Topband: (2wire) Beverage transformers

Sat Jan 2 16:09:37 EST 2021

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> 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>
> Sent: Saturday, January 2, 2021 11:44 AM
> To: Lee K7TJR <k7tjr at msn.com>
> Cc: HA3LN <list at ha3ln.hu>; topband <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>> 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>> On Behalf Of HA3LN
> Sent: Saturday, January 2, 2021 4:59 AM
> To: 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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