Is quieter antennas always better? - Page 1
Forum section: electronics / rf-microwave

author: vinlove
author_rank: Frequent Contributor
timestamp: April 14, 2021, 08:40:02 pm
content: Receiving 9515 kHz KBS World Radio with MLA30+ and Wellbrook 1530 loops.The Wellbrook is quieter than MLA30+ on the 9Mhz, but S/N ratio and readability of t he actual signal seems lower than the MLA30+.The MLA30+ sounded noisier but the signal was louder and clearer, giving better readability.It made me to ask, if quieter antenna on HF and MW is always better. Is it not better antennas that give louder, clearer and more readable signals?It is not the whole MW and HF Spectrum is like this. But interesting to notice this difference on some of HF and MW bands.0:00​, 2:00​, 4:00​, 6:00​, 8:00​ to The End = MLA30+ loop is RXing.1:00​, 3:00​, 5:00​, 7:00​ Wellbrook 1530 is RXing.

author: ElizatronicWarfare
author_rank: Contributor
timestamp: April 14, 2021, 09:25:15 pm
content: Here, the critical aspect is S/N ratio. A quiet antenna that doesn't provide much power is still very usable if it has a correspondingly low noise floor, as you can simply bring everything up to a working/audible amplitude with an amplifier. Meanwhile, an antenna with a small S/N ratio will provide objectively lower-quality signals, even if it doesn't need an amplifier to be useful or audible.If the low S/N antenna meets your needs, then congrats! You should be good to go, and it may suit your situation better than the other one, but the decision should be made knowing that a high S/N ratio antenna provides better quality reception than a low S/N antenna (all other things being equal).

author: vinlove
author_rank: Frequent Contributor
timestamp: April 15, 2021, 11:53:39 am
content: I always had impression MLA30 is noisy, therefore poor antenna.But that is not the case. I have been listening and comparing various different antennas for weeks and months.MLA30 can be noisy, but it has good S/N Ratio which gives clearer, louder and more readable signal.So, quietness is not the only factor for being good antennas. Of course it is best for antenna to have quietness and good S/N ratio.But S/N ratio is more important. Quietness is bonus.So that is why I have been saying, "What weak and exotic DX signals have you heard with the antenna?" rather than what noise floor the antenna has.

author: Co6aka
author_rank: Unknown
timestamp: April 15, 2021, 02:17:52 pm
content: Quote from: vinlove on April 14, 2021, 08:40:02 pmMany things seem to be lots of things; beauty is in the eyes of the beholder. Your statements are very contradictory though. Anyway...Behold then that in your video the apparent S/N ratio of many signalsincreasessignificantly when the Wellbrook is switched to. But, this is all entirely a subjective analysis because signals aren't steady and the two antennas aren't occupying precisely the same space with the same orientation and directivity. Do you have the 3D antenna pattern analyses of both antennas at their exact mounting locations so that the slightest amount of scientific method can begin to be applied here? Otherwise comparing signals is all Kentucky windage.The performance of the transimpedance amplifier component of each antenna is properly measured in the lab, where it's isolated from all those signals displayed in your video. Similarly, the performance of the antenna assembly is measured in a RF-tight anechoic chamber, where it's isolated from all those signals displayed in your video.Otherwise, you've way too many variables involved and any analysis is subjective, i.e. NON-scientific.If you want to try a slightly less-non-scientific test,disable the AGC on your receiver, couple a signal generator to each antenna, set its level to a few dB under your receiver's saturation point, using the same signal level displayed by your receiver for each antenna though, and then switch off the signal generator and measure the noise floor. Repeat for several receiver bandwidths to maybe get some idea of how much receiver performance affects your measurements. Also, if your receiver is supported by Linrad, and if so after calibrating the combo, and disabling your receiver's AGC, you may be able to make better subjective measurements. What you're using for a receiver matters a lot if you're actually trying to measure something.Another similar test you can try is to replace the loops with inductors having the same value as the loop element, and then measure noise floor and S/N ratio as above. Differences between inductor and loop can reflect reciprocal mixing in the amplifier, oscillations, etc. Again, the proper place to do definitive analyses is in the "RF lab" and not in the field where influencing variables can't be eliminated.

author: Co6aka
author_rank: Unknown
timestamp: April 15, 2021, 02:36:52 pm
content: BTW, the quietest antenna is a dummy load at zero degrees kelvin.The quietest active loop (and e-field whip) amplifier I've messed with so far is my design from about 20 years ago using the CP666D dual JFET, but the cost of that transistor will make anyone cry loudly.

