Protection board(s) for transmitters.

[Radio Garfield]

Hi everyone. Hope You re fine.

I could not find here or anywhere else few free protection boards for our toys.

I am finally in mood for building one complete RIG but I would like to include protection boards in it, at least few basic ones, like SWR and temperature protection. Any additional circuit would be good because I would like to build really nice transmitter.

I bought some extra tools for this project so I would appreciate if someone is willing to share these circuits and give some advice cause I dont have much experience with protection circuits yet. I am slowly in progress, just like many of you guys were.

It is really nice to see all those LEDs and options on the panel of the transmitter and You know that you have protection for expensive devices inside.

I have one complete Elenos 150W BLF177 no-tune PA, power supply, PIRA stereo encoder, with its limiter-compresor-cliper unit, some analog and digital instruments for panel and some other stuff.

Exciter will probably be RDVV 5W with 2sc1971, suitable for this BLF177 PA.

So, my plan is to share the pictures and notes here, while project is in progress and after everything is complete, so it will be nice reference for future builders.

Many thanks in advance, hope that this will be nice mutual project!

[Sietedj]

Hi, I used this thermostat for the temperature and it worked well for me. I suppose there will be better circuits but this is simple and cheap.
A greeting!!!

[Radio Garfield]

Oh my dear God, this thing is only 2 USD! Interesting to try. Did You had any RF problems with it?
Thanks for tip.

[Sietedj]

I had no problem, I changed the cable and I put a compatible thermistor, it is not very aesthetic but it works.

[Radio Garfield]

Huh, the picture is small. Is that the sensor on the left side of that RD30 MOSFET?

[radio-berlin]

Google how to make a swr bridge.
It's just a strip on copper clad with parallel lines next to it to detect current direction
Here's a link here
http://213.114.137.49/use/vswr-00.htm

You can then use the swr bridge to drive a small transistor to adjust bias or to trigger a shutdown circuit such as a simple thrister powering a relay.

Another neat little way of making a swr bridge is to remove the plastic sheath off a short length of rg58 or similar, pinch up the braid slightly and push a length of wire down the inside so it runs parallel with the inner core, you can then solder components such as diodes resistor and caps at each end, that's how nrg once did it.

[sinus trouble]

Hello Mr Garfield!
I don't have SWR protection as such? But I do have SWR detection in my rig!
I have been meaning to sort something for a long time and a comparator would probly be the best option?
I think it would need some kind of latching switch circuit following the comparator? Eg transistor or relay?
Anyways heres my rig pics!

D coupler.png

LED pcb.png

LED ext.png

The LED circuit is basic and just a pair of BC547s to drive the LEDs! Probly not the best way to do things? but it is very sensitive, Loosening the plug socket on the antenna makes the Red LED light dramatically!

[Radio Garfield]

@radio-berlin and @sinus trouble . Hello folks, nice to hear You all. Thanks for replies and ideas.
There are some solutions on the web. Here is one: http://jugglingpirate.net/swr-protectio ... imple-way/

Also, I saw nice free project on web page of radio-amateur from USA and that seems to be real thing! His project is for 144MHz, but that is just what I had in my mind, one control board for everything!
To be honest, I did not read all the article yet but I am looking forward to see it! Have a look at this:

http://www.w6pql.com/amplifier_control_board.htm

[sinus trouble]

Nice examples Mr Garfield!
As with all problems there are many ways to solve them! The question is how far do you want to go?
The objective is to save your PA transistor in the event of fault conditions? which is the most effective?
SWR? Current? Bias? Over voltage? Temperature?? None are really fast enough to prevent failure!
I have had these thoughts going through my head a thousand times lol
SWR and temperature seem to be the best options but as I mentioned earlier? Once the protection has kicked in, there is nothing to sample? I would favour some kind of latch shutdown which can only be reset manually?
Just a thought lol

[shorty]

You can use an scr to latch the relay so the relay will switch from normally closed to normally open and cut off the the supply voltage to your transmitter, you can either put a push button reset to unlock the relay or shut down the main supply voltage to the tx to reset, a buzzer and led added to the normally open side off the relay will indicate when theres an high swr detected.

