Home made receiving vertical antenna, HF

[nevesjerry]

Hello.
I have been trying to build a vertical passive antenna for reception between LW frequencies up to about 30 MHz. Please note I do have an RF Systems GMDSS PASSIVEantenna that works quite well at the above frequencies, However, I have tried to wrap copper foil on a 6 foot piece of PVC pipe. Decided to attach a 9:1 balun and connected a coax cable at end. Very poor reception! The RF Systems antenna discribed above uses a spiral like wound wire, as far as the balun they use I have no idea! Should there be a balun? Should I use a different balun? Also when you use coax cable for transmission line, where is the ground part of the balun attached to in the spiral wound write in the PVC? What am I dong wrong?
Any help appreciated.
Thanks, Jerry

 

[prcguy]

A 6ft long whip on the lower bands like AM broadcast through much of the SW bands is very high impedance, somewhere in the few thousand ohms range. For that a 50:1 or higher ratio transformer would perk things up and that's what most commercially made passive 3ft to 6ft HF receive antennas use. These types of antennas are non resonant and can work ok across a wide range of VLF through upper HF frequencies.

If your winding wire around a PVC pipe then it is resonant somewhere and it will probably receive something at one specific frequency but will suck everywhere else. Its like using a commercially made Hamstick amateur antenna on the wrong band, they only work well at one narrow frequency range and out of band is pretty grim reception.

Adding a ground plane or large ground screen will usually help any vertical antenna and that's where you would connect the ground of the coax. Without a good ground plane or counterpoise the braid of the coax wants to become part of the antenna and that usually gets messy.

Is this antenna your making for indoor or outdoor use? Indoors has its own additional problems from shielding in the structure to lots of potential interference from every electrical item in the house.

Hello.
I have been trying to build a vertical passive antenna for reception between LW frequencies up to about 30 MHz. Please note I do have an RF Systems GMDSS PASSIVEantenna that works quite well at the above frequencies, However, I have tried to wrap copper foil on a 6 foot piece of PVC pipe. Decided to attach a 9:1 balun and connected a coax cable at end. Very poor reception! The RF Systems antenna discribed above uses a spiral like wound wire, as far as the balun they use I have no idea! Should there be a balun? Should I use a different balun? Also when you use coax cable for transmission line, where is the ground part of the balun attached to in the spiral wound write in the PVC? What am I dong wrong?
Any help appreciated.
Thanks, Jerry

 

[nanZor]

Note that if you DO end up using a transformer, most off the shelf amateur types only cover down to 1.8 mhz, and would be very loss at vlf.

For that kind of coverage, I'm thinking looking at the likes of dx-engineering, or other swl specialists that go down that low in frequency without being super lossy. Note too that if you are going to diy a vertical, use an UN-UN type of winding, and not a BAL-UN.

 

[krokus]

Unless you are really want the vertical, or have no room for it, a long wire might be the better idea.

Sent using Tapatalk

 

[ka3jjz]

At HF, sure, if you have the room and can put something outside and away from the home as much as possible. But as you get lower in frequency, a wire antenna would need to be utterly huge to be efficient. On MW and LW, loops are the weapons of choice. There are many such designs, and even clubs devoted to these ranges that would likely have even more on this subject

But we still haven't heard from the OP as to whether he can put something outside, which is most all cases, is preferable, as noted previously

Mike

 

[WA8ZTZ]

Check out the "broomstick antenna". Don't have any personal experience with this antenna but others claim it works quite well.

 

[ka3jjz]

I actually built one of these on a 1 inch diameter wood dowel about 7 foot long and fed it through a L network transmatch (no I didn't say antenna tuner - see the other discussions on this very topic). It worked OK for what it was. I did find that mine didn't quite tune down to 3 Mhz like I wanted; so I added a very crude capacitive hat by scrounging up an old large aluminum pie tin and wiring it up at the top of the dowel.

