MLA-30 Plus vs 40m Dipole VLF - HF Shootout
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- Опубліковано 12 вер 2024
- I thought it would be a lot of fun (and educational) to compare these two antennas from the middle HF bands down to VLF from here in the midwestern part of the USA. The 40m dipole is 2/3 full sized and rotatable with the feedpoint at 71'. It is fed with ~200' of LMR400. The MLA-30+ loop is fed with about 50' of RG-6 coax and about 8' off the ground. Both antennas utilize my newly built CMC's made of Type-W cores which are mounted to the outside of the house where all my SWL cables enter the home. The MLA-30+ has an additional (and identical) CMC at the feedpoint. The 40m dipole may or may not have a CMC (I just do not remember since I made a quick lightning repair last year). The loop exhibits a figure-8 pattern firing east & west and so does the dipole at frequencies near 40m. The azimuth pattern becomes complex at frequencies away from 40m. I hope this quick look will be of interest to others. If you would like to see other antenna comparisons just let me know in the comments section.
There are a few qualms I have with this video.
A) Both antennas are in different positions relative to elevation and noise source.
B) It is likely that you’re using different coaxial cable/connector types, and it is also possible they are different lengths.
C) Your MLA-30+ has a preamp, and gain should be adjusted to optimize the signal-to-noise ratio when switching antennas.
D) The grounding and ground plane are likely to drastically differ between antennas.
E) The YouLoop and its associated hardware could have a measurable effect on your signal.
F) Your MLA-30+ is a magnetic loop, and it is also designed to rotate. You could be nulling out specific signals by accident.
All things considered, it is my opinion that the MLA-30+ performed exceptionally well.
Thanks for taking the time to comment but you are missing the boat big time here which I will explain below.
A & B & D & E) Of course both antennas are in different positions relative to elevation and noise ! That is the purpose of the tests. They are two COMPLETELY different antennas mounted intypical configurations.
The purpose of this video is to specifically illustrate DIFFERENCES between a common HF dipole to the loop. I have room here to put up a 1200' beverage antenna for receiving.....how would you expect a 1200' long wire on the ground or 6' off the ground be made to be "the same" as this test loop? What if I wanted to compare my phased verticals to the loop? Again, different antennas are by necessity going to be mounted differently, using different coax, different coax lengths, etc, etc, etc. You cannot turn an apple into an orange......the goal was to compare the apple to the orange.
C) this was done in my lab prior to deployment.
F) The loop antenna is inherently bidirectional over a broad range of frequencies. It is IMPOSSIBLE for a single dipole at a fixed height to have a similar bidirectional AZ pattern or similar EL pattern at other frequencies other than 40m. Again, the purpose was to illustrate to others who may have antennas similar to this what they may expect to see under comparison.
I have found that one can never have enough DIFFERENT receiving antennas at your disposal. There will be times when one antenna will work better than another depending on time of day, time of the year, solar and geomagnetic conditions, distance to DX, local QRM & QRN, ground conditions, and dozens of other variables. I am sure you have found this to be true as well. 73
Ok, now you got my attention, enjoyed the heck out of the video. I may have to get into VLF, what a leep 12GHz to 20Hz. Thank you so much for sharing. 73 Leo.
Hi Leo, that is awesome to hear ! Thank you for taking the time to comment. By all means give it a try...... and, what I found out like so many others is that a pair of very effective common mode chokes is critical to knock down the ambient hash and noise level that hides these weak signals. I think I should post a quick video on the chokes that I made here and how they are implemented hoping they will help out others. I sure noticed a huge difference here. 73
The problem of MLA30 is the bias tee, it inject noise from 5V power supply and has an inverter to make 12 V from this 5V that create also noise. You have to take out the chip in the bias-tee and to power the bias tee with a linear 12V power supply, the noise will decrease about 10 to 20 db
Yes you are right. It is a shame they do not make it properly to start with. I now power mine with a linear (old fashion) regulated wall-wart. 73
Interesting results comparing a nice horizontal dipole up high vs your loop
What would happen if you ran a VNA on the loop ?? We know way more about dipoles than loops.
