160-20m LOG loop-on-ground

[nanZor]

Did some BCB and low-band swl listening last night....

Portable - the loop mated nicely to a Tecsun PL880. External shortwave gain was set to "local" and not normal or dx. So plenty of signal output that's for sure.

BCB listening

The good: despite the loop being mounted on the ground horizontally, it is vertically polarized.

The bad: Other than being able to point the bidirectional lowest angle lobes by moving the feedpoint to an adjacent corner of the square, for the most part the antenna is an omni. That can be a problem and a lot of co-channel interference was to be found. Maybe I should be thinking of point nulls instead.

Of course now the "bog" antenna comes to mind - like the loop on ground, enforcing a vertical polarity, which I think is important for BCB, and not so much shortwave. Different project with different directivity. Maybe more experienced BCB listeners can chime in. I'm an amateur at BCB dxing but my inclination would be to run a bog, rather than an above ground beverage for BCB. Could be wrong - not much experience here.

What's even more amazing is that when run on EZnec at 1mhz with this 60-foot total square, at the lowest 15 degree angle, one is -55 dbi, yet I'm still hearing plenty of BCB stations. AND, my 9:1 transformer / isolator is not even designed to work that low - so plenty of attenuation going on there too. Time to up my game with better componentry if I wanted to get *real serious* about BCB.

Low band swl - now things are a bit different of course where polarity is not super important. Mostly religious broadcasting was to be found, but I just don't know the times and best frequencies to hunt down the non-religious stations. The same directional properties holds true - you can "point" the two lower angle lobes by moving the feedpoint to an adjacent square, but we are still mostly omni at higher angles.

But it did prove that there is ample signal strength for a portable, the proper polarity for BCB, and of course the convenience of ground mounting and the s/n that goes along with that. But yes, being a "vertical" for BCB, you will hear vertical noise if that is around.

 

[kilokat7]

The BOG rocks!

Back in 2009 I installed a permanent phased BOG array at home through the woods behind my place. I've been using the array every season since for BCB DXing. The wires run on top of the ground and are now completely covered by the forest floor. A 100% stealth antenna that works just as good as when I first "planted" it.

As good as it performs for BCB DXing, you can do even better by laying two wires out and phasing them. I use two parallel wires on the ground, one measuring about 500 FT and the other slightly shorter at about 450 FT (the unequal lengths are important when phasing.) They are spaced about 2 feet apart and both are left un-terminated at their far ends. If you leave a BOG un-terminated at its far end, it becomes directional off both ends. Phase the two wires with something like a DX Tools Quantum phaser and you have a highly directional array that can be reversed with the flip of a switch, all from the comfort of your shack.

My wires are oriented roughly east/west and tend to null stations off the sides of the wire, as expected. To give examples, from Michigan, it's common for me to hear California in the morning on 640, 680 & 1070 since my array is "aimed" towards the southwest and phasing allows me to null stations from the opposite end of the antenna (towards the northeast). I owe some of my best MW DX to the phased BOGs including hearing Australia, New Zealand, Tahiti & the Marshall Islands on medium wave from Michigan.

The BOG is really a simple design that is easy to deploy if you have the space and the results can be extreme. Highly recommended by this DXer!

 

[a29zuk]

I have lain out about 400' of wire on the ground at the park with great results with my Palstar R30 in the past. I've always wanted to try my MFJ-1025 with two antennas but haven't yet. I didn't realize you could run the wires so close together. When the park dries up and the mosquitos go away that will be my next DX project.

I do have good luck phasing with the two shorter antennas I have in my back yard. They start out around 2' apart at the feed point but go in opposite directions.

Yes Kilokat, I am envious of your roomy backyard!

Jim

 

[nanZor]

Just remember that the more or less onmi directional pattern of the loop on ground, with 2 lower angle bidirectional lobes, is nearly the opposite that of a highly directional narrow beam straight-wire bog.

Two different extremes, but at least both are on the ground.

