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Author Topic: MLA-30 Mod Step 1: Complete...NOT SO FAST :(  (Read 1575 times)

Offline Erik Mattson

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MLA-30 Mod Step 1: Complete...NOT SO FAST :(
« on: January 20, 2022, 1942 UTC »
After getting the thing in hand it was painfully obvious that this was 100% necessary.
Now, I'm wondering how well these things hold up outdoors. Maybe if I hosed it down with Flexi-Seal  :P ?!?

« Last Edit: January 25, 2022, 1609 UTC by ErikMattson »
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Offline Elf36

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Re: MLA-30 Mod Step 1: Complete...
« Reply #1 on: January 20, 2022, 1959 UTC »
The one time I took one apart, I found that all of the circuitry was covered in epoxy. Very little chance of water intrusion issues. I did of course put a bead of silicone on the sides and a bit on the screws just in case. Did you see anything exposed when you opened it to install the new coax connector?
« Last Edit: January 20, 2022, 2002 UTC by Elf36 »
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Offline Erik Mattson

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Re: MLA-30 Mod Step 1: Complete...
« Reply #2 on: January 20, 2022, 2012 UTC »
The one time I took one apart, I found that all of the circuitry was covered in epoxy. Very little chance of water intrusion issues. I did of course put a bead of silicone on the sides and a bit on the screws just in case. Did you see anything exposed when you opened it to install the new coax connector?
Yeah, it's nearly entirely covered in a black epoxy. So, I just pulled about 2 inches of the RG-174 (?) back into the compartment, trimmed it off and connected that to the F bulkhead.
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Offline Erik Mattson

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Re: MLA-30 Mod Step 1: Complete...
« Reply #3 on: January 20, 2022, 2316 UTC »
And these things (loops in general) don't need to be super high do they? Was thinking I'd just stick on a tripod on my shed. Should end up about 12 to 16 foot up or so. Didn't wanna waste the effort getting it on the roof. Saving that for a discone.
 Then figure out the best direction to "point" it (edge-on).
« Last Edit: January 20, 2022, 2319 UTC by ErikMattson »
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Offline JustGreg

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Re: MLA-30 Mod Step 1: Complete...
« Reply #4 on: January 20, 2022, 2351 UTC »
I have one for months.  It is OK for listening to shortwave broadcasters, but, it is not the ticket for chasing weak signals.  Depending of the frequency, signals on it are about 10 to 15 dB below that of my 50 foot End Fed Long Wire.  If you cannot put a decent wire antenna, then it is a good alternative.  I have increased the loop size.  It seems to help.  In the spring, I want to try mounted outside to see if that helps.
« Last Edit: January 20, 2022, 2359 UTC by JustGreg »
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Offline Elf36

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Re: MLA-30 Mod Step 1: Complete...
« Reply #5 on: January 20, 2022, 2351 UTC »
Yeah. I wouldn't worry too much about the height. Of course, higher is usually better, but it should be fine. A lot of times now, your just trying to distance from various electronic noises from common devices in your home and neighbor's homes. What were you using before for an antenna?
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Offline JustGreg

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Re: MLA-30 Mod Step 1: Complete...
« Reply #6 on: January 21, 2022, 0007 UTC »
I still have the 50 foot end fed random wire.  It works fairly well.  The best improvement to reduce noise pickup by the EFRW was to add a decent RF choke balun. 

Another interesting loop to experiment with is the You Loop.  You can get it from AirSpy.  Once again it works OK for for stronger stations. It also have some VHF coverage (FM broadcast).  The stock version does not have a preamplifier.  The NOOELEC HF/VHF Preamplifier is a good accessory to add to it.  If you are limited to only indoor antennas, both are good candidates.  But, you do have to do some experimenting to find the best (low noise) spots.  Attic crawl spaces should not be over looked. 
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Offline Erik Mattson

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Re: MLA-30 Mod Step 1: Complete...
« Reply #7 on: January 21, 2022, 0018 UTC »
I just wanted to try it out. Something to goof around with. I have a 60 ft dipole and end-fed sloping random that's a little longer.
Just something for the workbench, that's all.
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Re: MLA-30 Mod Step 1: Complete...
« Reply #8 on: January 21, 2022, 0206 UTC »
Quote
don't need to be super high do they?

