Been reading all the antennae threads and have to ask, if I put up a ladder fed dipole at 40 to 50 ft in the air with one side over a metal roof, how unbalanced will it be?

I have plenty of distance and all materials on hand.  Currently scheduled to take exam on 4/11 so have to fill the time with studying and building.

Going to build one like the 80-10 one discussed in a previous thread.

Thanks in advance

A good "current balun" will try to equalize the current on both sides of the dipole. You won't really know if there is a problem until you try it. Balun Designs sells a somewhat specialized balun for unbalanced ladder line fed antennas for exactly your reason, but this may only be a consideration if you are running in excess of 700 W. hth
73,
Rob

Thanks,

I will only have a 100w Kenwood for now.  I have been reading the trueladderline web site and have found a lot of good info.

As a side question, will a hybrid ( solid state receive and tube transmit) be any easier to match the antennae ? I mostly will be swl.

If the tube transmitter has a Pi Network output, it may be able to match it on some bands without an antenna tuner. You will need the balun, though.

How to tund a Pi Network final

Have to do a little research on that, it is a Kenwood ts 820s

ETA. Thanks

I had a TS-520. The output tuned a pretty wide range.
Watch your grid drive, though. Those finals don't like to be overdriven.

The free space impedance of a resonant, half-wave, center-fed dipole is somewhere around 72 ohms, so ladder line won't match very well without a balun.

The antenna output of your TS-820S is 50 ohms unbalanced, so you will need a balun there too unless you have an antenna tuner with a balanced output.

I hope I have remembered this stuff correctly.

Thanks,

In order to start simple, I will use a 4:1 eave mounted balun  with a short run of coax.

I found a couple of good tutorials on adjusting the radio and plan to stay on the conservative side

Thanks

The roof won't bother it at that height. You may have better luck with a 1:1 balun.

Nice to hear, I’m shooting for as high as possible. It may have a slope but not much.

Thanks

The length of the ladder line will change the impedance as seen by the radio. All I can say at this point is try it and see how it tunes up. I run a manual tuner but my radio is 50 Ohms output. Matching a final stage network and a tuner can be done by tuning up into a dummy load and then matching the tuner to the output of the radio. It's one reason I went with a solid state amplifier. A fan dipole with coax feed will be more predictable and easier to get along with but it restricts the number of bands that are easily accessible. hth
73,
Rob

This.

Feedlines (transmission lines) are also impedance transformers, which repeat every electrical half-wavelength.

As the above two posts indicate, do go back to the trueladderline website and make sure you read about ladder line lengths vs. frequency (band). I doubt you will be able to arrange things so that you can use the TS820 without an external tuner.

If you want an auto-tuner get an MFJ-939. If you want to go old school with a manual, balanced line tuner, where you bring the ladder line right into the shack, get an MFJ-974HB (but it's pricey).

Finally, you said in another post you want to SWL. You will not be able to do that on your TS-820, it only covers the amateur bands.

With a TS-820 I earned WAS, WAC, DXCC, all with a wire antenna about 35' in the air.

Learn to operate your station, not try to outshout everyone else around.

Try not to blow up your finals, I don't know how easy 6146s are to find these days.

Best of luck.

Yes,
Swl was misspeaking, I like to mostly listen. I have a little receiver that I might be able to use with this antennae.

I am outside right now plotting out the dipole and it is turning into an inverted v due to tree obstruction.
I read closely and bookmarked the section about different lengths of ladder line and the effects of such.
I think I will be able to stay in the thirties as to length. (34-40)

Thanks

Receiving, it isn't important, but things get critical when you transmit into an antenna.

Tubes are a hell of a lot more rugged than solid-state finals.

I have the (old) Kenwood antenna tuner. (AT-180 I think without going downstairs to look)

This^
I've been on the air since 1954 and only used an amplifier for a few years, mostly to check into 75M phone nets. It's been in its box in the closet for ~15 years now.
I used dipoles exclusively now and often run 5 watts of less on CW.

