Low band antennas

630m (472 kHz) - 10 m (29 MHz) antennas, propagation, operating, etc

Low band antennas

Postby VK4WDM » Mon Feb 25, 2008 10:10 pm

My recent failed attempts to work VP6DX on 160 and 80m suggests that I need to do something to improve my antennas for those bands. At present I use a windom cut for 160m and fed with a balum and 50 ohm coax and a tuner. It loads ok but the on-air results are poor.

I have an acre of land with the long axis running roughly east west and a 50ft tower. I have considered using a vertical but this is a very noisy location up here in the static-filled tropics.

I am thinking about putting up a horizontal delta loop. The feed point will be at 50ft but it will have to slope down to only 20 feet as I can't put up higher poles on that boundary. It will point down the long axis of the block i.e towards the west.

Is a delta loop the best option? If not, what is?

I would appreciate some advice.

73

Wayne VK4WDM
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Re: Low band antennas

Postby VK2OMD » Tue Feb 26, 2008 6:16 am

Wayne,

Lots of antennas today are described as a Windom. If you are using a true Windom, assuming a significant length of coax, I don't know how you can efficiently coax feed the antenna without some intermediate impedance transformation.

If a vertical is noisy on receive, does that exclude it for transmitting? Lots of serious low band stations use separate tx and rx antennas. Google for "Beveridge Antenna".

A low loop is a bit of a sky warmer, which might not be optimal for DX. A vertical depends on the ground system for efficiency and low angle radiation, so there are challenges there as well.

Hams seem to rank antennas on three main criteria:
    VSWR;
    bandwidth; and
    efficiency or gain.
It is real hard to optimise all three, so you usually need to compromise on one and optimise the other two. Hams usually compromise efficiency (or gain) in order to optimise the others. Keep in mind that a dummy load has optimal VSWR and bandwith at the expense of efficiency.

Owen
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Re: Low band antennas

Postby VK4APN » Tue Feb 26, 2008 9:00 am

A good place to start is possibly this book - Low Band DXing by ON4UN
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Re: Low band antennas

Postby VK4RF » Tue Feb 26, 2008 12:18 pm

This is one book that is well worth a look. Low Band DXing by ON4UN

I just use a 6 wire combo for 80, 40 and 30mtr. It does tune elsewhere but not as efficient as a dipole for that band.
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Re: Low band antennas

Postby VK3PA » Tue Feb 26, 2008 12:36 pm

try a 90 ft top loaded vertical with gnd radials u hve enough room es a fleg Antenna for RX'n for 160m ..For 80m 4 square i use a triangle phased array es hve Beverage ant x 6 es a rotateable flag for RX'n.. I hve 250 plus on 80m!!
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Re: Low band antennas

Postby VK5PJ » Tue Feb 26, 2008 6:11 pm

VK4WDM wrote:My recent failed attempts to work VP6DX on 160 and 80m suggests that I need to do something to improve my antennas for those bands. At present I use a windom cut for 160m and fed with a balum and 50 ohm coax and a tuner. It loads ok but the on-air results are poor.
I have an acre of land with the long axis running roughly east west and a 50ft tower. I have considered using a vertical but this is a very noisy location up here in the static-filled tropics.
I am thinking about putting up a horizontal delta loop. The feed point will be at 50ft but it will have to slope down to only 20 feet as I can't put up higher poles on that boundary. It will point down the long axis of the block i.e towards the west.
Is a delta loop the best option? If not, what is?
I would appreciate some advice.
73 Wayne VK4WDM


There are a couple of options that come to mind for your tower height, you could try a simple 1/4 sloper (fed at the top of the tower via coax and a simple BALUN) and going down to a tree or fence line if you have something handy. Another is a 1/4 wave inverted L which you can feed from the bottom of the tower and use a cross arm from the tower to hang the bend on. I have both of these here for 160mx and while I am no Dx gun, they seem to perform quite well. There are a few designs for the Inverted L that use a 3/8 wave on 160mx which turns into a 3/4 on 80mx, these generally need some matching at the base but are supposed to be quite good... any way hope you find a solution that work for you.
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Re: Low band antennas

Postby VK4WDM » Tue Feb 26, 2008 6:37 pm

Dear All

Some good ideas, thank you. Owen has prompted me to mention that I feed the windom via a 4:1 balun. I used Beveridge Antennas at my previous location in Tasmania and they worked quite well but they were 300 yards long. Maximum run here would be about 60 yards and it would point east west, not a favourable direction for an end fire antenna.

