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Author Topic: Magnetic loop or vertical for 20 and 40 meter TX RX  (Read 1316 times)
SIMON123
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Posts: 128




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« on: December 29, 2018, 11:38:20 AM »

For multi stories building roof top, not large enough for length of a dipole, what are the factors, for choosing between a magnetic loop, vertical or others types of antenna?

20 and 40 meters, both tx and rx. For digital mode, so freq is narrow and per-known. I have near zero HF experience. I used VUHF at work.

73

Simon
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NK7Z
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« Reply #1 on: December 29, 2018, 12:27:08 PM »

If it were me, I would start with a vertical, raised a few feet off the roof, with two tuned radials for each band...  If you have a huge RFI issue, (and you probably will if the building is in use), then I'd next try a loop.  I am assuming you are aware loops don't take a lot of power unless you specifically build them for that type of duty, and can be quite dangerous to those close to them, both in RF field strength, and the voltages developed on the loop itself at high powers, while a good vertical will take 100 watts all day, and is still dangerous if too close, or touched...

Mag loops are great for nulling out a RFI source, but in a large building, you are likely to have hundreds of sources.  I might place the loop on one side of the building, so I could null out as many RFI sources as possible at once.  Verticals will hear noise from all directions it won't matter where it goes, it will just be noisy no matter where I put it... 

My guess is that the loop will hear far better than the vertical...  Why start off with the antenna that might not work first?  If it fails due to high RFI, use the vertical as your transmit antenna, and the loop as your receive antenna...  Once you are atmospheric noise limited, it is all about S/N ratio, not signal strength.  The loop will probably give you better S/N on receive but far lower signal overall levels than the vertical, while the vertical will take power.  Thus you are avoiding the loop weak spot, while using the loop to avoid the verticals weak spot... 
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Thanks,
Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
WA7ARK
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Posts: 590




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« Reply #2 on: December 29, 2018, 09:59:00 PM »

... The loop will probably give you better S/N on receive but far lower signal overall levels than the vertical, while the vertical will take power.  Thus you are avoiding the loop weak spot, while using the loop to avoid the verticals weak spot... 

Good advice...
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Mike, WA7ARK
SIMON123
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Posts: 128




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« Reply #3 on: December 30, 2018, 09:56:57 PM »

Please suggest pointers to

a) brand, model of factory vertical antenna. 20 and 40 meters. Best if no tuner needed.

b) home build antenna

c) digi mode low 20 watt continuous power or may be a bit flexibility for slightly higher, 100W PEP SSB.

How is radial work for multi band vertical?  Should it be a few 'same length' radials for the lowest freq band?  Or two set of lengths for each of 20 and 40 meters band?

How many radials are needed to reasonable perfromance under the building roof constraint? Some articles states 40 radials buried under ground for un-resticted installation of open land.

I have near zero HF experience. Was no HF ham, as I did not take morse examination. I used VUHF in work

73 Simon
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NK7Z
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« Reply #4 on: December 31, 2018, 04:51:15 AM »

Hi,
While I could do this, it is far better if you Google those questions...  This subject is vast, and it would take a long tom to answer your questions correctly...  It is far better if you do the research, you will learn far more than if I just fill in the blanks...  

I would use the following search terms...

Vertical Radial Field
Vertical Antenna

Hustler 6BTV for the antenna...
I would not home build the vertical, a dipole is easy, but one band.
More radials are better...
You will lover HF!

Hope that helps Simon...
« Last Edit: December 31, 2018, 04:56:21 AM by NK7Z » Logged

Thanks,
Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
K4CQO
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Posts: 1




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« Reply #5 on: December 31, 2018, 07:55:48 AM »

Another option for an antenna is to use one of the end feed antennas. I am using an Ultimax 100 that is only 24' long. It works great with an antenna tuner for 40m and above. My tuner does not do a very good job for 80m, but does less then 1.5 on 40m and above.

I have it mounted on an angle going up to the eve on the second floor and over to a gazebo that is on the end of the deck. They say it can be mounted vertically -- so it could run up the side of your building -- but not sure what pattern that would give you.

