Topband: (2wire) Beverage transformers

[Mike Waters]

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> 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> On Behalf Of
> HA3LN
> Sent: Saturday, January 2, 2021 4:59 AM
> To: 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...
>
>
>