Fan dipole question

[KC2UGV]

Ok, people, got a zinger for you to help me out with.

Just got done putting my fan dipole for 40-20-10 up. MFJ Analyzer (Not the digital one, with the Z meter, just SWR), everything tuned down to 1.5 or better; fed with RG8(?) Rat shack cable (I know, crap cable and all). No balun.

40 Meters - I can get full 100 W output.
20 Meters - Max 20 W Output
10 Meters - Full output

My first thought? Something blown in the 20 meter band portion of the radio, or similar reasons. So, I grab the dummy load, plunk it down to 14.275 (In case of RF leakage), and voila! I get full 100W output.

Now, why, oh why do I only get 20W when connected to the antenna. In fact, on the frequency I use most on 20 (14.070) SWR is 1.2:1.

If there's not enough data, what else do I need to check? And what tools do I need to get my hands on? Or, what texts are out there I can read up to get a feel for where I need to look?

[w3bny]

Some stupid questions if I may.

1. What freq did you use on 20m?

2. Did you cut/prune the antenna for that frequency?

3. What is the resonant frequency of the antenna as it stands now?

4. Did you hook up your analyzer and see what its telling you about swr/Z at the operating frequency of question?

It sounds like the transmitter may have folded back. Just check and see what the antenna is telling you. Others should chime in shortly

[W5RB]

Let's get some details . How high's the antenna , and how close to the TX ? What kind of radio ? How long's the feedline ? What mode are you in when testing , and is there an external meter , or how are you measuring power ? If there's a jumper involved , how long is it ?

[N9FE]

Need some lengths. whats your spacing between the elements. lastly. you got to get a dip meter. Or a MFJ that shows impedence

[KC2UGV]

Some stupid questions if I may.

1. What freq did you use on 20m?


14.070 MHz


2. Did you cut/prune the antenna for that frequency?


Yep. Got a 1.2:1 at that frequency. 1.5:1 at 14.275 (Test frequency).



3. What is the resonant frequency of the antenna as it stands now?


7.035MHz, 14.070MHz, and 28.120MHz (Three element fan dipole).



4. Did you hook up your analyzer and see what its telling you about swr/Z at the operating frequency of question?


Analyzer only shows SWR, and at the operating frequency in question(14.070), it is 1.2:1



It sounds like the transmitter may have folded back. Just check and see what the antenna is telling you. Others should chime in shortly

That's what it sounds like to me as well. But why it does, I have no idea.


Let's get some details . How high's the antenna , and how close to the TX ? What kind of radio ? How long's the feedline ? What mode are you in when testing , and is there an external meter , or how are you measuring power ? If there's a jumper involved , how long is it ?

Antenna is about 30 ft high at the feedpoint, and the ends are about 26ft up. Distance (Straightline) from the TX, 10 ft. Feedline, 30ft (a 10ft cable + Union + 20 ft cable). Mode is PSK31 during operation and testing. Power measured by the power meter built into the rig. And no jumper, just fed through a hole in the wall.

[KC2UGV]

Need some lengths. whats your spacing between the elements. lastly. you got to get a dip meter. Or a MFJ that shows impedence
Spacing between elements, well, at the feedpoint, obviously none. At the ends, 10 ft or so. I droop subsequent legs down a little, by about 10 deg or so from the feedpoint.

Do you need lengths of the actual elements? That could take some time, as I would have to physically measure them.

[N9FE]

You got the legs one on top of each other. That will work. But thats not a true fan. Fans look like spokes of a wheel. Allways tune your highest band first. Which is 10. Don't cut nothin. Just fold back on itself and wrap around the end.

[KJ3N]

I'm leaning towards RF in the shack on 20m.

What additional grounding did you add?

What's the grounding system like?

[N9FE]

I don't like the splice in the coax either.

[KC2UGV]

You got the legs one on top of each other. That will work. But thats not a true fan. Fans look like spokes of a wheel. Allways tune your highest band first. Which is 10. Don't cut nothin. Just fold back on itself and wrap around the end.

