Topband: (2wire) Beverage transformers

Sun Jan 3 08:52:11 EST 2021

Hi All,

Yes, I refer to this 2-wire design:
http://ha3ln.hu/2wire.jpg

73!
Csaba

On 2021-01-02 22:53, Don Kirk wrote:
> 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> 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> 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...
>>>
>>> _________________
>>> Searchable Archives: http://www.contesting.com/_topband - Topband
>>> Reflector
>>>
>>
> 