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Author Topic: Need Help on MFJ Super Hi-Q Loop Antenna  (Read 1589 times)
KA3QOT
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Posts: 24




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« on: June 28, 2002, 07:09:59 PM »

Well, I just bought a MFJ Super Hi-Q Loop and have some questions. The "manual" is horrible and while their tech support guys are nice, they are not really forthcoming.

Here are my questions:

1. The manual says for testing purposes I should first cycle through Auto Band Select Down up and down and then I should cycle through slow up and down. Do I press these slow buttons simultaneously?

2. When finished tuning with an AM carrier, I do not hear a beep as the manual says I should, though the light goes out when finished.

3. After this step, one of the slow lights is lit. I press the button, as instructed, and supposedly there should be a "rapid dip in reflected power," and again I should hear the tone, but I do not.

Any ideas?

Should I just use the MFJ as a tuner and worry about the SWR at my rig?

73,

Dennis KA3QOT
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AA5TB
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Posts: 81


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« Reply #1 on: July 10, 2002, 10:53:16 AM »

Hi Dennis,

I have used the MFJ small loop although with a different control box and I have designed my own loops for many years.

I can't really help you with the "beeps" and other functions of the control box but I may be of some help with the antenna itself. DO NOT tune the antenna at the rig with an external tuner as the efficiency will be horrible. The antenna MUST be tuned itself. This can easily be done by first tuning the capacitor (via the control box) for a peak in receiver noise. This peak will be very sharp an can be easily missed. Once you find a peak in noise, transmit into the antenna with low power and fine tune the capacitor for a dip in SWR. The 2:1 SWR bandwidth will vary from about 10 kHz at the low frequencies to about 50 kHz on the high end (off the top of my head).

If for some reason you cannot obtain an SWR of 1.5:1 or better at resonance, try moving the antenna away from other objects, such as the ground, metal desk, etc. I have been able to reliably work into Europe with 5W CW with my homebrew 3ft loop in the shack only 8 inches off of the floor.

If not properly tuned you may come to believe that the antenna is a poor dummy load but with proper care a small transmitting loop can be a fine antenna. For more information you may want to check out my page at the following URL:

http://aa5tb.home.texas.net/loop.html
or
http://www.qsl.net/aa5tb/loop.html

Be sure to check out the links at the bottom too.

73,
Steve - AA5TB
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K1BRF
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Posts: 36




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« Reply #2 on: July 16, 2002, 10:03:55 PM »

Some general comments on this type of antenna.  Have not used this model.

Agree this must be tuned at the loop for a variety of reasons.

If you could borrow an analyzer you could diagnose the issues quickly; they can be frustrating to tune.

They work great when tuned.

They have a very narrow bandwidth and a very sharp curve so tuning it is not something you will do quickly.  You can pass right by the peak without realizing it which is why the visual aid of an analyzer is so useful
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DF5SF
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« Reply #3 on: August 31, 2002, 03:44:23 PM »

Hello Dennis,
I have the same magnetic loop with the
MFJ Super HI-Q Loop Remote control. For tuning the antenna do the following:
1.) Press one of the button UP/DOWN (from AUTO BAND SELECT) to the ON-Position One of the yellow LED is on and now wait for the BEEP. Press the botton (from AUTO BAND SELECT) to the OFF-Position. The BEEP is going away...
2.) Now the fine tuning begins. On of the two LEDS (green or red) is on. Now press the button on the side with the LED on (a yellow LED is blinking) till you get a minimum SWR on the meter. If you have overrun the minimum press the other button and go back till you get minimum. You have to repeat this step till you get a minimum SWR. There is _NO_ BEEP. If you use the buttons of the FINE TUNE you have to look on the meter.

Sometimes you cannot reach an SWR of 1:1, because of the environment(metal, wires ...). But you must get a minimum.

I hope this was helpful  
73 ang cu
Uli DF5SF
e-mail: uli@df5sf-qrp.de
           
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ADAM12
Member

Posts: 28




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« Reply #4 on: October 09, 2002, 01:18:19 AM »

If you can't get the SWR low enough and have moved the loop away from metal objects, try opening up the cover and re-shaping the small driven loop from oval to circle (or vice-versa). It's held in shape with some rubbery goop but that can be peeled off of the casing (and re-stuck if you can be bothered).

I had to do this on my MFJ 1786 and could then get SWR down to 1:1 almost everywhere.
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ADAM12
Member

Posts: 28




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« Reply #5 on: October 09, 2002, 01:24:43 AM »

Re. reshaping the driven loop.

Do not of course do this (or ever touch any part of a magnetic loop antenna) whilst transmitting as there are *very* high voltages induced in these loops.
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W2DI
Member

Posts: 133




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« Reply #6 on: May 14, 2003, 10:06:50 AM »

Dennis;
I used the same loop with very good results. You've received some good info from all the responses amd hope you get it working to your satisfaction.
Just my 2ยข for another approach. Since tuning these antennas is so touchy, I used a noise bridge rather than transmitting and adjusting for swr. These units are sold by Palomar (Tuner-Tuner) MFJ and as an inexpensive kit by Ten-Tec. The bridge goes in your transmission line between the transceiver and the control box. When you turn on the bridge you'll hear an s-9 or so noise in your receiver. You then use the 'fast' buttons to find a sharp dip in the noise - listening closely as it is easy to miss. Then, for example, if I were tuning from a higher to a lower frequency, I would 'tap' the fine 'up' button until I zeroed in on the null, as the fast button would have take me silghtly past the null in the lower direction.
After a little practice, it became easy to null the noise and (after turning off the bridge) have a better than 1.5:1 SWR without transmitting any signal at all! Having the bridge in-line, in the 'off' position should not add any significant loss to your system.
Good luck, and enjoy.
Joe, W2DI
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