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Receive Antennas (below 30MHz) - For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

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  #81 (permalink)  
Old 06-22-2018, 4:13 AM
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Pattern degradation from un-balanced open loop version:

Quick answer: use a common-mode-choke right after the transformer on your feedline.

EZnec predictions - I ran a horizontal "5th wire" off the loop about 100 feet long to simulate the common mode of a long transmission line. There isn't much common mode actually, BUT there is ENOUGH interaction to skew the omni pattern badly depending on frequency.

So I emulated a common mode choke by putting a 4K load inline with the "5th wire" at the feedpoint, and later at the receiver end. Right after the transformer worked.

Smaller runs of feedline, are accordingly less affected by this, but still - use a choke near the feedpoint.

There are decades long message threads about this on usenet and other boards. So I let EZnec do the talking and am taking it's advice. I'm actually overkill with only 25 feet of feedline, and both the transformer isolator and common mode choke inline right after the 9:1 (5:1 for test) transformer.

Reminder that there *is* a counterpoise if you will with this unbalanced version - the 15 foot long "4th side" of the loop which doesn't connect with the other 45 feet.

Monitoring notes: There seems to be no significant difference between the closed-loop / BALun combo and the open-loop / UN-un combo. I'm hearing all my usual targets, however, I do notice a slight change of direction of the lower angle lobes when I go lower in frequency with the unbalanced open loop.

Long story short - put a choke at the feedpoint.

Ordered the PAR / LNR Precision EF SWL antenna. I'll let you know what happens...

Last edited by hertzian; 06-22-2018 at 4:17 AM..
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  #82 (permalink)  
Old 06-23-2018, 3:24 AM
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Beueller? Anyone out there - this is not my own private thread! Feel free to jump in!

I'm at the limit of my ability with EZnec and empirical comparisons. Anything more requires a professional evaluation.

While waiting for that magic day, the log is easy enough to lay down and see if it suits *your* needs. And like potato chips, you don't only just have to have "one" antenna. They all serve different purposes.

While I have been totally pleased with the log's performance, make no mistake - I take it for what it is, and not for what it isn't, especially when comparing it to other antennas with different purposes - like beverages or bogs that have a totally different pattern / gain / usage scenario. And directly comparing "S" meter signal levels is a total mistake. Don't fall into that trap. Are you hearing things you have never heard before? Or, are you spending more time behind the cans because your ears aren't bleeding for a change?

Don't worry - I'm not about to market this thing and put it into a bag proclaiming that the MKII version now comes with "even more ground loss to reduce pesky noise so you can work the dx like never before !! "

The Log - it is what it is. You either find it useful, or you don't. Simple as that. Just another tool in your toolbox should the need for it arise. My poor-soil condition (think dust bowl) might be different from your lush golf-course lawn. With different results....

Last edited by hertzian; 06-23-2018 at 3:53 AM..
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  #83 (permalink)  
Old 06-26-2018, 6:14 PM
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Normal DX heard ...

I really hate these kinds of "what I heard" reports because a lightbulb under the right conditions can dx.

Just to give some hope to swl's too ...

Best dx on 75m ssb from Los Angeles: Hawaii. Clean. No headphones.

40M ssb - Usual Australians, New Zealanders, and Hawaii. No Rora-Tonga heard tonight. Of course these guys are doing all the work with their big-gun stations. Japanese amateurs coming on strong too.

Early morning east-coast ragchew/dx net on 7.165 +/- LSB provides good testing for directivity. My favored direction is the pacific ocean pointing towards Hawaii / VK / ZL. Yet I can still hear the net control op and others in Florida and the Midwest - albeit just above the noise floor. When I change my feedpoint to an adjacent corner, the east-coast / midwest guys come up stronger, and the Pacific suffers a little bit. These are those two minor lower-lobes and slight side rejection coming into play. But unless you isolate your feedline properly, all bets are off.

