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Author Topic: Radials vs. ground rod in condensed space  (Read 2586 times)
KC2ZUX
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Posts: 4




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« on: March 19, 2013, 10:21:00 AM »

Greetings, I am trying to work a new antenna for my base station.  I am considering a MFJ-2990 or something similar in function.

My Neighborhood is a subdivision with tent-pole power delivery.  What this means is that on 3 sides of my house there's a running power cable.  The cable is between 10 and 15 feet in the air.

I am thinking that since  I don't have the ability to run a dipole at 80' in the air, was to go vertical, and put the vertical in the center of the yard.  I was looking at the MFJ-2990.  the only issue is that the radials necessary according to the system is extreme for my situation.   eight 14-foot radial wires. 

My two problems with that setup is 1, it takes too much area on the ground....and 2, I have two siberian huskies that will dig them up...make no mistake, they will dig them up.

I was reading an article about using a 8 foot ground rod, and going straight down into the ground.  I can go down, that's easy...
I was wondering, would a ground rod work? and if so, would it propogate as good as the cables?

Thanks.
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AD4U
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Posts: 2150




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« Reply #1 on: March 19, 2013, 11:02:42 AM »

If you have typical USA soil with depleted mineral content, a ground rod will make a very poor counterpoise for a vertical antenna.  You will make a contact here and there, but the vertical will not be a good performer at all.

In typical USA soil unfortunately there is no alternative to a good radial system.

Dick  AD4U
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AD6KA
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Posts: 2232




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« Reply #2 on: March 19, 2013, 11:03:35 AM »

Quote
I was wondering, would a ground rod work? and if so,
would it propogate as good as the cables?

Almost anything will radiate and "work" per se.
People have run coax to a balun and a 250w light
bulb 10 feet in the air and made contacts.

But a vertical will just not work very well without
a radial system. And I don't think that 8 14' radials
will work very well except perhaps on 10-15-20.

Can you put a shorter, loaded vertical like a 5BTV or HF6V
with two tuned radials for each band up on the roof? This would
work a whole lot better than a 43' vertical on the ground
with just a ground rod. If you don't want to or can't put
up radials on the roof, maybe a counterpoise type vertical
like a Cuschraft R8 could fit the bill for you.
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W1VT
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Posts: 804




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« Reply #3 on: March 19, 2013, 11:07:16 AM »

If a ground rod worked as well as the radials, nobody would go through the hassle of installing radials.

Not only can you expect much weaker signals using a ground rod instead of radials with any of the 43 ft verticals, but you can expect more RF in the shack issues, as radials also decouple RF off the feedline.  

In your proposed installation, the feedline acts as the sole radial--straight back to the shack!

Zack Lau W1VT
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W8JX
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Posts: 5350




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« Reply #4 on: March 19, 2013, 12:02:00 PM »

If you have typical USA soil with depleted mineral content, a ground rod will make a very poor counterpoise for a vertical antenna.  You will make a contact here and there, but the vertical will not be a good performer at all.

In typical USA soil unfortunately there is no alternative to a good radial system.

Dick  AD4U

I have to disagree. You can use a few of them in a angled pattern to increase ground rod soil contact area. I have used a hustler 5btv for nearly 20 years with no radials and it works far better than it should. Most of my work is on 40 with a little on 20 and 15. I always get great signal reports on 40 too. I am not saying that radials do not help but what I am saying is that sometimes it is possible to do fairly well without them.
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KC2ZUX
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« Reply #5 on: March 19, 2013, 12:23:47 PM »

The big concern for  me is space ...or lack thereof. (I fall into that pit)

Because I rent, and my backyard is small, I cannot put up multiple antennas.
One of the reasons I was looking into the MFJ-2990 is because of it's span of coverage.

I can't put things on the roof.  No permission...

I can't put multiple items up because I fear the RF distortion from the surrounding power cables.

It's a lose lose...
ok...how deep can I put the guide wires?  Can I put them like two feet in the ground and run them out?
Or do they need to be on the surface?
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AG6WT
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Posts: 431




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« Reply #6 on: March 19, 2013, 12:24:44 PM »

Evan,

Before you consider a 43' vertical, is your yard big enough so that you have more than 43' from the vertical's base to the nearest power line? You need to make sure that there is no way your antenna can touch a power line!

If there is room, install as many radials as you can, in any direction you can, for the maximum length you can. The more the better for getting your signal out but even a few will work for the purpose of making contacts. If you don't have enough your feedline will act as a radial and you'll get RF in the shack. A ground rod at the antenna's base might help as will a feedline choke.

If your yard is too small for a 43' vertical, consider putting a shorter one on the roof with 30 or more radials. You can work 40 meters and up with great results.

Ray KJ6AMF
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M6GOM
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Posts: 862




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« Reply #7 on: March 19, 2013, 12:55:11 PM »

if you have an 8ft x 8ft space, even above your house or in the loft/attic consider the G3TPW Cobwebb antenna. 5 full size resonant dipoles for 20-10m in an 8ft x 8ft square.
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WA9FZB
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Posts: 171




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« Reply #8 on: March 19, 2013, 05:10:03 PM »

You could also use a trap vertical, ground mounted.  I have been using a Hy-Gain 14-AVQ, ground mounted with about 6 or 8 radials for many years.  It isn't the answer to all pile-ups, but it makes plenty of contacts on 40 through 10 meters.  It is only 18 feet tall, so no worry about it hitting power lines if it goes down.  With ground mounted verticals, radials do not need to be resonant - in fact they really only need to be as long as the vertical is tall.  If you can't make then that long, bend them to one side or the other.  Bury them a couple of inches below the sod and get on the air.
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N4CR
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« Reply #9 on: March 19, 2013, 06:20:37 PM »

The bigger problem I see is low power lines surrounding your area. The last thing you want is to set yourself up for your antenna to fall into a power wire. That's your #1 safety concern.

