Indoor Antenna for Short Wave (+ LW + MW) listening with DSP radio - Page 1
Forum section: electronics / rf-microwave

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 14, 2018, 10:53:12 pm
content: Hey!So, now I got one of those Chinese DSP radio receivers, XHDATA 808, which can receive shortwave bands in the range 2...29 MHz, medium wave, and long wave. It can demodulate SSB, switcheable LSB/USB.I am interested in all of the bands, but particularly HAM radio SW, and generally LW - with lower priority if it's too effortful to get something there...But it would be nice to cover all those bands.With just the supplied wire antenna of a (very) few meters, I can get some reception, in the evening, on short wave, but very limited.MW is just noise, LW is just dead.The latter, LW, is especially mysterious because it's also dead with some 10ths of meters wire in my father's garden, while his fancy ICOM does get some clear stations on LW with the same antenna. Sure I don't expect it to be as sensitive as the $$$$ thing, but totally dead? Hmm...SW is pretty decent with the long antenna.(btw, Germany does not have analog public broadcast stations on LW,MW,SW anymore, so I can only receive somewhat further away stations)Which is why I guess it's worthwhile to build some indoor antenna, like those olden days wooden, diamond-shaped frame with "high frequency coil wire" around it or whatever.Some people seem to like to use magnetic loop antennae, because they won't pick up all the electric noise a city is full of these days.Then again, I was told, they are very narrow band, so I have to tune them properly in advance to probably pick up anything, esp. with a not very sensitive receiver - which is not great for manually scanning around to find some frequency where something's going on.It doesn't have to be a passive antenna, I'd also build some amp behind it, but I, weekend soldering iron wielder, couldn't design it.What would you say are good options here?--------------------Now, some "luxory" points, perhaps a bit much effort, but it's just some wild ideas:*If* there is no way around the necessity to somewhat accurately tune the antenna to receive anything with my weak radio - it would be nice to have some way of measuring the resonance frequency of the thing (If a microcontroller can help there, I'm all ears).Or super luxury: actually have some MCU set the proper settings on demand. I remember some project someone had a box of coils, capacitors of doubling values and bistable relays, to binary-switch in a frequency, but that was for SWR compensation or such for TX, I have no idea if this concept is viable here, also from accuracy for tuning standpoint.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 14, 2018, 11:23:04 pm
content: Where are you from?City/ Countryside?

author: chris_leyson
author_rank: Super Contributor
timestamp: July 14, 2018, 11:36:58 pm
content: QuoteThat would explain why I haven't heard Deutshe Welle on 3.995 MHz, they seem to have dropped their English programs but still broadcast to Africa.An indoor loop antenna might be the way to go but you have to tune it to the correct frequency. You can make a reasonable loop using coax cable, no need for copper pipe. One link herehttp://oh8stn.org/blog/2017/02/09/diy-portable-magnetic-loop-antenna/#

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 14, 2018, 11:51:05 pm
content: Quote from: Lord of nothing on July 14, 2018, 11:23:04 pmCity.

author: CopperCone
author_rank: Super Contributor
timestamp: July 14, 2018, 11:53:33 pm
content: I never experimented too much with my active magnetic loop but it seems pretty decent. I was able to pick up down to like 600KHz on some radio station from very far away. I used a 1 meter loop made of an aluminum bar that was bent (2 meters long).I used a matched low noise audio transistor pre-amp for mine. I used a spectrum analyzer to demodulate AM though.They are pretty easy to build, maybe you should give a active antenna a try before you try to make a expensive more difficult to build passive one.

author: innkeeper
author_rank: Unknown
timestamp: July 15, 2018, 05:37:52 am
content: I would highly recommend you research active magnetic loop antennas.hams usually refer to tuned magnetic loop antennas which are narrow band, that's NOT what you should be looking forwhat you want is an untuned (wideband) active magnetic loop antennaif you are somewhat mechanically inclined, go for thehttps://active-antenna.eu/antenna kitbasically, it comes with the electronics, and you supply the actual loop hardware and power supply. i personally use that setup from under 100Khz to 30Mhz continuous with very good performance.the advantage of an untuned magnetic loop is that its relatively low noise, wideband, it's not very susceptible to e-field interference... which means in a home environment or urban environment it doesn't pick up a lot of electrical noise. I've run about every kind of antenna you can imagine, and if you're serious, then this is the way to go. the only thing to be aware of is it's directional, so its good if you want to null something out, bad if you want omini-directional receive.if you just wanna get something up and running quickly though, a long piece of wire and a good ground is a great way to start pulling in some signals.oh, and its going to be tempting to get one of those tuned active antennas with the whip on them... yea save your time and money and don't do that, they kinda work, but there just going to frustrate the hell out of you.there's also another popular way to go, is the active mini whips one of the more popular ones is The PA0RDT Mini Whip. they re omnidirectional but are more susceptible to e-field interference, however, are wide band, and require no funning, like the active magnetic loop.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 15, 2018, 09:12:19 am
content: ::)depend on the Country he lifed in the could be local station who are avaiable.Beside of then in the most City People use Powerline who block quite the entire Band.

