to keep it on 'this one' and the lack of 28V kicks it back over to the other?)
3) What is the typical current draw of these coax relays?

I suggest you make contact with your local microwave club. Google tells me you are in Vancouver, WA which means you are not that far from Seaside Oregon where there is a very good hamfest coming up. I mention this because I have purchased the sort of relays you are looking for from there in the past.

Mike

Thanks for that. I haven't made it to SEAPAC yet but I go to Rickreall in Febuary each year. I'll try to get to the big one in Puyallup as well.

Yep, despite a 3 area call I'm just outside Portland, Oregon on the Washington side. We don't seem to have a microwavers club locally but there are a few people in the Pacific NW VHF Society that do microwave--albeit its almost all transverters and weak signal stuff. I'm only using FM TV as a cheap way to get on the band. Ideally I too would get a decent transverter and fire away. But if I can grid hunt 5 grids, I doubt I'd do better with a transverter here due to geography.

Are you in the Pacific NW?