Topband: (2wire) Beverage transformers

Sun Jan 3 17:38:52 EST 2021

I question the wisdom of grounding the feedline shields at the antenna 
for either open wire or coax designs.  Was this a error in the schematic?

The bidirectional design using a coaxial cable shield for the antenna 
does not need center tapped transformers. Good RG6 is ridiculously cheap 
and impervious to foliage contact or drops and certainly easier to 
"make". The transformers are much easier to wind with no center taps and 
fewer turns.  See 5th ed of ON4UN figure 7-118.  When connected to a 
direction selection switch, the unused feedline needs to be terminated 
in its characteristic impedance.

So, I'm a bit baffled why the open line design with surplus steel wire 
is so in vogue. Is there a performance benefit to open wire?  What am I 
missing?

For transformer windings, 28 gauge Kynar insulated wire wrap wire is 
tough but has a higher dielectric constant than TFE if reducing winding 
capacitive coupling is important. Good chokes and buried feedlines are 
additional insurance against noise insertion.
https://www.omnicable.com/docs/default-source/technical-resources/dielectric-constants-insulations.pdf?sfvrsn=2

Grant KZ1W

On 1/3/2021 05:52, HA3LN wrote:
> 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
>>>>
>>>
>>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector