Antenna recommendation for listening to faraway DRM broadcast inside a city

Comments

• Bjarne

  July 2019 edited July 2019

  Antennas designed for bluetooth, wifi and gps frequency ranges will perform just as you describe - nothing heard. You need an antenna designed for the HF (i.e. shortwave) spectrum. A magnetic loop such as the W6LVP amplified loop seems to be popular with many DX-ers, and possibly the way to go in your environment. For the Alibaba links, I'm not too sure about the quality. Link to the W6LVP: https://www.w6lvp.com/product/amplified-receive-only-mag-loop-antenna-with-power-inserter/ Remember also that an antenna's feedline, usually a coaxial cable, needs a male SMA connector to connect at the Kiwi end, but may need something different, like a UHF connector or BNC connector at the other end. Not my intention to discourage you but there are a few pitfalls for a newbie. The swling.com article lists a few alternatives (including the W6LVP), that are of generally good quality. When you buy, describe the receiver you use and ask if they can make a feedline for your specific antenna port.
  
  Bjarne Mjelde
  arcticdx.blogspot.com
• mahaju

  July 2019

  hi thanks for the reply @Bjarne
  I'll look in to the w6lvp as well
  About the alibaba links, do you think they will work though?
  It turned out to be very hard to find receiver antennas specifically for 0-30MHz, and the ones I found linked above at least claim to be able to tune in this range
  I'm okay with experimenting with a few different types of cheap antennas, just don't want to buy something that wouldn't work at all
• Bjarne

  July 2019

  Alibaba: Well, not really. They are electric field antennas, which are not recommended in a noisy environment. And the dipole - how are you going to fit that in your appartment. Magnetic field antennas are less susceptible to noise (but far from immune), so I'd go with the magnetic loop design. Mind you I haven't used these kinds of antennas much. I prefer those that can run hundreds of meters. Since I have the space. Noise will be an issue - grave or less grave. You can't do much to prevent noise from your neighbours, but there are some potential noise sources within your domain you may need to address. Switching power supplies are very often very noisy. Mobile phone chargers, light dimmers, power supplies for TVs, routers, PC displays, UPS and whatever gadget you need to power up. When your antenna is connected, zoom all out on the Kiwi and turn one power source off at the time and check if the waterfall improves (gets darker). Turn your loop to see if this reduces noise.
  
  Bjarne Mjelde
  arcticdx.blogspot.com
• Powernumpty

  July 2019

  On the Alibaba links -
  When I say "No" I mean you may pick up some signals but very few.
  
  1. No (mainly higher end of HF, not much use)
  2. No (mainly for HF single band use, low efficiency)
  3. Yes that work but will be HUGE so no good for your location
  4. Just about work - but only if you could get it outside on a mount clamped to a balcony
  
  As modern apartments are full of electrical noise it pays to get an antenna outside, or has "Nulls" for pointing at noise sources to reduce the affect, or antennas that can be tuned to the frequency you want.
  
  I'd say a wideband magnetic loop as Bjarne suggests is your best hope of reception.
  
  One other option you could try (if you can put something outside) is a short fibreglass/bamboo/wood pole holding a long piece of wire dangling out of the window (pole to keep it off the wall).
  If you do use the green connector on the Kiwi the ground side also needs connecting to something as a "ground" - try different things like plumbing, something metal but decent size.
  
  With HF the antennas need to be long, using a bluetooth/wifi/vhf antenna on a HF radio is like trying to write with a pen that is half a milimetre long.

  
• Powernumpty

  July 2019 edited July 2019

  On the later edit ones -
  
  The MLA-30 may be OK but I don't know what circuitry that is a copy of (harsh but probably true) the "Megaloop"name suggest an expensive antenna clone but I doubt it.
  I did think of trying one myself to see how it performs, I tend to prefer loop antennas anyway.
  
  The Transverters-Store type active-whip is fine outside, probably going to be noisy inside, the instructions do say use ferrite on both ends of the coax, I have a couple of those and will use them outside but have too much noise to use them inside.
• Bjarne

  July 2019

  Possibly a MegaLoop lookalike: https://hamradioshop.net/en/Antennas/MegaLoop-FX-Active-Loop.html. I seriously doubt it's a clone...
• Powernumpty

  July 2019

  I figured that was the "sounds-like, piggy back on search results" product but expect it is a simple beast inside.
  I fancy having a look, even if only to put it somewhere it might get stolen, cheaper than many active antennas (loops).
  I've offered for one to test from ebay.co.uk, I dislike they way they are around $43 international but £43 ordered here...
• G8JNJ

  July 2019

  The Bonito MegaLoop FX Active Loop has a very impressive specification in terms of IMD performance, with a stated IP3 value of typ. +40 dB and a IP 2 value of +85 dBm for something that only draws 40mA at 5v. I've built quite a lot of loop amplifiers and it's very difficult to get anywhere close to this sort of performance with such a low supply voltage and current.
  
  However it comes at a high price of nearly 400 Euro's, although I bet there's a healthy profit margin, it's still about ten times the cost of the Chinese look alike. In fact the cost of the materials is probably not much less than the sale price. So I suspect the Chinese version is something a lot simpler, probably just a MMIC chip as used on a lot of the broadband pre-amplifier boards you see being sold from China on various auction sites.
  
  However I'd love to be proved wrong and find that it is a genuine Bonito clone, in which case it would be a real bargain.
  
  Go on buy one - you know you want to - I'd be quite keen to see whats inside and test it too.
  
  In the meantime, I'll ask on the Loop Antennas forum to see if anyone else has tried one.
  
  Regards,
  
  Martin - G8JNJ
• Bjarne

  July 2019

  It's not a Bonito, the manufacturer is NTi. Bonito sells it. I tested the MegaDipol over a few weeks this summer and it performs remarkably sell. Story here: http://arcticdx.blogspot.com/2019/07/antenna-test-nti-megadipol-md300dx.html. Online here: http://arcticsdr.proxy.kiwisdr.com:8073/
• Powernumpty

  July 2019 edited July 2019

  I found myself looking at the Megaloop some time back but the price was like three of my current loops plus a phasing box with all the hardware, seemed a bit steep.
  As there is only one mode on my current loop that masks my local noise i'm very reluctant to shell out silly money for a single mode item.
  
  Can we just get this straight nobody was seriously suggesting that $40 MLA-30 is a Bonito , the fact we are talking about it in the same thread probably has some "sales ideas" team in Shenzhen spilling their lunch laughing.
  
  And yes I'd love to try the real thing but can't justify £400 on the off chance it doesn't survive mains-borne qrm, £40 though,, that's worth a punt.
• Bjarne

  July 2019

  I agree that the Alibaba "Megaloop" is probably not worth its money, even at that price level. However, my reference to Bonito was the NTi MegaDipol/MegaLoop, not the Chinese thing. People seem to think this is a Bonito brand. It isn't, and NTi is clearly marked on the box. Bonito merely sell them.

  
• Powernumpty

  July 2019 edited August 2019

  OK didn't separate NTi from Bonito, I get it now.
  While looking at NTi items sold by Bonito I searched Google "Bonito MegaLoop ML200", one link (ebay.com) was to one of these Chinese MLA things, definitely trying to sell off the NTi device names, maybe even replacing sale items to catch the unwary. I suppose that could just be a scrape of my searches linked to an item, looks wrong though.
  
  
  
  
  I'm still probably going to buy one just to see if it is of any use.
  I was also thinking about the MagaLoop FX when talking about the £400 item, love to try one, just not that much.
  
  --next morning--
  On the MLA-30 (UK listing which was nearly £44) I offered closer to the $ equivalent in £ and they took it only a £5-6 saved but easier than using another listing in $ and guessing what Paypal would exchange at. Will report back, though at my current success rate getting things from China I will be lucky if it arrives before Xmas.
• Bjarne

  August 2019

  Someone on an SDR facebook group reported good results with the MLA-30 a few days ago. Don't know his mileage though.

