Feeding a vertical with ladder line

[Watt’s that?]

Hi all,

This is my first post here.

I have installed a non resonant vertical ground plane antenna in a position close to where I plan to build a shack next spring. In order to use the antenna this winter I would need to run 220’ of feed line. The losses… with even good Lmr400 type coax seem too great. I’ve read a bit about feeding a vertical with ladder line but have no experience or expertise with it. My long question is… will it work? Exactly what do I need to make it work? How would I set it up? (Position of Balun etc?)
The antenna has a 4:1 unun as it sits, I have a good manual tuner at the operating position.

Thanks for reading my post.

 

[SuperLid]

What is a loss that is "too great"? You are only taking into consideration the feedline loss. There will be losses in the transformer and matching network as well. The feedline loss of RG-8/U at 30 MHz of 220' is slightly over 2 dB.

 

[The DB]

There are several options.

1) You can measure the impedance of said antenna and build an antenna tuner for it. This would allow the use of said LMR-400. You would get 1.397dB of loss in the coax (or with 100 watts in you will get 74.495 watts out) and a little more in the matching circuit.

2) You can run said LMR-400 into a remote autotuner, more expensive than 1 above but requires less technical knowledge, and have similar loss numbers to the above.

I don't like these options as I typically limit myself to 1 dB of matched feed line loss, which is what I used above, although not everyone agrees with this. However, if it were a temporary setup for a year or two, I wouldn't hesitate to use this setup.

3) 450 ohm window line or 600 ohm latter line to an antenna tuner on your desk. Between these two, the 600 ohm ladder line will do better, but would be homemade (and the option I would prefer). From here, I need the impedance data of said non-resonant antenna. 600 ohm ladder line starts with a matched loss of 0.224 dB (or 94.981 watts out with 100 watts in), but this is being fed into a "non resonant" or mismatched load, so said numbers can will go up quickly depending on the impedance of said load. A 13:1 SWR, for example, would bring said overall feed line losses in line with what the LMR-400 naturally has into a matched load as stated above.

Most antenna tuners already have a 4:1 step up balun built in. Putting a 4:1 balun between the 600 ohm feed line and antenna might or might not help depending on the impedance of said antenna. In most cases, running in in step down mode would be better with a vertical setup, but its hard to say for sure without knowing said impedance.


The DB

 

[The DB]

What is a loss that is "too great"? You are only taking into consideration the feedline loss. There will be losses in the transformer and matching network as well. The feedline loss of RG-8/U at 30 MHz of 220' is slightly over 2 dB.

The problem is the fact that the antenna isn't going to be a tuned antenna.

Lets take a look at what happens to said efficiency when SWR goes up, this is with 220 feet of LMR-400 at 27.2 MHz. Here we have SWR in the first column, dB loss in the second column, and percent of transmitted power absorbed by the antenna in the third column.

1:1 SWR	1.397 dB	72.495%
2:1 SWR	1.647 dB	68.437%
3:1 SWR	2.035 dB	62.596%
4:1 SWR	2.424 dB	57.224%
5:1 SWR	2.794 dB	52.55%

As the SWR of the as specified "non-resonant" antenna is potentially even higher, the losses with LMR-400 could get even higher than this, and by more than I think many people realize. Further, the hit to the RG-8/U that you mentioned would be even bigger then what is shown here. Also, a 5/8 wavelength vertical without a matching circuit will have an SWR of around 8:1 (give or take depending on specific design), which would be even worse than the above numbers.

Coax is great as long as you have a matched antenna on the other end, but it quickly falls apart when feeding into unknown impedance loads like the OP is doing.


The DB

 

[SuperLid]

The problem is the fact that the antenna isn't going to be a tuned antenna.

Lets take a look at what happens to said efficiency when SWR goes up, this is with 220 feet of LMR-400 at 27.2 MHz. Here we have SWR in the first column, dB loss in the second column, and percent of transmitted power absorbed by the antenna in the third column.

1:1 SWR	1.397 dB	72.495%
2:1 SWR	1.647 dB	68.437%
3:1 SWR	2.035 dB	62.596%
4:1 SWR	2.424 dB	57.224%
5:1 SWR	2.794 dB	52.55%

As the SWR of the as specified "non-resonant" antenna is potentially even higher, the losses with LMR-400 could get even higher than this, and by more than I think many people realize. Further, the hit to the RG-8/U that you mentioned would be even bigger then what is shown here. Also, a 5/8 wavelength vertical without a matching circuit will have an SWR of around 8:1 (give or take depending on specific design), which would be even worse than the above numbers.

Coax is great as long as you have a matched antenna on the other end, but it quickly falls apart when feeding into unknown impedance loads like the OP is doing.


The DB

Frankly, I don't like what the OP is doing. I would use an antenna coupler at the antenna, to maximize efficiency. I can deal with 2 dB of feedline loss other ways.

 

[The DB]

I would use an antenna coupler at the antenna, to maximize efficiency.

That is an option, and if you or the op chose that path I would have no complaints. In fact, it was listed at the top of my recommended list. Although calling it "maximizing efficiency" is at best a stretch, especially from someone who is willing to "deal with" said additional loss.

The OP has chosen a path that has the potential to have even less loss, and the potential to gain knowledge as well. I, for one, think that that should be applauded. It also looks like he made investments in this path as well...


The DB

 

[SuperLid]

That is an option, and if you or the op chose that path I would have no complaints. In fact, it was listed at the top of my recommended list. Although calling it "maximizing efficiency" is at best a stretch, especially from someone who is willing to "deal with" said additional loss.

The OP has chosen a path that has the potential to have even less loss, and the potential to gain knowledge as well. I, for one, think that that should be applauded. It also looks like he made investments in this path as well...


The DB

The transformer loss has not been included in the OP's ERP, so "less loss" is not necessarily true.

 

[nomadradio]

Best solution, but not cheap would be a tuner at the base of the antenna. Coax feeding the low SWR on a tuner's input will lose very little power in a 200-foot run.

73

 

[HarryUSA]

A couple of comments for the OP; If you are running balanced transmission line, you will need a BalUn at the antenna end, for one reason, you are feeding an unbalanced antenna, but also, I'm guessing your feed point is ground level, and your transmission line is going to enter the antenna system in the same plane as your counterpoise system, and as a consequence, the fields and reflections presented to your transmission line, will present themselves from the radiator and the counterpoise, un-evenly, to the balanced transmission line, unlike they would in a center-fed dipole, where the matching "problem" is evenly presented to the balanced transmission line, (since a dipole, whether horizontal, vertical, or inverted V, typically has the transmission line enter the antenna's structure, symmetrically between the two radiators) and can be contained very well back to your tuner. So with that in mind, you should put your BalUn, 1 wavelength from the antenna feedpoint, and run coax from there.

The other question is why is your antenna non-resonant? Is it because you are using it for multiple bands? Or did you build a 5/8 wave without adding any inductance? If you posted your antenna dimensions, and limitations (like how long/tall the structure you're using to support it), you might find others here could help you optimize your design.