Stripline SWR, how ?

Well that shouldn't be a too big problem with the help of a simulation package. You need a directional coupler with some directivity over a certain bandwidth. Until it does what you want, the effort and pcb cost... you possibly rather buy one. Have a look at the directional couplers at minicircuits.

Rene

My advice is to see if anyone has already done it commercially. If the vendors of directional couplers and packaged filters aren't using stripline at these freqs and power levels, ask yourself why before investing lots of time in it.

At 300W, even tiny losses will generate lots of heat. An (exceptional) directional coupler with only 0.1 dB loss will dissipate 7 watts.

Stripline at 144 MHz is going to be pretty large. Do you know how much heat is present in the frequencies you have to filter out? With a 300W fundamental, its possibly many watts heating your filter components.

Steve

Thanks,

You maybe right... It's perhaps easy to build an outboard directional coupler and not use the PCB technic... I have a transverter with a PCB stripline SWR meter but i have only 25W runing in it... What i need are the dimensions of the traces with FR4 PCB...

Thanks anyway,

Patrick

Try this:

Steve Roberts

Here is some math background to design a stripline directional coupler:

IIRC this commercial SWR meter uses stripline coupling:

As Steve has said, make sure you don't cook your board material.

Regards, Joerg

Hello Rene,

But not at that power range. If they offered that I could have funneled quite some sales in their direction.

Regards, Joerg

My suggestion would be to get a copy of the following:

The ARRL handbook The UHF experimenters handbook The ARRL antenna handbook

One of these will have directions for an SWR meter at your freq and power range.

Another suggestion I have is to forget about stripline and use microstrip using G-10 glass epoxy. 50 ohms is about .1 inch in width. Real easy to do with an exacto knife.

Trying to do it using coax might work, but is a lot more trouble than microstrip..... stripline isn't that much harder, but microstrip will work just fine, and you can see stuff......

Good luck. It's been done before by people with less brains and you should have no trouble if you just look around first...

Andy W4OAH in Eureka, Texas

Hi All,

Perhaps did i use the wrong term stripline instead of microstrip ...

Google gave me more results using microstrip and i've found some infos. Btw, i have a 300W amplifier which seems to use ordinary FR4 PCB, so i'm quite confident that i will not cook my board ! The only problem is to find the right dimension to have a 50 Ohm line and the right coupling. Thanks for the answers.

Greetings,

Upon thinking a bit longer about the subject, I think the stripline coupler should have dimensions longer than the wavelength. Even with an epsilon of

But I remember an application note at minicircuits about doing yourself coupler.

Rene

I didn't really have a look at their bigger parts.

Rene

The "right coupling" is not particularly important. There is no right coupling, you are measuring ratios, not absolutes. Good directivity is more important.

Hi All,

You're right ! Directivity is the most important.

I used a Minicircuits directional coupler to measure return loss, but it can't handle power...

I've found a nice page with descriptions of what i'm looking for ! Will try to see if it does not cook.... Why should it ?

Here the link :

Patrick