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>
Sent: Saturday, January 2, 2021 11:44 AM
To: Lee K7TJR <k7tjr@msn.com>
Cc: HA3LN <list@ha3ln.hu>; topband <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>> 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>> On Behalf Of HA3LN
Sent: Saturday, January 2, 2021 4:59 AM
To: 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...
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband
Reflector
