HFU HF Underground
Technical Topics => Equipment => Topic started by: i_hear_you on May 24, 2019, 1911 UTC
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While I enjoy experimentation, I must balance cost and return, as I'm sure the vast majority of you do, as well. I preface with this to head off the "just try it and find out" replies!
Over the last two months I've grown and improved my SWL antenna system passing through the following phases:
1) A long wire strung as straight as possible along the ceiling from one corner of my house to the other on the second floor,
2) 80' or so of wire outside the house leading off into the trees and connected directly to the center conductor of rg59 that makes ingress into the house to a wall plate, and a jumper leading from the plate to the radio,
3) Adding a 1:1 ferrite binocular isolation transformer between the coax center/shield and the radio's two antenna terminals,
4) Adding a 9:1 ferrite toroid isolation transformer, one winding connected to antenna wire and ground, with ground being a short wire leading to and soldered onto to a pile of old audio cables that are sitting on the ground (covered with woodchips for marital bliss), and the other winding to coax center/shield.
The final refinement I am considering is to add 100' or so of wire into the air, and push the coax connection off into the woods with a proper Earth RF ground. The thing is, the steps I've taken so far have given me a very strong S/N, I'm very happy with the results. However, 15Mhz and up is very quiet, and I realize that is probably due to propagation conditions, and probably also my ferrite choices for the transformers. I also have a lot of fading on some SW frequencies, but my understanding is more wire won't help that, and this requires tricks like diversity receive, antennas that are a wavelength apart, etc.
I'm interested to hear if anyone has made a similar jump and heard a noticeable difference by adding that last 100', and moving it terminus that extra 50' from the house.
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I doubt an additional 100ft will add much save for in ambc and vlf work, I suggest a vertical antenna if you have none. On hf rx antenna length, the USN did a study and found a 6ft vertical probe, matched for maximum energy transfer to the feedline, would do in most any instance. That being said, they had a US warship and an entire ocean as the ground plane.
Dipoles and "longwires" are desirable antennas, but for low angle reception you can't beat a vertical, low angles are where you find the dx.
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Adding the additional 100' may help on longwave and AM BCB but don't expect much if any improvement much above
40 meters. The material used in the 9:1 matching device also has a big influence... hard to get a certain material and
winding configuration to be optimum over a wide frequency range.
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Thanks for the reply.
Seeing as this is for receive only, if I hung a wire over the tallest branch I can snag, let it drop straight vertically, would this be an improvement over the longwire? Would it require a ground rod? Or whatever counterpoise I can muster?
My understanding is that for RX purposes, we are trying to deliver the highest signal voltage as compared to ground as possible, so a RF ground rod provides that "zero" against which the antenna can be compared. But a counterpoise is needed for TX because of EM fields within a wavelength of feed point. I have zero experience with verticals, but I can say that once I added my mess of wires as a "ground" to my random wire, there was a noticeable increase in signal strength.
It has been fun and rewarding so far, but my next steps will be more costly, time consuming, frustrating (I'm not very good with my wrist rocket) and its appreciated when the experience of others prevents the frustration of failure ;D
EDIT:
Regarding the 9:1, I'm ready to experiment, I have two other mixture types, and enough to try 1:1, 1:4 and 1:9.
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Any specific bands of interest? It's tough to beat a resonant dipole for a single band.
If you're looking for general reception, consider something like a T2FD. It seems like you may have enough room for a reasonable sized one.They're fairly broadband for reception.
My experience with verticals has been limited. Mostly because each time I tried one, it was a noise magnet. So I have tried to limit my time wasted on them :-X
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On the vertical noise paradigm, it helps to place a say 100k ohm carbon comp resistor - or a high value choke - across the coax at the antenna to reduce static buildup and other noise. Also, you want it well grounded and as far from dwellings as possible to reduce noise pickup. A friend with a rosette of beverages has to replace his termination resistors often as they get popped by nearby lightning strikes, so use a higher wattage resistor in your vertical, bev, or whatever antennae if available. A high value resistor or choke across the legs of a dipole is also a good idea.
