Antenna woes

[W7SOE]

Finally, finally, after months, I have the antenna up on the new house.  Two story house, a 15 ft pole with an inverted V cut for 1/2 wave 3870. 

Unfortunately I felt obliged to run coax to ease the whole thing to the XYL as I could run it through the attic and down the laundry chute.  I have a 1:1 balun at the feed point.

Performance seems not so good...   I have an easier time loading the thing up on 40m that at the frequency that it was cut for.  :-O
I am not sure why this is.

It may be a mute point as when the XYL saw the tripod/pole/balun extension of "her beautiful house", well let's say her feelings were not ambiguous.  Once she calmed down I agreed to make some changes.

I think I will get rid of the radio shack tripod and have a small 3-4 ft metal pipe with some thin guy wires.  This means that the ends of each leg will have to do some meandering to fit them into my lot. 

Part of this "plea bargain" was that I need to use ladder line, probably window line.  This was accepted.  :-)

I am hoping that, even though the antenna will be lower and geometrically challenged, that the ladder line will helkp the performance.

Any thoughts or ideas would be appreciated.

Rich

[K1JJ]

Hi Rich,

The 75M coax fed dipole shud have loaded up easily on 75M.  Check the balun. Put a 50 ohm load across it and check it with the MFJ-259B or swr meter with the rig. Be sure it's working.

If you go to openwire, then matching won't matter. The openwire and ant tuner shud solve your current problem and make the antenna work well on all bands.

However, I wud find out why the dipole doesn't work well on 75M anyway. It's rare, but there may be something in the house like wiring or plumbing that is resonating with the dipole causing bad coupling. This will still show up as a distorted radiation pattern with the open wire ant version, but you may not know it cuz the ant tuner will match anything.

Good luck -

Tom, K1JJ

[N2DTS]

What is the balun for?
I dont like them and never use them on AM.

The coax made ones are ok I guess, or one of those huge (and expensive) ones are ok I guess, I just dont know what advantage one would give you.
I cut a dipole, put it up and feed it with coax, then find where it is resonant, and trim till its close to my operating freq.
It seems a balun would only add trouble.

The only thing better than a resonant dipole is a lot of wire fed with owl and a big balanced tuner, but I like resonant antenna's for each band I operate on, no tuning...

Brett

[K1JJ]

Yep, good question... what kind of balun is it?  Is it a W2AU smoker or a good ole coil of coax acting as a choke?  The coax choke is FB, but the W2AU may have already burned up if you had it at 1KW AM service....

T

[W7SOE]

Don't remember who who makes it, it is a typical chunk of PVC....  I think, before I do the complete antenna model, I will take your advice and go up there and remove the balun.


Rich

[W9GT]

That W2AU balun is just wound on a ferrite rod and I have smoked them running AM also.  They work ok on SSB or CW, but seem to break down with a continuous carrier like AM at 375 W. or so    The heavier baluns that use a toroid may or may not be adequate.  The coil of coax method is generally bullet proof, if you must use a balun.

73,  Jack, W9GT

[K5UJ]

Don't remember who who makes it, it is a typical chunk of PVC....  I think, before I do the complete antenna model, I will take your advice and go up there and remove the balun.

Hmmm sounds like Radioworks or Cal-Av.    Radioworks are pretty easy to smoke.   purpose of the balun is to keep RF off the outside of your feedline so it doesn't radiate and get back to the shack.    A coax choke coil is okay if the feedpoint is supported.  I usually use 213 because it can handle being coiled without the center migrating through the dielectric.  I really don't like any kind of ferrite stuff anywhere between the tuner (or rig if there is no tuner) and the feedpoint.   That's what I like about open wire line--the "balun" is between the tuner and the rig and always sees 50 ohms.

[Bill, KD0HG]

Don't overlook the possibility of a bad connector or pinched coax.
I like the W2DU balun. Get yer ferrites out!

I don't know which floor your shack is located on, but a bottom-fed inverted-L might be worth considering. No feedline needed.

[KF1Z]

Do you know the exact length of the coax?

May be an issue...

