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Author Topic: 10 meter antenna questions  (Read 2034 times)
KC9MIB
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« on: November 15, 2007, 08:26:35 AM »

I am a new ham, and I have some very basic (probably pretty stupid) antenna questions.
I have asked several hams around here, but I keep getting different, conflicting answers.
I have a tech license, and I just started studying towards my general license. I have a long way to go. While I study, I wanted to start operating on ten meters so that I could learn some basic HF operating procedures.  
My HF radio is an ICOM IC-735. I asked at a shop what would make a good, inexpensive, 10 meter antenna that would get me on the air quickly.
My plan was to use this until I could make a more informed decision about the purchase of a more permanent antenna that would cover more bands. I could then start listening on other bands while I study too.
Since I already had a tuner (MFJ 949E) the guy in the shop said the easiest and least expensive way to go would be an old fashioned 102" steel whip.
So I went home and mounted it:
102" steel whip, screwed into a standard threaded mount, 50 feet of RG 213 coax runs into the shack to the tuner. The mount is screwed onto a 1 foot piece of PVC pipe, which is attached to a 10 foot piece of steel conduit. The conduit is attached to a fence post. So the antenna is 10 feet off the ground, and there is no direct connection between the mount and the earth (there is a piece of PVC in between).
Last evening I asked another (much more experienced) ham to try contacting me. He was using a beam antenna from about 20 miles away. I could not hear him and he could not hear me. It was as if we were not on the same frequency. Yes, we checked, we were on the same frequency, I was set to USB, he went over most of the basic settings with me, and I went over the operator's manual. I can't see what I'm missing.
But obviously, I am doing something wrong.
I am wondering about a gound plane. The guy who recommended the steel whip said that as long as I was using a tuner, I didn't have to worry about a ground plane.
From what I read, I'm not sure that this is correct. Another person told me that I could use only one ground plane antenna, and it had to be the same length as the whip.
If I would try adding some homebrew ground plane antennas to this set-up, now long should the be? What angle should the be at in relation to the vertical antenna? What else am I missing?
Thanks.
Dave KC9MIB    
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G8UBJ
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« Reply #1 on: November 15, 2007, 08:46:34 AM »

20 miles ground wave on HF is quite a haul unless you have a fairly good antenna. Without a ground plane most of your signal is probably not going where you want it. Also to work someone over that distance will require both your antennas to be quite high.

My suggestion would be to build a simple wire dipole for 10m and if possible mount it at roof level or above. if possible the wire should be side on to the person you are trying to work.

Personally I don't think 10m is the ideal band. You would have a lot more luck and fun if you put up a dipole or inverted v for 20/40 or 80m

http://www.hamuniverse.com/dipivcal.html

73 G8UBJ

 

 
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WB2WIK
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« Reply #2 on: November 15, 2007, 09:14:28 AM »

There's no such thing as "20 miles on ground wave" on 10 meters -- impossible.  Ground wave is a much lower frequency phenomenon and the highest frequency amateur band where it's of any real use is 80 meters, and at amateur power levels, it's not good for much distance (consider AM BC stations commonly run 50,000W output to highly efficient antennas and get out about 50 miles via ground wave).

Whoever gave you the advice about "if you have a tuner, you don't need a ground" gave you very poor advice.  This directly conflicts with the accumulated wisdom of antenna engineers from the past 110 years or so.

RF is an AC signal conducted by two conductors, either twin lead or coax (center conductor + outer conductor), or even a single line plus a very good earth ground (in which case the very good earth ground is the "other" conductor -- and it's not great).

If you connect coax to your 102" whip, that takes care of one connection.  What's the outer conductor connected to?  Nothing?  Ever try lighting up an electric light bulb using only one wire?

This doesn't work, at all.

Try mounting the same whip on a metal mast/pipe with the outer conductor of the coax well bonded to that mast.  Then, right at that point where the coax attaches to the mast, add three or four 98" long wire radials clamped/soldered (somehow well connected) to the coax braid/mast connection and sloping downwards towards the ground at about a 45 degree angle or so.  The far end (bottom end) of each radial wire can be tied to a string which is then anchored to something down below (tent stakes work fine -- whatever will keep the radials in position and hopefully not allow people to trip over them).

Now, you have a "ground plane" antenna, which works fine and will be a hundred times better than just the whip without any radials.