A 90ft vertical is out of the question because we live in "cyclone alley" and it is very hard to get permission to put up even a 50ft tower. One option might be to mount a loaded vertical on the garage roof and use the roof as a ground plane for transmitting and a long wire for receiving. A sloper would be possible but an inverted L would be difficult because the far end would only be 18 ft off the ground - more like an end fed inverted V.

Obviously plenty of room for experimentation!

73

Wayne
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Re: Low band antennas

Postby VK2OMD » Tue Feb 26, 2008 7:04 pm

VK4WDM wrote:Dear All
Some good ideas, thank you. Owen has prompted me to mention that I feed the windom via a 4:1 balun. I used Beveridge Antennas at my previous location in Tasmania and they worked quite well but they were 300 yards long. Maximum run here would be about 60 yards and it would point east west, not a favourable direction for an end fire antenna.


A true Windom has a vertical wire attached to a horizontal wire, and the vertical wire (offering a load of 500+ ohms) would usually be attached to an unbalanced transmitter output. It isn't clear where your balun fits into the configuration.

The multi-band use of a Windom is a bit like an Inverted L, is behaves predominantly like a capacitively loaded short vertical on frequencies that are low wrt its total length. Like any loaded Marconi antenna, efficiency is very dependent on the loss in the ground system.

A 60m wire is 0.75 wavelengths at 80m and 0.375 wavelengths at 160m, it does not give an endfire pattern on either band.

VK4WDM wrote:
A 90ft vertical is out of the question because we live in "cyclone alley" and it is very hard to get permission to put up even a 50ft tower. One option might be to mount a loaded vertical on the garage roof and use the roof as a ground plane for transmitting and a long wire for receiving....


It must be a pretty big garage to figure at 160m. Again, efficiency of shortened Marconi antennas is very dependent on the loss in the ground system. An elevated wire counterpoise might be quite feasible if the garage isn't all that huge.

VK4WDM wrote: A sloper would be possible but an inverted L would be difficult because the far end would only be 18 ft off the ground - more like an end fed inverted V.


A sloper is another sky warmer which is probably not optimal for DX work.

I think you are telling us that you don't have room for even a half wave dipole on 160m.

Nevertheless, you could use a shortened centre fed dipole for a horizontally polarised receive antenna and work on a Marconi of some kind (eg loaded vertical, inverted L etc) with an adequate counterpoise for a transmit antenna. (I hate the work counterpoise because it is so misused and I use it here to mean a system of conductors that are used to decouple the feedline, and where the net contribution to radiation of currents on the counterpoise conductors is very low because currents in conductor segments are offset or canceled by opposite currents in segments of symmetrically opposite conductors. Thing is that hams cannot agree on a shared meaning of the term "counterpoise" but insist on using it freely.)

Are you able to model different configurations in NEC?

Owen
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Re: Low band antennas

Postby VK4WDM » Wed Feb 27, 2008 6:08 pm

The windom I am using is a copy of the BuxCom 160-6m model. 260ft long, off centre feed with a 4:1 balun and 50 ohm coax. It is 50Ft in the centre and 18ft at the ends and runs corner to corner across the block. I am suprized that it does not work better on 160 and 80m. It works quite well on 30, 20, 17 but not as good as my dipole on 40.

A 160m inverted V would fit in ok, should I just opt for that? Perhaps dual 160 & 80?

