New file uploaded to PHSNA (Balun meaqsurement unsatisfactory)


Steven Dick
 

Hi Nivar_P. Your writeup says you are using two identical cores with identical 8 turns of bifilar windings configured to work as a 4:1 balun. Not sure how you are electrically interconnecting the bifilar windings on the two cores. Maybe you could post a schematic? Most baluns I've seen use a single core.  It is acting like you don't have good enough coupling between the windings in the bifilar pairs.  What is your physical configuration of the bifilar windings? The wires need to be closely adjacent to each other in the bifilar pairs to act as a transmission line at high frequencies.

"Digital Steve" K1RF


EB4APL
 

Probably he is using a 4:1  current type "Guanella " balun. These do several functions:

1- Transform the 200 Ohm line (or antenna) impedance to 50 Ohm.
2- Transform the balanced line to unbalanced one (coax) . This where the name BALUN comes from.
3- Insure that the currents in the balanced line are symmetrical and avoids common mode currents. So it is also a common mode choke.
Functions 1 and 2 can be done with a voltage balun, the type commonly found in antenna tuners with symmetrical output. These uses a single core.
The Guanella balun needs two identical cores and windings. There is a lot info about them on internet.

73 de Ignacio, EB4APL



El 24/01/2017 a las 0:35, sbdick@... [PHSNA] escribió:
 

Hi Nivar_P. Your writeup says you are using two identical cores with identical 8 turns of bifilar windings configured to work as a 4:1 balun. Not sure how you are electrically interconnecting the bifilar windings on the two cores. Maybe you could post a schematic? Most baluns I've seen use a single core.  It is acting like you don't have good enough coupling between the windings in the bifilar pairs.  What is your physical configuration of the bifilar windings? The wires need to be closely adjacent to each other in the bifilar pairs to act as a transmission line at high frequencies.

"Digital Steve" K1RF



Pravin
 

Hi Steve,
                    Thanks for responding to my post . As requested please find attached the balun schematic and also how it is wound . Yes the wires in the transmission lines are  as close as possible and parallel to each other . Also being dual core there is sufficient space to make the turns well apart so as to reduce the self capacitance and increase high frequency response. But whatever I do like change cores change number of turns etc the SWR plotted using PHSNA and the associated RLB is invariably as shown in the attached graph!! . Now I think I have to try same type cores (FT140-61 and FT140-43) from a different manufacturer. Also when I plot the SWR of a 50 Ohms coaxial load using the same setup  the curve is almost flat even beyond 30MHz ! .

73
DE AB9XC
(Pravin)
 




From: "sbdick@... [PHSNA]"
To: PHSNA@...
Sent: Monday, January 23, 2017 4:35 PM
Subject: [PHSNA] Re: New file uploaded to PHSNA (Balun meaqsurement unsatisfactory)

 
Hi Nivar_P. Your writeup says you are using two identical cores with identical 8 turns of bifilar windings configured to work as a 4:1 balun. Not sure how you are electrically interconnecting the bifilar windings on the two cores. Maybe you could post a schematic? Most baluns I've seen use a single core.  It is acting like you don't have good enough coupling between the windings in the bifilar pairs.  What is your physical configuration of the bifilar windings? The wires need to be closely adjacent to each other in the bifilar pairs to act as a transmission line at high frequencies.

"Digital Steve" K1RF



Pravin
 

Hi Ignacio,
                     As suggested by you I wound 4 bifilar turns (13.5uH) on a pair of FT140-43 cores and configured it into a 4:1 balun and repeated the test on the PHSNA with exact same old results as shown in the attached graph. This time I used a 30MHz LPF between the PHSNA output and the RLB GEN input so as to rule out the possibility of any harmonics coming into the play. But absolutely no change with or without it.  Once again thanks for your time.

