Transformer help

[K6JEK]

I need help designing a transformer:  75 ohms to dual 50 ohms about 100 watts, 75 meters and maybe 40 meters in the future.

Huh?, you say.  OK.   I'm finally building "Possibly the world's best antenna" variant.   Two driven dipoles phased.   But they will be driven by separate amps with phasing adjustment on the input of the amps.  I'll need the phasing adjustment, too, because the dipoles are fed with ladder line to KW matchboxes which will make for who knows what phasing.   Cool, huh?   But the exciter is two stories up and the feed line to this whole set up is RG-6, 75 ohms.  Maybe  I can stand the mismatch 75 ohms to 25 ohms (if I just T the two 50 ohm set ups) but wouldn't it be more satisfying to match this a little better?

Can anyone out there help with either a 3:1 unun design or even more interesting a 75 ohm to dual 50 ohm transformer?    I don't have a lot of watts to spare. 

Jon

[W1GFH]

I'm finally building "Possibly the world's best antenna" variant. 

Ah, so Bob Heil's "possibly, the world's best sounding Ranger" comment wasn't enough?

 

[Steve - WB3HUZ]

Grab any ARRL Handbook from the 80's and early 90's. There's a 50 to 75 Ohm transformer design in there targeted at those using CATV hardline.

Or try Google.

[K6JEK]

I'm finally building "Possibly the world's best antenna" variant.

Ah, so Bob Heil's "possibly, the world's best sounding Ranger" comment wasn't enough?

 

Possibly the world's best sounding Ranger deserves possibly the worlds best 75 meter antenna, don't you think?  That's what K1JJ calls driven phased dipoles. 

Jon

[Steve - WB3HUZ]

And, of course, it will be used by possibly the world's best operator.

[WA1GFZ]

Feed line length to each antenna equal to each other and an even quarter wave multiple. Tie them to each other and you have 37.5 ohms. That should work directly into the ranger. If not try a short stub of 50 ohm cable in series. (unless you have a 1/4 wave electrical of 44 ohm coax) You can steer the array with 1/4 wave electrical of 75 ohm.

What I did. 2 equal lengths 50 ohms RG214 to each antenna. At the transmitter end add 1/4 wave electrical RG11 to each feed line jumps the Z of each to 100 ohms. Now T them to one lead and you have 50 ohms. You want to steer it add another quarter wave electrical 50 ohms to the front dipole. Add a transfer switch and move the delay line to the other dipole and you flip the pattern. Equal length 50 ohm is the cloud burner position.

[K6JEK]

Thanks for the advice.   I guess I confused people with the set up:  Ranger (or other exciter) on the second floor.  In the basement two amps.   One dipole off of each amp    The matching issue is on the input side of the amps, not the output to the antennas.    The amps are in parallel presenting 50 || 50 = 25 ohms non - reactive to the 75 ohm RG-6 which winds its way upstairs to the Ranger.   It's that 3:1 SWR I thought I might work on, not the matching from the two amps to the two dipoles.   I have a plan, two actually for that.

Inititally, I think I'll live with the 3:1 SWR.   It probably won't matter.

Jon

[W1GFH]

Why don't you run some ladder line to the Golden Gate Bridge and load it as a Sterba Curtain?

[WA1GFZ]

OH you want a splitter. Easy. T on the back of the ranger. A quarter wave electrical of 75 ohm coax on the two other T ports. connect the open ends to the load. 50 ohm load with 75 ohm line now jacked to 100 ohms each. Tie them in parallel and 100 in parallel with 100 ohms =50 ohms at the ranger. if the 75 ohm cable about 42 feet long doesn't make it to the amplifier just add 50 ohm coax to make the rest of the run. (Wilkensen divider)