73

Wayne
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Re: Low band antennas

Postby VK2OMD » Thu Feb 28, 2008 7:00 am

VK4WDM wrote:The windom I am using is a copy of the BuxCom 160-6m model. 260ft long, off centre feed with a 4:1 balun and 50 ohm coax. It is 50Ft in the centre and 18ft at the ends and runs corner to corner across the block. I am suprized that it does not work better on 160 and 80m. It works quite well on 30, 20, 17 but not as good as my dipole on 40.

A 160m inverted V would fit in ok, should I just opt for that? Perhaps dual 160 & 80?

73

Wayne


Wayne,

Here is a diagram of a Windom from the ARRL Antenna Handbook.

Image

You seem to have one of the many commercially produced "Windoms" that are significant departures from the Windom as described by Loren Windom in 1929. Many of these antennas have unsupported extravagant claims and are hard to independently analyse because they incorporate magic proprietary components (such as undescribed line isolaters, baluns etc). Some magic antennas even claim to defy conventional analysis... that is alway a warning sign.

It seems that an antenna with an off centre radiating feedline is classed as a Windom these days.

Any dipole or variant close to ground is a cloud warmer and as I think I have said twice already, you have to ask yourself if that is optimal for transmission for DX on the low bands. Further, efficiency may be compromised my unknown magic components and coax loss.

Owen
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Re: Low band antennas

Postby VK4QB » Fri Feb 29, 2008 7:40 am

You are one of many who have tried the windom antenna and got poor results. A company that I used to work for once, used to swear by them but I tried a diplole one day and the results were VASTLY improved. I really don't think that you can beat a dipole centre fed with a balun of course. You can use it as a top loaded vertical on other bands., with a tuner naturally, but you MUST have a good earth system to get good results as a top loaded vertical. Remember, the weakest point will let you down. A poor earth system is the weakest point on all verticals, and verticals are good at receiving noise.
Have Fun. :)
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Re: Low band antennas

Postby VK4WDM » Fri Feb 29, 2008 8:20 pm

This is obviously a "hot" discussion topic! With regard to windoms, the classic design was very common when I came on the air in ZL in 1964 but quickly died out later for two reasons: TVI, and the later still the advent of solid state equipment that does not tolerate high SWR (tuners were rarely used). I used one back then and it worked very well (DXCC on 80m) that why I was attracted to the modern version (as Own says, really "windom-like" rather than windom) as per the following site:http://www.packetradio.com/windom.htm.

Whatever I put up as a replacement is going to be sub-optimal - I only have planning permission for a single 50ft mast or tower. I will put up an inverted V this weekend and see if there is an improvement. If not, I will think about a loaded vertical of some sort.

73

Wayne
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Re: Low band antennas

Postby VK2OMD » Sun Mar 02, 2008 6:51 pm

VK4WDM wrote:This is obviously a "hot" discussion topic! With regard to windoms, the classic design was very common when I came on the air in ZL in 1964 but quickly died out later for two reasons: TVI, and the later still the advent of solid state equipment that does not tolerate high SWR (tuners were rarely used). I used one back then and it worked very well (DXCC on 80m) that why I was attracted to the modern version (as Own says, really "windom-like" rather than windom) as per the following site:http://www.packetradio.com/windom.htm.

Whatever I put up as a replacement is going to be sub-optimal - I only have planning permission for a single 50ft mast or tower. I will put up an inverted V this weekend and see if there is an improvement. If not, I will think about a loaded vertical of some sort.

73

Wayne


Wayne, the article you quoted and entitled "The Original Windom" is really devoted to a commercial product that is not the original Windom, and as such is misleading and deceptive. Still, that is par for the course on commercial sites advertising antennas.

Any Marconi type antenna, any antenna with significant common mode current on a vertical feed line is going to be more susceptible to noise on receive than a purely horizontally polarised antenna. Count verticals, Inverted Ls, (classic) Windoms, OCF dipoles, and slopers in this group. That is not to say they won't work, but if you are wanting to minimise response to vertically polarised signals, they are poorer.

