Pages: 1 [2] 3 4 5   Go Down

Author Topic: Magnetic loop TX antennas  (Read 1378 times)

AI5BC

  • Posts: 456
    • HomeURL
Re: Magnetic loop TX antennas
« Reply #15 on: September 10, 2022, 06:22:47 PM »

I have some experience with STL's and would never go back. Here is what you get to look forward to. Forget about any kind of modern radio with a Panadapter, band scope, or scanning capabilities. You will have no use for such things because the bandwidth is so narrow on STL's, you will not see anything other than the frequency the antenna is tuned too. No spinning the dial looking for signals are in your future unless you can figure out how to synchronize both the antenna and radio at the same time. The bandwidth on some models is so narrow at the ends, they are only good for CW work. They make a great narrow band filter with an attenuator. 

Get yourself a cellphone and save your contacts phone number so you can call them and ask them to meet you on a specific frequency or get used to working NVIS Nets on specific frequencies. DX will only be something you read about.

Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #16 on: September 12, 2022, 07:49:50 AM »

Thanks for the "heads up."

I understand there are compromises in every antenna system.  It's a matter of how many and what types of compromises one agrees to endure to get on the air.  I also understand that once folks who own an MFJ (a 1788, for example) get over fixing the QC issues, the great majority of reviewers believe it to be a worthwhile setup for their given situation.

In my "given situation", mag loops appear to be a viable option.

As for not being able to view the signal on a panadapter, I doubt that is the case with the RSPdx/SDRuno because the waterfall can be zoomed in quite a bit - 10kHz to one inch.
« Last Edit: September 12, 2022, 08:05:51 AM by KK4GMU »
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

AI5BC

  • Posts: 456
    • HomeURL
Re: Magnetic loop TX antennas
« Reply #17 on: September 12, 2022, 08:36:34 PM »

As for not being able to view the signal on a panadapter, I doubt that is the case with the RSPdx/SDRuno because the waterfall can be zoomed in quite a bit - 10kHz to one inch.
Quit fooling yourself. Unless you have a dedicated HF antenna for the SDRuno, the SDR will be just as death as your HF rig receiver. If you had a dedicated or separate HF antenna, you would not need or want a mag loop. Your HF rig has a batter receiver. What makes you think a SDRUno is going to do better? Makes no difference what radio is in the shack with a death and mute antenna.
Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #18 on: September 13, 2022, 05:29:45 AM »

I DO have a dedicated receive-only antenna for the SDR.

And you posed a red herring.  I never claimed the SDRuno is going to "do better." Where did you make that up from?  Avoid claiming I claimed what I never claimed.  It's unbecoming.  You do need to be more concise and accurate with your accusations.

I do write my share of stupid things, but that wasn't one of them.
« Last Edit: September 13, 2022, 05:33:35 AM by KK4GMU »
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

VE3PP

  • Member
  • Posts: 260
    • HomeURL
Re: Magnetic loop TX antennas
« Reply #19 on: September 14, 2022, 05:05:25 AM »

How far should a magnetic loop transmit antenna be kept from a metal chain link fence or from metal patio furniture?

I have a very constrained small patio area only 8' by 20' surrounded by chain link on two sides and concrete block walls on 2 sides.

I am looking at the Pracomm SML-1000-1.

I worked a guy in Poland on 15 M SSB one day who was using this antenna, mounted on the roof of his condo. He had it on a rotor. He was only running 100 watts and was 10/9 into SW Ontario. I have a 2 element tri band at 33 feet. So it is not like I have a big gun yagi way up in the air.
When he told me what antenna he was using I looked it up. And here it is! Mind you it is not cheap!

https://www.dxengineering.com/parts/mzz-baby

And here are the reviews posted on this site. As you can see the antenna gets a lot of good reviews.

https://www.eham.net/reviews/view-product?id=6666

You can watch this video

https://www.youtube.com/watch?v=N98uqdbnsc0
« Last Edit: September 14, 2022, 05:11:30 AM by VE3PP »
Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #20 on: September 14, 2022, 05:54:31 AM »

Oh yeah.  That "baby" is made in Italy.  During Dave Casler's review of the MFJ-1788, he referred to that antenna and said "that ain't no baby."  The Mercedes of mag loops.  Maybe after I win the lottery. Oops.  Forgot. I don't play the lottery.
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

K6BRN

  • Member
  • Posts: 2229
Re: Magnetic loop TX antennas
« Reply #21 on: September 14, 2022, 06:16:14 AM »

Regarding a wire vs. magnetic loop...

