simple but good wire antenna

Useful information regarding antennas for SDR products.
ZL2BMH
Posts: 21
Joined: Wed Jun 13, 2018 11:49 am

simple but good wire antenna

Postby ZL2BMH » Sat Jun 16, 2018 3:32 am

Hello All.

I am severely disabled and close to 80 yrs old. I want to put up a wire antenna, something simple but easy but works good covering all the bands, frequencies that this receiver offers. I will have to find a neighbour to do it for me. I am about to receive my RSP1A receiver.

I have enough room to use a wire antenna. I am confused as to whether it should be cut to a certain length ( I want it to cover all the freq.500khz to 2Ghz that they advertise for this products coverage.

I had always believed that the more wire you can get as high as possible is best.

Could someone please advise me what they would do.

Thank you all for your replies.
Hemi
Last edited by ZL2BMH on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Sat Jun 16, 2018 5:24 am

Make a horizontal triangle as large as you can, anything from a few meters in total circumference right up to 170m.

Mounting points required: 3
- one at your house
- try for the other two so as to make the enclosed area as large as possible.
- height above ground is "as high as convenient" up to say 6-12m

Wire: use aluminium MIG welding wire
- available cheaply on small spools
- 0.9mm diameter wire
- ultra light so you can keep it reasonably taught with light nylon cord

Feeder: Old 300 ohm TV ribbon if you can get it
- if you can't, just run cheap TV coax and connect it to the two aluminium ends using small screw connectors for mains wire.

I could elaborate forever but if you do the above you'll have a nearly invisible, cheap and ultra quiet, efficient antenna that will do exactly what you want. If you tell me the total length and height off the ground I'll happily post the performance at any frequency/s you nominate in the form of screen dumps of models from an antenna modelling program.

Cheers, Phil VK7JJ

PS. If you want to try it, just say, and I'll show you how to best fasten on to it with the nylon cord at the corners and feed point.

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Sat Jun 16, 2018 7:01 am

Had a spare half hour so thought I'd get pre-emptive:

Here is the path from me to our local beacons on 50Mhz, 144MHz and 432MHz.

As you will see the 53 kilometre path is a large rocky hill.
The pink line is the Line of Sight path and is 397 meters below the peak.
The beacons are 25 watts into vertical dipole antennas.

The pics show the signals at my place received on a 160m perimeter triangle wire loop average height 10m above very ordinary ground and among trees, as heard on an SDRPlay RSP1A using Gqrx.

The morse code beacon callsigns are readable in the waterfall. HF loops perform very nicely at higher frequencies.

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50.png
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144.png
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Darn... this Forum software only seems to permit three attachments at once.

[to be continued]

Phil VK7JJ

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Sat Jun 16, 2018 7:12 am

... here is the 432 beacon:

432.png
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Now for attaching the aluminium wire. I did this specially just for now :-) Timed myself and while I do have that sort of stuff lying around - I also fed the chooks while fetching the black poly. Total time taken was 32 minutes.

Corner:
- uses a slice of 90mm PVC drain pipe to keep the curvature
- feed the wire through a short length of 4mm flexible irrigation poly pipe
- that way, as you tighten the nylon to raise the antenna, the wire slides through and evens itself out.

Mast feed point:
- speaks for itself, uses 12mm irrigation poly pipe
- drill three holes in each side
- thread the aluminium wire through the holes and it's held captive
- fasten the aluminium to the copper with small mains power screw connectors
- if you are worried about corrosion and water there is a special paste just for Al and Cu joins at industry type electrical suppliers

Regards, Phil VK7JJ

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feedpoint.jpg
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PS. I felt a bit guilty at being so critical of the commercial short vertical whip antennas in another thread I thought I'd better offer some alternative.

Even very small horizontal loops will outperform those tiny short verticals by many orders of magnitude in terms of efficiency, noise, and angle of radiation.

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Sat Jun 16, 2018 7:22 am

... and they work even better on HF.

Two WSPR screen dumps. The first is from a ship in the arctic circle to Tasmania transmitting on 7MHz using 0.02 of a watt.

The second is from the UK to Tasmania showing successive contacts again using just 0.001 of a watt on 14MHz.

RSP1A's work very well, as do horizontal loop wire antennas :-)

Regards,

Phil

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M0BOB.jpg
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PS. I wrote the software used for the screen dumps in both posts above, including the path profile and the WSPR, @ http://www.vk7jj.com

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ZL2BMH
Posts: 21
Joined: Wed Jun 13, 2018 11:49 am

Re: simple but good wire antenna

Postby ZL2BMH » Tue Jun 19, 2018 4:53 am

Dear Sir.