While this worked OK on HF, I never tried it lower than 2 Mhz or so. Designing a homebrew solution that goes from LW to 30 Mhz is not trivial, it is, however, a great learning experience. If you really want to learn about antennas, the ARRL Antenna Handbook (and it's associated publications) and any books by Joe Carr are well worth having in your library.

Mike

 

[majoco]

Dare I suggest...

 

[ka3jjz]

You can suggest it Martin (heh) but its use is quite another matter. This is a well known example of a so-called E Field antenna, as it uses a vertical for its receiving element. Unfortunately in an indoor location, it would likely perform very poorly, picking up every dumb noise source in its vicinity.

Outdoors it would also need to be as far from the home as possible for the same reason. Using it in urban areas might produce some extra challenges - if memory serves me, this is the same kind of antenna that is in use at the well-known University of Twente SDR in Holland - and it's famous (infamous?) for picking up pagers and other junk on the upper HF ranges due to intermod.

We haven't heard from the OP as to whether he can put something outdoors; still, this is one possibility but it does come with significant challenges...Mike

 

[nanZor]

From an rx-only standpoint for verticals, why not just make it easy and use a resistive load in the center of a vertical.

Ex: Let's say one build a 16 foot high vertical. Since we aren't using this to transmit, load it in the center of that by putting a 100 ohm resistor in the middle up at 8 feet. Of course you'd have to support it, but hanging a 100 ohm resistor across an insulator in the middle of the vertical element isn't too hard.

This will purposely make the vertical broadband and lossy (ok since we're chasing s/n and not absolute signal strength). NOW, you use a 4:1 un-un to be able to match to a much broader / lossier bandwidth than by not using the resistor at all.

Using the resistor in the center of a vertical element for rx-only beats emulating that with wrapping 100 feet of wire as a tight broomstick helix only 6 feet long.

I guess the point here is that for rx-only users, loss isn't such a scary word if it improves your s/n ratio, not to mention making your rx-only project one heck of a lot easier from the start. Admittedly it is hard to think this way if one comes from mostly trying to optimize for transmit, and seeing what compromizes one can live with for rx-only.

While I've used the simple 100 ohm resistor in the middle of bare wire verticals before of a few (8 foot minimum for me), and then using a 4:1 un-un for broadband matching, you now have me thinking about trying to resistively load a loaded / trapped vertical for rx-only service...never did that one.

 

[nanZor]

So what's the real question?

Is it better from a signal-to-noise standpoint, to make the rx-only antenna a bit lossier / broadbanded, to reduce the noise floor level in the first place, or to simply reduce the rf-gain at the radio?

Ie, lets say you have a consistent S7 noise floor. Is it better to reduce the receiver's rf gain, or to attenuate the antenna first, (while trying to maintain the original directivity) and run with the rf-gain control more or less wide open? Would that be better for the first rf amplifier and other front-end circuitry?

Put another way, rather than using a high-q, resonant antenna well off resonance, would a lossy broadband rx-only resistive method provide a better overall broadband match so that transmission line losses would be less so that in the end, it would be actually more efficient than thought in the real world, even if one used a tuner at the receiver side?

I think this is pointing me into studying flags and loops, but wonder if the same sort of techniques could be used on a simple vertical?

Anyone ever do something like this for a vertical?

 

[prcguy]

I've played with several short broad band verticals with matching transformers at the base with good success. They can be fairly quite while preserving the signal to noise ratio. I recently got a TMC (Technical Material Corporation) VRA-6, which is an 18ft whip with something around a 4:1 or 6:1 transformer at the base and used with a ground system.

The one I got was new surplus from I believe the US Embassy in Venezuela and is a common antenna used in Embassy and other US Govt installations to supplement their main antennas. These things are real expensive new. Here is the manual for the series and you can sort of figure out what ratio transformer they use for the different frequency ranges. http://www.tmchistory.org/tmc_manuals/manuals_db/vra/tm_vra_4_89.pdf

I need to play with it some more and compare to other known antennas I have to see how well it actually works.