I think that those that are into bogs or beverages, might be interested in the loop on ground for omni coverage - as long as they keep in mind the two totally different purposes when comparing. When the D/E - layers goes away and short skip is no longer there, the antenna is truly interesting for long-haul.

A29zuk - try laying out the loop in the park - and to maintain the pattern so it doesn't go really NVIS or totally squirrely, make the loop no longer in circumference than 1 wavelength at your highest desired frequency. (936 / f mhz = feet * 0.9 velocity factor for insulated wire does fine).

 

[a29zuk]

A29zuk - try laying out the loop in the park - and to maintain the pattern so it doesn't go really NVIS or totally squirrely, make the loop no longer in circumference than 1 wavelength at your highest desired frequency. (936 / f mhz = feet * 0.9 velocity factor for insulated wire does fine).

Yes, we could try experimenting with some loops, too. Thanks for the info.

Jim

 

[nanZor]

I just hope it proves useful, most importantly to anybody who has no choice in the matter of using an above ground antenna. As always, I'm grateful to KK5JY for making me look into this from BOTH an amateur and swl standpoint.

LOADING THE LOOP:

Once again I'm running out of wire and time to make "improvements", but as always I'm thinking about the severely space restricted op, be it trying to use a relatively small 60 foot loop on 160, or the condo / ground floor apartment dweller that may only have 8 square feet available.

Right - so the signal-to-noise is set by the antenna itself. And that usually means the largest aperture possible. Or longest dipole approaching a half-wave for dipole users (if they want to maintain a normal directive pattern)

BUT we still have the issue of making the broadband matching as efficient as possible for the typical 9:1 transformer. We can improve that.

Instead of going with baluns made of gold, maybe we can load the antenna a little bit to coax a bit more output from it when operating at the extremes.

I have not tried these for lack of time and available wire reasons, but maybe someone out there might want to experiment with these UNTESTED and UNMODELED ideas:

1) Capacitive loading the loop. I suppose one could always do the usual like making a "dual turn" loop to see what happens. Or perhaps capacitively load it. Ie, using zip-cord, connect one side of the zip cord to the balun terminals as usual. (ribbed or smooth - you get the idea) Now use the other wire of the zip cord pair and connect that wire to itself, but not to the terminals, to form a secondary capacitive loop/load.

2) Dipole on ground users - linear load each arm. The simplest would be to attach a wire to each side of the balun, run it out to the desired length and then run it back near the feedpoint, with a few inches of spacing, but leave the end unconnected.

Or the more classical version - run a wire out from each side of the balun only half-way, run it back near the feedpoint, turn it around again and run it all the way out. Space it a few inches of course.

While thinking about this, NOW I know what the old coax "grasswire" really was. Ie running a length of coax out, shorting the end, but at the rig only using the center conductor with the shield floating.

That is just a "linear loaded" wire. Using coax. The shield did the actual reception, and the inner conductor was just some resistive loss and linear loading. So it was a little bit more complicated than being just a wire replacement. Similar to example #2 above.

Again, these have NOT been tested by me. But maybe it will help the space-restricted guy get a little more output without having to resort to using a preamp. I am really trying not to do that, but improve the antenna instead.

 

[nanZor]

Quick note about testing ....

The bands have been just awful for me that past few days. So if this your first outdoor antenna, and have nothing to compare it to - like maybe just using your portable whip indoors - give it some time for a longer evaluation to see if propagation improves.

It is so frustrating to have the perfect storm of poor propagation, yet a beautifully low noise floor, and sometimes not much band activity until a contest comes along and blows the band(s) open.

Just a warning for swl'ers or amateur-swl'ers to keep in mind that poor propagation is usually caused when I install a new antenna system. Guaranteed. If I pull up the stakes and wrap up the wire, that usually fixes things for everyone else.

 

[nanZor]

Modeling reminder for EZnec - for SWL'ers too, not just hams...

Even though we aren't transmitting, if you are running swr plots against this thing, be sure to use the ground type of "Real - High Accuracy". This gets me close to what I'm seeing on the analyzer.