author: medical-nerd
author_rank: Regular Contributor
timestamp: July 15, 2018, 01:44:37 pm
content: HiyaCheck out the reviews for the Wellbrook Loops:https://www.eham.net/reviews/detail/2780for this antenna:https://www.wellbrook.uk.com/loopantennas/Loop_Antennas/ALA1530ALI have 2 of the original version for years and they are very good.Cheers

author: CopperCone
author_rank: Super Contributor
timestamp: July 15, 2018, 02:22:07 pm
content: I build this one but I changed the bias on it so my transistor was happyhttp://www.qsl.net/m0ayf/active-loop-receiving-antenna.html#The_loop_amplifier_circuit_diagram_isI think you might be able to get better performance if you use a differential amplifier IC but I can't find good schematics meaning I would need to experiment my self.http://www.analog.com/en/products/amplifiers/differential-amplifiers.html

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 15, 2018, 02:39:19 pm
content: All interesting, guys!The most budget friendly seems CopperCone's suggestionAlthough it's apparently not as wide band as innkeeper's link.Then again, I could build Copper's linked one, and make an additional one for Long Wave which is more tuned with several turns around a box like I've seen on YT.

author: CopperCone
author_rank: Super Contributor
timestamp: July 15, 2018, 02:40:29 pm
content: Quote from: TinkeringSteve on July 15, 2018, 02:39:19 pmThat design should work to the end of the HF band I think. The transistors have a good HFE and they are pretty fast.This is a primer on the amplifierhttps://wiki.analog.com/university/courses/electronics/text/chapter-12The author wroteDuring the testing phase it was found that a good test for overloading was to listen around 28 MHz after dark when the 10 Metre band is normally closed. Assuming you are using a receiver with good dynamic range then any trace of broadcast stations on that frequency might indicate overloading within the loop amplifier or distortion due to a pair of badly mismatched devices.I don't feel like messing with trying to categorize it right now. I have yard furniture projects going on lolAlso to build it, what I did is use a junction box from home depot, and aluminum bars from home depot. I welded two of the bars together using gas welding to make a 2 meter long aluminum strap (which they probably sell premade, and copper tube might be better) and bent it over something round to make the loop, and hammered the edges to bind to my junction box. I put the PCB on standoffs on the junction box cover, drilled the BNC hole. For the PCB i just use a piece of copper I glued to a piece of wood and deadbugged the circuit on top of it carefully. For the ghost power box I just use an alotoids tin with some BNC connectors and some power supply jacks so I can use double ended banana cables to connect the altoids tin to one of my low noise lab power supplies. I think maybe I put some kind of extra capacitors in the ghost box.I did however skimp on the GDT, I just used a neon bulb... I doubt it will do much but it was laying around.It's actually really durable with the aluminum strap. I mean something like 1 inch wide and 3/8 inch thick.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 15, 2018, 02:50:02 pm
content: Would it be possible to make the antenna somewhat less in diameter? I need to fit it inside here, and preferentially also be able to actually turn itThanks for the primer!

author: CopperCone
author_rank: Super Contributor
timestamp: July 15, 2018, 02:52:54 pm
content: I think I asked this question on the forum before, I don't remember what happened exactly. I wanted to build a more portable one too.I think I just decided to try it some time with a loop half the size.

author: CopperCone
author_rank: Super Contributor
timestamp: July 15, 2018, 02:55:02 pm
content: https://www.eevblog.com/forum/rf-microwave/small-loop-antenna-performance/msg1480925/#msg1480925basically means I am too lazy or occupied to remove a few screws and untighten a few bolts. I think part of the problem was that I made a copper screen inside of my amplifier box that was soldered together and the wires were glued in place and it was just a hassle to take apart so starting the thread was easier then doing the experiment.My plan was kind of to research using a differential amplifier IC to make my own preamp design then to experiment with different loop sizes, I don't really like that discrete amplifier too much*. I also wanted to make some kind of socket/jack for the loop part of the antenna so you can put different loops on the same amplifier base or at least break it down for storage without surgury.*It's a fine amplifier but I just wanted something more modern and I don't mind using things like bipolar supply rails.. I don't really like single supply amplifiers.I would still love to hear first hand what kind of frequency performance you can get out of really small loops though.

