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Author Topic: Magnetic loop use inside shack  (Read 870 times)
KK4ASK
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« on: May 25, 2019, 08:03:19 AM »

Is it safe to use magnetic loop inside shack at 100w?
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K6AER
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Posts: 5694




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« Reply #1 on: May 25, 2019, 08:55:21 AM »

Probably.

Why would you put an antenna next to your computer, printer and switch mode noise made in the shack? Your noise level will be very high.
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F8WBD
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« Reply #2 on: May 25, 2019, 09:55:35 AM »

If you or any family member has a defibrillator implant for a very serious heart condition, it is not recommended that a magnetic loop be used. Far removed from contact may be ok. This from my YL's cardio surgeon. Such a person must avoid airport scanners.
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KE6EE
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« Reply #3 on: May 25, 2019, 10:24:55 AM »

Certainly it is questionable regarding safety using a magnetic loop and 100W if you are less than 10 to 15 ft.
away.

A better notion about safety can be had by modeling the antenna in its environment and including its
orientation towards the operator and others and the mode in use.

Using a nearby loop with QRP power (to 10 watts) is another matter.
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NK7Z
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« Reply #4 on: May 25, 2019, 10:38:13 AM »

Is it safe to use magnetic loop inside shack at 100w?
I would not do it...  The voltages developed on the loop are quite high, see:

http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx

If you are running a normal loop on 20 meters, you are looking at around 4000 V on the loop at the cap... 

Further this does not address the RF exposure issue either...  See:

http://www.arrl.org/rf-exposure

read it, then run the calculations...

As if all of the above is not enough, the RFI you will pick up from every RFI radiating device in your home, will be horrendous...  I ran some tests by setting up a loop inside, then taking it 60 feet from the house, and setting up up 10 feet lower, and 6 feet over ground.  I saw a 20 db loss of noise by moving the loop outside, and no change in signals...  So overall, it seems to me to be a very bad idea to run a loop in a home with people in it...
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Thanks,
Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
WA3SKN
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Posts: 6991




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« Reply #5 on: May 25, 2019, 04:33:46 PM »

Safe? Probably.  The magnetic loop radiates very poorly and most are used for receive only.
However, with all the noises inside the house reception will be quite poor also.  So it is not your best option... by far.
So, what are you trying to do?

-Mike.
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W9IQ
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« Reply #6 on: May 25, 2019, 04:42:44 PM »

With 100 watts applied power, the typical small loop will not fail an RF exposure assessment. Consider that its gain will be in the vicinity of -10 dBi so the peak, directively radiated power will be ~10 watts.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
NK7Z
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« Reply #7 on: May 25, 2019, 05:07:33 PM »

With 100 watts applied power, the typical small loop will not fail an RF exposure assessment. Consider that its gain will be in the vicinity of -10 dBi so the peak, directively radiated power will be ~10 watts.

- Glenn W9IQ
Good point Glenn...  Did not think about the loss in the antenna...  THANKS!
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Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
G3RZP
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Posts: 1225




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« Reply #8 on: May 26, 2019, 02:16:02 AM »

Medical implants are required under ISO standards to be immune to 10V/m. Except in the case of the radio telemetry section, which is 3V/m.

Converting that to the magnetic field strength in the near field of a loop is another matter....

vy 73

Peter E. Chadwick, G3RZP, Chairman of ETSI ERM Tg28 Committee on Wireless Medical Applications, from 2007 2013
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W1VT
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« Reply #9 on: May 26, 2019, 05:29:21 AM »

I wouldn't advise it.  Magnetic shielding is harder than E field shielding with known materials. 

Is there some way of putting up a flagpole that can be used as an antenna, perhaps invoking the Freedom to Display the American Flag act of 20065
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NO9X
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« Reply #10 on: July 08, 2019, 06:41:33 PM »

With 100 watts applied power, the typical small loop will not fail an RF exposure assessment. Consider that its gain will be in the vicinity of -10 dBi so the peak, directively radiated power will be ~10 watts.

- Glenn W9IQ

This is very helpful to know in my situation, I am in a difficult situation here in a third floor apartment with no balcony. I do happen to have a magnetic loop (never used) and TS-130V (10 watts output). Would this mean the most radiated power would be about 1 watt?
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W9IQ
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Posts: 3241




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« Reply #11 on: July 09, 2019, 02:16:55 AM »

On the lower HF bands, it will be about a 10 to 1 reduction on transmit and receive. As you get into higher frequency bands, the losses will diminish. The near fields of the loop antenna are dominated by magnetic waves so take extra precautions if you have a pacemaker, etc.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K4SAV
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Posts: 2620




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« Reply #12 on: July 09, 2019, 06:23:47 AM »


The RF Safety Calculators don't work for mag loops or for other unusual antenna shapes.  Those calculators give far field data for a dipole.  Electromagnetic fields in the near field of a mag loop are much higher than the far fields of a dipole. Also because of the way a mag loop is typically used, most people are likely much closer to it than they are for a dipole. 

The only way to determine the RF exposure is to measure it or model the antenna in NEC and compare the results to the controlling document.  That document is
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

To comply with FCC rules, we are all required to make those calculations or measurements for our antennas (with some limited exclusions).

Complying with those rules are much more confusing with some other kinds of antennas, like an end fed antenna or maybe a VHF/UHF HT.  I don't know what you look for in the results when you are holding onto one end of the antenna.  If you do that literally, you won't pass.

Jerry, K4SAV
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AA5MT
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Posts: 248




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« Reply #13 on: July 10, 2019, 10:04:21 AM »

Loops and any other hf antenna are generally considered safe at the 100 watt level.  In fact, 27 MHz is used by hospitals on their rf treatment of bedsores, which promotes healing!  I ask around every few years, and no one knows of any proven heart failure case due to airborne rf.  Direct contact, yes there are known cases, usually involving an amplifier.

On the other hand, a loop will light a flourescent bulb quite nicely just by holding it in proximity. 

I worked a guy who got WAS award running 100 watts to a short vertical(MFJ-1621) which sat right beside his radio.  I got his card a week before QST, which had featured in the QST up front section, with the same qsl card pictured.

You have to make your own decision.

Tom
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WA3SKN
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« Reply #14 on: July 11, 2019, 03:47:07 PM »

http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf
Table 17 page 30 indicates 2 meter distance for controlled and 4 meter distance for uncontrolled area (Lots of other factors ignored).
So how close are you to your antenna... inside that shack? ( 1 meter loop antenna at HF).

-Mike.
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