For FM antennas, should you get a beep when testing for continuity?

[davenn]

Yes its working as a ( in this case) a 4 : 1 transformer

but keep in mind that its transforming impedance rather than voltage

Dave

 

[Willen]

When in stand alone use the 2 dipoles have the feedpoint impedances as I have shown on the diagram.
When they are incorporated into a yagi system their impedance will drop... the 75 Ohm dipole can drop as low as 25 Ohms, the folded dipole can drop from 300 Ohms down as low as 200 Ohms.

-Then how to match 50 ohm TX to 25 ohm yagi dipole? Using 1:2 balun? How?

You will find that many users of the plain 75 Ohm dipole will use 50 Ohm coax to feed it. The resulting mismatch and return loss isnt really a problem. say for a good match of a near 1 : 1 SWR ( near 0W reflected power) when using a 75 Ohm feed point, cable and transmitter. Using a 50 Ohm transmitter and cable to a 75 Ohm feedpoint may result in a ~ 1.2 - 1.3 : 1 SWR.

-What kind of balun can i use to perfect match 50 ohm Tx to 75 ohm coax or yagi?

 

[davenn]

the mismatch in either case 50 to 25 Ohms or 50 to 75 Ohms is not a major problem from a loss perspective
its well within acceptable range
and very rarely would some one try to change things to produce a better match

 

[cachehiker]

So you're implying that my pair of folded dipoles stacked a half wavelength apart (150Ω) won't see much benefit from a matching transformer for a 75Ω input?

I've already wound one, 2:1 balanced to unbalanced, 10 turns to 7 turns, on an FT37-61 mostly for personal "educational" purposes but I've yet to compare the SWR with and without it using the seldom used meter we have here at work.

I'm getting a kick out of all the stations I pick up now that my directivity no longer extends both into space and into the ground.

 

[davenn]

describe the dipole stacking better
are they horizontal and stacked one above the other or side by side?
.... vertical and side by side or one above the other ?
one directly in front of the other as a dual feed similar to a ZL special ????

your description didnt really tell me much to make any suggestions

Dave

 

[cachehiker]

Basic twin lead horizontal dipoles stacked one above the other on the wall of my living room.

Collinear would still have the directivity including outer space and below ground and would compromise the two local stations that aren't within 10° or so of the north-south. The only place I could easily put one in front of the other is likely to underperform due to incidental director/reflector effects from house wiring that would end up in between and parallel to the dipoles.