Topband: (2wire) Beverage transformers

Lee STRAHAN k7tjr at msn.com
Sat Jan 2 19:06:40 EST 2021 

Sorry Guys, I miss interpreted Csaba’s transformer problem. My email program truncated the URL’s and most of the information past that point. What I did get I misread as a result so now I am curious also of his dilemma.
Lee   K7TJR OR

From: Don Kirk <wd8dsb at gmail.com>
Sent: Saturday, January 2, 2021 3:03 PM
To: Lee STRAHAN <k7tjr at msn.com>
Cc: HA3LN <list at ha3ln.hu>; Mike Waters <mikewate at gmail.com>
Subject: Re: Topband: (2wire) Beverage transformers

Hi Lee,

I don’t think he needed any tools (formulas, etc.), he is just trying to figure out why his recently made transformer does match closer to one he made a year ago.  He too agrees that the SWR with his new transformer is likely not an issue, he is just trying to figure out why his new transformer is different than his previous one, and that’s why I measured one of my own so he had another data point to work with.

His transformer from a year ago was 1.16 to 1 whereas his new transformer measured 1.29 to 1 and that’s bugging him from an obsessive standpoint.

The reason I mentioned 2 windings was because of how you responded to Mikes question.  I'm really not familiar with reversible beverages and jumping into this topic helped me learn a bit about them (I love learning).

Just FYI, and Happy New Year to you and yours too.
Don (wd8dsb)



On Sat, Jan 2, 2021 at 5:15 PM Lee STRAHAN <k7tjr at msn.com<mailto:k7tjr at msn.com>> wrote:
Hi Don,
    Regardless of the transformer whether it’s a tapped or separate. I gave him the tools that should make whatever he does correct. Personally I keep my Beverage when I make one at 450 ohms which makes the matching much easier for me. I just put up my first one yesterday in several years to test a new brainstorm antenna.
   From what I saw he had a 1:1.16 SWR which could not get much better in my opinion. Apparently he thought it could be better.
All is good  HNY
Lee  K7TJR  OR


From: Don Kirk <wd8dsb at gmail.com<mailto:wd8dsb at gmail.com>>
Sent: Saturday, January 2, 2021 1:54 PM
To: Lee STRAHAN <k7tjr at msn.com<mailto:k7tjr at msn.com>>
Cc: HA3LN <list at ha3ln.hu<mailto:list at ha3ln.hu>>; Mike Waters <mikewate at gmail.com<mailto:mikewate at gmail.com>>; topband <topband at contesting.com<mailto:topband at contesting.com>>
Subject: Re: Topband: (2wire) Beverage transformers

Hi Lee,

Csaba also refers to this transformer as T2 and based on what he has said so far I suspect he is constructing something similar to the two direction beverage shown in figure 7-115 in the 5th edition of Low-Band DXing.  And T2 is indeed a two winding transformer with center tap.  This transformer transforms the impedance of the open wire transmission line (745 ohms in Csabas case) to the coaxial feedline (75 or 50 ohm).  The center tap is used to feed another transformer (T1).

I could be wrong but reading between the lines I probably am correct.

Just FYI,
Don (wd8dsb)

On Sat, Jan 2, 2021 at 4:09 PM Don Kirk <wd8dsb at gmail.com<mailto:wd8dsb at gmail.com>> wrote:
Hi Lee,

Csaba said his transformer was  " n1=3T/n2=12T tapped @6T ".  This sure sounds like a transformer with two separate windings (3 Turns on the Primary, and 12 Turns on the Secondary and then it also has a center tap on the secondary), but I could be wrong.  I think Csaba needs to clarify exactly what his transformer is, and his test circuit.

Don (wd8dsb)

On Sat, Jan 2, 2021 at 3:22 PM Lee STRAHAN <k7tjr at msn.com<mailto:k7tjr at msn.com>> wrote:
Hi Mike,
   Assuming that you did not miss that this was a tapped winding and not separate windings as Csaba mentioned. I see on reflection that he measured 1:1.16 on one of his tests. In reality it wont likely get much better than that. That test was likely the 3:12 he mentioned using. The high impedance side of these transformers are a little unpredictable using simple formulas with winding capacitance and magnetizing inductance added in the mix.
  Sometimes I use wire wrap wire if it is not going to be used outside otherwise I use #27 high temp motor winding class insulation wire which helps keep from shorting the wires to the core. I have the benefit of many part spools of motor winding wire scraps from a best friend and Ham in the Motor rewinding business. By the way, Norton amplifiers require 1:11:4 which is the same problem to solve as they are separate windings in the ones I use. I also fit shrink tubing in the Norton amp cores for insulation first. I don’t use Teflon because it has a dielectric constant around 5 which increases the capacitance from the wire to the core. Its tedious but can be done easily. And in the case of the Norton amp it leaves room for a larger wire on the 1 turn winding. Yes 4 AND16 for 20 total can be done but yes it takes time and lots of patience. For those turns counts I go to # 75 material toroid cores which have slightly more winding room but require more turns usually for 160 meter stuff.  All this probably more than you wanted to know. HNY
Lee  K7TJR  OR

