...no problem Lee, actually each new idea helps.
I'll give a try the n1=4T version with a 0.3mm (~AWG 28/29) wire to see
if I can push a bit better matching.
Sorry for the links I tried to avoid sending fairly large pics to the
list directly.
I have the same measurement setup as Don's sent yesterday, the loading
resistors are similar too, soldered them from 2W metal oxide pieces,
resulting 744 Ohms, which is within 1 Ohm to the open wire calculated value.
What I see comparing the "old" transformer and the new ones that it has
less linearity and as Don said it has significantly worse Z(s). @7MHz.
It might suggests that the core has different mix which gave the higher
results. I wound as least 15 transformers with ~10 different BN73-202
cores from different sources to avoid similar manufacturing batches but
I could not see improvements, so I concluded this as core independent
reason.
http://ha3ln.hu/old_new.jpg
(green=2020 version, white=2019 transformer version)
Interesting that the SWR curve minimum inflection point is roughly
halved, which was @850KHz, it is @400KHz in 2021.
Tried Don's advise to twist the prim/sec ends of both n1 and n2.
Interestingly enough if I twisted the one made from 0.3mm wire, I could
reach the 1:1.16 measurement values again, but if I did the same to one
made from 0.5mm diam wire it became worse.
73!
Csaba
On 2021-01-03 1:06, Lee STRAHAN wrote:
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@gmail.com>
Sent: Saturday, January 2, 2021 3:03 PM
To: Lee STRAHAN <k7tjr@msn.com>
Cc: HA3LN <list@ha3ln.hu>; Mike Waters <mikewate@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@msn.com<mailto:k7tjr@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@gmail.com<mailto:wd8dsb@gmail.com>>
Sent: Saturday, January 2, 2021 1:54 PM
To: Lee STRAHAN <k7tjr@msn.com<mailto:k7tjr@msn.com>>
Cc: HA3LN <list@ha3ln.hu<mailto:list@ha3ln.hu>>; Mike Waters
<mikewate@gmail.com<mailto:mikewate@gmail.com>>; topband
<topband@contesting.com<mailto:topband@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@gmail.com<mailto:wd8dsb@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@msn.com<mailto:k7tjr@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@gmail.com<mailto:mikewate@gmail.com>>
Sent: Saturday, January 2, 2021 11:44 AM
To: Lee K7TJR <k7tjr@msn.com<mailto:k7tjr@msn.com>>
Cc: HA3LN <list@ha3ln.hu<mailto:list@ha3ln.hu>>; topband
<topband@contesting.com<mailto:topband@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@msn.com<mailto:k7tjr@msn.com><mailto:k7tjr@msn.com<mailto:k7tjr@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@contesting.com<mailto:msn.com@contesting.com><mailto:msn.com@contesting.com<mailto:msn.com@contesting.com>>>
On Behalf Of HA3LN
Sent: Saturday, January 2, 2021 4:59 AM
To:
topband@contesting.com<mailto:topband@contesting.com><mailto:topband@contesting.com<mailto:topband@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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