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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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  #61 (permalink)  
Old 06-17-2018, 8:24 PM
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Originally Posted by prcguy View Post
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?
Cool thanks and no I do not have any ferrite stuff around here at all.

I do have about a mile reel of this small high grade aircraft wire.
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Old 06-17-2018, 8:35 PM
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I made this today off the page linked by the OP. It's 2 turns on the radio side and 5 on the antenna side. I used the 15' per side measurement and it's fed with RG6.

It works. I'm hearing some 80 meter, 40 meter and of course several shortwave stations. I'm still getting quite a bit of noise though.

I don't know if that transformer is correct though. The ferrite is just two clip on types with the ferrite halves removed and glued into a ( )( ) type of configuration.


Last edited by mancow; 06-17-2018 at 8:51 PM..
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Old 06-17-2018, 10:00 PM
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A lot of snap on ferrites are #43 mix and probably ok for what you made. You can make a second identical transformer, put them back to back and test insertion loss over your desired frequency range looking for maybe .1dB total loss for both transformers in line. Then terminate one with 600 ohms or whatever its supposed to match and check the match over your desired freq range. If all is good, its good.
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Old 06-17-2018, 10:02 PM
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For a piece of wire on the ground it seems to be doing pretty well.


Last edited by mancow; 06-17-2018 at 10:19 PM..
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Old 06-18-2018, 3:02 AM
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mancow - also be sure to follow up with some sort of common-mode coax choke at the end of the feedline before the transformer. And we're not talking ugly-balun's either. At a minimum, we're talking about an MFJ 915 1:1 inline choke or better. Or wind your own 1:1 coax choke around a ferrite. Or at least 6 inches or more of clamp-on ferrites. A small jumper between them is ok.

You just want to be absolutely sure you are listening to the loop, and not a loop/feedline combo "lollipop" random wire.

If you have this loop attached to an antenna switch to others in your antenna farm, try running the loop as the ONLY antenna attached to your receiver to see if there is any common-mode swamping coming from the antenna farm.

Sure enough, this loop does pick up noise too, but you want to make sure it is from the loop and not from your feedline.

A loose analogy would be like operating a small vertical loop that is fixed in one position. But, you may not need any preamps. Or, if you do, just a small amount like 10db on the lower bands is enough. Many rigs might have a mellow 1st preamp you can use.

Put some tape over your S-meter, and enjoy. Tonight *great* propagation all around - even my 20m pipeline to VK/ZL/Hawaii is happening - which proved my "folded vee" configuration works about as well as the classical loop.

So if this proof-of-concept antenna works for you, you'll find yourself thinking like the beverage guys do about common-mode shielding, efficient transformers etc. Welcome aboard!

Last edited by hertzian; 06-18-2018 at 3:09 AM..
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Old 06-18-2018, 6:47 AM
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Quick test for common mode reception from the feedline:

Disconnect the loop wires.

Listen for the usual suspects, like local AM broadcast stations during the day. Listen again when the bands are supposed to be open as well....
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Old 06-18-2018, 9:55 AM
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Good ideas. I'll work on getting the chokes and try the disconnect idea for testing.

I have a patch panel at home with some pass through f connectors and the cables have quick push on adapters so I can quickly switch them around for testing which should make it easier.
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Old 06-18-2018, 7:39 PM
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Nice - a panadapter should make seeing rogue signals and any noise floor changes easy. You guys are really dragging me into that.

Drill motor:
one technique I've used in the past is with the aid of a helper in the backyard, and with the antenna wires disconnected, have them pull the trigger on a battery operated drill-motor. Run it up and down near coax feedline and see if there are any "hotspots", or mere movement of common-mode reception.

I've used the drill motor tecnnique to make sure that my small vertical loops could null out a point-source of noise that way too from across the yard.

Switched back to the classic loop - the folded vee version worked, but had slightly less output. My modern gear had no problem, but the less sensitive Nasa/Target SSB receiver noticed the slight drop under it's own noise floor.
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Old 06-18-2018, 7:56 PM
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My neighbors already think I'm nuts. Imagine them looking out as I duck walk around the yard drilling phantom holes above the ground with a Makita?

Last edited by mancow; 06-18-2018 at 8:08 PM..
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Old 06-18-2018, 8:40 PM
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Tell them your drilling holes in the air to let the ozone out.

I just remembered I have a small broad band 4:1 balun and a 12:1 that I should have sent to cow for testing along with the 9:1 I already shipped. A spectrum plot would have been great to see which one works best with the on the ground antennas.

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My neighbors already think I'm nuts. Imagine them looking out as I duck walk around the yard drilling phantom holes above the ground with a Makita?
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Old 06-19-2018, 4:28 AM
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I'm not too sure that exact matching is that critical. As long as it is decent enough to get over the noise floor of the receiver. And at low frequencies, swr loss may not be that critical. For example, on 160m the swr on my setup is about 12:1, yet I have enough signal to work with.