RADIO JAPAN: talk about melting my wires! A big thank-you for putting out such a good shortwave signal. Not only is it loud, but the modulation is clean, and yes, fidelity is awesome. A signal to be proud of, and an example for others.

But the point is, that while yes, this kind of loop is primarily a higher-angle omni, thousand-mile or more contacts without headphone-earbleed can happen. At the right time of day, or more properly now, night.

Feedline isolation / choking is critical. Your loop won't tell you if common mode coupling has it pointing straight up in a pencil-like nvis lobe, or off to the middle of the uninhabited ocean somewhere.

Last edited by hertzian; 06-26-2018 at 6:40 PM..
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  #84 (permalink)  
Old 06-26-2018, 7:06 PM
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On-ground loop's closest relative:

The irony of irony's here. The physically horizontal LOG antenna is actually vertically polarized. Yet the closest cousin to this in directional pattern is the physically vertical 1 wavelength loop fed for horizontal polarization. Mind - blown.

This type of vertical loop is understandably not popular for transmit or even rx-only use with it's near-ground loss. Everyone wants those ground-hugging lobes, even if the stations are not able to be heard anyway during the wrong times of propagation or you are sleeping at those times. Going with a vertical polarization feed on this type of loop means you need a good ground. Trust me, I've tried it, and the poor ground, even when I used vertical polarization feed was barely different from my horizontal feed of the close to ground vertical loop.

BUT - look at it this way - it has about 10dbi more signal output than it's on-ground cousin. But that's *IF* you can couple to it properly. Feedline isolation still critical.

While the close-to-ground vertical loop is another project entirely, the pattern is much the same as the LOG, and don't automatically discount it if that's all you can do, as witnessed by my reception of some tame dx above with this usually undesirable pattern.

Last edited by hertzian; 06-26-2018 at 7:39 PM..
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  #85 (permalink)  
Old 06-27-2018, 5:55 AM
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Come to think of it - a slightly different version on a pivot!

Mount the LOG (or dipole on ground too I suppose) onto a lightweight support frame.
During the day, it lays flat horizontally.
At night, pivot it upwards into a vertical position.

Untested by me. Anyone?
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  #86 (permalink)  
Old 06-27-2018, 11:47 PM
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Quote:
Originally Posted by hertzian View Post
Come to think of it - a slightly different version on a pivot!

Mount the LOG (or dipole on ground too I suppose) onto a lightweight support frame.
During the day, it lays flat horizontally.
At night, pivot it upwards into a vertical position.

Untested by me. Anyone?
Wouldn't that change the characteristics, considering the proximity to the ground is part of the design?

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  #87 (permalink)  
Old 06-29-2018, 2:51 AM
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The ground loss seems to have the tendency to turn almost anything (other than a very long bog), into a high angle radiator - and if you hunt around the pattern and isolate the feedline you might find something useful.

I think the best treatise on low down loops is covered by ON4UN's Low Band Dx'ing book. It might be in the ARRL books, or perhaps one of Joe Carr's loop books but I have a feeling it will get short mention. Nobody in their right mind would purposely put an element that close to ground - it seems so obviously bad, but under *some* conditions - if one knows what they are getting into and some traps, it may be useful nevertheless.

Both it and my own EZnec show the same overall pattern between a horizontal log, and a vertical low-down loop - if horizontally fed.

The main characteristic of the in-air vertical loop, with just the bottom leg containing the feedpoint 1 inch above ground, is much less loss of course, but the overall reception pattern is the same.

Electrically, it seems like the ground loss wants to just wrap it's hands around our low down wires, and crumple them up mathematically.
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  #88 (permalink)  
Old 07-23-2018, 6:57 PM
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Default EF-SWL / LNR Precision makes a GREAT log!

My EF-SWL arrived today, and I'm really really happy with how it works as a loop on ground.

The ferrite material they used provides an even better low frequency response than my other diy attempts.

Yes, very simple:

1) Run 45 feet of the flexweave connected to antenna terminal 3 away from you so that it forms 3 sides of a square. That is 15 feet away, 15 feet left or right, and then 15 feet back.