Just another option …
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ONAIR
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« Reply #6 on: January 01, 2019, 12:16:29 PM »

Another option for an antenna is to use one of the end feed antennas. I am using an Ultimax 100 that is only 24' long. It works great with an antenna tuner for 40m and above. My tuner does not do a very good job for 80m, but does less then 1.5 on 40m and above.

I have it mounted on an angle going up to the eve on the second floor and over to a gazebo that is on the end of the deck. They say it can be mounted vertically -- so it could run up the side of your building -- but not sure what pattern that would give you.

Just another option …
  That Ultimax-100 is a remarkable little antenna.  I've used it with an LDG tuner on 80 meters (NVIS), with the wire strung horizontally just 15 to 20 feet off the ground!  Smiley
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SIMON123
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Posts: 128




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« Reply #7 on: January 02, 2019, 11:44:27 AM »

Does the Ultimax-100 needs a 'full capacity' antenna tuner that is sold by factory in a box, at relatively high cost

or, it can work with those rig built in antenna tuner, like ICOM 7300, which has a smaller tuning range

Is that just a simple 1:9 Balun or something more complex? Some articles state that long wire, plug 1:9 balun, plus rig built in limited range tuner, is working fine

73 Simon
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KE5PPH
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Posts: 64




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« Reply #8 on: January 02, 2019, 12:26:33 PM »

the built in tuner should handle that just fine. Unless you do a bad install.
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VA2DV
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Posts: 169




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« Reply #9 on: January 03, 2019, 11:58:22 AM »

Magnetic loop are great for tight spaces but keep in mind that they must be retuned every time you move on frequency.
I've tried many "random" wires types antennas, with 9:1 balun, 64:1 balun and a remote tuner.
The best compromise as far as noise and performance is the resonnant 64:1 variety.
They are available from MyAntennas. HyEndFed is another provider that carry shorther models at 53' and 70'. They can be bent to fit the surroundings and are already resonnant on 4-5 bands.
Diamond and Comet also make a shortened 5-bands dipole at 63'. It's balanced and the balun is included.
In a high noise area, you may also want to use a antenna noise canceller. Believe me they do make the difference when properly installed.
Good luck !

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G4AON
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Posts: 1359




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« Reply #10 on: January 04, 2019, 10:07:33 AM »

The lowest cost solution is to home build a trapped vertical using a heavy duty fibreglass flag pole and home made trap resonant on 20m. You can either make the trap using coax, or for slightly better efficiency at the expense of needing a doorknob cap and weather proofing, a parallel tuned circuit. Glue the sections of the pole to avoid it collapsing.

Use two radials per band, spaced 180 degrees apart and arrange the ends of the 20m radials to be at least a metre away from the 40m radials to minimise interaction. You will need a feedline choke to avoid the feeder acting as a radial, a few turns of RG58 through an FT240-43 ferrite core will work well.

I use a 30/20/15m home made dual trap vertical from Spain, it works great and has been in use for several years. Some building info at: https://www.qsl.net/g4aon/vertical/

73 Dave
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SIMON123
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Posts: 128




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« Reply #11 on: January 04, 2019, 08:37:52 PM »

After more reading, I amend my requirement a bit, 80, 40 and 20 meters, no tuner, 100W PEP or 25 W continuous 100% duty cycle

===========
This works for 80/40/30/20/17/15/12/10m at 1kW.
https://myantennas.com/wp/product/efhw-8010/

No tuner need, all band. BUT look heavy for SOTA.

Any recommendation for a similar one for light weight SOTA operation, 30W continuous 100% duty cycle
 
This one is 300g, very light, 100W PEP, However it does not cover all band.

https://www.hyendcompany.nl/antenna/portable_mini_hyendfed_antenne/product/detail/197/Portable_4_Band_Antenna_Ultra_Light_Mini_100_Watt#prod
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VA2DV
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Posts: 169




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« Reply #12 on: January 08, 2019, 10:27:33 AM »

Hi Simon,

This one is perfect, I am currently using one between my second-story balcony and a three.
I've push 200w into it without any issues.

https://www.hyendcompany.nl/antenna/multiband_80402010m_/product/detail/214/HyEndFed_4_Band_Extra_Short_80_40_20_10_Black_Clamp

Very lightweight. Could be attached to a fiberglass pole and then sloped to a support near by.

Dave VA2DV
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