Technical Topics > Equipment
MLA-30 Loop antenna
TRI International:
I have one up / not impressed it amplifies just about everything it hears good or bad my long wire seems to do much better so I go with that.
ChrisSmolinski:
--- Quote from: TRI International on November 17, 2022, 2218 UTC ---I have one up / not impressed it amplifies just about everything it hears good or bad my long wire seems to do much better so I go with that.
--- End quote ---
[Relatively] small loop antennas can work well, my 2m x 2m crossed parallel loop for example. OK, that's a bit larger than an MLA-30, but you get the idea, still relatively small vs a passive HF antenna. And others have made smaller loops using a quality pre-amp, like the LZ1AQ designed I used.
But that's (one of) the key factors - you need a decent pre-amp. I've lost track of the loops discussed in this thread as well as the "best MWDX antenna" thread, but I recall one loop used a video amp IC as the pre-amp, with the expected dismal results.
The other is you absolutely need to get the loop antenna outside if possible. If it was still 1975 when the only real sources of indoor RFI were dimmer switches and a TV, sure you could use it inside. But today the average home is a cesspool of RFI/QRM generators. Once the antenna picks up RFI, no amount of ferrite cores will fix that. A simple random wire antenna outside will quite likely outperform a loop antenna in the shack. Perhaps by a wide margin.
Yet another factor is that many receivers, especially portables, easily suffer from overloading. This results in images and all sorts of other problems. A stronger s meter signal does not mean the active antenna is going to perform better. In addition to overloading, you have possible problems due to the (low cost) pre-amp itself. Any amplifier adds noise, some more than others.
JustGreg:
I have a MLA-30. It works, but, a bit noisy. I did check and the MLA-30 uses a video amp IC which is neither matched or has a good noise figure. It does work well to listen to shortwave broadcasters. It is not the best for free radio stations or weak signal stations. For its price, it is not bad. It does beat a the whip antenna on a portable radio for shortwave.
RobRich:
On the potential local noise issues with the MLA-30 is the power supply being used. Many USB wall warts are quite noisy. True OEM Apple chargers tend to be the quietest consumer models I have tried. Otherwise a battery power bank might be a better option if intending to use the USB port.
A basic bias tee is easy to build or cheap enough to buy, and I recommend either a 9v-12v linear regulated power supply or battery power source.
The included bias tee can be modified as well. You can bypass the voltage converter by tracing the circuit back from the USB port, then breakout your new power feed to an external source. I popped out the now-unneeded USB port to run the new power supply wiring.
I have yet to actually use my original MLA-30 much, but what little testing I did was using a 9v battery.
Also I received a MLA-30+ awhile back. I might do some experimenting with it in the near future.
Ray Lalleu:
to Kenotic :
you got lots of good advices, I just can add one :
begin by weeding out the pesty devices in your own home,
for those you can't remove, add an EMI/RFI filtered power cord extension,
don't mind about the dB announced (the differences are about the way they are measured and announced), just put them drawn so that the noise can't easily jump from one side to the other.
Beware, some devices are making more noise when set waiting 'off' than when being on, and also some have kind of energy stocking so the on-off switching has no immediate effect.
Of course, if you have any kind of networking through the power lines, throw it in a hurry to the dump !
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