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This is meant for wide-band receive, so a traditional mono-band dipole is probably out for now. I have some 300-ohm window line available, I'll look into the T2FD.
Josh, regarding the resistor for static discharge, would that be in addition to the ferrite isolation transformer at the antenna side?
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This is meant for wide-band receive, so a traditional mono-band dipole is probably out for now. I have some 300-ohm window line available, I'll look into the T2FD.
Josh, regarding the resistor for static discharge, would that be in addition to the ferrite isolation transformer at the antenna side?
It can't hurt anything, if the antenna has a dc ground via the xformer it's not needed but can help in the case of a nearish lightning strike by sharing the pulse, possibly making the xformer last longer or comes open. This is one of the reasons I like any balun with a dc grounded antenna unput(s), free static drain! I think once you get above 10k ohms or so a resistor will do, I'd use a 2 watt or even 5 watt resistor and use lectrical tape or somesuch to waterproof it
On the t2fd, some people hate em, some love em. They're useful for rx on the hf band but should be tilted from horizontal if possible. I've not tried them in an inverted v config but they may work well there too. Also, if you ever get one of those insanely expensive B&W T2FD marked for RX/QRP only, don't tx thru it with more than a few watts or you'll discover why it's marked for RX only.
The odd thing is, a T2FD is a folded dipole with a resistive load placed at the center. A true folded dipole, aka one without a resistive load, rejects energy fed to it at twice the resonant freq, but a T2FD is fine with it.
Antennas are weird.
Here's some input on T2FD from a guy who knows antennas pretty well;
"It should not be surprising that the shorter T2FD shows much higher losses at the lowest frequencies of operation, since the antenna is about 0.2 wl long at 2 MHz. Basic antenna efficiency increases rapidly as the antenna length passes the 0.3 wl mark, which is well above 3 MHz for the shorter antenna. Indeed, we may call the frequency at which the antenna is about 1 /2-wavelength long the "knee" frequency. Below the knee, gain frops rapidly and losses (as well as dissipation in the terminating resistor) increase with equal rapidity.
The losses incurred in the terminating resistor occur in the form of heat. For reception-only applications, simple low-wattage non-inductive resistors may be used. For transmitting purposes, heat dissipation for the terminating resistor assembly becomes a major factor in antenna design."
https://archive.org/stream/ModelingTheT2fd/ModelingTheT2fd_djvu.txt
I tried to find the old NSA and Naval Research Labs docs on the T2FD, if I find em will post.
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Josh,
Thanks for the detailed information.
In other news, I had major storms last night and so was stuck listening to AM on inside antennas. I've only just begun SWL in earnest April 1st of this year when I received my Tecsun PL880, and so this was a first. I learned that the static crashes begin well before the first flash, and I was using this as a cue to look out the window in order to see some bolts.
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I had a T2FD several years ago, before the famous 670 ft sky loop :) It worked very well overall. From memory it was 132 ft long, so it worked well down into the lower part of HF. I have been toying with the idea of making another, for the Icom R71A that sits in the basement workshop, as a general purpose antenna. Although I actually find myself not using it, and instead using the Mac next to it, connecting to my KiwiSDR (which is on the sky loop).
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If your using the Tecsun PL-880 I'm not sure how much wire you could put up without overloading the radio and damaging it? Not sure if you have a different receiver your using with the outdoor antenna. I may have missed something.
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My true "first" is a CountyComm GP-5 SSB, and I remember thinking "this is going to f**king ROCK" when I hooked about 70' of speaker wire I'd strung on the ceiling to it. There were images and ghosts EVERYWHERE across that thing and I immediately started looking to upgrade.
The Tecsun was my first serious world band radio, but I made some rapid acquisitions in the last month. I now own an ICF-5900W, RF-2200, RF-1150, and ICF-2010.
I have ferrite-wound isolating transformers at the receiver and antenna ends. I suspect this adds some attenuation, and most certainly it protects from static buildup. There was only one night a couple weeks back where the Tecsun started having image problems, I assume from frontend overload. Signals were just booming in. I either did not see this issue with the other radios, or the issue was resolved by switching to "local" from "DX" on the offending frequencies.