Glad you liked the video. I know I am always fascinated by seeing how one antenna compares against another. As far as running a VNA on the loop I would need to ponder that one because this loop is basically made up of two key elements: The small loop and the active amplifier/buffer circuit. If I connected up a VNA to the output of the "antenna" I would be characterizing the output portion of the amplifier which may not be too exciting or reveling. Still it might be interesting to do and take no time. If I separate the loop from the amplifier and measure the loop by itself it will of course have an impedance with an extremely low resistance and extremely high capacitive reactance. I think the key is all in the LNA.
I think what I may do is readjust the gain pot inside the amplifier to see how it affects the NF and if after adjustments I am not happy with the results I will look into replacing the amplifier with one of my own design.
interesting and nicely done video...9395 MHz was WMRI and 7425 MHz was probably at that time NHK Japan...
Hi there and thank you for taking the time to comment. I am having a blast getting back into SWL'ing after so many years of not being able to. 73
Thanks for this video. I may have missed it, but what does the larger diameter loop have to do with the MLA30 Plus? SInce the larger diameter loop is pretty close to the MLA30 Plus, could that be affecting the performance of the MLA30 Plus?
73 de Arnie W8DU
You are welcome. The larger loop was being compared against the MLA-30+ in a different video. Since the larger loop seemed to excel at frequencies below around 7 MHz I found it convenient to just leave the two of them on the same cross mounting. I have not specifically investigated the interaction between the two loops on this mount. I suspect they each influence each other slightly but not drastically.
Sorry What is a CMC made of type-W cores? Is it some kind of a choke? And where do you buy one from? Thanks for the video
A Common Mode Choke made of type-W core can be used to help eliminate unwanted noise of antenna feedlines. You can do searches on UA-cam for Common Mode Chokes to learn how to make them. GL
I did not hear you say you tuned the MLA to the particular frequency you were monitoring. I have a MLA and it has a very Hight Q so you must tune it to the frequency you are listening to. Did you do that in this video? Regards, Tom - AB5ZJ
Hi Tom. No tuning was done with this particular MLA-30+ antenna. Do you have the exact same model as I do and how do you tune yours? This loop, as sold, does not suggest any required tuning because of the broadband amplifier used. The amplifier that IMO stinks big time !
@@w8bya my mag loop is home brew. Check out my call on QRZ - AB5ZJ. The amplifier will not be of any use except near where the resonant frequency is on that loop you have. To determine that, I would take your capacitance and the diameter of the loop and put those numbers into a Mag loop calculator and see what the resonant freq. is. Of course, if this is a receive ONLY loop (mine is both transmit and receive) the broadband amp may give you some small gain in the areas before and after the resonant frequency point, once you calculate that. So, for example; if you have a Diameter of 40 inches, and a capacitance of (estimated) 15pf, then your resonant frequency might be in the middle of the 18meter band. All frequencies before and after that can be somewhat amplified to hear some of the signals, but it is a very non-technical way of working with a Mag loop. I would agree that in the case you have the amplifier will be of little use. 73, Tom - AB5ZJ
@@tomphillips3253 Hi Tom, nice job on your homebrew loop. I like the use of heliax for the loop. I have some LDF7 that I was going to do the same with but never got around to it. Even got the vacuum variable ready. Like you I knew not to expect too much from this loop esp at the lower frequencies esp being non-resonant. My goal was to simply do a quick comparison of this popular loop with some other antennas and let the viewers decide it's suitability. I am however still interested in the amplifier they use and just for giggles sweep it with a TG/SA to see it's frequency response. I will need to 1st design up & build a low Z toroidal transformer to transform the 50-ohm TG to a very low value suitable for the LNA input. 73
@@w8bya Very good. Everyone learns a lot when they fool around with Mag loops, especially when they can transmit with them, and not do just receive. 73 - Tom AB5ZJ
I don't mean to be disrespectful... But honestly all I hear is a bunch of racket and static and I get to listen to that for free from my wife lol...
LOL....none taken. Remember one man's racket is another man's DX ! But seriously, over 1/2 the video is filled with rock solid, stable, and very listenable signals while the other 1/2 is mostly noise & not listenable. The small loop with it's poor bias-T and low quality amplifier are responsible for all the noisy signals and that was the purpose of the video.