You have already noted that the classic Windom became unpopular due to incidence of TVI. Why? Was it feedline radiation which is after all radiation, nothing magic there, but it is closer to the TV antenna, its downlead and the power wiring. Today, Windoms (like Marconis) have RF safety issues.

No magic isolators or baluns can prevent the feedline of an OCF dipole, Carolina Windom or Buxom Windom from picking up noise... it is the asymmetry wrt the dipole halves that is the fundamental contribution that cannot be overcome with magic boxes, despite the advertising hype.

Just reviewing the fundamentals of noise and vertical polarisation, local noise created with random polarisation arrives by ground wave. The horizontal component of ground waves is attenuated more rapidly than the vertical component, depending on soil parameters. So locally created noise will tend to have a higher vertical component than horizontal component, and an antenna insensitive to vertical polarisation will receive less local noise power relative to ionospheric signal which tend to be of random polarisation.

Owen
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Re: Low band antennas

Postby VK7AXZ » Sun Mar 02, 2008 10:54 pm

Don't just put up a standard 80m inverted V, get a roll of cheap RG58 and put up a double bazooka in the widest Inv. V formation you can - wide band, low noise and very effective. At a centre height of 50ft it should work very well.
http://www.bloomington.in.us/~wh2t/bazooka.html

There is much more info than this avail. but this gives the basics.

Another useful tool is a recieving loop only a few feet off the ground, often stuck around a perimeter fence - very quiet but effective if tuned to freq. Then use a tuned vertical for transmitting only. Verticals might be noisy on recieve, but remain a most effective transmitting antenna.
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Re: Low band antennas

Postby VK2OMD » Mon Mar 03, 2008 7:04 am

VK7AXZ wrote:Don't just put up a standard 80m inverted V, get a roll of cheap RG58 and put up a double bazooka in the widest Inv. V formation you can - wide band, low noise and very effective. At a centre height of 50ft it should work very well.
http://www.bloomington.in.us/~wh2t/bazooka.html

There is much more info than this avail. but this gives the basics.


Wow, "Dr Ace" claims 98% efficiency... but he gives no supporting detail. That is less than 0.1dB of loss, unbelievable!

Here is another perspective on the Double Bazooka and Cross Connected Double Bazooka that properly considers losses in the Bazookas and in the feedline: http://www.vk1od.net/DoubleBazooka/index.htm .

A true comparison of the Bazooka and an uncompensated dipole can only be made by analysing the entire antenna system because the benefit of the lossy Bazooka sleeves is actually manifest in reduced feed line loss.

I have not seen any other analysis that treats the Bazookas as a lossy transmission line, the closest they come is to pretend it is a lossless s/c stub. Nor do they take a system view that considers feed line loss... and after all, the Bazooka is intended to reduce feed line loss.

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Re: Low band antennas

Postby VK4WDM » Sat Mar 08, 2008 8:54 pm

The double bazooka look's very interesting! I wonder if you can short the end of the feed line of an 80m one and feed it against ground for 160m like you can with a standard 80m dipole?

73

Wayne
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Re: Low band antennas

Postby VK2OMD » Sun Mar 09, 2008 6:24 am

VK4WDM wrote:The double bazooka look's very interesting!


At the risk of offending devotees of the Bazooka, why?

In case you didn't follow up the article I offered, here is an extract:

The following conclusions are made:
    * the Double Bazooka marginally increases VSWR bandwidth, but may easily increase system loss;
    * the difference in performance probably denies measurement in a typical ham installation;
    * the improvement in bandwidth probably does not offset the disadvantages of wind resistance, weight, strength and cost;
    * some claims of the advantages in typical low HF antennas are unsubstantiated, and plain wrong;
    * the Cross-connected Double Bazooka has greater bandwidth extension at the expense of even higher stub loss;
    * analyses that ignore or incorrectly size stub loss or transmission line loss are incomplete and unreliable; and
    * a system view provides a true picture of performance .

