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 <k7...@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....@contesting.com> On Behalf Of > HA3LN > Sent: Saturday, January 2, 2021 4:59 AM > To: 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
