4:1 balun on 20 foot vertical with auto-tuner at feed point?

[AB5ID]

I want to put my LDG autotunner at the feed point of a 20 ft vertical with counterpoise.
The auto tuner runs on internal batteries and will need to go into a waterproof container.

I have a 4:1 balun, should I use it on the output of the tuner? Should I direct connect the unbalanced tuner
output to the vertical?

I have a ammo can that I can use but was wondering if anyone else may have some suggestions
for a waterproof box???


Thanks,
Steve

[W5DXP]

I have a 4:1 balun, should I use it on the output of the tuner?

The tuner has an UNbalanced output and the vertical's feedpoint is UNbalanced. No, do not use a BALUN. If you need a 4:1 transformer, it should be a 4:1 UNUN. First, try it without a UNUN and see what bands you can cover.

[AB5ID]

What is the best ground mounted vertical I can put up with 20 foot of vertical space. I’m thinking homebrew and fed with an auto-tuner at the bottom. I want to use it on 80-10 if possible. Can I helically wind a PVC pipe? Or run a wire up the vertical support then back down the other side, or just use a conductive vertical no loading? What is the best configuration???

Kind Regards,
Steve

[NA0AA]

I want to put my LDG autotunner at the feed point of a 20 ft vertical with counterpoise.
The auto tuner runs on internal batteries and will need to go into a waterproof container.

I have a 4:1 balun, should I use it on the output of the tuner? Should I direct connect the unbalanced tuner
output to the vertical?

I have a ammo can that I can use but was wondering if anyone else may have some suggestions
for a waterproof box???
Thanks,
Steve

I have a suggestion: The ARRL antenna book. It will explain to you why you don't need a BALanced to UNbalanced 4:1 transformer. Also it will explain to you why a 20' vertical will be hard pressed to serve on 80 meters.

Helical winding has been attempted before, some guys who do SWL swear by 'em, but I was less than thrilled with my experience with one.

If you can manage 31' of vertical radiator, you can probably work 40 and up without too much problem with your tuner.

A metal can for weather proofing is not optimal - with this antenna, the actual radiating element begins at the center pin of the output of the antenna - you want to run a short wire from there to the vertical element.

[AB5ID]

I understand the radiation resistance will get very low on 80 and the take off angle will burn the clouds. I'm just interested in optimizing my signal on 80-10 with the restrictions stated.
If it is possible to operate 80 mobile, it should be possible to operate 80 meters with a 20 ft long radiator and a counterpoise. I understand this is far from ideal.
Given the limitations given above what is the best configuration for the vertical?

[G3TXQ]

Folding another 20ft of wire back down from the top will achieve little.

Helical winding is just another form of inductive loading - probably less efficient than a well-designed loading coil mid-way up.

The best way to improve the performance on 80m is to add some form of top-loading.

No, the take-off angle will not "burn the clouds" on 80m - it will have a null overhead.

Steve G3TXQ

[NA0AA]

I understand the radiation resistance will get very low on 80 and the take off angle will burn the clouds. I'm just interested in optimizing my signal on 80-10 with the restrictions stated.
If it is possible to operate 80 mobile, it should be possible to operate 80 meters with a 20 ft long radiator and a counterpoise. I understand this is far from ideal.
Given the limitations given above what is the best configuration for the vertical?

20' is pretty long for 10 meters, so if you put loading or a top-hat on, you will probably reduce the overall performance on 10 and up.

It's not that you can't tune it and get a match, is is just that you are asking a lot from 20' to act as though it were 66' long, even with a good tuner.

You might have an adequate 30 meter and up vertical.

I would simply insulate it from the mount, feed it from the center conductor of the tuner output and use radials tuned to each band - at least 2 for each band, laid down on the roof.

For lower band, you simply have to break the vertical in the center and add some loading - how much you would have to calculate.

A capacity hat at the top would also improve the match, although it's a bit more busy visually.

[W8JI]

I understand the radiation resistance will get very low on 80 and the take off angle will burn the clouds. I'm just interested in optimizing my signal on 80-10 with the restrictions stated.
If it is possible to operate 80 mobile, it should be possible to operate 80 meters with a 20 ft long radiator and a counterpoise. I understand this is far from ideal.
Given the limitations given above what is the best configuration for the vertical?

One problem you will have is reactance at the antenna feedpoint.

A THIN 20-foot vertical will have an impedance of 2.392 - J 1051 ohms at 3.5 MHz

This means to radiate 100 watts you would have to pump 6.5 amperes at 6800 volts into the end of the wire. This is almost 10,000 volts peak voltage into the wire. This means the VAR power is 6.5*6800= 44 kilowatts with only 100 watts real power applied.

There is no way on earth your tuner would do that, nor would any amateur radio tuner you could buy.

The only possible way to get any power into that 20 foot wire would be to use a big high Q loading coil.

A tuner would never work unless you eat up a whole lot of power in losses. If you could add 10 dB of loss, so radiation efficiency was 10%, then you would have 2100 volts RMS and 2 amps. Some bigger tuners would handle that, but not many.

If you added 20 dB loss, so 1% of the 100 watts power radiated, the voltage at the base would be 680 volts RMS and .65 amperes.
If you slopped up the system and made it so the antenna only radiated 1% of the applied 100 watts, the auto-tuner would work if it could match the impedance.

So you see, there is a big problem with a 20 foot vertical antenna on 80 meters. Even a 40 foot antenna would have some problems on 80, as would the 20 foot antenna on 40 meters.

You could put an 80 meter loading coil in the antenna and physically short it out for operation on other bands. That's what I would do.

73 Tom