VK4WDM wrote:I wonder if you can short the end of the feed line of an 80m one and feed it against ground for 160m like you can with a standard 80m dipole?


Yes, of course you can. It won't be much less efficient than doing so with an uncompensated (ie plain) 80m dipole. What you have then constructed is a top loaded Marconi, and to assess its efficiency, don't look up, look down... the answer is in the dirt... the ground system dominates system efficiency.

This, of course is a predominantly vertically polarised antenna (refer back to the noise discussion) and in your original posting you said "I have considered using a vertical but this is a very noisy location up here in the static-filled tropics".

You started this thread looking for a better antenna for working DX, and you are now exploring a makeshift vertical antenna. That must mean that we have closed the loop.


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Re: Low band antennas

Postby VK3HJ » Sun Mar 09, 2008 9:50 pm

Well, I did manage to log ssb contacts with VP6DX on five bands, including 160, 80 and 40m using my dipoles.
And I regularly work dx on at least 80 and 40m - the VP6 being my only 'exotic' on 160m. Will try for Clipperton this week.
The ground here could be described as "poor" being granite, elevated and generally very dry. I have horses in the paddock, so am not prepared to lay down an effective ground system - expense of copper a factor too! Consequently, I have opted for the "bits of wire up a tree" solution. Whilst it would be wonderful to have several 70m towers and full sized quads and yagi-uda arrays, and four squares, most of us mere mortals make do with more modest antennae - and exploit the mega antenna capability at the other end!
My system here consists of a multi-dipole (160, 80, 40, 30 and 20m) at 20m which took quite some setting up, but I am achieving very satisfactory results, and a W5GI multiband antenna at 10m. I spent the time to resonate all the dipoles - common halyards, 160m on top, with others suspended below, held apart with a couple of fibreglass rod spacers each side. It has a W2AU commercial balun and is fed using RG213. I currently use no antenna matching unit. The 80m is a bit narrow with about 80kHz bandwidth between 2:1 VSWR points, so I have set this up for the dx window.
I believe the balun at the feedpoint may help in making this a very quiet receiving antenna, with no "rain static" that I hear others experiencing, and this is a very quiet rural location, with no TVI. Also, I have no issues running up to full legal power, and find my FL-2100Z will make the difference between a marginal or no copy, and a successful contact.
Anyway, I just wanted to let Wayne know that a simple dipole antenna can work very well indeed.
73, de Luke VK3HJ
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Re: Low band antennas

Postby VK4WDM » Mon May 05, 2008 9:27 pm

Well, it took a while, but I have finally got the the 160/80m antennas up. After carefully considering all the helpful advice I settled on an 80m inverted V with the feedline shorted out and loaded against ground for 16Om (i.e top-loaded Marconi variant).

I did not like the idea of trying to bury radials on the rock-hard ground but I have a wire and star picket fence 100m long only a few metres from the shack so I attached that to my ground system - which is already attached to the all-metal garage and shack.

Initial tests are very good. It loads very well on both bands and I have got strong signal reports from VK and Zl on 80m. Have not had any contacts on 160m but the signals are certainly much stronger than on my "windom like" antenna. I even heard two Ws on CW.

I have used it in both inverted V and top loaded style on 80m and the latter gave a better signal report to ZL than the dipole, a reflection I guess of the low angle induced by the vertical component. I also accidently used it in top loaded mode on 40m and it worked very well - obviously room for experiments there.

The noise on 160 is still a bit higher than I would like so I intend to use a separate antenna for receive. I was taking to a W station on 20m and he suggested an "end fed inverted V" (really just a long wire elevated in the middle. Apparently they were a common antenna for 500kc on ships. A Beveridge is the other option.

Again, thank you for the discussion and suggestions. That is what makes AR such a fine hobby!

73 :D

Wayne
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