I want to thank you for an utterly amazing reply. Never have I had such an informative yet described so easily that it is a pleasure to read and understand.

Antennas are your obvious choice of radio's. You are sir extremely passionate and now so well versed on the subject.

Congratulations, I'm sure I won't be the only one who reads your reply and learns so much from it.

I will have a talk to my helper (neighbour) and see what transpires as he suffers from arthritis (talk about dad's army) :lol:

Again thank you, and now to print it out so it won't be lost.

73's Jim
Last edited by ZL2BMH on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Tue Jun 19, 2018 9:14 am

I want to thank you


You sure did that Jim, thank you in turn. A large part of it is pure selfishness because I do love antennas.
Antennas and discussions about them usually invoke a lot of passion, I'm sure there are readers groaning or teeth gnashing at the post.

Anyway ... Wait! There is more!

---

Here are some antenna models created using a free copy of MMANA modelling software which anyone can download and play with.
Models are great for enhancing one's understanding of what's actually going on (their numbers are indicative not definitive), they are also great at exposing key differences between different antennas.

The table of results is for an aluminium wire triangle with 170m perimeter, equal length legs, height of 10m over 'ordinary' quality ground.

It's beyond the scope of a post like this to go through all the figures and point out the good and bad bits, most amateurs will be quite familiar with the terms. The major good things to point at in this table are
- pretty good R and SWR figures with no dramatic excursions across the bands
- good gain, yet an omnidirectional pattern, eg. compare with 6 el Yagi above 30m: http://yagi-uda.com/six_elements_yagi-uda.php
- excellent angle of radiation (the Elev. column), especially given the low height above ground
- horizontal polarisation means less susceptibility to man made noise
- it's a loop with balanced feed point: a really important feature for reducing noise. This can be an issue of hot debate and I'm willing to hotly debate it :-)

loop_bands2.png
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Aluminium v Copper
Many people will worry about the resistive losses of aluminium compared with copper. MMANA provides a pop-down menu with a choice of metals. The table below shows the R (Ohm) figures for copper at the bottom, aluminium at the middle and iron/stainless steel at the top. Clearly, aluminium's slightly higher resistive loss makes negligible difference to the gain. The big lesson is DON'T use stainless steel!

loop_Cu-Al-Fe.png
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In the next post I'll present an "inverted L" antenna for comparison. The inverted L is like the "end fed wire" that appears to be used by quite a few people on the forum.

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Tue Jun 19, 2018 9:33 am

The model assumes a 10m high metal mast with an attached wire that is one half wave long at 1.8Mhz
In the case of a non-metal mast the coax braid takes it's place electrically speaking.

Here it is for visualisation:
inv_L.png
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Here is the table for comparison with the loop:
end_fed_bands2.png
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- there are large excursions of R and SWR across the bands
- the gain is not as good
- the Elev. figures show the angles of radiation are poor; the lowest 3 bands might look OK but the SWR is too bad
- it is vertically polarised, which may surprise a few people, meaning poorer immunity to man made noise
- it is an unbalanced antenna effectively driven against ground and prone to all the nasties caused by common mode electrical interference.

Hopefully the modelling exposes some of the key advantages of a loop and helps justify it's selection.

Having said all that there is still more to say by way of the possible use of a common mode choke, plus looking at the options for connecting the loop's feed line to the RSP depending on whether one uses ladder line, twisted pair or coax as a feed line.

Cheers, Phil VK7JJ

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CaptainNemo
Posts: 146
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: simple but good wire antenna

Postby CaptainNemo » Wed Jun 20, 2018 6:50 am

Hi All.
Very interesting post.

Phil, can I submit my problem?
I have a sort of "quadrant" random wire, one leg (A-B) about 9m due NE, one leg (A-C) about 10m due SE, near right angle in A.
Now "your" suggestion of an "horizontal delta loop" seem interesting to me...
Can i ask you to model this configuration and compare it with a loop A-B-C-A ?
I'm sending a private message on this forum with all detail, then if you feel the item is interesting you/we can post the result.
Bye
Gio

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: simple but good wire antenna

Postby vk7jj » Wed Jun 20, 2018 11:39 pm

Hi Gio, files send by email. 73, Phil

And welcome to the solstice to everybody!

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