I'll have to keep that in mind next time. I got all of them pruned and tuned already, but I did 40 first, then 20, then 10; then back to 40, 20, 10; until they were all where I needed them.


I'm leaning towards RF in the shack on 20m.

What additional grounding did you add?

What's the grounding system like?

RF ground? None. How would I RF ground on the second floor of a building? I figured I would just be inviting more issues trying to make an RF ground in my situation.

Electrical ground? House ground system.

[W5RB]

I'm inclined to agree , RF getting in the radio . If you were TXing on SSB , the receiving op could probably hear the RF symptoms . Could be from leaky coax , or just proximity to the antenna . Coax is cheap , I'd be inclined to replace it with something better shielded . A good RF ground near where the cable comes thru the wall might fix you up , the splice point would be an easy place to try . What's your power supply ?

[KC2UGV]

I'm inclined to agree , RF getting in the radio . If you were TXing on SSB , the receiving op could probably hear the RF symptoms . Could be from leaky coax , or just proximity to the antenna . Coax is cheap , I'd be inclined to replace it with something better shielded . A good RF ground near where the cable comes thru the wall might fix you up , the splice point would be an easy place to try . What's your power supply ?

First thing getting replaced: The coax. I'm getting a new run of it (Right length) in the next week or so.

I also forgot, and this would most likely be an important part of the equation: This is an attic dipole, so, the legs are not out 90 degrees. More like a horizontal V.

Power supply is an older Pyramid 25A, switching, I think.

[W5RB]

You must have a big attic . You're almost certainly radiating RF from the antenna back into the radio . Any way to get the antenna outside ?

[N9FE]

It might better to make one of those with four wire rotor cable. A friend made one, It worked well.. But its an all day tuning affair..

[KC2UGV]

You must have a big attic . You're almost certainly radiating RF from the antenna back into the radio . Any way to get the antenna outside ?

Yeah, big attic. Like 30 ft across and 70ft down or so. Working on getting the antenna outside, but will have to wait for the big run of cable to come in first.

[w0aew]

Do you get RF burns off of the chassis when key down?

[KC2UGV]

Do you get RF burns off of the chassis when key down?

Nope. Which is why I never bothered with an RF ground. I just figured it would introduce more problems.

[KJ3N]

Nope. Which is why I never bothered with an RF ground. I just figured it would introduce more problems.

In the case of second floor shacks, I agree.

I'm still leaning towards RF feedback into the shack / radio / power supply on 20m. Possibly something attached to the radio or tuner that is close to 1/4 wave (16 feet) in length. Proximity to antenna is also not good.

[KC2UGV]

In the case of second floor shacks, I agree.

I'm still leaning towards RF feedback into the shack / radio / power supply on 20m. Possibly something attached to the radio or tuner that is close to 1/4 wave (16 feet) in length. Proximity to antenna is also not good.

Hm, several things come to mind here. I'm starting to think maybe I should remove the UPS from the link as well here, since the power for the radio + power supply + UPS power line comes close to 16ft of cabling in all (6, 6 and 6).

[w0aew]

You might also try about six turns of coax where it joins the fan (if you have enough coax).

[kf0rt]

Got a car battery you can try for power (just to eliminate the PS)? I've seen RF do some odd things with switching supplies.

[KJ3N]

Hm, several things come to mind here. I'm starting to think maybe I should remove the UPS from the link as well here, since the power for the radio + power supply + UPS power line comes close to 16ft of cabling in all (6, 6 and 6).

Plug the power supply directly into the wall. No surge suppressor, no UPS, nothing. See what happens.

[KC2UGV]

Going to try these out tonight (Remove the UPS, and try to get a coil near the feedpoint).

[N4VGB]

Power supply is an older Pyramid 25A, switching, I think.



An old Pyramid would be a linear PS not a switcher. I have 2 of the 25A models I've used for years.

[ki4itv]

FWIW, if everyone used 20W for psk on 20m the whole world would be a kinder, gentler place. ;):lol:

The coil choke mentioned earlier couldn't hurt. Fixed a similar problem on 40m for me a while back.

Have you tried 15m? the 40m section should tune reasonably well on 15 too.