author: vinlove
author_rank: Frequent Contributor
timestamp: April 15, 2021, 02:49:31 pm
content: yes, I agree with you all your points. Thank you for the instructions for lab level testing of the antennas.But I don't have lab facilities, nor the measuring equipment. I am just a hobbiest shortwave listener.To me what is important from the antennas and radios is, which one gives me better readability of the weak signals.For that, I don't need to go through lab level rigorous testings and find out specs. of the noise figures etc.But the video is just a rough conclusive testing of the 2x antennas from my observations of the antennas and RXing capabilities for weeks and weeks.Not saying that MLA30 is best antenna, but it works well on some frequencies.I don't feel it needs any modifications apart from replacing the element to different length for making it more resonant to your preferred bands.Because it simply will not make too much difference with whatever mods. due to its inherent design limitations, and the millions external factors which will affect its performance.OK, the 2x antennas are not exactly sitting on the same spot (impossibility). But they are pointing to the same directions and they are also on the same height.But the whole thing is just to show - how changeable the hf band conditions and propagations can be. And also budget priced antennas like MLA30 can be working good on some frequencies and signals under certain band conditions and certain time of days = that's allI decided to have more different types and makes of the antennas, and switch them over for the best RXing performance for the time and signals, rather than trying to modify it

author: Co6aka
author_rank: Unknown
timestamp: April 17, 2021, 02:33:39 am
content: Radio Algeria, 252kHz, 28 January 2021, as copied in QRM-overloaded NYC...https://www.dropbox.com/s/73aimx9mzdeu62n/VID_20210128_223549.mp4Antenna is a Wellbrook ALA1530LN; the latest version. Performance is similar to that of my old CP666D design, in which I killed the transistorseveral years ago.The new Wellbrook uses a bunch of JFETS in parallel, a technique that Leif, SM5BSZ, uses in his interferometer project featured in many of his recent (past year or two) videos. I built a loop amplifier with two CM640 JFETs that were part of a military surplus lot (CM640 is the military version of the CP640) and performance is similar to the ALA1530LN. The Wellbrook might be slightly "better" though. I think designs using many JFETs in parallel are probably the way to go, especially considering the cost of the specialized JFETs. But, an optimum loop antenna farm is probablytwo loops: One such active loop for 1.8MHz to 30MHz, and a large passive loop for under 1.8MHz along the lines of what Paul, W1VLF, has recently been experimenting with - see his recent videos on YouTube. I'd first try a smaller size and structure (for the passive loop) so I could mount it on a rotor, relay-switch the coupling transformer taps, and use a very low noise amplifier in the shack.BTW, common mode chokes (over coax feedline and any control lines) just outside the shack and just before the antenna usually produce a significant noise reduction. Also, swapping between a battery and mains-derived power for active antennas is a must-test; even linear "wall warts" can couple mains noise into your antenna (and not just into the active antenna.) The DC/DC converter used in the Chinesium loops is a doubledesign and engineering error.

author: A.Z.
author_rank: Super Contributor
timestamp: April 17, 2021, 06:52:24 am
content: hi co6aka, willing to go for garden variety components, this loop preamphttp://f6aoj.ao-journal.com/crbst_capture_02012010_171721.jpgwill work rather well over the whole HF rangefor further infos, see the review near the bottom of this pagehttps://www.g8jnj.net/activeantennas.htmalso seehttps://www.w8ji.com/pre-amplifiers.htmThe 2N5109 can be replaced by NTE278 which have the very same characteristics, btw they'll still need heathsinks

author: David Hess
author_rank: Super Contributor
timestamp: April 17, 2021, 02:34:32 pm
content: I agree with ElizatronicWarfare. It is the signal to noise ratio which matters for recovering the signal. The absolute noise level is only important if it results in distortion from lower linearity or overload.

author: vinlove
author_rank: Frequent Contributor
timestamp: April 18, 2021, 04:23:48 pm
content: My Wellbrook ALA1530 is an old version. Bought it used / 2nd hand in very good price.It is fed by -12VE to the centre, so it is a bit rare design these days.I thought it was over loading sometimes, but positioning it good spot is very critical for good RX.Also the power supply is a bit suspicious for its quality, which feeds noise into the antenna too.It was actually far more noisy than my cheap MLA30+.But lots of ferrite choke filters on the PSU leads and also coax fixed the problem.So many factors affect the antenna's performance, I learned.