Usually 1 loop diameter off the ground (minimum 3 feet) is sufficient.

Some discussions seem to indicate that DX performance of loops would be enhanced over a good ground and that perhaps a ground mat or radials would be beneficial. For short hop and NVIS the difference would be barely noticeable.

https://forums.qrz.com/index.php?threads/optimum-height-above-ground-for-a-magnetic-loop-antenna.512778/

Offline RobRich

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Re: MLA-30 Mod Step 1: Complete...
« Reply #9 on: January 21, 2022, 0401 UTC »
My MLA-30 is collecting dust. I never really it used for much.

I installed a RCA connector with a F adapter at the preamp to use RG-6. It was probably whatever I had in the bulk connector parts box.

Also I removed the USB connector and bypassed the potentially noisy 5v to 12v voltage converter in the bias tee. If nothing else it now works fine with a 12v PSU or even just a 9v battery if preferred. I probably should have added some extra filtering caps in the bias tee just to cover the bases, but "whatever" I suppose. Think I potted my bypass mod with hot glue anyway, as I ended up soldering the positive side to a copper trace on the PCB. o.0




About mounting height, that is more a concern with horizontal loops due to ground losses, unless you are explicitly designing a NVIS or loop-on-ground antenna.

As for a vertical loop, you might consider localized ground clutter when planning the deployment height to maybe improve low-angle performance, but even consider that a huge YMMV depending upon ground conductivity and a myriad of other issues.

Best approach IMO and as noted previously here, move it around to find a hopefully nice low RF noise location, as improving SNR will tend to net the most gains for such an antenna. Moving a small loop, e-field probe, or similar antenna a few feet sometimes can make for a considerable difference if in a high-RFI location.
« Last Edit: January 21, 2022, 0605 UTC by RobRich »
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Offline TRI International

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Re: MLA-30 Mod Step 1: Complete...
« Reply #10 on: January 21, 2022, 0943 UTC »
I have been using one of these for over a year now and it seems to works fairly well. I  also add a RF choke balun which it is connected to my Kenwood Ts120s at the moment for the ham band. It is up about 16 feet. Still have a bit of wire to put up higher.
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Offline JustGreg

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Re: MLA-30 Mod Step 1: Complete...
« Reply #11 on: January 22, 2022, 2046 UTC »
Here is a useful accessory for the MLA-30.  It is a four (4) AA battery USB supply.  I have found it to be lower noise than most AC operated USB power devices and 12 Car USB jacks.  It is  USB Emergency Portable 4AA Battery Charger for Apple iPhone/iPad/Android Phone from BatteryGalaxy in Orem Utah via EBay.  It works well.  I have used in a local park where the electronic device noise is almost non-existent.



Finally got it right.
« Last Edit: January 22, 2022, 2119 UTC by JustGreg »
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Offline Erik Mattson

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Re: MLA-30 Mod Step 1: Complete...
« Reply #12 on: January 23, 2022, 1412 UTC »
What does increasing the loop size do to reception?
I've got an idea on making one that's sturdier. The existing loop's diameter measures about 26", and the one I'd make would only add another 10" at the most.
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Offline JustGreg

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Re: MLA-30 Mod Step 1: Complete...
« Reply #13 on: January 23, 2022, 2102 UTC »
The value of the voltage induced into the loop is determined by area of the loop and frequency.  Area goes by the square of the dimensions.  So if you double the diameter of a loop, then the induced voltage increases by a factor of four.  As long as the circumference of the loop is small (less than 1/16 of wavelength, my criteria) compared to wavelength then the above holds.  For indoor use, bigger is better.  The element on my MLA-30 is a square about 26 inches on a side.  It is better than the stock element.
I hope this helps.
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Re: MLA-30 Mod Step 1: Complete...
« Reply #14 on: January 25, 2022, 0225 UTC »
Oh no, no, no, no. You will not get the RSP to power that antenna. The MLA-30 ships with a 12 volt power supply and the specifications are: Power Supply: 5 volts and Current Drain: 750 mA.

The RSPdx's Bias T will only provide 4.7 volts at 100 mA and most computer USB ports only deliver 5 volts at 500 mA. The RSPdx alone requires +/- 200 mA to operate.