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Author Topic: 160M Dipole 20 Feet Above ground  (Read 3720 times)
K0BT
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Posts: 180




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« on: February 02, 2013, 06:17:02 PM »

Here in the Phoenix area, we are a bit limited when it comes to trees and we have extremely poor soil conditions.  My house sits on a 1+ acre lot with a large shop 120 feet behind it. My primary antenna is a 6BTV with a very good radial field. It works well on frequencies from 40M to 10M and on a narrow slice of 75M, but I would at least like to operate (at least locally) on 160M and 80M. I can string a 246' long 160M dipole from building to building, sloping down a bit on the final 30 feet at either end, but I can only get it about 20-25 feet above ground. I could feed it with 600 ohm ladder line and use my MFJ-989D to tune it for other bands.  

Modelling shows that a dipole this low is certain to be a cloud warmer on both 160M and 80M but practical experience will sometimes trump modeling.

My question.  Am I wasting time stringing the wire for a 160M antenna this low?  My thinking is that any signal is better than no signal and that I need to operate with what I have available to me. Can  anyone speak from practical experience about this?

Thanks,
Bob, K0BT
« Last Edit: February 02, 2013, 06:27:31 PM by K0BT » Logged
K3VAT
Member

Posts: 704




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« Reply #1 on: February 02, 2013, 06:50:36 PM »

<snip>

My question.  Am I wasting time stringing the wire for a 160M antenna this low?  
<snip> Thanks, Bob, K0BT

No, very low to ground 160M dipoles sometimes surprise you like they did me when I heard and worked VK6!  Low band propagation is not well understood.  Besides low dipoles there are several forms of askew ducting: the DX is geographically to the NE (like EU from here), but the 160M DX signals are coming in loudest on a bearing of SE !!

Go ahead and install the antenna and let us know how it goes.  You may have to tweak the feedline to match on the bands of interest.

GL, 73, Rich, K3VAT
« Last Edit: February 02, 2013, 06:53:03 PM by K3VAT » Logged
WB6BYU
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Posts: 13113




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« Reply #2 on: February 02, 2013, 06:58:04 PM »

A low dipole is a good choice for relatively local work on 80m and 160m, especially because poor
ground conductivity in your area will limit the likely ground wave coverage.  "Cloud warmer" is
exactly the pattern you want for NVIS, where the signal goes nearly straight up and straight
back down to cover out to a few hundred miles.

20' is a bit low for good efficiency on 160m, but it will still work fine for what you need.  The
antenna will have a bit of gain over a dipole on 80m since it is too half waves in phase.  Or
you can use traps or a parallel wire element for 80m and feed it with coax if you want to
eliminate the need for a tuner, at least on portions of the band.  
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WD4ELG
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Posts: 869




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« Reply #3 on: February 02, 2013, 09:09:51 PM »

Been there, done that.  Had surprising results.  No VK6, though (Rich, please share your story with us!)
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K0ZN
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Posts: 1542




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« Reply #4 on: February 02, 2013, 09:23:12 PM »

You will make contacts at night, but just don't expect to be the Big Signal Band Master.  160 is actually surprisingly forgiving for
"poor" antennas. The feedpoint impedance of a dipole that low is pretty low; you likely would benefit from a balun that is a 50 to 12.5 ohm ratio.
You want to try to maximize antenna efficiency via proper matching in this case. Baluns of that ratio are commercially available. In a situation like
that a good amplifier would help too because that antenna is going to have some modestly significant ground losses.  i.e. losing 35% of a 100
watt transmitter output is worse than loosing 35% of 1 KW ! Reality is that most typical horizontal ham antennas are "pretty low" on 160..... an antenna
that is 65 ft. high is still electrically LOW on 160 !

Put it up and give it a try!

73,  K0ZN
« Last Edit: February 02, 2013, 09:26:03 PM by K0ZN » Logged
K2DC
Member

Posts: 1351


WWW

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« Reply #5 on: February 03, 2013, 03:32:43 AM »

If you have room for the vertical and the dipole, you certaily have room for an Inverted L.  Get the vertical portion up at least the 25' you have, and it might really surprise you. 

73,

Don, K2DC
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WB3CQM
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Posts: 116




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« Reply #6 on: February 03, 2013, 03:35:39 AM »

Sounds like good advice given you by all and my test showed the same thing . Except no great dx. lol.

I have spoke years ago to stations local and as far as 250 air miles away using low dipole 20 feet above ground.

I tested G5RV-M one at 70 feet and one at 30 feet or less. My signal on local stations within 50  miles or bit more were always louder on the lower G5RV-M , this was on 160 ssb.