I have to agree with Mark.  I've yet to see a residence where a good pre-made (solves the antenna building problem) multiband EFHW wire antenna could not be made to work, especially at the 100W and under level.  It takes some thought to lay it out and make it invisible if it's inside, and it's invariably a less than optimal arrangement, but that's done ONCE, while the magnetic loop is a constant excercise in movement and tuning.

If the wire can be moved into an attic space, so much the better.  And one HOA end-fed arrangement I had was outside and deployable - I unrolled it, hooked it to a tree, operated and rolled it back up.

One other concern with a magnetic loop is that IF a cheaper and smaller one is used, arcing might cause damage to the RF amp in the radio, even at low power (25 watts).

That said - nothing wrong with experimentation.  But it's always nice to have a "Plan B"

Brian - K6BRN
Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #22 on: September 14, 2022, 07:08:28 PM »

Quote
And one HOA end-fed arrangement I had was outside and deployable - I unrolled it, hooked it to a tree, operated and rolled it back up.

That sounds like a somewhat repetitive task.  Especially if one has no trees, yard area or attic access.  I'd rather take a minute to retune from the comfort of my AC'd shack then to "redeploy" and "undeploy" each time I use HF.  That would put a huge damper on my operating.

Believe me, I would do "once and done" to achieve 15 to 40 meters if it was feasible for me at my location. May as well tell an elephant to levitate.
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

AC7CW

  • Member
  • Posts: 1789
Re: Magnetic loop TX antennas
« Reply #23 on: September 15, 2022, 08:29:12 AM »

One little-acknowledged fact about transmitting magloops is that they are only efficient when the loop circumference is a little less than a half wave. I find the whole idea of multi-band tuneable magloops offputting really: ridiculously low efficiency and narrow bandwidth are not good for much. Setting up a monoband transmitting loop for CW or for FT8 makes more sense to me and is almost the elegant solution for those situations perhaps if a low takeoff angle can be achieved without a tower.
Logged
Novice 1958, 20WPM Extra now... (and get off my lawn)

K6BRN

  • Member
  • Posts: 2229
Re: Magnetic loop TX antennas
« Reply #24 on: September 16, 2022, 08:33:44 AM »

Quote
And one HOA end-fed arrangement I had was outside and deployable - I unrolled it, hooked it to a tree, operated and rolled it back up.

That sounds like a somewhat repetitive task.  Especially if one has no trees, yard area or attic access.  I'd rather take a minute to retune from the comfort of my AC'd shack then to "redeploy" and "undeploy" each time I use HF.  That would put a huge damper on my operating.

Believe me, I would do "once and done" to achieve 15 to 40 meters if it was feasible for me at my location. May as well tell an elephant to levitate.

I'm going to guess that you're in a Senior Assisted Living community, which puts pretty close oversight on residents, varying with their level of care chosen and apartment type.  Putting in ANY antenna can be pretty difficult under those circumstances and requires a lot of enterprise and effort which you do not seem to be in a position to supply.  I understand.

I hope the MagLoop works out for you.  If it doesn't, perhaps remote operation of a rented station will, and barring that, you at least have the forums.

Best Regards,

Brian - K6BRN
Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #25 on: September 16, 2022, 08:52:04 AM »

Here are some widely acknowledged facts about mag loops for transmit in the 15 to 40 meter bands:

Cons: 

  • Very narrow bandwidth at 15 and 20 meters, becoming narrower at 30 and 40 meters.
  • Requires retuning when frequencies are changed, even a little.
  • Efficiency decreases from <60% in lower bands to <15% at higher bands.
  • Expensive compared to most better performing antennas in these bands.
  • Unless for portable use, weather resistance, remote tuning, and higher power (100+ watts) are essentials.