author: Emo
author_rank: Regular Contributor
timestamp: July 15, 2018, 04:14:34 pm
content: Not knowing what country or city we are talking about, it might very well be that he is experiencing a very high noise level originating from DSL services. ADSL and VDSL services do occupy LW, MW and SW frequencies. Ie profiel 17A on VDSL goes up to 17 Mhz!. Especially in countries with outside plant copper networks running on poles above the ground noise levels can be as high as -35 dBmI myself experienced a complete blockout on MW and SW when working in Belize city.

author: wolferl1210
author_rank: Contributor
timestamp: July 15, 2018, 05:28:14 pm
content: @CopperConeyou did change the bias of the transistors - let us please know whatexactly the R in your design is.

author: CopperCone
author_rank: Super Contributor
timestamp: July 15, 2018, 05:59:55 pm
content: I don't remember rand I don't want to take it apart and I used a different matched transistor I don't remember the name of. I chose my bias current value by seeing the current draw and estimating what my transistor could take with a little round heatsink clip on it.I would just use his design. I actually had those transistors on hand but I used a matched one because it said it might have a performance increase, and I had to mod the circuit for the matched one because I was near or exceeding the absolute dissipation in it.I did not really try to engineer my solution either, I might have plugged in the values from the other circuit somewhere on his website and plugged it into the other one. I don't know if it even works right, I don't have experience with these types of amplifiers or antennas. I want to engineer a proper one and then compare. It did have strong directional attenuation and I was able to demodulate some stuff with it.

author: innkeeper
author_rank: Unknown
timestamp: July 15, 2018, 09:14:01 pm
content: Quote from: TinkeringSteve on July 15, 2018, 02:39:19 pmyou may want to look at lz1aq's project pagehttp://www.lz1aq.signacor.com/he has a lot of info there and a few schematics that are pretty easy buildshttp://www.lz1aq.signacor.com/docs/fa-eng/Weak_signals-mag_loop_engl.htmhttp://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htmalso on his commercial page, you will find various loop designshttp://active-antenna.eu/antennas/and application notes on working with loop antennas solving various issueshttp://active-antenna.eu/antennas/anyway, i just touched on the surface of what LZ1AQ has documented. it's good to reference material if you're going with a loop no matter whose design you build.

author: bd139
author_rank: Super Contributor
timestamp: July 15, 2018, 10:30:03 pm
content: This is all very complicated. As a counterpoint, I’ve got a bottom end general coverage transceiver (Yaesu FT-450D). If you grab a roll of 7/0.2 or 22AWG stranded wire, jam one end loosely into the PL259 socket and string it up around the ceiling around your house randomly you will be surprised at what you can pull in signal wise. Even my antenna which is on a ground floor in the middle of London.The low HF bands are terribly noisy generally at the moment. Things improve above about 12Mhz.With the above “shittena” as it is known as, I can pull in quite a few signals with a simple direct conversion receiver based around an SA602 as well.I have a proper outside 20/40 loaded dipole but the indoor antenna is pretty good.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 17, 2018, 09:13:43 pm
content: Quote from: bd139 on July 15, 2018, 10:30:03 pmProblem #1: No houseQuoteWell, the radio came with a wire antenna (alas no earthing wire).This mostly picks up all sorts of nasty noise.I now was able to get around 20..30 stations on short wave, maybe 10 of them really strong, 10 so-so, rest weak.Between maybe 5 and 15 MHz. It's far better & a lot less noisy than with the wire,using this rather primitive active antenna - the author lists a couple of inherent problems, but for its simplicity, it works well enough for now:I made this because I happened to have some plastic pipes, wire straps and RG58 laying around the evening I did itSo while that works ok for short wave, I received exactly one MW station, and LW is still entirely dead on that DSP radio of mine, this night.

author: VK5RC
author_rank: Unknown
timestamp: July 18, 2018, 02:59:43 am
content: A thought as to why LF may appear 'dead', do you have a high power transmitter near you, and close in frequency to the edge of the LF pass band of the radio? It could be getting into the IF's passband and then overloading the ADC part of the DSP. Once overloaded, nothing else will be heard. This is a very common issue for any LF receiver esp those with some digital part in the 'chain'. In analogue radios - the 'just in band' but unwanted loud signal will turn down the AGC.One solution is to put a small pass band filter (for the frequencies that you want to hear) in line with the antenna.VK5RC