Since I'm running a 9:1 transformer at the end of my 50 ohm coax, I use an "ALT SWR Z0" of 450 and look at it that way too. This is not really the way to do it, but just a quick, somewhat innacurate shortcut that jives with reality a little bit, rather than seeing a >100 swr flatline using a 50 ohm direct feed.

While SWR isn't a total indicator of efficiency (a 50 ohm resistor dummy load with a 1:1 swr doesn't receive well), what this can show you is that while a 9:1 transformer is advisable, you can "get by" with a 4:1 transformer / balun (alt swr Z0 = 200) .. followed by an rf choke/isolator just for proof of concept or if that is all you need. Long runs of coax and high frequencies may suffer, but we're not trying to receive the 13 / 11 meter shortwave broadcasting bands very much these days.

Seek better advice on how to do EZnec the right way. This is just jumping into the ballpark.

 

[nanZor]

NOOELEC Balun One Nine

Testing the tiny rx-only 1:9 balun from NOOELEC that is typically used for SDR receivers. Of course that is followed by an isolation transformer / coax choke.

Shows nearly the same response from the analyzer as the high-power RadioWavz 1:9 balun. Low frequency response below 4mhz is actually better on the analyzer, but can't determine if this is due to more loss at those frequencies or if it is somehow more efficient.

I don't have the test gear to put it through it's real paces on that, but so far, it seems to be doing ok with the loop-on-ground.

Reports seem to indicate that the Nooelec is actually an UN-UN, not a balun, with a definite antenna side and a ground connection, typically used for long wires, but so far the loop seems to be working ok with it.

It will take more listening time to determine if the Nooelec is lossier than the Radiowavz balun at low frequencies, or if the Un-Un winding is skewing my pattern.

But so far so good.

 

[nanZor]

NOOELEC balun nicer than I thought..

It comes wired as a BALUN, not an unun. Not only that, but it has isolated windings!

Schematic here:
http://www.nooelec.com/store/downloads/dl/file/id/40/product/192/balun_one_nine_schematic.jpg

For an Unun with a longwire, I suppose you would cut jumper R1 and choose if you want to ground it or not.

From the factory as a balun, it is doing pretty well on the loop.

 

[nanZor]

I was wrong with the Nooelec balun. Not the first time.

I think I understand the schematic. As per the factory, there is a center tap to ground. On the backside of the balun, is a "zero ohm" resistor, aka an easily identifiable trace. I cut through that trace on the back with a little jewelers screwdriver, rather than a knife to keep me safe.

NOW I have isolation between input and output.

If you want to restore the center tap, you could solder-blob it back, or put it on a switch connected to the empty through-hole next to it.

Not too enamored with the push-in temporary wire lead connectors, so may solder small jumper wires, or just remove the push-pin connector altogether and stuff it inside a little box or pvc pipe.

I already have an external galvanic-isolator 1:1 transformer inline, so that fooled me at the start. When sun rises, I'll put this modified one (I got two baluns just to be sure), put it on the analyzer and loop and see how well that goes.

 

[nanZor]

Modified Nooelec 1:9 balun works great!

Placed the modified balun in service with the 60-foot loop on ground, and it works great. (cut through the only small trace on the backside). While swr isn't everything, it seems to have a better response than the high power Radiowavz balun overall.

That gives me the 1:9 impedance transformation, along with physical galvanic isolation. While that alone is great, I STILL followup with a 1:1 ferrite coax choke, like an MFJ 915, W2DU choke etc etc. NO bandwidth-limited "ugly baluns" here.

Can't wait to listen again tonight when the bands open up. Noontime 40m net is rockin' in the meantime.

 

[nanZor]

What about a VEE version ?!?!

So what if you can't put up (down) a loop or dipole? Save some space with a VEE configuration.

Pulled up stakes and played around with that today. Same basic coverage, 160-20m, with each leg of the on-ground-vee at 15 feet each. Fed from a 9:1 transformer / isolator and sleeve choke.