I feel like Rain Man, but one of my biggest joys currently is A/B/C/D/Etc testing these radios and seeing how they stack up.
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The Tecsun was my first serious world band radio, but I made some rapid acquisitions in the last month. I now own an ICF-5900W, RF-2200, RF-1150, and ICF-2010.
I've often seen SWLs mentioning owning a bunch of portable radios. I'm curious, why not get one nice (used) communications receiver instead, for about the same total money?
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That's a great observation and question.
Several reasons come to mind:
1) I enjoy portability. My first personal electronics were a Sony Sports Walkman that I took with me everywhere and I used until it finally gave out. I also preferred portable gaming systems to wired ones when I played vidya.
2) I am interested in off-grid comms, so I prefer battery-op radios, even for RX-only.
3) I enjoy comparing the various radios against each other.
4) I'm interested in preserving them and passing them down. My little girls already have their own (RF-1170) in their room and are discovering a love for radio. I intend to make a "radio room" with a museum feel to it.
5) I love the styling of all of them. I would have a hard time picking a favorite, and while I've never had the collector's bug before now, I think it has taken hold.
When you say "nice communications receiver" I assume you mean something like an Elecraft K3, or top of the line Icom, Yaesu, or maybe something older like the Drakes that are highly praised. These are amazing radios, but they can't be carried from room to room or out on vacation like a shortwave "boombox." And there is a certain "fun factor" that I cannot explain, but I'm sure you understand what I mean, that I find in the several portables I now own that my KX3 does not have.
If I decide to get more serious about radio performance, I've decided I'll go the SDR route. Based on posts I've read of yours, I'm sure you appreciate this. My understanding is that you need to start spending 5 figures to outclass a powerful computer with a good SDR attached.
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I feel you on the portability. Also if you take a portable radio into an area without RF interference and are running on battery power it makes a huge difference. Being a SWL and a Ham I would say buy a transceiver. If you ever decide to pursue the route of wanting to transmit then your ready to go, minus a tuner. I currently have an Icom 718 which is very basic and simple for both. Sure a JRC 545 is better, but I can go either way with what I have. Just a thought. As long as your enjoying what you do that's all that matters.
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One more thing I would like to advise when buying any rig is to think about buying some fancy rig for 400 dollars that's 10/15 yrs old vs buying a newer unit for maybe 500/550 that is a bit more simpler, but has way less usage Kinda like having $15,000 to spend and deciding if you want a 1993 BMW or a 2019 Honda Civic. That's my 2 cents
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If I decide to get more serious about radio performance, I've decided I'll go the SDR route. Based on posts I've read of yours, I'm sure you appreciate this. My understanding is that you need to start spending 5 figures to outclass a powerful computer with a good SDR attached.
A reasonably decent SDR starts around $200. (SdrPlay, AirSpyHF+, or the under appreciated for the money AFEDRI). Yes you can spent more for more performance, but any of those will already by way ahead of any portable radios. You don't need a super powerful computer, I've seen acceptable used laptops in the $150 range. You could always get a KiwiSDR, all the processing is done in the unit itself, you just need a computer with a web browser. Or even a tablet. And you can share your SDR with the rest of the world.
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When you say "nice communications receiver" I assume you mean something like an Elecraft K3, or top of the line Icom, Yaesu, or maybe something older like the Drakes that are highly praised. These are amazing radios, but they can't be carried from room to room or out on vacation like a shortwave "boombox." And there is a certain "fun factor" that I cannot explain, but I'm sure you understand what I mean, that I find in the several portables I now own that my KX3 does not have.