If that wasn't a problem, an antenna like a Cushcraft R-8 is a self contained vertical antenna. You can mount it on a 10' tripod with the tripod legs bolted to buckets of concrete in holes in the ground. It must be guyed. it's not a beam on a tower, but it is a solid performer.

But that would make it 10' + 28.5' tall and would likely fall into a power line if it came down. I would never mount anything that could fall into a power line, regardless of my desire to get on the air. If your calculations allow a 38.5' antenna to not fall onto a power line, it's great solution.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JX
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Posts: 5350




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« Reply #10 on: March 19, 2013, 07:14:01 PM »


Because I rent, and my backyard is small, I cannot put up multiple antennas.
One of the reasons I was looking into the MFJ-2990 is because of it's span of coverage.


The problem with a non resonant antennas like the one above is they tend to be more fussy about ground radials. Also they are not magical on all bands and  are a compromise at best and a 43 footer is also at a disadvantage on 20 and above with a higher angle of radiation that increases with frequency. I limited space i would a resonant vertical like a Hustler 5 BTV or Hygain 18AQV. You will likely get better results and have to "fuss" with it less.
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KC7YE
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Posts: 91




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« Reply #11 on: March 20, 2013, 08:20:29 AM »

Have used 4 / 5 BTV ground mounted with & with out radials over the last 40+ years. All worked, radials were better. What use now is a HB "S9" type antenna with Icom AH 4 at feed point and what ever radials can string out, 80 - 10. As live in condo, most ops are P/M. Set up for QSO parties in a state park cabin/ KOA cabin. Spent all of Feb in vacation rental in desert with this set up. Missed very few that I heard in MN, LA, NC, MS QP's. Hey it works and did I mention had fun. Do find a good ground for shack helps too, water pipe most times.
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KF7CG
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Posts: 799




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« Reply #12 on: March 20, 2013, 09:23:44 AM »

Consider one of the GAP Antennas, Or even the MFJ-1798. I had very good luck with the MFJ except that it was susceptible to damage from the high winds that occur too frequently in my area. That is why I am in the process of installing a GAP Titan DX on a ten foot pole at my location. Initial testing shows it to be a good performer 80 through 10 with no radials needed. Only covers 130 KHz of 80 though. Full coverage other bands.

KF7CG
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WB6BYU
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Posts: 12979




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« Reply #13 on: March 20, 2013, 12:00:37 PM »

You have to read advertising claims about frequency coverage with a bit of a
jaundiced eye in many cases:  I've seen antennas that claimed to "work" on a
band when only 1% of the power was actually radiated.  While many of the
untuned vertical types can be tuned to a low SWR across a wide frequency
range, ground losses are often high on the lower bands (160m and 80m especially)
due to the short length, and the radiation pattern may not be ideal (though
probably still usable) on the bands where the antenna is longer than 5/8 wave.
In addition, tuning the antenna through a length of coax operating at a high
SWR will also increase losses.

Here is one analysis:  http://vk1od.net/antenna/multibandunloadedvertical/index.htm

The details might not be quite the same as what you are considering, but the
general principles should apply.


Sometimes in the practical world we need to choose options that may not be
ideal in other conditions.  If all you can manage is a vertical on a single ground
rod then do it.  True, your signal won't be as strong as it may be with a good
set of radials, but even the worst antenna up in the air works better than the
best one still sitting in a box in the garage.  You can try using several ground
rods around the base, tying them together with heavy wire.  Or you can use
heavy wire for the radials and let the dogs dig it up.  Or put down welded cattle
panels or reinforcing mesh for concrete - let the dogs try to dig through those.
I have some 1 1/4" structural steel tubing from a greenhouse that collapsed in
the snow that you could use for radials that probably wouldn't be bothered by
the dogs, either.  (Magnetic materials such as steel aren't as good as copper
for radials or antennas, but sometimes you need the durability.)

If you are using a poor ground, then there may be some advantage to choosing
a trapped antenna such as the 18AVQ or 6BTV rather than one that requires a
tuner, even though it may not be advertised to operate on as many bands.  That's
because, on the bands where it is intended to operate, the coax losses are likely
to be lower.
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WH7DX
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Posts: 1029




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« Reply #14 on: March 20, 2013, 12:25:06 PM »

I looked on the satellite map for your area and it looks like you might have some trees?

I would start with a 10M or 15M dipole antenna.   Just put it up somewhere - doesn't really matter.. (throw it up on something) keep the line above the dog for now..  try it out.

Probably a 15M dipole because it's still small and more on 15M than 10M.

Stay away from the power lines and go from there.

If the simple dipole works (contacts, noise doable) (it's as cheap as can be)..  get a 20M up and you're good to go.

If you use black wire from hardware store and paint center connector black and ends.. it's very hard to see.   DX Engineering has good antenna wire.

Have fun!

WH7DX

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