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 18, 2018, 09:08:31 pm
content: Very interesting, food for thought!I don't think it could apply here, but interesting insight nonetheless.In 2015, Germany ceased operation of all analog radio below the FM bands, AFAIK. There was one notorious > 350 meter (?) high tower for one of the antennas which thereafter was used by some people to climb and then post it on youtube or something, which is why it was recently blasted to bits with dynamite or whatever those kids are playing with these days.There may be some foreign radio programs which rent some of the remaining stations and broadcast here for different reasons, though. I don't know details about those, though.The strongest LW station was probably "Deutschlandfunk", and that's no more (on AM bands).I am already pleased that I can hear, at night, stations from China or the US, Russian and even some Arabic, with the crappy indoors antenna sketched in the post above. All between 6 and 15 MHz, which seems to be what works best with this setup and china DSP radio receiver.

author: Andros
author_rank: Newbie
timestamp: August 03, 2018, 07:24:17 pm
content: FYI - HF radio propagation is in the gutter right now, so don't expect much. We are near the bottom end of the 11 year sunspot cycle. Sunspots have a profound effect on the planets ionosphere, and consequently - propagation. When the number of sunspots are low, propagation sucks, and right now, it's almost as bad as it gets. Sorry to report - we are NOT at the bottom , yet.Whatever antenna you choose, there's little point in bothering with anything above 15 MHZ, at least for the next few years.The frequency that works at night, will probably be useless during the day, and vice versa.Try 3.5 - 4 MHZ (LSB) in the early morning - up until 08:00 local. after that, it's useless until the sun goes down. 7.15 - 7.3 is useful until around 9AM, then picks back up again at sundown. 14 - 14.350 (USB) is good after noon until evening, then craps outAs far as an antenna goes, a long lencht o wire is an easy, effective way to get started. I used to unwind the deflection coils - removed from the necks of dead TV's. The thin wire was quite stealthy. 30 - 50 feet stretched out and deployed into a tree will give you good results. Keep in mind, you will have to endure considerable noise - both natural and man made. Sorry to say, the man made crap is the new normal...Loop antennas can be remarkably effective. Since they are directive, you can often null out noises from man made sources by repositioning the antenna.Cheers,Steve KG4LJB

author: cdev
author_rank: Super Contributor
timestamp: August 14, 2018, 01:46:02 am
content: If you are using a long wire antenna you need to be using something like a 9:1 unun and a good ground - not your house's power ground which will be the default, something like a ground rod or counterpoise. This will make a huge improvement in noise and smooth out the signals quite a bit.Another idea is an active 'e-field probe' antenna.If you can stick a small antenna outside a bit, even just a short distance on a pole or something, I would strongly recommend trying an e-field probe type antenna (seehttp://dl1dbc.net/SAQ/miniwhip.html) or something similar made with a modern MMIC ( seehttps://www.g8jnj.net/activeantennas.htm)Even indoors I have also had good luck with a magnetic loop, which has to be tuned as you change frequencies. They each have their advantages and disadvantages.Noise is a big problem if you live near lots of people. I would try all of these. Its good to have several options.Like the Pa0rdt Mini-Whip and similar a magloop is very quiet as antennas go and additionally it can null out noise and act as an RF preselector. It has a sharp null in the broadside direction. Its directional in the plane of the loop. The angle of radiation of the loop is lower than that of a dipole or wire antenna unless you can get them up pretty high. (so better for DX)The "Mini Whip" type device also works better the higher you can get it. In its case just a few feet outside can make a huge difference because inside of a house its surrounded by "e-fields".And not the ones you want!For the same reason, you should (must!) power it's preamp off of a battery to minimize AC line noise. Also, use a common mode choke on the feedline. The PA0RDT miniwhip is also a good MW-LF antenna - very good for its size.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: April 30, 2019, 05:23:05 pm
content: Btw, just a little update:I now also have an oldtube radio from the 1950's, and whereas my DSP radio is basically deaf on LW and MW, thesimple active, shielded magnetic loop broadband antenna circuitI posted above worksverywell for LW and MW reception with the tube radio (and SW also "of course"). I get a few dozens of stations on each band at night (vs. almost zero on the DSp radio on LW, MW), although we don't have local stations. (well a very few that have not been demolished might have been rented out to foreign services, I was told, I don't know of any close by, though).