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Author Topic: 6BTV/Radials and RX  (Read 1802 times)
KF7DS
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Posts: 174




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« on: September 04, 2012, 06:44:47 PM »

All:

I have had my 6BTV up for about a year, and have enjoyed it's performance. I am primarily a CW op and have it tuned well on all bands, including the 17m add-on. It is mounted at ground level in a challenging location (1/2 the yard is flat; 1/4 pitches down quickly in stairsteps, and the rest goes downhill more quickly at a 30+ degree slope).

It is installed with approximately 22 radials averaging 20' in length, buried about 2" each. I have enough DX (Tasmania/Lithuania/Chile/etc...)to know that my signal gets out, and I am sure it could be better, but I think I am missing stuff on RX.

And, it gets increasingly frustrating. During the last SKCC WES, W7SRM/Steve, who lives about 4 miles from me at the same 600'+ elevation in the hills, has a Hexbeam and he could hear France/Bert 569 when, at the same time, Bert was barely 329 at my QTH.

Yes, I know I am comparing apples to oranges, but it got me thinking that if I redid my radial field (XYL says I can rip out some shrubs and take over a part of the yard) to be a more symetrical (though some will be 8' and most will be 18'-25' with a few at 35') pattern around the antenna base, and say do 50 total, would my RX improve? I know I will have to re-tune the antenna , but that is the fun part.

Feedback welcome.

Don KF7DS
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KC7YE
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Posts: 91




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« Reply #1 on: September 04, 2012, 09:13:34 PM »

Not apples & apples. Hex beam should be better on receive.
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KF7DS
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Posts: 174




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« Reply #2 on: September 04, 2012, 09:50:42 PM »

Not apples & apples. Hex beam should be better on receive.

True, and I understand that, but would RX benefit from a better radial field?

Thanks,
Don KF7DS
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WX7G
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« Reply #3 on: September 04, 2012, 10:24:42 PM »

Your radial field is just about maxed out. The ground loss with what you have should be 10-15 ohms resulting in 60% or better radiation efficiency.

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KK5J
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Posts: 76




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« Reply #4 on: September 05, 2012, 06:59:39 AM »

Don-I also use a 6BTV. I, too, ran about 24 radials for a while. When I went to 40 radials I noticed a distinct improvement in RX/TX compared to the 24. Its anecdotal evidence only. Nothing scientifically measured. When I went to 60 radials I did not see any added performance in any way.  Your results may vary. Im also not comfortable burying radials since the intended use takes it up to 10 meters. I use lawn staples and over time they disappear into the grass.

Its always a pleasure to work Bert, F6HKA, during the WES. He is a good op.
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W5DQ
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« Reply #5 on: September 05, 2012, 10:02:52 AM »

It is installed with approximately 22 radials averaging 20' in length, buried about 2" each. I have enough DX (Tasmania/Lithuania/Chile/etc...)to know that my signal gets out, and I am sure it could be better, but I think I am missing stuff on RX.

And, it gets increasingly frustrating. During the last SKCC WES, W7SRM/Steve, who lives about 4 miles from me at the same 600'+ elevation in the hills, has a Hexbeam and he could hear France/Bert 569 when, at the same time, Bert was barely 329 at my QTH.


Don,

Sounds like you've got a decent radial field but I might suggest for 40M and lower that a few more longer radials might help out the mix. I have a 6BTV also and have 48 radials, averaging around 35 ft long. A half dozen or so are 10-12' since they are against a wooden fenceline and another dozen+ are 45' to 65' going out into the back yard open area. The antenna is mounted at the side of the yard to please the XYL. My ground type is poor being mainly sand and small rocks with no vegetation here in Mojave Desert but with the radial field I have, I get good results with my 6BTV. Of course, I get better results with my Force 12 C3S at 40'.

While comparing 'fruit', don't forget to consider the take off angle of each antenna. A well designed vertical antenna system (ie proper radial field layout) should exhibit a very low TOA. Also a not so good radial field would most likely push that TOA up in elevation while a Hexbeam may or may not have a low TOA, basically determined by height above ground. Many small beams are not mounted at the optimum height to achieve the best TOA but still get decent results. You didn't specify what band your comparison was done on but I assume it was between 20M and 10M as that is what a Hexbeam usually covers. Also depending on your placement of the vertical with relation to nearby metallic objects, it is possible for you to have nulls in your patterns that may account for the loss of RX to certain areas. Before I got to excited about a bad system, I would do some additional comparisons between your setup and Steve's, noting the difference in heard / not heard and signal strengths. By mapping this you should be able to determine, with some accuracy, if you indeed have any nulls and to what impact they appear in your system performance.

Good Luck,

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
WB2WIK
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« Reply #6 on: September 05, 2012, 10:43:28 AM »

More or better radials might possibly help, but offhand I doubt they will.

I've used BTV verticals for decades and still have one.  Mine is elevated at about 25' (roof tower) with 24 "tuned" radials sloping away under it.

But comparing that to any kind of beam is apples and hand grenades.  I have beams for 20m and "up" and I can't recall any time when the 6BTV with a good radial system could hear anything as well as my 20m beam could, from any direction, at any angle, with any propagation.

Not only does the beam get a huge ground reflection boost that verticals can't enjoy, but being directional nearly always improves S/N ratio because it's receiving noise from a much smaller radius than a vertical, which receives noise from all directions.  There are lots of stations I can "hear" perfectly well with the beam that are right in the noise with the vertical.  Ditto on 15 & 10m, where I can also switch from the vertical to a beam.
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W8JI
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« Reply #7 on: September 05, 2012, 02:54:50 PM »

Unless you have common mode noise following the coax shield out to the antenna, radials will not do a thing for receive.