2) Disconnect the ground jumper between terminals 1 and 2 to isolate the transformer. Better yet, just swing the jumper out of the way leaving one end on terminal 1 so you don't lose it!

3) Grab 15 feet of your own INSULATED wire, and run it out from terminal 2 to the hole in the end of the plastic insulator of the flexweave.

4) Optionally ground the shield at terminal #1. Unless you are making this a safety-ground, running a small jumper to a nearby spare metallic garden stake will do for rf grounding.

In my situation, I had enough isolation already to ensure that my shield was not becoming part of the loop. Some might want to add an inline rf-choke, or other measure to make sure their shield is not really the antenna.

Since this is not a totally closed loop, the low-down directional pattern will change a little depending on what bands you are listening to, but the overall pattern is very similar to the closed loop.

If you want to ensure that the low-down bidirectional lobes are ALWAYS in line with the corners just adjacent to the feedpoint, then close the loop. I didn't have the heart to hack up that nice flexweave, so I'm content with the open-loop version.

Note: changing the corner of the feedpoint will change the low-down lobe directivity to put it in an area you want with more precision than the open-loop version. However, if you just want to have a *little* bit of an option, one could easily put a knife-switch, remote relay, or other device to turn the open loop gap into a closed one, which slightly changes the directivity down low.

The ease and quality of the EF-SWL makes this a no-brainer recommendation for anyone who want to try out an on-ground loop that covers AM BCB to about 15 mhz with a reasonably predicable pattern.

Right now it is undergoing a 115 F degree bake-in here in the heat.
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  #89 (permalink)  
Old 07-23-2018, 8:23 PM
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Wow, I'm in Dallas this week and thought the temps here were outrageously high. I screwed up and forgot to bring some extra radio items to make a loop on the ground as there is a huge back yard to experiment with here. I do have a 4:1 good for 1-50Mhz but its attached to an 80-10m offset center fed at the moment. Gotta keep a 9:1 and some extra wire in my go kit as I've been traveling a lot these days.


Quote:
Originally Posted by hertzian View Post
My EF-SWL arrived today, and I'm really really happy with how it works as a loop on ground.

The ferrite material they used provides an even better low frequency response than my other diy attempts.

Yes, very simple:

1) Run 45 feet of the flexweave connected to antenna terminal 3 away from you so that it forms 3 sides of a square. That is 15 feet away, 15 feet left or right, and then 15 feet back.

2) Disconnect the ground jumper between terminals 1 and 2 to isolate the transformer. Better yet, just swing the jumper out of the way leaving one end on terminal 1 so you don't lose it!

3) Grab 15 feet of your own INSULATED wire, and run it out from terminal 2 to the hole in the end of the plastic insulator of the flexweave.

4) Optionally ground the shield at terminal #1. Unless you are making this a safety-ground, running a small jumper to a nearby spare metallic garden stake will do for rf grounding.

In my situation, I had enough isolation already to ensure that my shield was not becoming part of the loop. Some might want to add an inline rf-choke, or other measure to make sure their shield is not really the antenna.

Since this is not a totally closed loop, the low-down directional pattern will change a little depending on what bands you are listening to, but the overall pattern is very similar to the closed loop.

If you want to ensure that the low-down bidirectional lobes are ALWAYS in line with the corners just adjacent to the feedpoint, then close the loop. I didn't have the heart to hack up that nice flexweave, so I'm content with the open-loop version.

Note: changing the corner of the feedpoint will change the low-down lobe directivity to put it in an area you want with more precision than the open-loop version. However, if you just want to have a *little* bit of an option, one could easily put a knife-switch, remote relay, or other device to turn the open loop gap into a closed one, which slightly changes the directivity down low.

The ease and quality of the EF-SWL makes this a no-brainer recommendation for anyone who want to try out an on-ground loop that covers AM BCB to about 15 mhz with a reasonably predicable pattern.