  
• Powernumpty

  August 2019

  My MLA-30 arrived.
  So far
  Delivery - Fast considering where it came from
  Packing - Good.
  Build - Better than I expected
  Reception - (usual caveats for this place) Better than mini whip's, lower gain/noise so seems more useable than my ALA1530S, couple of issues but not bad, lowish gain at 5V but that works better than high in the small garden, people with low noise areas will probably add bigger loops and or higher voltage supply.
  Issues - supplied micro USB lead may be faulty (currently powering it from the 5.2V linear) certainly won't power (40mA) using supplied lead from the BeagleBone USB port
  Only power input option is the micro USB, probably par for the course but makes it a little harder to try over 5V options
  
  I've put it up as the second (:8074) Kiwi here
  
  There seems to be some noise issue around 5MHz I'm not getting on other antennas, might try another kind of loop later.
  
  I'd give it about 7/10 so far.
• G8JNJ

  August 2019

  Hi Stu,
  
  Seems OK mid frequency range, above about 20MHz the noise floor is a bit high and below about 3MHz it's performance drops off a bit.
  
  It will be interesting to see how will it performs once you have played with it a bit more to optimise the performance.
  
  I still suspect that it's based on the M0AYF design, but for the price it's not bad.
  
  Regards,
  
  Martin - G8JNJ
• Powernumpty

  August 2019

  Hi Martin,
  
  It is a bit weird on the reception, once it stops raining I'll try assembling it in a clearer spot and test loop materials.
  You are probably right on the type, it's internally covered in black potting/epoxy so it's hard to identify much beyond a wire wound toroid and a few electrolytic caps.
  
  I'm not sure about the serious sub 450kHz noise, I do see it with active whips here but normally more obviously switching type noise.
  
  Anyway glad I got one, might get another to leave at work to throw out at lunch for tests, packs down nice and small.
  I think they will sell quite a few, more potential than whips if loop types can be tailored to suit the location.
  
  Regards
  Stu
• G8JNJ

  August 2019

  Hi Stu,
  
  As an experiment would you be able to compare the MLA-30 using the loop and then replace it with 2 x 1m long wires as a short active dipole ?
  
  This would give an indication of the amplifier input impedance.
  
  Taking some screen grabs of the 0-30MHz spectrum display in each case (but using the same amplitude range and scales) would be very helpful if you could manage it.
  
  Regards,
  
  Martin - G8JNJ
• Powernumpty

  August 2019

  Hi Martin,
  Will do, probably tomorrow morning, the local noise is a more consistent before people get up.
  I might switch to 8 channel mode now and leave some WSPR going on it for the noise plots overnight.
  Regards
  Stu
• G8JNJ

  August 2019

  Good plan :-)
• Powernumpty

  August 2019 edited August 2019

  Loop as supplied then 2x 960mm 6mm aluminium tubes
  I know not exactly what you asked but awkward spot and suspending it away from too much damp wood may have delayed it and risked the QRM noise floor jumping.
  Checked before and after (back to loop) about the same.
  Peak at 6MHz with loop, missing with dipole.
  
  
  
  --Later--
  Swapped the thin loop for one of the 622mm ? bike rims, that moved the noise peak up to around 7.9MHz not much else obvious. Still unusable below about 430kHz. Russian CB'er popped up quite strong unheard on other antenna (perhaps null).
  I do see a noise peak at about 7.1-5MHz on the Wellbrook, just not as obvious as this (from memory).
• G8JNJ

  August 2019

  Hi Stu,
  
  Thanks for doing that, it's a bit too wet and windy here to try anything outside today.
  
  I'm a bit surprised that the levels of the broadcast stations below 1.6MHz are so similar in strength and also that the noise floor when used in 'dipole' mode wasn't that much higher, as normally when amplifiers like this have a low impedance connected to the input, the noise floor drops.
  
  However all of this suggests that the amplifier has an input impedance in the region of a few hundred Ohms or thereabouts, so I'm fairly sure it's something based on the M0AYF design.
  