As a point of reference, to increase your signal 1 S-unit, you have to increase your power 4 times. That's like going from 100 watts to 400 watts

I would like to thank everyone for the helpful advice.
Since I last posted, I have made a 80 meter inverted V dipole fed with 35 ft of ladder line to a 1:1 balun.
The middle is at 35 ft in height.  The ends are at 10 ft.  This was taking the advice to get something in the air and try it.

The Kenwood came in today and I have it set up receiving only until I get my license. It seems to receive great and I will be listening to the net on Tuesday.  The last parts (resistors) should be here tomorrow and the dummy load can be finished. I ordered them from K4EAA’s website.

I am already eyeing a AT-230 tuner and some higher trees, this is worse than BRD.

Thanks again

ETA 25 ft RG8 from balun to radio

I went online to order one, but soon had information overload and could not decide on a particular unit.
Between building an antenna and studying for tech and general, my head is full.

Side question:  I’ve driven a grounding rod right outside the “shack” and grounded the radio to it.  Do I need to bond this rod to electrical service ground 30 ft on other side of building?
My reading seems to suggest it’s required by the NEC

Thanks

Yes. A nearby lightning strike can create a difference of several thousand volts between your ground rod and the service ground.

Apologies for resurrecting an older thread, but I am pushing the order button on a new balun.  The cheap Chinese kit I received seems pretty junkie.

I bought a Nano VNA and am unable to achieve less than 1:5.8 see no matter how I adjust the antenna.

Now it’s a choice between 1:1 or 4:1

My tuner will be a Kenwood AT 250 (automatic). Research indicates it does not have the widest range.

Thanks

Doublets are non-resonant by design. You will not see low VSWR from that antenna.

That Kenwood tuner will flat out not work. It will only handle 2.5:1 VSWR max., over an impedance range of 20-150 Ohms. If that's what you are determined to use then you can not use a doublet antenna. Strongly recommend you obtain an MFJ-939 antenna tuner.

The best baluns are from DX Engineering. You want one of these. Yes, they are expensive. No, the 5KW rating is not overkill, a doublet can generate some very sporty voltages during tuning (another reason you want the MFJ-939 tuner and not some weak sauce LDG tuner). Whatever you do, do not buy an MFJ balun. Unlike MFJ tuners, MFJ baluns are junk.

Conventional wisdom says use a 4:1 balun. That is what the "book" says you should try first.

If you are using 50 ohm coax to a 1:1 balun to 450 ohm window line, and getting a 5.8 SWR, then the balun looking up to the antenna is seeing about 290 ohms at the frequency you are getting the SWR at. So if you went with a 4:1 balun you will get an SWR at the rig of about 1.45.

That means the tuner you have should work for you at that freq, in fact you don't even need a tuner at 1.45 SWR. With a 4:1 balun and that tuner that has a max match of 2.5:1, it means the most impedance it can match with a 4:1 balun will be 500 ohms. So that is similar to a 10:1 match without a 4:1 balun. The tuner might work on other bands

However that tuner is meant for low SWR antennas, like a built in tuner in a rig is.

However if you are using this antenna as a multiband antenna, you may run out of tuner on other bands as the impedance changes and goes up.

With ladder / window line you can not read the antenna SWR directly like you can with a coax fed antenna because you have a coax ladder / ladder line junction impedance mismatch in the transmission line and you need a coax connection to attach to the SWR meter /  VNA so you can't read the ladder line directly and unlike coax, the ladder line does not have the same impedance of the output of the radio. But we don't really care about SWR with ladder line fed antennas because unlike coax, ladder line has very little loss at high SWR. So as long as you can match the SWR and produce close to 50 ohms at the radio the SWR doesn't matter.