Of course, a regular "CB" type ground plane, which is built as I described but usually made of all aluminum elements (vertical plus radials) and can be elevated as high as possible above ground, preferably above your roof and other stuff nearby, will work even better.

If you do that and *then* try contacting the other station 20 miles away, you'll probably make contact.  But it won't be "ground wave," it will be tropo.

A plain 1/2-wave dipole (horizontally polarized) actually will work better for tropo than the vertical will; however, for "DX," when the band is "open," the vertical or dipole will work almost identically.

WB2WIK/6

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KE5ICG
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« Reply #3 on: November 15, 2007, 09:15:48 AM »

First, welcome to the hobby.  The whip is an ok idea, but I'd take it down and put it on a vehicle (that's where mine is).  A wire dipole would probably do better for you, and they are easy and fun to make with plans all over the internet (wire, insulators and such are plentiful and inexpensive).  As for 10 meters, long distance communications are only fair right now, but you never know when opportunities to work some DX may present themselves.  I keep an inexpensive scanner (radio shack NASCAR type) around and let it scan from CB through 28 and 50 to 54 Mhz.  When I start to hear lots of distant stations in CB land, that is often a sign that the Maximum Usable Frequency (MUF)-- read about it on the net -- is climbing.  Other times you may be able to work some stations after a front comes through or when there are temperature inversions -- again the scanner comes in handy.

I too, am looking forward to getting my general class license -- after all, 20 meters is usually going pretty good all the time.  But in the meantime, there are all kinds of things to do on 10 and 6 and even 2 meters.  With eham you've got a very good resource for information too.

73 and good luck -- Ray
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WA3SKN
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« Reply #4 on: November 15, 2007, 09:24:56 AM »

20 Miles and cross-polarization is your problem.
And, without radials, your signals are going straight up!
Now a dipole for 28.4 Mhz (center of tech portion of SSB 10 meter band) is 8ft 3 in per leg, total length of 16 ft 6 inches.  Feed that with coax and mount the dipole either horizontally as high as possible, or vertically (low angle radiation for DX).
You can expect E-skip during the daylight hours and local activity at evening/night.
You could add radials (the more the better) to the present antenna, but your friend 20 miles away with horizontal polarization will still not hear you. DX might, though.

-Mike.
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KC9MIB
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« Reply #5 on: November 15, 2007, 10:02:04 AM »

Thank you all very much.
As I stated before, this antenna was only meant to be temporary until I decide on which antenna(s) to put up for more permanent use on HF. I realize that 10 meters isn't the ideal band, but I am operating there (or trying to anyway) right now because I can as a tech. Also there is a club in that town that is about 20 miles away, that is trying to get a 10 meter net going on Thursday evenings. The purpose is to get new guys like me operating on HF and using their 10 meter priveleges.
So when I threw this antenna together Monday evening I was really hoping to get at least something. But that's how you learn.  
WB2WIK your information about the ground radials is just what I was looking for. The mount that the whip is screwed into actually has four spaces to screw ground radials into. So I'll try to get some on it and see what happens.
Would #6 bare copper wire work for those?
Again, thank you all very much. I am enjoying this hobby more than just about anything else I've done in quite some time.

Dave KC9MIB
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AG4RQ
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« Reply #6 on: November 15, 2007, 10:04:40 AM »

G8UBJ is right. Twenty miles groundwave on 10m is a pretty tall order. The hillier the terrain, the less range you will get. Go to qrz.com and click on "Name Search". Do a search of your zip code. I already did. There are 110 hams in your zip code alone. Find someone a lot closer to you to try to make contact with.

For your immediate purposes, the 102" whip with the tuner should be fine. Just don't expect 20 mile groundwave range.

As for building a groundplane antenna, the radials should be sloping down from the radiator at a 45-degree angle. For a resonant groundplane antenna on 28.4 MHz, the radiator should be 98.87". The 4 radials should be 103.82". I have a chart on my web site. See:
http://www.geocities.com/ag4rq/
Click on the "Dipole" link and scroll down. You can right-click on the graphic and download it to your hard drive for future reference.

My main antenna is a 40m shortened dipole antenna that I use with 450 ohm ladder line and a tuner. I can use it from 6 through 80m.

Welcome to ham radio. good luck, and don't wait too long to get the General. Like G8UBJ said, you will have better luck on 20, 40 and 80m. A dipole with ladder line and a tuner will put you in business.