  Regards,
  
  Martin - G8JNJ
• Powernumpty

  August 2019

  I just had one of those "Ah that explains it" moments
  
  Decided to try another PSU due to the LF "swtiching??" noise. Wired a lead from a 10V linear to Micro USB while thinking "do they really expect anyone to do this?".
  Looked at the label on the Bias Tee says 5V but I'm sure the antenna was listed up to 14V, decided to look inside.
  
  Not what I was expecting in there, decided to see what voltage was on the output side 12V OK, wait whaat!
  They are using a switching boost convertor to give a useable voltage on the output while trying to appear like the real megaloop "5V in" previously discussed.
  The speed my palm hit my forehead was a bit scary.
  
  Have swapped out the bias tee from one from a transverters-store whip and 12V linear from my welbrook (to not risk going too high) suddenly sub 450kHz is there.
  Not sure what happens if you feed higher voltage into the Chinese supplied bias-tee, probably would work will get a lens on the chip number.
  
  
• WA2ZKD

  August 2019

  what does that buy us!
• Powernumpty

  August 2019 edited August 2019

  Not sure if that is a question, the antenna claimed 0.1-30MHz so noise covering everything under 450kHz meant I couldn't see if that was true.
  It's not great now but it does have some reception down to 100kHz.
  
  I guess it is an easy way of allowing a wide range of input voltages* if the user doesn't not mind losing LW and anything else down there.
  
  *assuming it is set up for wide range but just labelled 5V 0.2A
• WA2ZKD

  August 2019

  it was a joke! buy as... bias
• Powernumpty

  August 2019 edited August 2019

  Doh, I'm bit slow today, might have been that forehead slap.
  --
  For the record they have removed the numbers on the semiconductors, probably to avoid cheap clones...I think that is called being ironic.
• G8JNJ

  September 2019

  Hi All,
  
  I see that RTL-SDR.COM have mentioned the MLA-30.
  
  https://www.rtl-sdr.com/reviews-of-the-low-cost-mla-30-wide-band-hf-magnetic-loop-antenna/
  
  Best of all, on one of the sites mentioned Matt, M0LMK has boiled away the sealant goo and revealed the amplifier PCB. Well done :-)
  
  https://www.m0lmk.co.uk/2019/09/12/inside-the-mla-30-active-loop-antenna/?fbclid=IwAR2G_OcFcLf5uAq8UqiTlXrw5NSpLQKrU-tWwGc_SUBFIcHj5PsSWeB5UKU
  
  Speculation is that it uses a differential Input OpAmp/Line Driver such as a LMH6550.
  
  Regards,
  
  Martin - G8JNJ

  
• Powernumpty

  September 2019

  The weird thing with mine was my "normal location noise, mains-earth" was less apparent, wasn’t really aware of the noise floor being too high but the rough common mode noise didn’t seem to hit the MLA-30 as bad as the Wellbrook. Even more strange considering the RG213 or low loss satellite WF100 feeding the Wellbrook compared to the RG174 on the MLA. I must out mine back up and try some more loops.
  It’s funny how the adjustment on the antenna board is marked “Gain” but the silk label is potted over and it fails to mention the adjustment in the instructions.
  I raised mine slightly but later the next day did see a bit of overload I could not tie to any local RF but was like local chat duty cycle rather than longer distance fade. I might try replacing the coax on mine but in its current state it is quite good for putting in a bag or portable use.
• G8JNJ

  September 2019

  Hi Stu,
  
  Matt has kindly offered to send me his boards so that I can test and perhaps reverse engineer them :-)
  
  I'll keep you updated.
  
  Regards,
  
  Martin - G8JNJ
• Powernumpty

  September 2019

  Hi Martin,
  
  I'll be very interested in your observations.
  Slightly ironic to be reverse engineering Chinese stuff (reverse engineered from elsewhere? chips defaced as they'd prefer nobody could work out where from?).
  
  Right going to stick the MLA outside with a big copper loop to see what that does...
  
  Regards
  Stu