It is currently Sat Aug 08, 2020 2:50 pm

Click the link below to visit the site sponsor

The Ham Radio Shop




Post new topic Reply to topic  [ 13 posts ] 
 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post high swr
Hello Steve.

I have made several balun s over time but never really checked them, just built them to spec and used.

I have made 2 ,1 to 1 this weekend with 240 by 43 ferrite with 10 turns and on testing i find that into a 50 ohm load there is a 4 to 1 swr.
from 160 to 28 megs.

Every thing I have ever read on the subject implies no insertion loss, but with that swr there must be?

They are so simple to make that i can't see where I could have made a mistake in building them? so is this swr correct?
All the diagrams that I have looked at had a level swr.

puzzled oap.
don


Mon Mar 16, 2015 7:09 pm
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
Did you wind with coax or a bifilar pair?

Steve G3TXQ


Mon Mar 16, 2015 9:08 pm
Profile Send private message WWW

 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post Re: high swr
with a pair Steve, I assume that the difference in impedance is causing the swr?
don


Tue Mar 17, 2015 11:01 am
Profile Send private message

 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post Re: high swr
I would add that the feeder (450) comes into the house and the balun is connected directly to the rear of the atu, no coax.
don


Tue Mar 17, 2015 11:04 am
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
If the characteristic impedance of the winding is not 50 Ohms, you can't expect to measure 50 Ohms at the input with a 50 Ohm load connected across the output.

But for use between a tuner and ladderline that doesn't matter at all!

Having said all that I wouldn't have expected such a big effect at the lower frequencies where the winding length is just a small fraction of a wavelength. Forgive me for asking, but you have wound it as a 1:1 current balun and not a 4:1 voltage balun have you?

Steve G3TXQ


Tue Mar 17, 2015 11:49 am
Profile Send private message WWW

 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post Re: high swr
sorry for the delay Steve been kept busy.
No it is 1 to 1 as you have described in your site, 2 parallel coils. I have wound it with twin moulded feeder which seem to be 10 amp power cable. It is flat from 160 to 28 at 4 to 1. the other one is made with stranded wire, again twin coils, I thought that i may have made an error some where but it is so simple to make i could not see how.

If you don't ask you do not learn. Thanks for the info anyway.

I have a mocvo balun from a previous antenna if i need a 4 to 1, and have made several with triple feeder.

don


Tue Mar 17, 2015 3:25 pm
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
I'm really puzzled by this, and can't help thinking something is wrong!

On 160m and 80m at least, the characteristics of the winding should have negligible affect, so you should never see a 4:1 SWR. Can you say a bit more about how you are doing the measurement?

Steve G3TXQ


Wed Mar 18, 2015 10:12 am
Profile Send private message WWW

 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post Re: high swr
hello steve.

I feed the balun from the tx and AV1000 via a short length of coax (4") and the output of the balun into a dummy load again via a 4" length of coax, the dummy load is a 25 watt termaline . I run 5 watts. The transceiver and the AV1000 both show a swr of 4 from 80 to 28 megs.

I would have thought that going from a unbalanced line to a balanced line on the ballan and back to unbalanced on the coax would have caused the swr. I made 2, one with individual cables and one with moulded twin, both are the same.

I have 10 turns on the ferrite.
don


Fri Mar 20, 2015 8:48 pm
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
sedge wrote:
I would have thought that going from a unbalanced line to a balanced line on the ballan and back to unbalanced on the coax would have caused the swr.

Not at all!

If you removed your balun in that test set-up, and replaced it with a length of 300 Ohm window line, you'd need 10ft of it before it produced a 4:1 SWR on 80m!

My guess is that you probably have about 2ft of line in your balun, and the line probably has a characteristic impedance of 150 Ohms at most. That should give you an SWR of 1.2:1 at worst on 80m.

Have you checked that the wire in the pair that connects to braid at the input of the balun is the same wire that connects to braid at the output?

Steve G3TXQ


Fri Mar 20, 2015 10:54 pm
Profile Send private message WWW

 high swr 
Advanced Member

Joined: Mon Dec 28, 2009 8:46 pm
Posts: 192
Location: pencoed, south glam (j35 m4)
Feedback: 18 (100%)
Reply with quote
Post Re: high swr
helo Steve.
my apologies for the delay all the time in answering but I have a lot of commitments at home and being over 80 I am slow.

Yes, you have cracked it, I must have had in mind that when coupled to the feeders it did not matter.

I have just checked it again making sure it was braid to braid and it is 1 to 1 on 160 and 3 to 1 on 28 megs. So I was at fault.

Thank you for your help, guidance and patience.
back in the 60's it was linked coupled always with our group and I can't ever seeing a balun

regards
don


Sat Mar 21, 2015 2:58 pm
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
Don,

Reversing the connections between input and output of a perfect 1:1 current balun would make no difference to the SWR; but no balun is perfect ;)

Actually, measuring the SWR with the connections deliberately reversed is a standard way of checking the common-mode impedance of the balun. It looks like yours may a bit lacking on 160m & 80m, but that's what I would expect for the number of turns you have.

Steve G3TXQ


Sat Mar 21, 2015 4:42 pm
Profile Send private message WWW

 high swr 
Novice Member

Joined: Sun Sep 09, 2012 8:33 pm
Posts: 11
Location: Tavistock IO70WO
Feedback: 0 (0%)
Reply with quote
Post Re: high swr
G3TXQ wrote:
Actually, measuring the SWR with the connections deliberately reversed is a standard way of checking the common-mode impedance of the balun.

Out of interest - what would be the method for doing that?


Sun Mar 22, 2015 10:41 am
Profile Send private message

 high swr 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: high swr
You do what the OP did inadvertently: place a 50 Ohm load across the output of the balun; short one side of it to ground and note the input SWR; then move the ground short to the other side of the load and note the input SWR.

The amount by which the SWR changes is a measure of how well the balun will impede common-mode signals. A perfect balun would produce an SWR of 1:1 for both readings.

Steve G3TXQ


Sun Mar 22, 2015 12:13 pm
Profile Send private message WWW
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 13 posts ] 


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.