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Stripline SWR, how ?

T

tk5ep

Jan 1, 1970
0
Hi,

I want to make a stripline SWR meter on a PCB that could handle 300W @
144 MHz. This SWR will be followed by a lowpass filter also made on the
PCB.

No need for great accurary, it's intended to detect a high SWR and
shutdown a supply.

Has anyone an idea on howto ?

Thanks,
 
R

Rene Tschaggelar

Jan 1, 1970
0
tk5ep said:
Hi,

I want to make a stripline SWR meter on a PCB that could handle 300W @
144 MHz. This SWR will be followed by a lowpass filter also made on the
PCB.

No need for great accurary, it's intended to detect a high SWR and
shutdown a supply.

Has anyone an idea on howto ?


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
 
S

Steve Burke

Jan 1, 1970
0
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
 
T

tk5ep

Jan 1, 1970
0
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
 
tk5ep said:
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:

http://www.hp.woodshot.com/

Steve Roberts
 
J

Joerg

Jan 1, 1970
0
tk5ep said:
Hi,

I want to make a stripline SWR meter on a PCB that could handle 300W @
144 MHz. This SWR will be followed by a lowpass filter also made on the
PCB.

No need for great accurary, it's intended to detect a high SWR and
shutdown a supply.

Has anyone an idea on howto ?

Here is some math background to design a stripline directional coupler:
http://atlc.sourceforge.net/determine_dimensions_of_couplers.html

IIRC this commercial SWR meter uses stripline coupling:
http://www.mfjenterprises.com/man/pdf/MFJ-864.pdf

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

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Rene,

Have a look at the directional couplers at
minicircuits.

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

Regards, Joerg
 
A

Andy

Jan 1, 1970
0
Andy writes:

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
 
T

tk5ep

Jan 1, 1970
0
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,
 
R

Rene Tschaggelar

Jan 1, 1970
0
tk5ep said:
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.

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
4, it still will be large.

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

Rene
 
R

Rene Tschaggelar

Jan 1, 1970
0
Joerg said:
Hello Rene,



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

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

Rene
 
W

Wes Stewart

Jan 1, 1970
0
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.

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

vk5ajl

Feb 1, 2010
8
Joined
Feb 1, 2010
Messages
8
Have a look at http://vk5ajl.com/projects/swrmeter.php

For 1.6 mm thick PCB meterial (standard) centre micro-stripline needs to be 6mm wide to maintain 50 ohm impedance through the meter. At 144MHz it needs to be only 50mm long to get plenty of signal at 1/2 watt. (SWR is independant of power). If you leave it in circuit at 300w, you will have to attenuate the signal heaps. At 1.5 mm spacing between centre conductor and pickup strips it will handle 2 kilovolts, plenty enough for your 300w.
 
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