[kf0rt]

An old Pyramid would be a linear PS not a switcher. I have 2 of the 25A models I've used for years.

If it's linear, RF in the PS probably isn't the issue.

Corey: Is it small and light, or big and heavy? :wtf:

[KC2UGV]

If it's linear, RF in the PS probably isn't the issue.

Corey: Is it small and light, or big and heavy? :wtf:

Big and heavy.

In the process of getting the UPS out of the loop, to cut down on the chance of my RF ground being the power lines right now.

[KG4CGC]

Got some ferrite? Get some clip on beads for the coax. Add beads from the connector at the radio until the RF feedback is gone. Since you're not using a balun, do the same stating at the feed point and work down the coax until the problem is gone.

[N4VGB]

Big and heavy.

In the process of getting the UPS out of the loop, to cut down on the chance of my RF ground being the power lines right now.

Unless you've run a separate ground, you're AC power line IS your RF ground.

[KC2UGV]

I think I figured it out.

My MFJ analyzer (MFJ-209) is not calibrated correctly for 14MHz. The dial is almost 1 MHz off! So, my antenna shows a perfect match for 14MHz on the dial, however, in reality, on 14.070 if 15MHz on it's dial...

Explains why there's not an issue with my pure 20M dipole that I used another analyzer to build!

[kf0rt]

Well, shit. That was a good one.

[KC2UGV]

Yep. Pruned, tested at "15MHz", connected to antenna, and full power :) Thanks for everyone's help here :) I think I ended solving some RFI problems to boot (No more squigglies on TV while xmitting).

[N9FE]

Yep in the future, Just fold back and wrap untill you have all tuned to where you want. Then cut. Makes life easyer.

[w0aew]

I also have an ancient MFJ-207 analyzer. To get around the dial inaccuracy, I just zero-beat the analyzer signal with the transceiver on the frequencies of interest, then mark those spots on some masking tape I temporarily apply to the panel. When I'm finished, I tear off the tape.

As they say in Walla Walla, ouila!

[KC2UGV]

I also have an ancient MFJ-207 analyzer. To get around the dial inaccuracy, I just zero-beat the analyzer signal with the transceiver on the frequencies of interest, then mark those spots on some masking tape I temporarily apply to the panel. When I'm finished, I tear off the tape.

As they say in Walla Walla, ouila!

Yeah, I zero beat the unit, and that's how I discovered the 20 Meter band's markings were off. I just assumed (I know, making an ass of me and Umption) after checking the 10 meter dial, it was good to go.

Now, I marked the unit up with, you got it: Masking tape for the owner :)

[N8YX]

If there's one to be had at Dayton this weekend I'm going to pick up a -269 and accessory pack.

[PA5COR]

I love the MFJ 269, used it almost weekly in my antenna and balun experiments.
You won't regret the purchase.

;)

[KC2UGV]

What I borrowed to build my first two dipoles (10 and 20 meter dipoles) I had a 269. Great unit. The 209 isn't bad, and had I RTFM'd I would have known.

[KG4CGC]

Finebusinessoldmanhihi.

[WØTKX]

I heard that in your FT-901 voice.

[N4VGB]

If there's one to be had at Dayton this weekend I'm going to pick up a -269 and accessory pack.

Wouldn't you rather purchase my complete General Radio RF bridge set and do it the old fashioned way???:lol:

Yeah, I know, don't bother to answer.:lol:

I stopped using that crap when MFJ came out with the complete analyzer (I also f'ed up and bought the one that only shows SWR) first.:yuck: The one that only shows SWR is cute but of little real use.:irked: Best for only taking a quick look at a known antenna to see if something has changed.

[KG4CGC]

I heard that in your FT-901 voice.
I did too strangely enough.

[KC2UGV]

Wouldn't you rather purchase my complete General Radio RF bridge set and do it the old fashioned way???:lol:

Yeah, I know, don't bother to answer.:lol:

I stopped using that crap when MFJ came out with the complete analyzer (I also f'ed up and bought the one that only shows SWR) first.:yuck: The one that only shows SWR is cute but of little real use.:irked: Best for only taking a quick look at a known antenna to see if something has changed.