[Bill, KD0HG]

Oh, I just figured it out..What if it's a 4:1 instead of a 1:1 balun ?

That might explain the apparent better match on 40.

[KF1Z]

Oh, I just figured it out..What if it's a 4:1 instead of a 1:1 balun ?

That might explain the apparent better match on 40.

That would do it alright     

[W7SOE]

Oh, I just figured it out..What if it's a 4:1 instead of a 1:1 balun ?

That might explain the apparent better match on 40.

Nope it is 1:1.  My shack is in the basement (subterranean).  I would guess the coax is ~35-40 ft.  Makes me wish I had an antenna analyzer, unfortunately they are $$$$.

Rich

OK, Rich, here's what you do.

Put up the highest mast (XYL practical) on the roof. Make an inverted L. A wire straight up from the basement shack, supported on plastic insulators, as necessary.
That'll give you a maybe 30--'40' tall vertical.

Run the wire over to a support as far away as possible. 30-60 feet would be fine.

Total length of antenna, hopefully 100' at least.

Use your buried water pipe for a ground. Better yet, bury as many radials as  you can in the yard.  That's your counterpoise. Tie them to your ground system. The XYL won't see them. The copper and iron help promote a green lawn. If you've got  a steel cyclone fence around the yard, tie it in as well.

You will need a single-wire antenna tuner. Find a Johnson Matchbox somewhere.

That gives you a semi-top loaded vertical. Far better radiation than a dipole would have at 30'-40'.  No obnoxious feedline. Make the whole thing out of #16-#14 enamel wire. Invisible.

Rock on.

I used a similar antenner when I lived in a small town, it kicked butt on 160-80-40.
Even worked Hawaii on 160 CW. Regularly worked the East Coast on 75 with it.

IMO

Mr. Marconi would be proud of you.

[W7SOE]

Here is the balun:

http://www.universal-radio.com/CATALOG/antsup/1019.html

I am measuring less than an ohm across the coax.  This could mean three things:

Shorted balun
Normal balun shorted coax.
normal balun, normal coax.

I see a long ladder in my future.   

Rich

[N2DTS]

Is it new?
Any sensable power on AM will fry it if there is ANY swr.

Baluns with cores can cause problems when overloaded, when the cores saturate they can generate all kinds of trash I have heard.

I look at baluns as a power loss device that is only likely to cause problems.

I never used one, never had RF in the shack, can get a lor swr, dont see the point...

DC resistance is not a valid test.

I would check the coax for shorts, scrap the balun, and sweep the antenna to see where the lowest swr is.

Brett

[WQ9E]

I am with Brett, I have never used a Balun for a dipole.  If you have RF in the shack then go with the coiled coax "choke" or ferrite rings around the coax.  For a Yagi, the balun makes sense but for a dipole it is more trouble than it is worth.

The balun will show a short across it since you are measuring the continuity of a transformer winding.

Bill's suggestion of an inverted L is one you should seriously consider and it is more practical than a dipole given your cosmetic constraints.  I feed my Hy Tower as an L for 160 and the setup was very simple.  With 100 feet of wire you can use a simple series capacitor to tune out the inductive reactance on 80 and 40; a tuner will be needed for 160 and probably the higher bands.  My L is cut slightly long for resonance on 160 and I use series caps made of RG-213 to tune it to resonance.  A tap switch from a BC-375 allows quick selection of different segments of 160 without need of further tuning.  It is simple and handles the legal power with ease.

Rodger WQ9E

[WA1GFZ]

Take the tripod off the XYL's roof and grow a tower in the back yard

[W7SOE]

Is the inverted L Bills idea?  How did his post end up inside mine?

I like the idea of the inverted L, but see if you think it is still a good idea after you hear how it would play out at my casa:

The wire would leave the basement shack near the foundation.  It would turn 90 degrees and follow the foundation for 10 feet to get to the middle of the house and then head up the side of the house, spaced away from the house by about 4 inches.

The house has large (3-4 ft) eaves and so the wire would curve under and over the eave with some sort of support to keep it about 6" away from the metal gutter.