[Sietedj]

Huh, the picture is small. Is that the sensor on the left side of that RD30 MOSFET?

if right. Attached another photo.

[yellowbeard]

I see you have the directional coupler on the board for measuring the SWR - here is a simple circuit you could use with that:

Code: Select all

http://www.radioaficion.com/HamNews/articles/2265-swr-protection-circuit.html

[radio-berlin]

I see you have the directional coupler on the board for measuring the SWR - here is a simple circuit you could use with that:

Code: Select all

http://www.radioaficion.com/HamNews/articles/2265-swr-protection-circuit.html

Hi Yellow beard

That circuit will not work
It will need a thryristor or some kind of component that will latch on and stay on adding to it.
Because the last red led is the trigger for the relay, as soon as the relay energizes it will switch off the rig and swr will be ok again therefore turning off the red led again, it will then oscillate your transmitter on and off at high speed.
Now a may be wrong, if the LM3914 holds its lights on then it will work and you can ignore the above

[sinus trouble]

Haha Nice Mr yellowbeard!
Mr Sietedj? It looks like you already have VSWR protection and just added thermal control??
As Mr Shorty said too, A relay or transistor is easily configured to latch under fault conditions!

Again getting back to my point! The simple way of solving this problem is to use a PA that runs @ half its rated power! What is your aim? To a rig builder whos margins are tight and a dedicated pirateer this is simply uneconomical!!
Protection also can be too evasive? If a bird sh*ts on my antenna and it shuts down? Its no big deal lol! Others may find this a massive inconvenience??

[yellowbeard]

You are right but it still could be used with a latching relay.

[Sietedj]

Haha Nice Mr yellowbeard!
Mr Sietedj? It looks like you already have VSWR protection and just added thermal control??

Hello,
The SWR protection already included the transmitter circuit, I added the thermostat for temperature control.

[sinus trouble]

@ Mr Sietedj That's a neat little PCB, Am I right in thinking the relay is a single pole double throw?

@ Mr Garfield Would you be up for designing and building your own circuit? Or only go for a pre built kit type?
With the first option I think you could come up with a decent SWR detection/protection and even include a simple thermal sensor via thermistor!

[Albert H]

My PA boards have 10A FF fuses in their supply rails. There is a big thyristor across the supply rail that goes into conduction on high VSWR or high temperature and blows the fuse. The VSWR detection is done with the usual line going to the output socket, and the temperature sensor is an ordinary plastic-encapsulated NPN silicon transistor (I use a 2N3904). The detectors feed into an LM393 dual comparator. With a bad enough fault condition, the fuse blows and a red panel LED lights. We supply one spare fuse inside the case. We found that the user of the rig will take proper notice of a blown fuse!

We also run transistors at about 60 - 65% of their full rated output. A favourite 28V device is the Thomson-CSF SD1019, which is capable of as much as 160 Watts (at "pirate rating"), but we use them as 75 Watt drivers (or outputs on smaller rigs). They're virtually indestructible at 75 Watts, and we drive them with SD1013, which is also under-run. We have hundreds of these devices, and so designed a standard PCB which fits directly on to a Redpoint heatsink and includes the protection circuits. It makes for a rugged, broadband PA which doesn't need critical adjustments of match or bias. It's old-tech, but it's pretty bomb-proof!

[Radio Garfield]

Good day everyone. I am sorry for not responding or being active in discussion. I have some other stuff that took the priority so I have to solve them first. I read all the answer and posts that are here on topic so many thanks for it all.

@sinus trouble . Well, plan is to make my own kit. That can be some combination of several known stuff.

@Albert H . Thank you sir for another valuable help.

Hear you all again with new information as soon as I can. Stay well.

[Sietedj]

@ Mr Sietedj That's a neat little PCB, Am I right in thinking the relay is a single pole double throw?

Hi, if it's a single pole.
Here is information on how it works.
http://hobbycomponents.com/sensors/684- ... rol-switch