Edit: And to answer your question, I think its better to preserve the signal to noise ratio at the antenna with hopefully enough signal to drive the feedline all the way to the receiver and reduce gain at the receiver if needed. Otherwise you can starve the receiver for signal and the end result will be a reduction of the SNR due to the signal falling below the receivers internal noise, etc.

So what's the real question?

Is it better from a signal-to-noise standpoint, to make the rx-only antenna a bit lossier / broadbanded, to reduce the noise floor level in the first place, or to simply reduce the rf-gain at the radio?

Ie, lets say you have a consistent S7 noise floor. Is it better to reduce the receiver's rf gain, or to attenuate the antenna first, (while trying to maintain the original directivity) and run with the rf-gain control more or less wide open? Would that be better for the first rf amplifier and other front-end circuitry?

Put another way, rather than using a high-q, resonant antenna well off resonance, would a lossy broadband rx-only resistive method provide a better overall broadband match so that transmission line losses would be less so that in the end, it would be actually more efficient than thought in the real world, even if one used a tuner at the receiver side?

I think this is pointing me into studying flags and loops, but wonder if the same sort of techniques could be used on a simple vertical?

Anyone ever do something like this for a vertical?

 

[nanZor]

Thanks prcguy - very interesting antenna. I didn't think they would specialize in an LF range, but apparently so. I wonder if there is any way you could attach a capacity-hat, even a small one up top to raise efficiency a little without going outside the various version's bandwidth?

I think where I'm headed with this down the road is a terminated-folded-monopole. Not for efficiency reasons, but just for making a quick two-hour broadband antenna project..

But is that more efficient than say a 50 ohm resistor with a wire attached? Or a Diamond BB7V / Comet CH250 lossy vertical with funky lobes higher up in frequency .... being rhetorical here ...

I'll give this a go later this summer - keeping in mind that it is a sliipery slope using a lossy/broadband antenna that actually serves a purpose, (like my on-ground-loop) and a true golden dummy load.

 

[dlwtrunked]

You can suggest it Martin (heh) but its use is quite another matter. This is a well known example of a so-called E Field antenna, as it uses a vertical for its receiving element. Unfortunately in an indoor location, it would likely perform very poorly, picking up every dumb noise source in its vicinity.

Outdoors it would also need to be as far from the home as possible for the same reason. Using it in urban areas might produce some extra challenges - if memory serves me, this is the same kind of antenna that is in use at the well-known University of Twente SDR in Holland - and it's famous (infamous?) for picking up pagers and other junk on the upper HF ranges due to intermod.

We haven't heard from the OP as to whether he can put something outdoors; still, this is one possibility but it does come with significant challenges...Mike

A properly designed E-field antenna has filtering and generallly has no problems with intermod; the pager at Twente SDR is on the same roof as their antenna so that is a special case.

I use a E-field antenna (from LF Engineer) for VLF/LF and at times HF that is on a pole on my roof. Works better than a wire antenna as I can place it more easily away from noise sources. I live in an urban area with commericial broadcasts (FM and VHF/UHF) less than 1 mile away on a 500 ft tower and have not problems with those. For many, a properly placed E-field antenna is a very useful one.

 

[ka3jjz]

I think you're likely talking about this one, which, unfortunately, is not the same one used at the Twente site;

https://www.universal-radio.com/catalog/sw_ant/4900.html

This antenna got an award, I think, from the WRTH and even Larry Magne (the chief editor of the late Passport to World Band Radio) liked it. It's really not a fair comparison, to compare a homebrew (basically) antenna vs. one that costs just over twice as much, even if you didn't have all the parts to build the PA0RDT mini whip

Still, for just about that same money, you can get a W6LVP loop, and not have the same potential for noise and intermod issues that many E Field antennas can and do have. Put away from the home and noise sources then yes, an E Field antenna may work well, but I'd still hesitate to use them - especially when there are much better options for just about the same money

Mike

 

[dlwtrunked]