Like the original author says, if you hear a drop in noise when you disconnect the antenna, you have enough gain. But yeah, the nag to always improve is there, even if the s/n ratio doesn't change.

I'm still getting used to having both high and low angle reception. When 10 opened up, it is weird hearing a neighboring state full smash in the middle of the day. My ground mounted vertical doesn't do that with it's overhead null.

On the other hand, that also means radiated noise junk, mostly on 40m during the day in the short skip zone being heard well too.

Lowband static crashes are tolerable - to the point that they don't kick in the receiver's agc and pump it, so that's a plus.

The log is not a total panacea, but so far I'm having waaay too much fun with it.
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Old 06-19-2018, 5:23 PM
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Shortwave broadcasting thoughts and high angles .. amateur vs broadcast notes ...

Right now for several hours, anyone on 20m within the short skip zone putting out any high angle radiation basically owns the band. On my ground-mounted vertical with it's overhead null - yeah not so much. I think it would be a LOT more fun to chase short skip with a low-mounted antenna on 20m during the day, rather than put up with the noise and d-layer absorption on 40. Seems to me that 20m daytime signals actually punch through the d-layer better. And a much lower noise floor to boot! This includes low-mounted dipoles, or from what I've heard, I may be listening to high-angle lobes coming from an amateur using a beam antenna not pointed my direction. I'm hearing stuff that I'm NOT supposed to hear!

But back to broadcasting ..

Getting away from a west-coast US amateur point of view, globally I'd think that this antenna would rock on 19 and 22 meters for listening to neighboring countries within a few hundred miles - during the right time of course.
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Old 06-19-2018, 6:40 PM
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What type of wire are people using for the antennas? It looked like the article author was using 12 AWG, with green insulation.

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  #74 (permalink)  
Old 06-20-2018, 5:21 AM
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Wire - nothing special needed, just has to be insulated so you don't accidentally ground it.

UNTESTED alternate setup other than making EZnec happy: UN-UN vs BAL-UN ...

While I'm using an isolated 9:1 bal-un with a "closed loop", I was wondering about the guy who has a more common "end fed" single-wire antenna, which uses an UN-UN sitting around in the closet. Maybe a PAR / EARCHI, MFJ, Radiowavz or any other commonly known "end fed" which uses a 9:1 unun ...

Instead of rewinding the transformer, how about just changing the balanced loop into a very similar, but UNbalanced antenna to go with the end-fed UN-UN??

YES - so instead of a closed loop with a true balun, now with an UN-UN common to most "end fed" antennas, lets introduce a slight amount of imbalance by attaching only 3 sides of a square loop to the main transformer connector. The 4th side of the square would go to your balun's ground if it has one, or just attach that to the shield of the coax and run that out. Do NOT make a physical closed connection - just leave it separated by an inch or two.

Visually - think of an off-center-fed dipole with the feedpoint 25 percent of the way in on one side. Form this into a loop, but leave a little space between the elements when you loop it around towards each other.

Of course all of this needs to be isolated from ground. As usual, follow up with a 1:1 ferrite common mode choke / isolation transformer etc.

When I ran the numbers and looked at the pattern in EZnec, I actually saw better low-frequency performance, with no major degradation of attenuation, nor any major change in directional pattern as compared to the closed loop using a bal-un.

Again - EZnec is one thing - real world is another and I haven't tried it since all my transformers are baluns and not un-uns. My Nooelec 9:1 un-uns got taken to another project for a quick test. Drat.

Guess I have to wind / order a 9:1 un-un or maybe put my money where my mouth is and get an off the shelf end-fed and compare. The point is, if you have one, try forming it into a loop, but don't totally close it. It might actually be a better performer than the closed loop.
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Old 06-20-2018, 7:05 AM
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UPDATE: small 8-foot square loop improvement...

Again - physically untested, but the above technique of using a 9:1 UNUN, and an unbalanced loop that is not actually physically closed as described above provided significant mid-band and slightly lower band improvements over a closed-loop with a 9:1 balun. At this small size, yeah, I think your rig's first preamp is called for.

Expect improved 20m amateur and surrounding 19 & 22m band sw broadcast improvements. Not so much on 160m with this little bit of wire. but still, this is the way I'd go with a very small "condo-lawn" loop.

As before, and especially with a purposely unbalanced antenna using an un-un, make sure you are listening to the loop, and not to the feedline - that means galvanic isolator transformer and coaxial rf chokes following the 9:1. Otherwise you really have a lollipop common-mode antenna.

This is all EZnec stuff right now mind you. I gotta' get some hardware and lay the un-un version down for real.