73
DE AB9XC
(Pravin)

 




From: "EB4APL eb4apl@... [PHSNA]"
To: PHSNA@...
Sent: Monday, January 23, 2017 5:48 PM
Subject: Re: [PHSNA] Re: New file uploaded to PHSNA (Balun meaqsurement unsatisfactory)

 
Probably he is using a 4:1  current type "Guanella " balun. These do several functions:
1- Transform the 200 Ohm line (or antenna) impedance to 50 Ohm.
2- Transform the balanced line to unbalanced one (coax) . This where the name BALUN comes from.
3- Insure that the currents in the balanced line are symmetrical and avoids common mode currents. So it is also a common mode choke.
Functions 1 and 2 can be done with a voltage balun, the type commonly found in antenna tuners with symmetrical output. These uses a single core.
The Guanella balun needs two identical cores and windings. There is a lot info about them on internet.
73 de Ignacio, EB4APL


El 24/01/2017 a las 0:35, sbdick@... [PHSNA] escribió:
 
Hi Nivar_P. Your writeup says you are using two identical cores with identical 8 turns of bifilar windings configured to work as a 4:1 balun. Not sure how you are electrically interconnecting the bifilar windings on the two cores. Maybe you could post a schematic? Most baluns I've seen use a single core.  It is acting like you don't have good enough coupling between the windings in the bifilar pairs.  What is your physical configuration of the bifilar windings? The wires need to be closely adjacent to each other in the bifilar pairs to act as a transmission line at high frequencies.

"Digital Steve" K1RF




Pravin
 

Hi Ignacio,
                  Yes you are correct .It is a 4:1 Gunella balun. Still I propose to use ferrite beads on the cable near the feed end to reduce any residual common mode currents possible on the cable braid as the OCF dipole is not a symmetrical antenna.

73
DE AB9XC
(Pravin)
 




From: "EB4APL eb4apl@... [PHSNA]"
To: PHSNA@...
Sent: Monday, January 23, 2017 5:48 PM
Subject: Re: [PHSNA] Re: New file uploaded to PHSNA (Balun meaqsurement unsatisfactory)

 
Probably he is using a 4:1  current type "Guanella " balun. These do several functions:
1- Transform the 200 Ohm line (or antenna) impedance to 50 Ohm.
2- Transform the balanced line to unbalanced one (coax) . This where the name BALUN comes from.
3- Insure that the currents in the balanced line are symmetrical and avoids common mode currents. So it is also a common mode choke.
Functions 1 and 2 can be done with a voltage balun, the type commonly found in antenna tuners with symmetrical output. These uses a single core.
The Guanella balun needs two identical cores and windings. There is a lot info about them on internet.
73 de Ignacio, EB4APL


El 24/01/2017 a las 0:35, sbdick@... [PHSNA] escribió:
 
Hi Nivar_P. Your writeup says you are using two identical cores with identical 8 turns of bifilar windings configured to work as a 4:1 balun. Not sure how you are electrically interconnecting the bifilar windings on the two cores. Maybe you could post a schematic? Most baluns I've seen use a single core.  It is acting like you don't have good enough coupling between the windings in the bifilar pairs.  What is your physical configuration of the bifilar windings? The wires need to be closely adjacent to each other in the bifilar pairs to act as a transmission line at high frequencies.

"Digital Steve" K1RF




Steven Dick
 

Hi Prevan. your schematic doesn't show polarities of each of the windings.  You may want to refer to the following link and make sure interconnections are all correct for the two core Guanella current balun.  Also insure that that neither side of the 200 ohm load is inadvertently grounded.  Here's the reference link:
http://www.hbphoto.com/Radio/Baluns_101.pdf

"Digital Steve", K1RF


Pravin
 

Hi Steve,
              Thanks to your reference I was able to correct the connections of the 4:1 Gunella balun and now it works as desired at least with a 200 ohms resistive load. I simply flipped one of the cores and re connected and it worked as desired over the whole frequency range of interest. I used the same two FT140-61 cores with identical 8T bifilar windings . I am attaching the SWR measurement curves for your info .Once gain thanking you for your timely suggestions.

73
DE AB9XC
(Pravin)



From: "sbdick@... [PHSNA]" To: PHSNA@...
Sent: Tuesday, January 24, 2017 7:01 PM
Subject: Re: [PHSNA] Re: New file uploaded to PHSNA (Balun meaqsurement unsatisfactory)

 
Hi Prevan. your schematic doesn't show polarities of each of the windings.  You may want to refer to the following link and make sure interconnections are all correct for the two core Guanella current balun.  Also insure that that neither side of the 200 ohm load is inadvertently grounded.  Here's the reference link:
http://www.hbphoto.com/Radio/Baluns_101.pdf

"Digital Steve", K1RF