Right now it is undergoing a 115 F degree bake-in here in the heat.
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  #90 (permalink)  
Old 07-23-2018, 9:32 PM
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Warning about the optional ground terminal #1 ...

In some instances, if you ground this, you may end up just grounding one of the transformer windings. Therefore, if you do this, you'll probably want to ground *after* an inline choke and not directly at the #1 terminal.

Your own station ground *may* do the same thing, so best to follow the advice of the beverage guys if you feel the need to physically ground things. This may involve additional galvanic isolation transformers and chokes so that one doesn't cripple the already low output.

I'm running it totally floating, with only a simple inline MFJ-915 ferrite sleeve for good measure. Then again, my feedline is only about 15 feet out the window, and the directional pattern seems to be well maintained. The rig-experts analyzer doesn't show much of a difference when tested from the loop on a short jumper, or after the feedline. Also, like running from a portable, my rigs are powered by large agm batteries in the shack.

prcguy - well, if the wire is insulated, you could try it out by pulling the whole thing down, laying it on the ground as an open loop, and either run it totally floating, or pop in an external isolation transformer unless your balun is already designed like that.

With this heat, keep a paramedic on standby.
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Old 07-24-2018, 12:45 AM
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NOT FUNNY MOTHER NATURE

Like clockwork, as soon as I try to do something interesting with shortwave antennas, mother nature reminds me she's in charge and delivers a geomagnetic storm.

Ok, shut off the radio and let it pass - Science channel is playing "Mysteries of the Sun" documentary, going into details like this and more.

Because of my long term relationship with her, rather than go into any technical details of how pleased I am with the EF-SWL / LNR Precision antenna for this application, I KNOW it has been given the thumbs up by mother nature because she loves to torture me so.
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  #92 (permalink)  
Old 07-24-2018, 8:12 AM
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I would recommend this common mode choke for receive only applications in the lower HF region and it should be perfect for these on the ground loops. Its got the highest resistive impedance I've seen, the common mode attenuation is around 47dB and the price is very fair. I have one but have not tested it yet.
https://myantennas.com/wp/product/cmc-0510-r/


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Originally Posted by hertzian View Post
Warning about the optional ground terminal #1 ...

In some instances, if you ground this, you may end up just grounding one of the transformer windings. Therefore, if you do this, you'll probably want to ground *after* an inline choke and not directly at the #1 terminal.

Your own station ground *may* do the same thing, so best to follow the advice of the beverage guys if you feel the need to physically ground things. This may involve additional galvanic isolation transformers and chokes so that one doesn't cripple the already low output.

I'm running it totally floating, with only a simple inline MFJ-915 ferrite sleeve for good measure. Then again, my feedline is only about 15 feet out the window, and the directional pattern seems to be well maintained. The rig-experts analyzer doesn't show much of a difference when tested from the loop on a short jumper, or after the feedline. Also, like running from a portable, my rigs are powered by large agm batteries in the shack.

prcguy - well, if the wire is insulated, you could try it out by pulling the whole thing down, laying it on the ground as an open loop, and either run it totally floating, or pop in an external isolation transformer unless your balun is already designed like that.

With this heat, keep a paramedic on standby.
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  #93 (permalink)  
Old 07-24-2018, 5:40 PM
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That CMC-0510-r common mode choke would be perfect for this up near the antenna transformer !

With the very high resistive impedance, I wouldn't even bother to ground the EF-SWL at terminal #1.

Even if you don't think it matters because your feedline may not be wiggling the s-meter when you attach it, the importance of not skewing your directivity into a very narrow NVIS pencil-beam is!

Thanks for the tip - the specs make me want to replace what I already have - especially if I have to change locations and use a really long cable run. I'd like to see how it performs up at 14/15 mhz though - theirs only spec out to 10mhz, but I got a feeling an additional 5 mhz higher might still be usable. If not, a few additional snap-ons might do the trick.