I also tested a G5RV-jr at 20 feet and worked 100 countries in 21 days using 100 watts, no contest qso. 40-10 meters

Like I read in N6BT book , any antenna works to a degree. I would expect you will have no problem making local contacts on 160 out to 100 miles and further.

I use to talk to a station in Ill. On 160 ssb and he used a mobile whip mounted over a radial field and I would have no clue of it due to his loud signal .

I agree with that a inverted L with 30 feet vertical section over radial field works ok. A friend of mine has over 50 countries on top band using one.

And please send me a email or post on this forum  if you start working dx with that set up. I will find space to test one out .

73 JIM
« Last Edit: February 03, 2013, 03:39:56 AM by WB3CQM » Logged
K2MK
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Posts: 391




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« Reply #7 on: February 03, 2013, 06:22:33 AM »

Hi Bob,

My 160 meter full length dipole has an average height of about 10 feet. The center is about 12 feet high. I only use it for 160 meter contests and the results continue to astonish me. Running 200 watts I achieved WAS in two winter contest seasons. Now running a KW I've managed to work and confirm 57 DXCC entities.

In the CQWW 160 meter contest a couple of weeks ago I had 479 contacts which included 46 states and about 30 DX contacts. All search and pounce.

I'm feeding it with around 300 feet of RG8 coax and the 2:1 SWR bandwidth is over 1MHz. The antenna is also pretty quiet. Forget the modeling and just do it.

73,
Mike K2MK
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WD4ELG
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Posts: 869




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« Reply #8 on: February 03, 2013, 07:08:00 AM »

Mike/K2MK- in ON4UN's book on low-band DXing he cites another ham with a low dipole who has worked DX on 160.  When was most of the DX worked for you? At their sunrise?  Was it EU?  Just wondering...thinking I should have a low horizontal antenna as backup for the inverted L, just in case...
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K2MK
Member

Posts: 391




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« Reply #9 on: February 03, 2013, 07:22:21 AM »

WD4ELG:

Good questions. Working any DX is not easy for me. I usually have to wait until there are very few callers. From New Jersey I can work the Caribbean and South America whenever I can hear them. So from 0000z to about 1100z but it's always easier after 0400z.

I can typically hear Europe after my sunset but I am not able to work them until about 0500z. So yes it is their sunrise.

73,
Mike K2MK
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AD4U
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Posts: 2156




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« Reply #10 on: February 03, 2013, 08:40:58 AM »

If you have very poor soil conductivity, that MAY mean that the electrical heighth of your antenna above ground may be considerably higher than its physical heighth above ground.  In other words your 20 foot high antenna may perform as if it were 50 feet or more.

Dick AD4U
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WB3CQM
Member

Posts: 116




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« Reply #11 on: February 03, 2013, 09:10:21 AM »

K2MK , That is very interesting information about your low dipole for 160 . I thank you for sharing

73 JIM
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WB6BYU
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Posts: 13113




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« Reply #12 on: February 03, 2013, 09:56:48 AM »

Quote from: K0ZN

...The feedpoint impedance of a dipole that low is pretty low; you likely would benefit from a balun that is a 50 to 12.5 ohm ratio...



Because of the poor soil conditions it is very unlikely that the feedpoint impedance
will be that low.  My models suggest 50 to 70 ohms for various types of poor soil, due to
ground losses.

Adding a set of reflectors under the antenna will reduce losses, giving a few dB of improvement,
and could bring the feedpoint impedance down to the 12 ohm range, however.
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K3VAT
Member

Posts: 704




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« Reply #13 on: February 03, 2013, 10:19:22 AM »

K2MK: I had about the same bandwidth as you and didn't need any matching network.

WD4ELG: All my topband QSOs to the west including Pacific/Oceania have been at my sunrise or just prior to sunrise.  When I worked the long-haul stuff it was most often at their sunset = double grayline.  I found it easier to work the Pacific than to work into central or eastern EU.

73, K3VAT


 
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W3HKK
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Posts: 595




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« Reply #14 on: February 03, 2013, 12:45:28 PM »

If your after 160 and 80,  a windom is another choice ( works at even multiples of the fundamental freq...)

And dont overlook 60m.   My 160/80 joint coax fed inverted L's work into Europe on 60m, running 100w.

Also, my  temporary 160m antenna when I first moved to the present QTH , was a qtr wave L, hung from a 20 ft tall tree, sloping back to the ground in an easterly direction, and grounded by a single ground rod.  ( no other trees on the property at the time)  One night I heard and worked a 4X4, and then an LZ1 back to back on the first call ( on 160 cw.)  A week later at my sunrise I heard a fairly loud KH6, and worked him as well.  A few weeks later, I worked a JA1.  All with 100w to that temporary antenna.

It wont be that way all the time, but it got out OK....better than you would imagine.  At least until you can  improve the antenna,  or try another option.
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