Worked nicely enough for building a fan dipole that needed to be fed with coax into a 50 Ohm impedance transmitter.

[N4VGB]

Worked nicely enough for building a fan dipole that needed to be fed with coax into a 50 Ohm impedance transmitter.

That's according to your definition of "nicely enough" and at your stage of development in RF knowledge it probably did.

When you advance to understanding the resistive, capacitive and inductive nature of antennas and transmission lines.........................what the hell am I talking about??? Not required for even an Extra class license and in the current plug & play world of ham radio, who the f' cares!?:lol:

Carry on.

Edit: ignore any talk of field strength meters and taking readings at designated points, ignore the idea of RF ground.

[KC2UGV]

That's according to your definition of "nicely enough" and at your stage of development in RF knowledge it probably did.


Yep, it worked it's function well.



When you advance to understanding the resistive, capacitive and inductive nature of antennas and transmission lines.........................what the hell am I talking about??? Not required for even an Extra class license and in the current plug & play world of ham radio, who the f' cares!?:lol:


None of which is really required to build a fan dipole, or even a simple dipole. Which was my point. The device works fine as long as you aren't expecting it to work miracles.


Carry on.

Edit: ignore any talk of field strength meters and taking readings at designated points, ignore the idea of RF ground.

I'll also ignore the banging of the cane on the ceiling :)

[KU0DM]

I'll also ignore the banging of the cane on the ceiling :)

:lol:

How has it been performing? I've had quite a lot of interest in fan dipoles, but have never manned up and built one.

[N4VGB]

None of which is really required to build a fan dipole, or even a simple dipole.



Yeah buddy.:ugh::lol:

Carry on.:lol:

[KJ3N]

I'll also ignore the banging of the cane on the ceiling :)

:rofl: :rofl:

[KC2UGV]

:lol:

How has it been performing? I've had quite a lot of interest in fan dipoles, but have never manned up and built one.

The cane or antenna lol

The antenna has been working fine business, even in in a cramped attic. But, I have a pretty open attic when compared to most. 40 meter (According to pskreporter) seems to working in an NVIS fashion as VA seems to be the furthest I can see reports from, 20 meter I get coast to coast coverage easily on 20 W, and 10 Meters, I was hearing a UK station, but I think the directivity killed me on closing that contact.

[N9FE]

Next time were on 75, I'll have to tell about a guy in the next town over who drove his upstairs nosey nieghbor crazy. Lets just say she kept hearing voices. over her TV. Her stereo. The voices The VOICES !

[KC2UGV]

:lol:

How has it been performing? I've had quite a lot of interest in fan dipoles, but have never manned up and built one.

I also have to add, the wires can become quite tangled easily while putting it up, unless you put physical spreaders in. Other than the mistake with the MFJ unit, that was the most difficult part.

[W1GUH]

Yes, that MFJ-269 is one of the best things since sliced bread. I'll never be without one again! One tip for it. Get an unused power connecter for the ext. power in jack, and leave it in the jack when you're not using the '269. It'll act as a "safety" and keep the power OFF. The only thing I don't like about the analyzer is it's easy for the power button to get pressed and run down the batteries. But this trick takes care of that nicely.

OK. We're talking about dipoles and tuning them, and pruning then, and using multiple dipoles on one piece of coax, etc., etc., etc. Look out, here comes my usual :rant: on the :soapbox: ! ;)

Last year doing the hamfest circuit I saw the small Johnson matchbox several times, and the prices were always < $100. I got one without the meter and other stuff -- but with the tuning network clean as a whistle - for $50.00. Here's why you, too, want one of those.

With one of those, or maybe better yet, one you've built (they're easy and cheap to build here's K1JJ's outstandingly easy and effictive design) (http://amfone.net/ECSound/K1JJ13.htm), you NEVER have to prune you antenna. You HARDLY EVER have to worry about "RF in the shack", and you'll have a very easy and effective antenna. The length of the antenna becomes completely non-critical -- the rule of thumb is that any length greater than or equal to a half wavelength on the lowest frequency of operation works just fine -- so you can measure your antenna, put it up, and be done with that part. Plus -- if you want to do an extended Zepp (fun to play with) or a lazy-H (even more fun to play with), the tuner'll tune that, too.