It then goes up the slope of the roof to the top of a mast the would extend about 4 feet up.  :-(

Then the wire extends horizontally (maybe sloping down a bit) for about 30-40 ft to a tree.

No place for burying anything.  Ground would be my 8ft ground rod.

Do you still think this would perform better than an inverted V on the shorter (4ft) mast, fed with window line?

I have a KW matchbox which I understand will tune single wire.

Thanks again

Rich

 

[Bill, KD0HG]

Is the inverted L Bills idea?  How did his post end up inside mine?

I like the idea of the inverted L, but see if you think it is still a good idea after you hear how it would play out at my casa:

The wire would leave the basement shack near the foundation.  It would turn 90 degrees and follow the foundation for 10 feet to get to the middle of the house and then head up the side of the house, spaced away from the house by about 4 inches.

The house has large (3-4 ft) eaves and so the wire would curve under and over the eave with some sort of support to keep it about 6" away from the metal gutter.

It then goes up the slope of the roof to the top of a mast the would extend about 4 feet up.  :-(

Then the wire extends horizontally (maybe sloping down a bit) for about 30-40 ft to a tree.

No place for burying anything.  Ground would be my 8ft ground rod.

Do you still think this would perform better than an inverted V on the shorter (4ft) mast, fed with window line?

I have a KW matchbox which I understand will tune single wire.

Thanks again

Rich

 

In spite of the wire being folded in places, why don't you try the inverted L, anyway?

It's going to have a significant amount of lower-angle radiation, likely better than an extremely low dipole. And the cosmetics are good.

There's just no way to accurately model either of your antennas, given their proximity to other objects. Intuitively, you're going to have an inverted L maybe 30' tall and 30' horizontally. That's a fairly high Z on 40, so your ground losses are going to be acceptable. On 80, you're probably going to lose maybe 3 or 4 db in ground losses, but that would be less than a dipole hugging the earth.

Again, there's no way to accurately predict what would work best in your situation without actually trying different designs out. I can only say that the inverted-L that I used at my former city-lot QTH *greatly* outperformed any low inverted vee that I tried, even those fed with balanced feeders. And its vertical portion also had bends.

It would really help if you could tie even one buried ground radial into the setup. Or run a counterpoise around the perimeter of your property, perhaps attached to any fence.

Remember- Even an infinitely small antenna is only 2 db down from a full sized dipole, IF you can keep its losses down.

[W7SOE]

A better way!  Please see the attached "artwork".

Thanks

rich

[Steve - WB3HUZ]

I use baluns on all my dipole and I've never had a problem.

You'll need many radials to make that Inverted-L work well.

[Bill, KD0HG]

A better way!  Please see the attached "artwork".

Thanks

rich

I like that!

But, it will be a real PITA, but put the tuner at the base of the tree. Maybe make your own tuners, one for each band that you use.You can lay radials out on the grass at that point, or use a spade shovel and slot them into the ground a few inches. You *don't* need a lot of- or long radials, 6 of them, ten feet long will be better than one or two 50' long.

A real XYL pleaser and maybe quite effective.  You're putting the high-current (radiating) part of the antenna well away from the house, too.

Again, I really like that one for your situation.

[WQ9E]

Hmmm, I bet the XYL would love a nice green lawn and well watered plants so how about a nice underground sprinkler system and the ground radials could be installed concurrently with the sprinklers. 

I installed some additional coax (mostly for receivers) while I was doing the piping for my new central vacuum system.  While you are doing other home improvements there are usually related ham projects that can be included at little/no extra effort and cost.

The tuner really should go at the base and anything from a "smart tuner" through a series of relay switched networks could be used depending upon your desired financial outlay and building desires.

Rodger WQ9E

[KB2WIG]

I've found the Cebik site to be vury helpfull, and Admission is Free.

I even bet that Fabio Master uses it.

The following is the 'all band inverted L'

http://www.cebik.com/content/a10/wire/ltv.html

klc

[Bill, KD0HG]

A *lot* of fertilizer in the lawn helps everything!

[K5UJ]

I have not tried them but the baluns, if you want to use one, sold at http://www.balundesigns.com look good.  If I were going to go out and buy one I'd get one of his.

Rob