Pros:
  • Better than nothing when other types of antennas are infeasible at your location.
  • Remote tuning for multiple bands.
  • Receive capabilities are excellent; a bit more noise-free than other types.
  • Performs nearly as well a few feet off the ground as 30' up.
  • Can be stealthy without a lot of effort (for us old guys who don't hang off ladders well.)

Fair enough?

Quote
From K6BRN
I'm going to guess that you're in a Senior Assisted Living community, which puts pretty close oversight on residents, varying with their level of care chosen and apartment type.  Putting in ANY antenna can be pretty difficult under those circumstances and requires a lot of enterprise and effort which you do not seem to be in a position to supply.  I understand.

I am convinced you do NOT understand.  That was a rather ignorant , mocking, and disrespectful comment, Brian.  I have no doubt that was your intention.  When you grow up you will learn to understand that after a certain age we older folk are wise enough to know our limitations.  One does not to be in assisted living to understand and practice that.

Wise marketers of ham equipment will heed the facts:

Quote
...the average age of amateur radio operators is quite high. In some countries, the average age is over 80 years old, with most amateur radio operators earning their license in their 40s or 50s. https://www.liquisearch.com/amateur_radio_operator/demographics/age

Others such as yourself will just belittle and mock.
« Last Edit: September 16, 2022, 09:12:59 AM by KK4GMU »
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

W9IQ

  • Member
  • Posts: 8862
Re: Magnetic loop TX antennas
« Reply #26 on: September 16, 2022, 10:01:19 AM »

All small loop antennas with uniform current start out with a peak directivity of 1.76 dBi (1.5 in linear terms) across the HF bands. It is the radiation resistance and the resistive losses of a particular antenna that determines the efficiency and thus the ultimately lowered gain of the antenna.

The radiation resistance is in direct proportion to the square root of the frequency so as frequency goes down, so does the radiation resistance and efficiency. You have no control over this. The radiation resistance is also directly proportional to the circumference of the loop. Here you can improve efficiency by selecting a larger circumference loop.

The construction details of a given loop determine the resistive losses caused by the RF resistance of the loop and its connections. So a larger diameter, better conducting tube and one with lower resistance connections will further improve efficiency.

So look past the marketeering claims and dig into the engineering details before selecting your antenna. You do have a great deal of control regarding the gain of the small loop you choose to deploy.

- Glenn W9IQ
« Last Edit: September 16, 2022, 10:05:20 AM by W9IQ »
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6BRN

  • Member
  • Posts: 2229
Re: Magnetic loop TX antennas
« Reply #27 on: September 16, 2022, 10:37:35 AM »

Hi Gerald (KK4GMU):

...
I am convinced you do NOT understand.  That was a rather ignorant , mocking, and disrespectful comment, Brian.  I have no doubt that was your intention.  When you grow up you will learn to understand that after a certain age we older folk are wise enough to know our limitations.  One does not to be in assisted living to understand and practice that.

You're right - I don't understand.  And you're VERY sensitive.  BTW - the second quote is not mine.  I don't care how old, what race or sex an operator is.  The stats are interesting, but nothing to perseverate over.

YOU need to understand - I'm not mocking you in any way and have been respectful of the nearly hermetic limitations you've placed on yourself.  Though I'm 13 years younger than you I'm VERY aware of the limitiations that have been remorselessly moving into my life.  Age is not to be mocked or laughed at - we all face that prospect, if we're lucky.

You've asked about magnetic loop antennas and pretty much received the same feedback over and over.  Clearly, you don't like the answers.  So I offered another option.  One that works for me in a very similar situation, and for others that I know.

