Monday, November 11, 2019

MLA-30 active receive loop antenna

After reading a glowing review of the low cost MLA-30 active receive loop antenna, I ordered one from Aliexpress for just AU$55. Here are my initial impressions.

The components are of good quality and you get a generous run of coax.

The phantom power box is good (although the power LED is very bright). It's powered from a micro USB socket which might add to the noise floor.

I installed it on the balcony on a PVC pipe. I haven't done a good job of getting the steel wire to be circular but it's a good start. At least it has a low wind profile.

Comparison here is rather unfair on 40m as I have an excellent dipole. Here's reception on the dipole.

Here's reception on the loop. The noise floor is certainly higher.

Of course, the benefit of the loop is that it covers all of HF so beats the dipole on bands like 80m.

Here's a snippet of the ARNSW Sunday broadcast received on 80m using the loop.

Connectors are SMA which works well with SDR receivers. Here is a recording of 9MHz shortwave using the loop. It's not as good as my big dipole but I'm really impressed with what you can hear with a small loop on the balcony.

I'm impressed with this receive loop. If you have space for a full size dipole then that's the way to go but if you only have a balcony then this is a great way to listen.

G8jnj has reverse engineered the circuit of the MLA-30 here.

Check out this comparison from "Scanner and SDR Radio" between several receive loops, some much more expensive.

The author has replaced the co-ax with better stuff and used a larger loop.


VE9KK said...

I have the LF Engineering H-800 active antenna it's not a loop antenna as you reviewed but I too have a higher noise floor when compared to my Endfed antenna.

Doctor Braun said...

Thanks for your awesome review. What is the connector type on your MLA-30? I just received mine and it has SMA connectors but they are smaller (about 75% of the size) of your typical cable TV box type coax SMA connectors. This is on the cable coming out of the antenna as well as the Bias-T connectors. Also I plan on using it with a RTL-SDRv3 which is still shipping. Do you know if the "mini-SMA" on the MLA-30 will fit on the RTL-SDRv3? Did your MLA-30 have a normal size SMA or did I get some fake?

Peter Marks said...

Doctor Braun,

that's strange. Mine has what I know as standard SMA connectors and they plugged straight in to an Airspy HF+ and an RTL-SDR. Perhaps you got a different version.

Doctor Braun said...

Hi Peter, I figured it out. I was confusing SMA and F type connectors. Due to my lack of familiarity with the subject, seeing only online pictures, I did not realise SMA was a different size than F type. The F connector would be what the average person would have experience with at home from the back of their TV and cable boxes. I am now looking for a cheap way to connect the MLA-30 loop to my Tecsun 3.5mm mono antenna input jack. I found an SMA female to 3.5mm online but cheapest option with shipping is $12. Alternatively I found for $1.50 I could by adapters (F female to 3.5mm mono, and F male to SMA female and so on). That means I can use the tons of regular coax I have laying around. I know it is 75 ohm vs. 50 ohm but I have heard it doesn't matter so much. Do you think it's an issue? Also I've seen many people online advocate removing the thin stock cable that comes with the MLA-30 and putting connectors on the box for BNC and so on. I really don't want to start modifying things if it works fine and the results produce minimal improvement. Your thoughts?

Peter Marks said...

Great you worked it out. Makes sense.
If you don't care about SMA connectors you could cut the coax and solder to a 3.5mm plug quite easily. It would certainly be cheaper than perhaps several adapters.
For an HF receive antenna I doubt you'd notice any difference using 75ohm coax compared to 50 and if you're connecting to a consumer short wave radio my guess is that the antenna input impedance would be much higher anyway.
The band noise in most locations is so high that it swamps coax losses.
I think you're over-thinking this, just hook it up and see what you can hear.
Best wishes.