Come to think of it - some of my first experiments were with non-isolating baluns / ununs and the MFJ inline choke on a small feedline, despite KK5JY's isolating transformer. When those turned out NOT to be pencil-beams, I got more into his project for myself.

The thought here is that with something with as good a spec as the CMC-0510-R, reasonable results *might* be obtainable from more common non-isolating garden variety 4:1's - at least enough to evaluate it to see if one wants to take things further.

Last edited by hertzian; 07-24-2018 at 6:19 PM..
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Old 07-24-2018, 7:52 PM
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More on the LNR Precision / EF-SWL loop on ground -

Although my time was limited a bit last night when the geo storm rolled through, further listening today and as the bands improve lower in frequency, it is really apparent that the lower-frequency response of the EF-SWL is worth it.

Normally I don't run any preamps as that just moves the s/n window around. But NOW, while I don't technically need it, on anything at 7mhz or below, I run with a 10db preamp because the noise floor is so much lower in the first place. While I'm still just moving the window around, the depth of what I'm listening to is perceptibly improved.

And it provides a little s-meter eye candy on the medium strength sigs.

However, AM BCB, at least at 1mhz and above, is definitely improved without the preamp, and on 160m I'm hearing not only the usual suspects at sunset but there is a whole new world of little squealies, heterodynes and other neighborhood junk I've never heard before! Not that I want to hear it, but the lower noise floor is allowing me to.

The difference between using my diy lash-ups, and the EF-SWL transformer is kind of like when I was doing tourist snorkeling in Hawaii. My diy stuff is like looking above the waterline. The EF-SWL is like putting my mask underwater and noticing a much different world.

Only now do I understand why the low-band dx'ers, ndb chasers, and so forth will go to the ends of the earth using transformers wrapped around moon-dust cores, along with surplus nasa rocket wiring for the turns.

So yeah, I'm VERY pleased with the EF-SWL for this loop on ground project.
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Old 07-24-2018, 9:08 PM
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As always, your welcome to borrow my CMC-0510-R for a week or so of testing before you buy one. I'm in Dallas at the moment but will be back in So Cal in a few days.


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Originally Posted by hertzian View Post
That CMC-0510-r common mode choke would be perfect for this up near the antenna transformer !

With the very high resistive impedance, I wouldn't even bother to ground the EF-SWL at terminal #1.

Even if you don't think it matters because your feedline may not be wiggling the s-meter when you attach it, the importance of not skewing your directivity into a very narrow NVIS pencil-beam is!

Thanks for the tip - the specs make me want to replace what I already have - especially if I have to change locations and use a really long cable run. I'd like to see how it performs up at 14/15 mhz though - theirs only spec out to 10mhz, but I got a feeling an additional 5 mhz higher might still be usable. If not, a few additional snap-ons might do the trick.

Come to think of it - some of my first experiments were with non-isolating baluns / ununs and the MFJ inline choke on a small feedline, despite KK5JY's isolating transformer. When those turned out NOT to be pencil-beams, I got more into his project for myself.

The thought here is that with something with as good a spec as the CMC-0510-R, reasonable results *might* be obtainable from more common non-isolating garden variety 4:1's - at least enough to evaluate it to see if one wants to take things further.
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Old 07-25-2018, 1:58 PM
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Thanks man, but it is already ordered.

Most of my amateur chokes rapidly lose their resistive choking abilities once you get below 80 meters really fast, so to see this one providing a truly useful choking impedance made this too a no-brainer. I was tempted by the transmit-type 5K chokes, but that might be a little overkill for this thing. Got the SO-239 connectorized version, although for those running 75 ohm coax, maybe the bnc connectorized version would be easier to adapt.

I like the resistive vs reactive charts. I've seen coil-wound "ugly baluns", that consist primarily of reactive choking merely MOVE a bad common-mode issue around making things worse rather than better. I used one before, and when doing the buddy-test of me in the shack, and him walking the transmission line with a battery-operated drill motor running up and down next to the line reveal the hot-spot move! That's when I went to using ferrite chokes as the only real solution - the tough part there is getting *enough* resistive choking impedance at low frequencies to do the job. I think the CMC-5010-R will do that handily.