You live in what is essentially a retirement state and are of retirement age.  And you've said you have no attic, etc. to put an antenna in.  Yet your registered address shows a home with a very nice peaked roof. low interior ceilings and presumably very good attic space for the antenna.  By code, there HAS to be access.  The Garage, by itself, looks workable, if the attic somehow isn't.  Doing the install yourself is not necessary - hire someone - many do that.  So you clearly have room for a wire antenna if you want one - but indicate its not workable.  Very odd.  If you simply don't like them, that's your preference - not something to argue.

So if you really live at your registered address, you have options.  If you don't, you're likely in a retirement community.  many are, in your state.  It's not a big deal nor does guessing at that denote disrespect.  It is what it is.  I visit Boynton Beach frequently for my own family reasons.

Assuming the worst intentions of people trying to help you is not a good path forward.  Perhaps at this point what you need to do is connect with other hams via a local ham club and share antenna solutions and installer info.  I always feel better when I have several options to try.  And locals always know the best people to help.  Plus, just talking to others with similar issues helps cheer me up  Maybe this will work for you, too.

One thing I've learned and am now applying liberally as I get older, is that paying others to do physical work that is now risky to me saves a lot of pain.  And pain is one of the penalties of age that is rarely emphasized in the brochures.  :)

Have a good day - life is short - and I know it.

Brian - K6BRN

« Last Edit: September 16, 2022, 10:49:33 AM by K6BRN »
Logged

KK4GMU

  • Member
  • Posts: 366
Re: Magnetic loop TX antennas
« Reply #28 on: September 16, 2022, 11:48:58 AM »

BTW - the second quote is not mine. 
Brian - K6BRN

This one?
Quote
Quote
...the average age of amateur radio operators is quite high. In some countries, the average age is over 80 years old, with most amateur radio operators earning their license in their 40s or 50s. https://www.liquisearch.com/amateur_radio_operator/demographics/age

Yes, I know.  That's why I added a link to it. Did you miss it? I hope it helps.

Quote
And you're VERY sensitive.

Sensitive when appropriate, yes. A presumptuous mocker when inappropriate, no.

Quote
You've asked about magnetic loop antennas and pretty much received the same feedback over and over.  Clearly, you don't like the answers.  So I offered another option. 
You're making this too much fun. ;D  You make one more erroneous assumption: You apparently believe that giving reasons  for choosing a given piece of equipment to help others understand the circumstances is disliking the answers.  Nope.  Giving reasons for choosing a given piece of equipment is NOT disliking the answers.  It is explaining the situations where use of a given piece of equipment may be most appropriate.  I understand there are those who lack an understanding of the logistical situation of some others - without assuming they are in "assisted living."  That was just a careless expression triggered by your disagreeing with my explanation.
Logged
IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

N8AUC

  • Member
  • Posts: 1007
Re: Magnetic loop TX antennas
« Reply #29 on: September 16, 2022, 02:09:20 PM »

Well, all the information about mag loops I've seen on this thread are accurate.
They're going to be inefficient, and touchy to tune, especially at lower frequencies.
But experimentation is part of the game, so if you've got the spare cash, why not give it a whirl?

Unless you've got your heart set on being on 75/80 meters, another possible option is to get a couple of hamsticks and the mounting bracket that lets you use two of them as a dipole, and set that up on something like a painter's pole when you want to operate, and take it down when you're done. Now this won't work for 75/80 meters (i tried it and it was deaf as a post), but for 40 meters and up they work pretty good. Even better on 20 meters and up. And it's a lot less expensive than a mag loop. I know guys who operate on 20 meters who live in apartments, and they do pretty well with a hamstick dipole.

But if you must be on 75/80 meters, in my experience, nothing beats a wire antenna if you've got a limited budget.

Is there a wooden fence around what little yard you have, like a privacy fence? If so, you could build a wire loop that runs around the perimeter of the property. Granted it would be mainly an NVIS pattern, but I've known people who've done that and were satisfied with the results.

Just a suggestion.

73 de N8AUC
Eric

Logged
Pages: 1 [2] 3 4 5   Go Up