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Maximum Power using FR4 board ?

simonchettle
 

This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 
 
I am thinking of combining two power amplifiers each of circa 100 W  O/P. 
 
 
Cheers
 
 
Simon
 
G8ATB
 

Murray Niman
 

Lots more if you happen to use 1oz copper clad, rather than the more usual 0.5 or 0.25oz

73

  Murray

Gordon REASON
 

If .............. you have a good load , 100 W should be ok .............

Some years back I made and  testee , low power , a 2,7 Ghz coupler .

The customer put 400 watts through it , and it melted ...............!

On 14 June 2019 at 17:56 simonchettle <simon@...> wrote:

This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 
 
I am thinking of combining two power amplifiers each of circa 100 W  O/P. 
 
 
Cheers
 
 
Simon
 
G8ATB
 


 


 

John Worsnop
 

So much depends on where the line is in the circuit, the dielectric thickness and the type of FR4. At RF, not all FR4 is the same! The thing is the the power density in the dielectric. The reason I used low loss RF35 in my 45W pa was the original FR4 version cooked the output line. In contrast, designs by  Goran AD6IW I've seen work perfectly well at similar powers. That may of course just be a reflection on Goran's design skills compared to mine!

Stick to proper microwave materials for power if you can.

73 John

On Sat, 15 Jun 2019, 01:01 Gordon REASON via Groups.Io, <gordonj.reason=virgin.net@groups.io> wrote:

If .............. you have a good load , 100 W should be ok .............

Some years back I made and  testee , low power , a 2,7 Ghz coupler .

The customer put 400 watts through it , and it melted ...............!

On 14 June 2019 at 17:56 simonchettle <simon@...> wrote:

This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 
 
I am thinking of combining two power amplifiers each of circa 100 W  O/P. 
 
 
Cheers
 
 
Simon
 
G8ATB
 


 


 

John Quarmby
 

I found 50W of 1296MHz through a 50 ohm stripline on FR4 cooked the board and discoloured it over time. Why not use suspended microstrip with air dielectric, that would avoid the problem entirely at any reasonable power level.

73

John G3XDY 



Sent from my Samsung Galaxy smartphone.

-------- Original message --------
From: John Worsnop <johnworsnop@...>
Date: 15/06/2019 08:28 (GMT+00:00)
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Maximum Power using FR4 board ?

So much depends on where the line is in the circuit, the dielectric thickness and the type of FR4. At RF, not all FR4 is the same! The thing is the the power density in the dielectric. The reason I used low loss RF35 in my 45W pa was the original FR4 version cooked the output line. In contrast, designs by  Goran AD6IW I've seen work perfectly well at similar powers. That may of course just be a reflection on Goran's design skills compared to mine!

Stick to proper microwave materials for power if you can.

73 John

On Sat, 15 Jun 2019, 01:01 Gordon REASON via Groups.Io, <gordonj.reason=virgin.net@groups.io> wrote:

If .............. you have a good load , 100 W should be ok .............

Some years back I made and  testee , low power , a 2,7 Ghz coupler .

The customer put 400 watts through it , and it melted ...............!

On 14 June 2019 at 17:56 simonchettle <simon@...> wrote:

This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 
 
I am thinking of combining two power amplifiers each of circa 100 W  O/P. 
 
 
Cheers
 
 
Simon
 
G8ATB
 


 


 

Chris Bartram G4DGU
 

My, perhaps slightly jaundiced, view is that although fully characterised FR4 from a decent manufacturer with 1oz copper is capable of handing a couple of hundred watts in amateur applications at 1.3GHz when used for microstrip circuitry, there are better ways. John, 'XDY, gets part of the way to the solution I'd use.

That is to forget microstrip! It is a useful transmission line medium for applications which are intended for some form of production, and with care and understanding, can be made to work adequately for many low-power applications - even using FR4 - up to 10GHz. However, as a way making a one-off power hybrid, it's a poor use of the available technologies.