So like AA said, you probably need a tuner that can match much high matches

If you already have a 1:1 balun, you can try the MFJ-939 ( I have one also, it works very well )  or you can get a 4:1 balun and see if your 2.5:1 tuner is enough to work all the bands 80-10.


What antenna is this?
What balun is on it now?

I'm confused, you're putting a balun in between a balanced feedline and a balanced antenna?!?! Where's the "un"?

A lot of this nonsense would be avoided if people just used reasonably matched antennas and feedlines.


Ugh. If you have a reasonably-resonant 80 meter dipole, then feed it directly with coax and get the ladder line transformer out of the feed system, it's doing nothing but screw up the works.

If you're trying to DIY a G5RV type antenna, you have to use the specific dimensions of antenna and ladder line to get the impedance transformations correct, randomly putting it together won't work right.

Manual MFJ tuner was my first choice, but don’t seem to be available til June.

Antenna is inverted v measured for 80 meters 35 ft at apex.

Balun is unknown Chinese 1:1

Tuner is coming cheap, so will probably try it and keep looking for MFJ tuner.

Thanks

So, just set length at calculated value?

Balun Designs 41113t was in my cart.

Thanks

Yes, I did not describe that fully.
Balanced antenna
Balanced feed line
Balun
Short coax to tuner

ETA
Starting to think I am overcomplicating this and you are correct. Lot of new info.


Thanks

So it is basically a G5RV doublet? an 80 meter dipole fed with 450 ohm window line so you can make it an 80-10 multiband antenna? Is that right?

yeah if you tune via coax and the coax goes to a balun then to the window line then the antenna, you need a 4:1 balun at the coax to window line junction.

If you bought this doublet complete with window line, then it should be fine adding a 4:1 balun to the coax.

If you put this antenna together yourself, then you may have to play with the length of the window line.

This.

If you have an 80 meter dipole cut to (reasonable) resonance, just connect it directly to the 50 ohm coax, and your low-range tuner should take care of the rest for the 80 meter band.


G5RV does not use a 4:1 transformer/balun; direct connection or 1:1 balun is the norm.

Here's some reading on G5RVs and derivatives:
https://www.dxzone.com/the-truth-about-the-g5rv-antenna/

I just don't recommend dealing with all this complication and tuners and crap for newbies.

You are right, I misspoke. Not a G5RV.

It is an 80 meter doublet that can be tuned 80-10 meters.
It terminates to a 4:1 balun then coax into the house.

I have a homebrew 160m doublet that I tune 160-6 meters but I don't use a balun, I bring the 600 ohm ladder line direct to the tuner in the shack.

He doesn't want an 80m dipole, he wants an 80-10 meter antenna.

Sure he doesn't want 160 too?

Just order this and be done with it:
https://www.dxengineering.com/parts/alf-dx-cc

This is correct

Nope on the 160

Already have antenna and feedline up

Really just want to concentrate on 80 and 40 initially

Thanks

Coax to center insulator, dipole for 80m, pull a second pair of wires out for 40 meters.

Balun or no balun?

Also at 250 tuner out and MFJ tuner ordered (manual with meter) ETA  941e verse tuner II

Can 80 and 40 run parallel, standoff, ect?

There used to be a member here who had "have you choked your feedline today" in his sigline, which I support.

That said, it will work without a balun/choke.

It's a fan dipole, I'm sure there are 87 hundred hits on any internet search engine.

You can run the wires parallel on standoff insulators, or if you have room and supports, separate them at the angle of your choice. About 60 degrees can give you a little bit of broadbanding when used with a tuner on higher frequencies. The shorter wire/higher frequency will have to be somewhat longer than the length of a standalone dipole to resonate, and the length will vary depending on parallel or angled installation.

Attached File

A manual tuner with ladder line all the way to the shack will be the most flexible. I have a 138 foot doublet at 35 feet and work 80-10 meters. You may have to play with ladder line length to get all bands. Nice thing about ladder line is that it is low loss even at relatively high swr.