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Ambrose_Wolfinger 05-01-2017 9:42 AM

Rf Exposure with a mag loop, and MFJ 1622, Buddistick effectiveness
Looking into the possibilities of HF antennas for an apartment. Magnetic loop antennas seem to be really popular but I'm concerned about RF exposure issues. It seems the voltage of these is quite strong however in doing an RF assessment based on the ARRL web page calculators, I I do not know what the gain of a magnetic loop antenna is so I do not know what a safe distance would be. My power output would be no more than 100 watts pep, which comes out to a maximum average power of 40 watts, per the assessment guidelines. I figure I would be 8-10 feet away from the antenna

Also, looking at the MFJ 1622 and Buddistick as a quick way to get on the air. How effective are these if mounted outside on the balcony? I also have attic access so that might be a possibility. The attic is all wood and composition shingles so very little metal that I can see.

Again, when calculating RF exposure levels is it safe to assume these have the same gain as a dipole?

N4GIX 05-01-2017 11:26 AM

Unless you have a mag loop with remote tuning, attic mounting is a non-starter. They are typically very high Q and simply do not have the bandwidth to cover any of the bands completely. Even then, since the "rough tuning" is mainly accomplished by listening to the noise level from the receiver as you turn the capacitor for a peak, doing so without the receiver near you as you tune would be difficult.

Fine tuning for lowest SWR would be even more difficult... ;)

I ordered MFJ's most expensive remotely-tunable High-Q magnetic loop to use with my shiny new KX3-PX3 rig. After waiting six weeks for my backordered MFJ-1786 to be built and delivered, when it finally arrived the control box proved to be DOA; it would not power up. Having traced the problem to a defective 2.5mm coaxial power jack (negative side had no continuity), and even batteries would not power up the control box, I called MFJ this morning. The technician said they have no control boxes available and it would take at least another five weeks for them to get another one for me, he was completely unsurprised when I requested a return label for a full refund.

I also ordered a Deluxe Buddipole (current in transit), so hopefully I'll finally get to try out the KX3! However, just as in the case of a mag loop antenna, ready access to the antenna is critical for tuning, but tuning a Buddistick (or pole) not nearly as fiddly as a mag loop!

TheSpaceMann 05-01-2017 12:38 PM

You might want to try one of those $15 MFJ Hamsticks. I have made a good number of contacts using them mounted on an outdoor balcony!

Ambrose_Wolfinger 05-01-2017 9:17 PM

Well at $15 the price is appealing. I wouldn't mind buying something inexpensive to get me going. And then experimenting with my own builds later.

Regarding the RF exposure concerns, does anyone have any input?

Ambrose_Wolfinger 05-04-2017 8:03 PM

Went to the local HRO store today. The salesman showed me a Super Antenna vertical. Similar to the Buddistick. I liked the way the coil is adjusted much better. Performance is probably about the same. Will probably consider that, as he really discouraged the MFJ 1622.

N4GIX 05-04-2017 8:46 PM

I receive my Deluxe Buddipole kit two days ago, and today was my first chance to set it up and play around a bit. I've already ordered a few more optional parts for it so that I can experiment around with 6m and 10m two and three element beams.

All I got a chance to check out this afternoon was 20m. I did hear a few folks on, but propagation was really bad today on 20m. At least I know that my KX3 works now! :)

I am impressed with the number of permutations possible with this clever bit of engineering. So far I've tried a horizontal dipole and vertical "L" configuration. I'm looking forward to some warmer weather so I can spend some time in the park DX'ing.

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