Directivity seems to be that the weaker lobes are pointed in a direction in a line that intersects between the middle of the vee arms. The lower lobes are 90 degrees away from that.

I actually prefer the vee configuration to the dipole, and to a certain extent even the loop!

Whether loop, dipole, or vee, they all share much the same mostly omni directional pattern with two lower down lobes. And, while you can "get away" with using a 4:1 transformer with the loop, you'll definitely want a 9:1 with either the dipole or the vee.

With the loop or dipole, once you get beyond a full wavelength at the highest frequency of interest (loop), or exceeding a half-wave dipole on the highest frequency of interest, the pattern starts to get very squirrely. However the VEE maintains a much more desirable original pattern, even up to 29 mhz or so. Not great that high up, but much better than the 60-foot circumference square loop. Not that any swl broadcasts go very high these days, but amateurs might desire this for the intermittent openings.

Unlike the loop where you can point it by moving the feedpoint to a different corner, both the dipole and vee means you have to pull up stakes and move the wires.

Although I didn't have the entire day to evaluate, what I did hear made me break out EZnec, and see if it correlated somewhat to what I was observing - and it did.

So now I'm kind of torn between using a loop, or a vee on the ground! I think for the space limited, the vee or dipole makes it much easier to incorporate lossy linear-loading techniques to get you down even lower in frequency. That's another weekend project.

So now loop, dipole, or vee - your choice.

 

[nanZor]

Folded VEE!

Just a weird skinny loop, like a folded dipole. Seems to be a better match for the 9:1 transformer, although 160m is still tough with only 60 feet total of wire.

Pulled up the stake on the corner of the loop opposite the feedpoint, and brought it back in towards the feedpoint spaced a few inches apart to create the folded vee. Analyzer likes it!

But bands are dead right now, visitors around (nobody notices it!) and most importantly nobody is tripping on the staked down wire.

So some form of loop seems to be the best performing, whether a classic loop, folded dipole, or folded vee with the 9:1 transformer. In these folded versions, now you might get away with a 4:1 transformer with the dipole or vee, but still prefer the 9:1.

Can't wait for the bands to wake up later...

 

[mancow]

I want to try this but the transformer part is stalling me. I have some clip on ferrite filters that are those rectangle blocks with a hold in the middle split in half. They are in a plastic box that folds over and clips on a wire. Could I remove them from the box and put the two of them together so I have a ferrite box with two side by side holes and use that for a core?

I have several spools of various enamel wire. Does the size matter? Is it just a matter of winding a few times for the input and a few times for the output on the other side? I don't recall the ratio right now.

 

[mancow]

It's about 30 x 30 x 15 mm in size.

 

[prcguy]

I have a bunch of military 9:1 balun/transformers, do I need to send you one?

I want to try this but the transformer part is stalling me. I have some clip on ferrite filters that are those rectangle blocks with a hold in the middle split in half. They are in a plastic box that folds over and clips on a wire. Could I remove them from the box and put the two of them together so I have a ferrite box with two side by side holes and use that for a core?

I have several spools of various enamel wire. Does the size matter? Is it just a matter of winding a few times for the input and a few times for the output on the other side? I don't recall the ratio right now.

 

[mancow]

I have a bunch of military 9:1 balun/transformers, do I need to send you one?

yes

 

[prcguy]

I'll stick one in the mail on Tuesday. Do you have any big #31 mix ferrite cores to make a common mode choke or should I throw one of those in?

yes

 

[prcguy]

The military 9:1s I have don't fit a small fixed rate box very well but I found something that should work better and fits in the cheaper shipping box. How bout a North Hills wideband transformer model 1701BA, 75 ohms unbalanced to 600 ohms balanced good for 300KHz to 100MHz? Its an actual isolated transformer instead of a tapped auto transformer and should give better common mode rejection than most 9:1 types. I can still toss in a #31 mix ferrite core for winding up a choke balun if you want.

I'll stick one in the mail on Tuesday. Do you have any big #31 mix ferrite cores to make a common mode choke or should I throw one of those in?