From: Mike Waters <mikewate at gmail.com<mailto:mikewate at gmail.com>>
Sent: Saturday, January 2, 2021 11:44 AM
To: Lee K7TJR <k7tjr at msn.com<mailto:k7tjr at msn.com>>
Cc: HA3LN <list at ha3ln.hu<mailto:list at ha3ln.hu>>; topband <topband at contesting.com<mailto:topband at contesting.com>>
Subject: Re: Topband: (2wire) Beverage transformers

Lee,

What kind of wire do you use that allows that many turns (4t and 16t)?

73 Mike
W0BTU

On Sat, Jan 2, 2021, 1:37 PM Lee STRAHAN <k7tjr at msn.com<mailto:k7tjr at msn.com><mailto:k7tjr at msn.com<mailto:k7tjr at msn.com>>> wrote:
Hello Csaba,
   I approach this problem this way your impedance ratio is 745/50 ohms or 14.9 . To get turns ratio use the square root of that which is 3.86 . So round that up to 4 as a good turns ratio.
  On a BN73-202 core I usually use a minimum of 4 turns on the 50 ohm side for 160 meters, so the secondary would need 4 turns ratio times that for 16 turns. Therefore 16 turns tapped at 4 turns should work for you. Some will say the 3 turns on the 50 ohm side should work and the secondary then would be turns ratio 4 times that or 12 turns. Therefore 12 turns tapped at 3 turns should work well also. Sorry, I do not follow your formula as shown but you can use the above and it will work fine as an 800 ohm load to the 745 ohm source. This will reflect 745/16 or 46.6 ohms to your cable. SWR for that at the 50 ohm cable  is 50/46.6 or 1.07 using resistance only for evaluation.
Lee   K7TJR  OR

-----Original Message-----
From: Topband <topband-bounces+k7tjr=msn.com at contesting.com<mailto:msn.com at contesting.com><mailto:msn.com at contesting.com<mailto:msn.com at contesting.com>>> On Behalf Of HA3LN
Sent: Saturday, January 2, 2021 4:59 AM
To: topband at contesting.com<mailto:topband at contesting.com><mailto:topband at contesting.com<mailto:topband at contesting.com>>
Subject: Topband: (2wire) Beverage transformers

Hi All and HNY for 2021.

Preparing for the CQ160m with new (2 coax) 2-wire beverages to cover the missing azimuthal gaps based on LBDX. The first 2x Bevs worked great back in last Jan.

Now I have difficulties with reaching good imped match with the
T2 transformer (responsible to transform the 745 Ohms wire impedance to 50 Ohm coax). I use n1=3T/n2=12T tapped @6T transformer (2m high, 20cm wide with 0.8mm wire)

What can be the reason for the impedance transformation is rather off to the calculated value?

This is the T2 transformer from 2019:
http://ha3ln.hu/VNA_190116_230811.jpg
...and this from yesterday:
http://ha3ln.hu/VNA_210101_153241.jpg

I have
- same wire with the diam (even from the same roll)
- same BN73-202 cores (tried to use several cores from different
   sources to eliminate the possible mix inconsistencies)
- same winding method (including n2 tapping)
- created a low inductance test resistor network for 744 Ohms

...tried to wind
- lousy, and precise (crossing windings vs. side-by-side, bunched
   wires, etc.)
- n1 first and n2, after n2 first and n1, of course no difference.
- without the tapping, same as above.
- difference turning ratios (3/12, 2/12, 1/12, 3/11, etc.) to see
   the change


The best I could reach now on 160m is
- SWR: 1:1.29 (Rs=40.4 Ohms, Xs=-5.4 Ohms) vs. in 2019:
- SWR: 1:1.16 (Rs=43.2 Ohms, Xs=-1.6 Ohms)

I know, Beverages are really die hard antennas and this increased mismatch might have zero effect on performance but still, the engineer part of me...

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