If I wanted to make a combiner for a couple of power amplifiers for 23cm, I'd use air stripline. In fact I've done it, and they are sitting on a shelf waiting for me to find time to get around to putting a decent 1.3GHz system on the air. Stripline, where a conductor is suspended between two ground planes, is capable of very much lower losses than any comparable microstrip design.  My 90degree hybrids use a pair of lines parallel to each other along their broad faces, and each each offset from the centre line of the sandwich. The design equations are relatively simple, and unlike microstrip are not approximations. Unfortunately, I don't think any of this has been published recently in the amateur literature. The classic book on the subject is Harlan Howe's 'Stripline Circuit Design'. That should be available in most decent engineering libraries. The maths which Howe uses isn't intimidating, and as the book was written before the age of the PC, there are a lot of design nomographs. I have a copy, but I don't currently have time to write anything further, however I'm sure that there are others here who could produce an article for 'Scatterpoint' summarising the design method.

73 and enjoy MMRT!

Chris

G4DGU

_._,_._

Neil Smith G4DBN
 

Hi Simon, if you need some metalbashing doing to make a stripline combiner, I would be happy to help with the fiddly bits. Drop me an email to neil@...

Seems sad to have to compromise your design for the sake of getting a bit of machining done.

Neil G4DBN

Simon wrote:
This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 

KENT BRITAIN
 

Are you looking for a 2 way or a 4 way?    I just picked up a dozen commercial 4 way power dividers.  Kent



On Sunday, June 16, 2019, 1:29:31 PM CDT, Neil Smith G4DBN <neil@...> wrote:


Hi Simon, if you need some metalbashing doing to make a stripline combiner, I would be happy to help with the fiddly bits. Drop me an email to neil@...

Seems sad to have to compromise your design for the sake of getting a bit of machining done.

Neil G4DBN

Simon wrote:
This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ? 
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider. 

simonchettle
 

Hi  All
 
Many thanks for the comments and advice.
 
Kent – It’s a 2 way splitter (Shame) but thanks for the offer.
 
Chris – Yes I vaguely remember building an air strip line back in the 70s and had all the maths – long since lost after several moves.  However that is the route I will probably take.
 
73s
 
Simon
 
 
 

From: KENT BRITAIN
Sent: Sunday, June 16, 2019 8:00 PM
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Maximum Power using FR4 board ?
 
Are you looking for a 2 way or a 4 way?    I just picked up a dozen commercial 4 way power dividers.  Kent
 
 
 
On Sunday, June 16, 2019, 1:29:31 PM CDT, Neil Smith G4DBN <neil@...> wrote:
 
 
Hi Simon, if you need some metalbashing doing to make a stripline combiner, I would be happy to help with the fiddly bits. Drop me an email to neil@...
 
Seems sad to have to compromise your design for the sake of getting a bit of machining done.
 
Neil G4DBN
 
Simon wrote:
This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ?
 
Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider.

Neil Douglas
 

Simon,

 

Try this

 

https://www.qsl.net/g0ruz/dj9bv_23cms.htm

 

its fairly simple metal bashing.

 

also

 

W6PQL has 500W ones on Rogers substrate.

 

 

&3

 

NeilD G4SHJ

 

 

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> On Behalf Of simonchettle
Sent: 17 June 2019 16:22
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Maximum Power using FR4 board ?

 

Hi  All

 

Many thanks for the comments and advice.

 

Kent – It’s a 2 way splitter (Shame) but thanks for the offer.

 

Chris – Yes I vaguely remember building an air strip line back in the 70s and had all the maths – long since lost after several moves.  However that is the route I will probably take.

 

73s

 

Simon

 

 

 

From: KENT BRITAIN

Sent: Sunday, June 16, 2019 8:00 PM

Subject: Re: [UKMicrowaves] Maximum Power using FR4 board ?

 

Are you looking for a 2 way or a 4 way?    I just picked up a dozen commercial 4 way power dividers.  Kent

 

 

 

On Sunday, June 16, 2019, 1:29:31 PM CDT, Neil Smith G4DBN <neil@...> wrote:

 

 

Hi Simon, if you need some metalbashing doing to make a stripline combiner, I would be happy to help with the fiddly bits. Drop me an email to neil@...

 

Seems sad to have to compromise your design for the sake of getting a bit of machining done.

 

Neil G4DBN

 

Simon wrote:

This is  a simple question what is the maximum power anyone would risk using a 1/4 length strip line on FR4 on 23cms ?

 

Why because my metal working tools and skills are close zero and I am thinking of building a Wilkinson divider.