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Author Topic: MLA-30 Loop antenna  (Read 4591 times)

Offline Josh

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Re: MLA-30 Loop antenna
« Reply #45 on: January 14, 2020, 2130 UTC »
Depending on the current draw, I'd be interested in running it on a battery, right at the antenna, with a small solar panel to charge with.
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Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #46 on: January 15, 2020, 0027 UTC »
For my trial run I used a small  battery with a USB port. Basically it's a back up battery for extended charge with cell phones or other devices. Can't think of anything better. At first iIwas going to use a small battery I use for QRP portable ops with a cig lighter type adaptor to lower the voltage to standard USB voltage. I still would if I planned on using on a camping trip or longer outing. Looking forward to playing with it more this weekend. I would like to try the 'Chanito' style double loop as well. Interesting idea and self supporting on a flat surface!
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #47 on: January 15, 2020, 1906 UTC »
Update on the small battery use. I have to test with another unit to confirm if the one im currently using is bad, but I noticed the battery unit powers off after a couple of mins and has to be reset. I will use a small 12 volt battery with USB adapter next.
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline kris

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Re: MLA-30 Loop antenna
« Reply #48 on: January 18, 2020, 2130 UTC »
    Hi everyone, thanks for your interest, it's worth tinkering with.
My technical adaptations use common knowledge described on the web, but I will add some details:

 
- the MLA box is solidly made of white ABS and has 4mm thick walls, so it won't deform easily or crack quickly. Colleague Ray rightly suggested to protect the material against UV degradation by spraying with varnish.

- the lid of the box is solid and has a channel with a well-fitted gasket, but the cable passes through the opening in the box without a sealing gland. There is enough space to fill a BNC, F / TV or SMA socket tightly. The socket can be easily soldered to the cable inserted into the amplifier board, without interfering with the board, it is flooded with black hard resin (probably epoxy) and the gouging will result in tearing off the elements and damaging the board.

- the loop is screwed through M-4 (stainless) screws through the box walls. In my opinion, it is worth sealing with epoxy resin, and on the outside of the box put (stainless, epoxy) washers to strengthen the mechanical connection with the loop. A large loop under wind pressure can exert considerable force on the box, and the box transfers it to the pole supporting the antenna.

- I have 3mm thick Ag / AL wire and I wanted to make a new loop larger than the original one. I had to slide it into a PE / AL layered pipe to shield against electrical interference from industrial interference signals.
I searched my apartment for the source of interference using the original MLA loop. It turned out that the TV, cable tuner, router, power supplies, computer, lighting and neighbors do not sow them into the environment (at a noticeable level).
In this situation I gave up shielding the loop and made a large loop from the pipe.
  Both ends of the pipe, about 3 cm long, must be flattened by crushing and then bent 90 degrees to allow it to be screwed to the MLA box. The aluminum layer is thin and breaks when bent, so the bend must be made on a flat length before you remove the PE layer. It is best to remove the insulating PE coating (about 2 cm) with a hot tip of the (large) soldering iron. Now drill holes for screwing the box. Screw the loop through the washers to ensure good electrical contact with the pipe surface and strengthen the connection.
- as I described in the previous post, the antenna works great if the large loop is tuned to resonance with a variable capacitor (or varikap), and the MLA amplifier box is connected to a small coupling loop (1 / 5D). The signal strength (and noise increase) is so high that it requires optimization of gain and attenuator - both blue potentiometers are visible in the pictures.
It is possible that even better results will be achieved by optimizing the degree of coupling of a small loop with a large one, but I haven't had time for it yet.
- DC 12V stabilized voltage is fed to the MLA amplifier with an antenna cable. There on the plate it is probably reduced to 8V resistors which is optimal for a well-integrated differential amplifier. I advise against gouging in resin - experiment safely with the voltage supplied through the cable.
- In the "Biasing Tee" box you can safely gouge: increase the capacity of electrolytic capacitors, bypass the DC 5 / 12V converter, change the USB power socket and SMA sockets connecting to the antenna and receiver.

- I use a widely available, convenient and good for HF coaxial cable type RG6. I use SMA / F or SMA / BNC adapter connectors, sockets, plugs and F connectors for TV installations, as required.
  Good luck and write about your experience!

For the record, here is the schematic diagram of the MLA-30 system
https://www.g8jnj.net/activeantennas.htm#MLA30
« Last Edit: January 20, 2020, 0947 UTC by kris »
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Offline kris

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Re: MLA-30 Loop antenna
« Reply #49 on: January 20, 2020, 1605 UTC »
I sent my MLA-30 back because it could hardly receive any stations on medium wave
   You did not hurry with the return. You had to take the wire about twice as long as the original loop. If you don't have free space, fold it up to form two scrolls. The loop diameter will be like the original, and you would lower the reception range to the MW band. You could also tune this loop to the MW range by adding a solid capacitor. The signal level will increase and the received bandwidth will probably be satisfactory, because the goodness of this circuit with the MLA connected is small.
   In the first days of using my MLA, I had a surprising glitch. For no reason at all, the antenna became very deaf. Moving the SMA plug on Bias Tee, I found that there is a fault in this place. It was not a bad soldering. In the plug I found an almost invisible thin brass hair left from the thread tapping. He sometimes made a short circuit between the plug nut and the middle pin of the plug. After removing this surprise, the reception returned to normal. It was good that it was in the cable to the receiver and not to the antenna, because I would have a DC short circuit and the ruin of the MLA undertaking.
- - I thought about winding my "huge" loop of PE / AL pipe in two turns. I will try to see if performance will get too bad. The large loop is now susceptible to wind, takes up a lot of space - it is difficult to turn it and hide it in the bush from the eyes of neighbors.
« Last Edit: January 20, 2020, 1623 UTC by kris »
SDR-FE-PLAY, Icom PCR-1000, RTL-SDR(R820T2) USB Tuner, Sony XDR-F1HD,
170m Sky Loop, Loop MLA 30 rebuilt, Discone Moonraker
QTH:N Poland,  Ru/Sp/Gr/Sb/Cn=Russian,Spanish,Greek,Serbien,Chinese
eQSL appreciated to: 13krzycho@gmail.com

Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #50 on: January 20, 2020, 2027 UTC »
Kris, Thank for posting your detailed photos. I haven't gotten to mess with my MLA-30 much, but I can say its a great improvement for my Grundig G3. I haven't run it through it's courses, but it definitely shows directional properties on higher bands such as 20m (14 mhz) and even a small bit on 10 mhz WWV. I will try a different type of loop at some point, but I'm happy with it for what it cost.
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline Josh

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Re: MLA-30 Loop antenna
« Reply #51 on: January 22, 2020, 0659 UTC »
Just saw this vid on the subject;
https://www.youtube.com/watch?v=RvXsywLbi9k
https://www.youtube.com/watch?v=FRhDHHpLoaM

the mla seems to be pretty fair for the price, and with Kris mod of lengthening the loop it might be a better showing on vlf
« Last Edit: January 22, 2020, 0710 UTC by Josh »
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Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #52 on: February 01, 2020, 1407 UTC »
After some various testing, my current conclusion with the MLA-30 is that it is well worth the $43.00 I spent on it, but I don't plan on mounting it permanently for a secondary antenna outside. I plan on drilling out the sides to make a firm 1/2'' PVC loop and make a small PVC stand for portable ops with my Grundig G3. If you are use to running a telescoping whip or small piece of wire this antenna will make your portable rig come to life and it definitely shows directional properties on frequencies above 10mhz, but my 135' OCF dipole seems to steal the show. It will also be perfect for running with an SDR receiver in the field while doing QRP portable ops to see whats going on on 10,12,15,17 and 20 meters.  Again no regrets and I would suggest purchasing one to try it out. Maybe when I have some more time I will try some of the mods I've seen.
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #53 on: February 25, 2020, 2205 UTC »
So I ended up installing the MLA-30 on the roof semi permanent. Now I can do a bit more side by comparison. I don't have much scientific data to report, but again I must say im very pleased with it. If I didnt have room for a large dipole it would really be a god send. Im now using the Bias T on the RSP2 to power it. Hope to do some more testing tonight on various frequencies. I'll post what I come up with.
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline ultravista

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Re: MLA-30 Loop antenna
« Reply #54 on: February 26, 2020, 0120 UTC »
Have you replaced the SMA connecter on the antenna box and added a longer wire loop?

Offline IZS4

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Re: MLA-30 Loop antenna
« Reply #55 on: February 26, 2020, 1216 UTC »
I do plan on adding a BNC connector and better coax. Haven't thought much about going with a larger loop, but i'd like to rebuild the loop a bit better.
Listening on an Icom-718 with a 135' OCF dipole or a RSP2.  Grundig G3 and MLA-30 when portable. When QRP I use a Hendricks PFR-3 I built. Coverage is 20,30 and 40 meters.

Offline kris

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Re: MLA-30 Loop antenna
« Reply #56 on: February 28, 2020, 2147 UTC »
    And I wound my large loop of 155cm in diameter into two turns. Now the diameter is 79cm.
The tuning range with the 750pF variable capacitor remained unchanged from 2.5 - 15.5MHz. From the bottom to about 10MHz, antenna performance seems to remain the same as for a large loop. The loop maintains a clear directional characteristic. Above - it tunes less sharply than before and gives a weaker signal. I am disappointed with the high noise level of the loop antenna compared to Sky Loop. I get a similar signal level, but readability is lost in the noise.
Maybe my neighborhood isn't as clean as I thought. I need to remotely tune and rotate the loop and set it aside about 6 m from the house. Maybe it will be quieter than on my balcony - without it,
 it makes no sense to use.
SDR-FE-PLAY, Icom PCR-1000, RTL-SDR(R820T2) USB Tuner, Sony XDR-F1HD,
170m Sky Loop, Loop MLA 30 rebuilt, Discone Moonraker
QTH:N Poland,  Ru/Sp/Gr/Sb/Cn=Russian,Spanish,Greek,Serbien,Chinese
eQSL appreciated to: 13krzycho@gmail.com

Offline redhat

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Re: MLA-30 Loop antenna
« Reply #57 on: June 09, 2020, 0130 UTC »
I bought one of these myself to see what all the fuss is about.  I'm considering getting a second one to keep in the 'go kit'.  I found its performance on medium wave to be acceptable, and the noise is no worse than my existing Chi-town special.  That being said, local noise around here is about s7 and the loop seems similar.  I may build a bias injector for it and see if any difference in performance is observed.  With it I did see WWV on 15, 20, and 25 MHz come in on it the other night, something I've never seen before here with the tune loop.

I will drag it with to a quiet location sometime and see how it behaves in a quiet environment.

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Offline alpard

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Re: MLA-30 Loop antenna
« Reply #58 on: June 09, 2020, 1033 UTC »
I am planning to get one too. It looks actually very interesting active loop antenna for good price.