I have a 7600G that I use for sniffing out RFI, or for my recent experiments with a big MW loop antenna: https://www.hfunderground.com/board/index.php/topic,54431.0.html But I don't use it for general listening. I started with a portable way back in the late 70s, which I used for a month or two before Christmas brought a shiny new DX-160 under the tree. It was communications receivers after that, until SDRs arrived. Once I got an SDR, pretty much stopped spinning the dial, since it was easier for me to see the entire band at once, and pick stations to check out. I suppose if I had a regular habit of listening to certain stations on a schedule, and away from the shack (say out on the deck or in the living room) a portable would make sense. Or use a tablet and KiwiSDR, but I confess to not getting the "fun factor" of a portable ;D
A lot of it probably depends on a particular hobbyists interests and workflow. I do a lot of time shifted DXing, particularly the 43m pirate band. I record it each night, and then check the results in the morning, having gone so far as to write an app specifically to make it quick and easy to check them all out: http://www.blackcatsystems.com/software/sdr_iq_recording_playback_program.html I can go through an entire night in about ten minutes, assuming i don't find anything to listen to. If I do, I listen to it while going through the recordings, or generate some WAVE files to listen to later. I can go back and look for a transmission reported by someone else. I don't miss anything (that I could potentially hear) and often get a few bumps in the night that escape other listeners. It really makes me wonder how many pirate transmissions from back in the pre-SDR days of the 70s 80s and 90s were completely missed, or at least never made it into the ACE logs.
I think my comment stemmed from seeing quite a few people (usually on the Facebook SWL groups) complaining about not hearing stations others are reporting, especially the pirates. But they usually have a slew of portables, perhaps a dozen or more. Every so often they'll talk about a new one they just got. I can't help but think that one decent communications receiver would have cost the same or less than all those portables, but would have significantly better performance. And of course you need a decent outside antenna - which could be the other part of the problem, living in an area where they cannot have an outside antenna, so perhaps they're almost restricted to portables anyway.
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Yes- I know you cant buy a new car for 15,000. I was thinking of a different time period.
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I think my comment stemmed from seeing quite a few people (usually on the Facebook SWL groups) complaining about not hearing stations others are reporting, especially the pirates.
Ah, now I follow you. When I say I enjoy DX with the portables, what I mean is I enjoy seeing what they can do and maximizing their performance. They have a coolness factor for me not unlike the fascination I feel when I see an old muscle car. Before I began SWLing, I would spend time with the KX3 monitoring ham chatter. Compared to any of my portables, the KX3 is the superlative receiver, but I just don't find it as fun to use!
I'm certain I'll eventually arrive at a dedicated SDR monitoring station. I have an rtl-sdr that I used for UHF/VHF monitoring, and was blown away when I realized I could have it recording several channels at once, limited mostly by the computer I was using. I saw a forum post at an FM and TV DXing site detailing recording a whole 10Mhz of broadcast FM during a sporadic E opening for later analysis, like you do for SW pirates. This is powerful stuff.
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If I had a kx3, it'd be my goto hf rx for portable use. Here I am lugging my IC-775DSP around like it was a ghetto blaster.
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lugging my IC-775DSP around like it was a ghetto blaster.
lol
I make a distinction between DXing and SWLing. If I want to pick out signals that are just barely above the noise floor, I plug headphones into the KX3 and use the combination of onboard physical and DSP filtering, noise reduction and antenna tuning. Lately I've enjoyed tuning a shortwave broadcast on a portable, turning up the volume and moving to the next room to do something else while listening.
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I also totally hear you on the magic of portable radios. There's something insane about picking up stations from Asia on a little hand-held unit, plus as you said: the aesthetics. things like the ICF-2010 are in the "they ain't never make this again" category, some of them are, historically, a peak of Japanese tech of the 1980's, rather like the Toyota 4Runners of the time. I mean, dozens of buttons for presets. Who on earth will understand that these days? I'm sad to say my '2010 needs repair which I would gladly do if I had the time, OTOH I can donate it to a thrift store and someone might get the bug themselves. The Tecsun stuff these days are very good too.
I would say that if you really want to get into antennas, which are another bug in themselves and a topic which will never grow old, there are some "entry level" Yaesus like the 891 which are reasonably priced and quite useable as SWL rigs. But of course, you need a power supply. Which brings up other interesting topics like battery packs and solar panels and so on. There are so many "bugs" in this hobby -- look at the Boat Anchors forum on eHam.