73 de Mark
AG4RQ
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AG4RQ
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« Reply #7 on: November 15, 2007, 10:10:36 AM »

"There's no such thing as "20 miles on ground wave" on 10 meters -- impossible."

Steve, don't say it's impossible. Contacts like that are possible where I live. Florida is as flat as a pancake. In most other places it isn't possible because of hills, valleys, mountains, etc. Here, you could even do 20 miles on 6m.

73 de Mark
AG4RQ
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WA3SKN
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« Reply #8 on: November 15, 2007, 10:24:52 AM »

Would #6 bare copper wire work for those?
Yes David, this will work fine.
(And, we all (most all) know he meant "direct wave" when quoting "ground wave".
Since they are starting a net, verify what polarization they plan to use.  At 20 miles (on ten meters), it will make a difference.

-Mike.
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AA4PB
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« Reply #9 on: November 15, 2007, 10:59:29 AM »

Steve didn't say that you can't work 20 miles on 10M. What he said was that it won't be "ground wave", it will be "tropo" propagation.
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K5CQB
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« Reply #10 on: November 15, 2007, 11:19:01 AM »

Dave,
Depending on how much of the #6 wire you have I would suggest using it for something else, #6 isn't cheap.  You can use a lighter wire for radials and it will work fine.  If you want something good for HF try a fan dipole or a ladder line doublet cut for 80 or 160 with an antenna tuner.  Either dipole will serve you well.  I currently use a fan dipole and it works great.  I suggest the ladder doublet  and a tuner.

http://www.cebik.com/edu/edu6.html
http://www.cebik.com/mu/mu6a.html
http://www.hamuniverse.com/multidipole.html

73,
Jim
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WB2WIK
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« Reply #11 on: November 15, 2007, 11:44:19 AM »

>RE: 10 meter antenna questions  Reply  
by AG4RQ on November 15, 2007  Mail this to a friend!  
"There's no such thing as "20 miles on ground wave" on 10 meters -- impossible."

Steve, don't say it's impossible. Contacts like that are possible where I live. Florida is as flat as a pancake. In most other places it isn't possible because of hills, valleys, mountains, etc. Here, you could even do 20 miles on 6m.<

::I didn't say you can't make 20 mile contacts on 10m -- or on 6m.  I just said they wouldn't be ground wave, and they're not.  They can't be.  They're tropo scatter.

WB2WIK/6  
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N1LO
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« Reply #12 on: November 15, 2007, 12:24:10 PM »

Hello Dave,
 I'm guessing that your local 10m net will be using vertically polarized antennas. I think you'll need 40 or more feet of height or so. Do you have a tree with at least one high branch you can set a rope over? You could use this to pull a vertical antenna up quite high.

Mark
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WA1RNE
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« Reply #13 on: November 15, 2007, 01:23:34 PM »


 With suitable height above ground, you can indeed communicate via "Ground Wave" on 10 meters. Ground wave consists of the
Surface and Space waves. The Surface wave is non-existent at 28 Mhz., but the Space wave is with sufficient line of sight.


 Line of Sight, miles (approx.) =  1.415 x SQRT(antenna height, feet) x2

 (Multiplied by 2 to get the total LoS, transmit and receive)


 So for antennas at 50 feet, LoS works out to about 20 miles - a perfectly reasonable possibility via Space wave, also commonly called "Ground Wave", though not technically correct.

Tropo is possible but usually covers longer distances, typically much greater than 30 miles or so.


 Anyway, to solve your 10 meter problem, add the radials to the whip - as without them very little of the transmitter power is actually being radiated - especially toward the horizon which is where you want it - and get the antenna up to about the 50 foot level. If you can't reach that height, try a small yagi at 20 feet or better.


 ...WA1RNE
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N0RZT
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« Reply #14 on: November 15, 2007, 01:31:03 PM »

Good afternoon,

Not to rush you, but why don't you see if you can get those radials installed Friday or Saturday?  10m has a funny way of opening during contests.  You might be able to make some 10m contacts on Sunday during the ARRL Sweepstakes.

Who knows?  You might even find a trans-equatorial path to South America open (it'd be more likely if there were a major international contest, but I have heard stations in Brazil and Argentina working pileups in the US and Canada on 10m during "normal" weekends, too).

73,
Chris
N0RZT/8
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