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Author Topic: MLA-30+ Experiment  (Read 760 times)

Offline JustGreg

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MLA-30+ Experiment
« on: January 29, 2022, 2212 UTC »
While storm Bob kept me in the house, I decided to do an experiment with the MLA-30+.  I found two old whips from an old TV rabbit ears antenna.  They were about 34 inches when extended.  I used them to see how the MLA-30+ would work as an amplified short dipole, similar to a mini-whip.

I was surprised by the combination.  I thought it would be terrible.  However, from about 1 to 4 MHz, the MLA-30+ was comparable to my 50 foot end fed random wire.  I used the S/N estimator of the AirSpy HF + Discovery to measure the difference between the two antennas.

Here are some of the results (frequency in KHz, S/N difference in dB):
880 -12, 1080 -9, 1310 -5,  1420 -6, 1550 0, 1700 -5, 3330 0, 3870 -5, 3885 -10, 5025 -17, 5950 -18.

The MLA-30+ in this configuration is still no weak signal antenna.  The test signals were all relatively strong signals.  But, it was nice to see the idea did work.

Here are my thoughts on why the MLA-30+ compares to the EFRW over the limited frequency range;
a. Below 3 MHz, the matching transformer is not working very well  to match the EFRW,
b. Also below 3 MHz, both are a short dipole,
c. The frequency region the S/N value is set by the environment noise and the high noise figure of MLA-30+ amplifier is not a problem.

Once you get above 6 MHz, this MLA-30+ configuration performance quickly becomes bad.  It is the self noise of MLA-30+ that does this. 

I wish I lived in an area with less noise sources in LF range.  I suspect with 6 foot elements, the MLA-30+ might perform reasonable well.

I am open to hearing other peoples thoughts.  Being married with children, I am used to be told I do not know what I talking about  ;)

Added, last night I tried it on the AM broadcast band.  Even the signals were not as strong as the EFRW, the stations audio was better.  It appears the balanced input of MLA-30+ amplifier is rejecting some of the local noise sources.    I also found I can orient it for the best signal.  I will be keep this around for future  listening.
« Last Edit: January 30, 2022, 1538 UTC by JustGreg »
Enjoy Life, JustGreg
Live Well, Laugh Often, Love Much
AirSpy HF + Discovery
66 Foot End Fed Half Wave with 49 to 1 transformer.
frw.greg@gmail.com

Offline RobRich

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Re: MLA-30+ Experiment
« Reply #1 on: January 31, 2022, 0229 UTC »
While the MLA-30 design uses an inexpensive video amp, ultimately it is still a single-stage preamp that should cope with a wide input impedance range. It is probably not any worse for noise factor and gain than some of the basic single-stage eBay preamp boards.

If up for further experimentation, consider trying it in a loop-on-ground configuration. Place a 60' loop of wire directly on the ground in a circle, square, triangle, etc. with the MLA-30 preamp at the feedpoint. The LoG might improve your signal-to-noise ratio, and the MLA-30 preamp should help with the typically high losses incurred in small LoG antennas, particularly as frequency and associated ground losses increase.
« Last Edit: February 05, 2022, 0030 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 2x 18' End-Fed Verticals | 31' Vertical | 2x PA0NHC MiniWhips

Offline JustGreg

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Re: MLA-30+ Experiment
« Reply #2 on: January 31, 2022, 2017 UTC »
Thanks for the pointers.  I have been considering another experiment.  The loop on the ground will have to wait until spring.  I did check on the video amplifier used by the MLA-30.  It is a Texas Instrument TL592B device.  The specification sheet does not list any noise data.  I am looking at various loop amplifiers to find what appears to be a good one.  Suggestions are apreciated.

Enjoy Life, JustGreg
Live Well, Laugh Often, Love Much
AirSpy HF + Discovery
66 Foot End Fed Half Wave with 49 to 1 transformer.
frw.greg@gmail.com

Offline ChrisSmolinski

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Re: MLA-30+ Experiment
« Reply #3 on: January 31, 2022, 2022 UTC »
Thanks for the pointers.  I have been considering another experiment.  The loop on the ground will have to wait until spring.  I did check on the video amplifier used by the MLA-30.  It is a Texas Instrument TL592B device.  The specification sheet does not list any noise data.  I am looking at various loop amplifiers to find what appears to be a good one.  Suggestions are apreciated.

There's an earlier thread here about the MLA-30 which discussed the problems with the video amp IC used. I forget the title of the thread, something along the lines of Best MW Antenna?  Which in retrospect might be somewhat ironic  :)   

Anyway, I've had very good luck with the LZ1AQ amp, a version of which is also available here in the USA: https://www.hfunderground.com/board/index.php/topic,89484.0.html

I use his version on my Crossed Parallel Loop and it works quite well.

Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline JustGreg

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Re: MLA-30+ Experiment
« Reply #4 on: January 31, 2022, 2232 UTC »
Thanks Chris for the information.  I will look into the  LZ1AQ amp.  In thinking about the configuration, I need an amplifier that has a high impedance.  Most of the loop amplifiers that I have checked, have a low impedance which is what is needed for a loop.  A dual FET  amplifier device would work.  I will keep at it.   The balanced input does reject some of the local noise sources, which there are more and more today. 
Enjoy Life, JustGreg
Live Well, Laugh Often, Love Much
AirSpy HF + Discovery
66 Foot End Fed Half Wave with 49 to 1 transformer.
frw.greg@gmail.com

Offline RobRich

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Re: MLA-30+ Experiment
« Reply #5 on: February 04, 2022, 0401 UTC »
The LZ1AQ is a great option. You would be hard pressed to find a better preamp design for similar money. Comparable commercial solutions tend to cost several to many times the price.

There are also various reverse-engineered and derivatives of the popular Wellbrook loop antenna preamps available, such as the "WellGood" preamp designs.

https://www.george-smart.co.uk/projects/wellgood-loop/

Here is assembled "WellGood" preamp in an enclosure offered by ra0sms for $44 shipped on eBay. Note I have not used it, but I have had good results with various others of Anton's products.

https://www.ebay.com/itm/203629015345
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 2x 18' End-Fed Verticals | 31' Vertical | 2x PA0NHC MiniWhips

Offline JustGreg

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Re: MLA-30+ Experiment
« Reply #6 on: February 04, 2022, 2339 UTC »
Thanks for information RobRich.   Right now I am experimenting with the YouLoop and Nooelec LaNA preamplifier.  I have good luck with it.  After this weekend, I will post what I found.
Enjoy Life, JustGreg
Live Well, Laugh Often, Love Much
AirSpy HF + Discovery
66 Foot End Fed Half Wave with 49 to 1 transformer.
frw.greg@gmail.com

Offline RobRich

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Re: MLA-30+ Experiment
« Reply #7 on: February 05, 2022, 0029 UTC »
An YouLoop hanging in a window with a Nooelec LaNA HF preamp inline is sometimes my fallback antenna when disconnecting outdoor antennas due to large storms or whatever. It is definitely not a weak-signal solution inside the concrete-block-stucco house here, but it works fine for casual listening of the usual powerhouse HF BCB broadcasters and even the 80/75 amateur band at night.
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 2x 18' End-Fed Verticals | 31' Vertical | 2x PA0NHC MiniWhips

 

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