Heh, maybe when that guy gets back, he might consider making an F-connectorized version, at least in the receive only to reduce the amount of adapters needed when cable-tv type coax is used.

Last edited by hertzian; 07-25-2018 at 2:17 PM..
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Old 07-25-2018, 2:34 PM
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Low angle issue in the suburbs -

I never thought about this, but while putting this directly on the ground forces the pattern to be a little bit squashed for the bidirectional lower lobes, my log antenna is in your typical suburban backyard. Surrounded by brick walls and other housing.

I've heard my share of nifty low-down stuff late at night, but if I had access to an open field, the low angle signals would be even better.

Raising the log off the ground a few feet actually hurts it - turning it into a spherical non-performer.

Just something to think about if like me, you are putting one of these in a cramped location.
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Old 08-11-2018, 9:40 PM
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Herz, you're killing me with these reports and updates! The closing on my no-RFI 2.5 acre rural lot got pushed back again (three times now). I'm dying to experiment with this and several other antenna designs.

Glad to hear that the PAR EF-SWL is working well, I have one and a My Antennas choke so I guess all I'll need is the wire and the math for frequency range, topping out at 12 MHz will do for me.

Question- can you suggest how long each of the four legs would be for NDB hunting? That might be a fun challenge with the LoG.
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Old 08-15-2018, 5:09 PM
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pjxii - ndb's from a purist standpoint are going to be tough - because both the EF-SWL and the MyAntenna CMC rx-only choke go down to about 1 mhz.

Still, I ran down to 500khz or so, and while the specs for the parts are becoming a bit less effective at what they are designed to do, I am still picking up stations very well - for broadcast. I'm not an NDB hunter, so I really can't comment.

The size isn't *that* important as long as you don't go beyond a full wavelength, where the pattern starts to go weird.

For 12 mhz, you could easily just stick to the 15 foot per side square, or maybe pull it back to 13 feet or so and still not have any issues there.

For ndb hunting, yeah, you could make it MUCH larger, but honestly for that I'd stick to a rotatable vertical loop. This on-ground loop can only change directivity to a point, unless you want to pull up stakes all the time.
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Old 08-15-2018, 5:27 PM
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Default CMC 5010-R works nicely!

Yeah! Swapped out the MFJ choke for the MyAntenna CMC-5010-R rx only choke and it *did* make a noticeable difference in noise floor.

My AA-50 analyzer showed some nice improvements, even on my short feedline. Although SWR is a poor indicator of efficiency, I first noticed that at 1mhz, instead of just going totally off-scale, I'm now at least measurable. Sure it is a 14:1 swr, but to have it actually measure was interesting.

I could bench-race r/x values all day, but did that result in anything tangible?

YES. Daytime AM-broadcast signals have a lower noise floor. While I'm not an AM dxer really, I did notice a *cleaner* noise-floor sound, and some super weak stations could actually be listened to, rather than just logged and moving on to the next due to ear-bleed.

(You can tell I've been on a hi-fi break from sw listening lately for a few weeks...

This cleaner noise floor also is noticed on HF. I haven't listened long enough to see how much it kept my log's pattern clean - that will take MUCH longer, but a quick run through 40 meters in the daytime enabled me to listen to what would be the equivalent of a micro-watt pair of amateur stations in comfort.

I can recommend this CMC 5010-R inline choke for this project without hesitation.

The biggest problem with the choke is that I'm going to have to etch some sort of "rx-only" label into it, because the label may degrade over time, and without something etched, I can see my self smoking this thing accidentally with a transmitter if I use it for some other antenna project.

This is a great off-the-shelf pairing of products. You can get by DIY certainly, but I'm at that stage where I'd always be questioning my ability.

Thanks to prcguy for the tip about this choke. I'm finally satisfied with the project.
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