Having portable radios as a hobby is cheap, as you said you can hand them down too. Radio per se goes so deep into physics and human history, it's just fun and gets you off the damned social media/internet, and I wonder why more people don't get it. Their loss. I suppose for the Angry Birds era it's all too much work. I appreciated your post, thank you!
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Interesting discussion!
I enjoy older radios and particularly portables but more along the lines of tabletops that operate from internal batteries, they are better at handling larger wire antennas than the traditional small portable, and I enjoy old fashioned bandscanning with a tuning knob.
I have both the Sony ICF-6800W (not the WA "Orange") and CRF-1, the 6800 is odd in that it's whip works better than an external into the SO-239. The CRF-1 is just the opposite, whip is useless but on an external it really shines. The Kenwood R-300 and Bearcat DX-1000 use D cells as do the Sonys. I enjoy both especially below 2 MHz (I read that its best to use a preselector with the Bearcat but I find its still enjoyable without one). I've wanted to try Panasonic's RF-B600 and the Yaesu FRG-7 but haven't yet. You might want to give one of these a try if you find one at a good price just for fun and a change of pace. The AOR-AR3030 operates from internal batteries as well but AA cells and they last only a half hour.
I've used a T2FD in the past and highly recommend it, very low noise even in a suburban enviornment allows for weaker signals to be heard. That report about a 6' whip is something I read before, maybe proper matching is the key to the Apex 303WA-2 getting good reports.
I'm kind of surprised that long wire doesn't cause problems on your portables.
It is fun using any radio that isn't expected to receive much but finding that you're listening to things completely unexpected with it. That's why I like my DX-1000, the bad reviews said to stay away but it's my favorite receiver (not best, just favorite).
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the 6800 is odd in that it's whip works better than an external into the SO-239. The CRF-1 is just the opposite, whip is useless but on an external it really shines.
Is it possible the 6800 has an attenuator on the external antenna plug? My ICF-2010 goes deaf on MW if I plug the skywire into the plug.
The AOR-AR3030 operates from internal batteries as well but AA cells and they last only a half hour.
:o Ouch, what's the point with that burn rate!?
I'm kind of surprised that long wire doesn't cause problems on your portables.
I have isolating transformers on both ends of the feedline and assume they aren't very efficient, introducing enough attenuation to prevent overloading. The Tecsun does have problems with this antenna system sometimes.
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I doubt an additional 100ft will add much save for in ambc and vlf work, I suggest a vertical antenna if you have none. On hf rx antenna length, the USN did a study and found a 6ft vertical probe, matched for maximum energy transfer to the feedline, would do in most any instance. That being said, they had a US warship and an entire ocean as the ground plane.
Vertical antennas can be useful. You can use two of them to support your horizontal dipole 8)
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"Is it possible the 6800 has an attenuator on the external antenna plug? My ICF-2010 goes deaf on MW if I plug the skywire into the plug."
I suspect insertion of the antenna jack disconnects the ambc loopstick.
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the 6800 is odd in that it's whip works better than an external into the SO-239. The CRF-1 is just the opposite, whip is useless but on an external it really shines.
"Is it possible the 6800 has an attenuator on the external antenna plug? My ICF-2010 goes deaf on MW if I plug the skywire into the plug."
Never considered that, it might be the case. I know that the later WA "Orange" version had a 20dB attenuator switch on the back which the earlier version did not. Perhaps giving users the option was one of the updates, though I've never heard of any reference about an external antenna attenuator on the original. The difference between external and whip is noticable on HF. I've never used the SO-239 for MW, just the internal ferrite.
The AOR-AR3030 operates from internal batteries as well but AA cells and they last only a half hour.
" :o Ouch, what's the point with that burn rate!?"
Good question!
I'm kind of surprised that long wire doesn't cause problems on your portables.
"I have isolating transformers on both ends of the feedline and assume they aren't very efficient, introducing enough attenuation to prevent overloading. The Tecsun does have problems with this antenna system sometimes."