You MAY have to tune the feedline. Impedance varies all over the place depending on the length of the feedline, and it can be tedious to find the length that's good on all bands that you want to opearate but that's a heckuva lot easier than pruning an antenna. And once you've got it, you're done.

Over the years I messed with tuned dipoles, sometimes with frustration, etc., and it took me a good 30 years to get the above about balanced line and link-coupled tuners through my thick skull. What a pleasure putting up a dipole became when I finally "got it!".

Finally, much as I post against them, a "fake" balanced tuner (e.g. single ended with a balun) will do nicely in a pinch. That's what I first used. It's not optimum but will tune a balanced antenna and won't eat up enough power to detract from your fun!

OK....off the soapbox!!! Have fun!!!!

[w0aew]

I've been using a balanced tuner I built from specs in the Handbook (I think it was). Anyhow, pix on "that other site".

[N4VGB]

http://www.miracleantenna.com/MMD.htm

Just use the Miracle Antenna!

They even have video!

http://www.miracleantenna.com/Miracle%20Antenna%20Videos.htm

[VK3ZL]

G'day Corey....I wonder if you have considered using a 40 meter dipole fed with 1/4 wavelength open wire feeders and a balanced tuner? With this set up you can then tune 20, 15, and 10 meters....Probably also the WARC bands as well....No more wire tangles and sorting out each antenna with the coaxial fed fan....Many of these old ideas have been lost in recent years and yet it is the simplest way to get on multi bands with the least bother....I would look at building a link coupled tuner....For 40-10 meters a simple inductor say 12uh, a parallel 75pf transmitting capacitor if you run more than 100 watts, and a few turn coupling link over the center of it with a series old 3 gang broadcast gang...You could breadboard this with a few alligator clips to select tappings for each band and you have the world at your feet...The 40 meter dipole then becomes 1 wavelength at 20 meters and so on up the spectrum...No more multiple wires all over the place..:chin:

Bob..VK3ZL..

[VK3ZL]

If you live in a multi story building and don't have a good earth connection it is a good idea to run a 1/4 wavelength of wire from the earth connection on your radio gear around the skirting or anywhere you can conveniently lay it....This will help eliminate RF feedback and other problems....Toss it out the window or stick it in the bathroom...Endless possibilities....

Bob..VK3ZL..

[N4VGB]

G'day Corey....I wonder if you have considered using a 40 meter dipole fed with 1/4 wavelength open wire feeders and a balanced tuner? With this set up you can then tune 20, 15, and 10 meters....Probably also the WARC bands as well....No more wire tangles and sorting out each antenna with the coaxial fed fan....Many of these old ideas have been lost in recent years and yet it is the simplest way to get on multi bands with the least bother....I would look at building a link coupled tuner....For 40-10 meters a simple inductor say 12uh, a parallel 75pf transmitting capacitor if you run more than 100 watts, and a few turn coupling link over the center of it with a series old 3 gang broadcast gang...You could breadboard this with a few alligator clips to select tappings for each band and you have the world at your feet...The 40 meter dipole then becomes 1 wavelength at 20 meters and so on up the spectrum...No more multiple wires all over the place..:chin:

Bob..VK3ZL..

We don't agree on much other than art, tank circuits and antennas Bob.:lol: I guess that's enough.

Open wire feeders and balanced-balanced tuners seem to be fading in popularity among all but the older hams. Why? I have no idea.

The concept of proper RF grounding as opposed to proper home AC distribution grounding is another sticking point that most seem incapable of grasping. Combining those functions is an invitation to problems.:irked:

[WØTKX]

Fixed my wind damaged open wire connection this afternoon.

It does amaze me that more folks don't do the "all band" doublet (or OCF) with a tuner and balanced line... balun or no.

Easy peasy antenna system. :dance:

[KG4CGC]

Been considering the folded dipole for 20m with the legs added for 40m.