I think you're likely talking about this one, which, unfortunately, is not the same one used at the Twente site;

https://www.universal-radio.com/catalog/sw_ant/4900.html

This antenna got an award, I think, from the WRTH and even Larry Magne (the chief editor of the late Passport to World Band Radio) liked it. It's really not a fair comparison, to compare a homebrew (basically) antenna vs. one that costs just over twice as much, even if you didn't have all the parts to build the PA0RDT mini whip

Still, for just about that same money, you can get a W6LVP loop, and not have the same potential for noise and intermod issues that many E Field antennas can and do have. Put away from the home and noise sources then yes, an E Field antenna may work well, but I'd still hesitate to use them - especially when there are much better options for just about the same money

Mike

I use wire, E-field (both cheap homebrew and purchased like above), and loops (Welbrook). For VLF and LF, the E-field has been the best (placement being crucial as with any antenna). For HF, the jury is still out.

 

[nanZor]

Martin, G8JNJ, went well beyond a terminated folded unipole, but a great article about the whole process can be found when you click on his article link at the bottom of the page:

TC2M Antenna

Instead of just a simple single wire, it is now a 5 wire cage. That's a bit beyond my quickie-project status, but the info about the simple progression to it might interest a few swl's / amateurs.

 

[pjxii]

Hello.
I have been trying to build a vertical passive antenna for reception between LW frequencies up to about 30 MHz. Please note I do have an RF Systems GMDSS PASSIVEantenna that works quite well at the above frequencies, However, I have tried to wrap copper foil on a 6 foot piece of PVC pipe. Decided to attach a 9:1 balun and connected a coax cable at end. Very poor reception! The RF Systems antenna discribed above uses a spiral like wound wire, as far as the balun they use I have no idea!
Thanks, Jerry

I had an RF Systems MTA years ago (same as your GMDSS but not optimized for longwave) and although I never opened it up I always believed it used their original MLB.

Just curious, why are you trying to build basically the same antenna that you already have? Are you looking for better performance or just want to try to replicate it to see if you can? Experimenting with receiving antennas is always fun!

 

[nanZor]

I had to revisit this interesting antenna question and have a suggestion or two...

A similar small passive vertical antenna that "covers" LW/MW/HF is the Apex 303WA-2. My own experience with it shows that it basically disconnects / attenuates the common mode of the coax shield. So much so, that radials aren't even detected when looked at with my antenna analyzer. No difference - like they aren't even connected at all!

Look Ma! No amplifier intermods from superior passive technology. I get it though.

And, a solid 50-ohm impedance all the way through the spectrum, which is nearly impossible, unless one introduces a resistive element to the mix.

We aren't talking about efficiency, but broadband vertical coverage, and common-mode isolation. In certain scenarios (like sw portables and other radios that are prone to overload due to massively amped front ends - and isolating the coax), this can work well in that scenario.

Stick with me here - in the end, if I were to try and duplicate the ops antenna from a diy standpoint here is what I'd do:

1) Instead of random 9:1 balun, use a *physically isolating* 9:1 transformer. Perhaps even a 16:1. Must be galvanically isolated.
2) Put a 50 ohm resistor across the input.
3) Run a small amount of wire, tubing, helical or whatever for the vertical portion to the secondary side of the 9:1
4) Optionally install a common-mode choke at the antenna/coax connection for good measure.

If I were willing to tear apart my on-ground loop, I wonder if a low-efficiency broadband rx-only vertical could simply be made from a PAR EF-SWL the same way. Disconnect 1 & 2 to provide isolation, 8 feet of vertical to #3, and run a 50 ohm resistor across the shield and center conductor - and use a common-mode choke / grounding as well.

Yeah, I'll let someone else try this.

 

[nanZor]

Option #2:

Use a 1:1 isolating transformer. Put a 50 ohm resistor across the antenna side. Attach 8 feet of vertical wire to it. Use common mode choke on side leading to receiver.

Hmmm, head is racing trying to swamp the common mode, and just broadband the whole thing resistively...