Receiving is dominated by pattern and directivity, not gain. You have an omni patterm, no real azimuthal directivity. Your friend has an antenna that has worthwhile directivity, and even if the gain is low from poor efficiency it will receive better.

http://www.w8ji.com/receiving.htm

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M6GOM
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« Reply #8 on: September 05, 2012, 03:33:02 PM »

Not apples & apples. Hex beam should be better on receive.

True, and I understand that, but would RX benefit from a better radial field?

Thanks,
Don KF7DS

In short it'll make little difference, certainly not to any level you'll notice.

You have a vertical which is more prone to noise than a horiztonal antenna.

You have an omnidirectional antenna which doesn't have the ability to null out noise like a beam can.

You have an antenna which is several dB down on a dipole at 1 wavelength high.
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KC4MOP
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« Reply #9 on: September 05, 2012, 05:08:53 PM »

A beam antenna will have a better chance of 'focusing' in on the intended direction than a vertical.
If 40M is your favorite band, would you consider a 50 foot tower and a rotatable dipole or HexBeam for your station?
The radial field would not make much difference in regards to better receive, when the vertical is omnidirectional and most of the noise is vertically polarized any way.

Fred
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K3VAT
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Posts: 699




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« Reply #10 on: September 05, 2012, 05:29:02 PM »

A beam antenna will have a better chance of 'focusing' in on the intended direction than a vertical. ...
Fred

Not always the case.  This is only 'generally speaking' or 'in most cases'.  A yagi (beam antenna) may exhibit a deep null in the intended DX direction because it is mounted too high or too low).  For example, for the Malpelo DXPedition earlier this year my 10M beam (@45') was too high to adequately work him.  I switched to a multiple band vertical where his signals were 59 + 10dB.
« Last Edit: September 05, 2012, 05:37:28 PM by K3VAT » Logged
KF7DS
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Posts: 174




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« Reply #11 on: September 05, 2012, 08:28:54 PM »

Thanks so much everyone....this has been a good discussion and given me a lot of ideas.

But, this convinces me more than ever that spending $ on the best antenna you can afford/not offensive to neighbqors/not offensive to the wife is better $ spent than chasing hardware.

Thanks again.

See some of you on WES.

Don KF7DS
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W8JI
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« Reply #12 on: September 06, 2012, 02:34:41 PM »

A beam antenna will have a better chance of 'focusing' in on the intended direction than a vertical. ...
Fred

Not always the case.  This is only 'generally speaking' or 'in most cases'.  A yagi (beam antenna) may exhibit a deep null in the intended DX direction because it is mounted too high or too low).  For example, for the Malpelo DXPedition earlier this year my 10M beam (@45') was too high to adequately work him.  I switched to a multiple band vertical where his signals were 59 + 10dB.

The problem is almost never that an antenna is "too high". The problem is most commonly that an antenna can be at a height that creates a null at the angle of the signal....or is just pointed the wrong direction.

If we look at pattern, we see for every 1/2 wave height a horizontally polarized system gets a new null. On ten meters at 45 feet, earth reflection would try to force a deep null at ~22 degrees. This isn't really a too high problem, it is a "wrong place" problem. At around 55-60 feet, the 22 degree null goes away and starts to be replaced by a peak. The null moves to 17 degrees.

The nulls create the problems, and are why we can't have too many different pattern antennas. We usually (incorrectly) blame it on take off angle. :-)

I think I wrote an eHam article about it.
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KC4MOP
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« Reply #13 on: September 06, 2012, 05:53:21 PM »

A beam antenna will have a better chance of 'focusing' in on the intended direction than a vertical. ...
Fred

Not always the case.  This is only 'generally speaking' or 'in most cases'.  A yagi (beam antenna) may exhibit a deep null in the intended DX direction because it is mounted too high or too low).  For example, for the Malpelo DXPedition earlier this year my 10M beam (@45') was too high to adequately work him.  I switched to a multiple band vertical where his signals were 59 + 10dB.

The problem is almost never that an antenna is "too high". The problem is most commonly that an antenna can be at a height that creates a null at the angle of the signal....or is just pointed the wrong direction.

If we look at pattern, we see for every 1/2 wave height a horizontally polarized system gets a new null. On ten meters at 45 feet, earth reflection would try to force a deep null at ~22 degrees. This isn't really a too high problem, it is a "wrong place" problem. At around 55-60 feet, the 22 degree null goes away and starts to be replaced by a peak. The null moves to 17 degrees.

The nulls create the problems, and are why we can't have too many different pattern antennas. We usually (incorrectly) blame it on take off angle. :-)

I think I wrote an eHam article about it.

RF and Take Off Angles for different bands is amazing stuff. Someone I know from another forum did an experiment on 40M and had 3 similar, 3 element Yagis mounted at various heights, up to 190 feet.
And was able to track that Take Off Angles would change constantly from different directions at various times of the evening.
Ultimately there was phasing coax for each antenna so that he could focus a strong signal into the middle East. A phased array. The system was able to selectively turn on one, two or three antennas.
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W8JI
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« Reply #14 on: September 06, 2012, 06:02:45 PM »

The last thing I look at is take off angle.

I look at absolute gain at the desired angles, and where the nulls are.

When a friend was writing EZNEC, and he lamented about even including TOA. He kept telling me he knew it would mislead people. He finally included it, because another software had it.
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