Last edited by hertzian; 06-20-2018 at 7:12 AM..
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Old 06-20-2018, 9:34 AM
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Not having the space to play with an on the ground antenna, I do have a PAR transformer from their SW end fed, plus a military 9:1 and one more North Hills 9:1 that covers 300KHz to 100MHz already in a waterproof PVC container and wired for a single wire end fed. If hertz can drive on down to the harbor I will gladly loan them to you for testing.



Quote:
Originally Posted by hertzian View Post
Wire - nothing special needed, just has to be insulated so you don't accidentally ground it.

UNTESTED alternate setup other than making EZnec happy: UN-UN vs BAL-UN ...

While I'm using an isolated 9:1 bal-un with a "closed loop", I was wondering about the guy who has a more common "end fed" single-wire antenna, which uses an UN-UN sitting around in the closet. Maybe a PAR / EARCHI, MFJ, Radiowavz or any other commonly known "end fed" which uses a 9:1 unun ...

Instead of rewinding the transformer, how about just changing the balanced loop into a very similar, but UNbalanced antenna to go with the end-fed UN-UN??

YES - so instead of a closed loop with a true balun, now with an UN-UN common to most "end fed" antennas, lets introduce a slight amount of imbalance by attaching only 3 sides of a square loop to the main transformer connector. The 4th side of the square would go to your balun's ground if it has one, or just attach that to the shield of the coax and run that out. Do NOT make a physical closed connection - just leave it separated by an inch or two.

Visually - think of an off-center-fed dipole with the feedpoint 25 percent of the way in on one side. Form this into a loop, but leave a little space between the elements when you loop it around towards each other.

Of course all of this needs to be isolated from ground. As usual, follow up with a 1:1 ferrite common mode choke / isolation transformer etc.

When I ran the numbers and looked at the pattern in EZnec, I actually saw better low-frequency performance, with no major degradation of attenuation, nor any major change in directional pattern as compared to the closed loop using a bal-un.

Again - EZnec is one thing - real world is another and I haven't tried it since all my transformers are baluns and not un-uns. My Nooelec 9:1 un-uns got taken to another project for a quick test. Drat.

Guess I have to wind / order a 9:1 un-un or maybe put my money where my mouth is and get an off the shelf end-fed and compare. The point is, if you have one, try forming it into a loop, but don't totally close it. It might actually be a better performer than the closed loop.
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Old 06-20-2018, 4:49 PM
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Great timing!!

Give the PAR / LNR precision version a try with the unbalanced loop version and let us know!

I found a 5:1 Un-Un in the closet, cut one leg of the wire loop open, and am trying it now. It has a ground connection, so I used that for one side of the square. So now the loop is totally unbalanced, which the un-un likes.

At my first chance, I'll grab a 9:1 UNUN and put that inline instead. But right now, it seems to be working as well as ever. I choked it the best I could by following the 5:1 unun with an isolated 1:1 transformer, and a bunch of large snap-on ferrites wrapped around the coax.

I'm just hoping that I don't fool myself listening to the feedline. I'll know tonight if the pattern is screwy.

This open-loop configuration, as long as you choke the heck out of it, looks promising.
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Old 06-20-2018, 6:35 PM
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I mentioned I don't have space to test an on the ground antenna and I'm offering you the baluns on loan for testing.

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Great timing!!

Give the PAR / LNR precision version a try with the unbalanced loop version and let us know!

I found a 5:1 Un-Un in the closet, cut one leg of the wire loop open, and am trying it now. It has a ground connection, so I used that for one side of the square. So now the loop is totally unbalanced, which the un-un likes.

At my first chance, I'll grab a 9:1 UNUN and put that inline instead. But right now, it seems to be working as well as ever. I choked it the best I could by following the 5:1 unun with an isolated 1:1 transformer, and a bunch of large snap-on ferrites wrapped around the coax.

I'm just hoping that I don't fool myself listening to the feedline. I'll know tonight if the pattern is screwy.

This open-loop configuration, as long as you choke the heck out of it, looks promising.
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Old 06-20-2018, 6:37 PM
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I received the package today. I'll give them a try and report back. Thanks.
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Old 06-20-2018, 8:11 PM
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Thanks for having fun with me here gang. I must apologize to RR for the blogginess of the thread - I never intentioned it to go this far.

PAR / LNR Precision EF SWL looks particularly well suited for the LOG, although one can make stuff themselves..

* The 45 feet of wire makes up 3 sides of the square.
* Unjumper grounds 1 & 2 to make them separate.
* Attach 15 feet of wire to antenna ground lug #2 to make up the 4th side of the square. Do not attach to the other end of loop. There is your unbalanced 60 foot loop total - albeit not a "closed" loop.
* Now you can ground the shield of the coax with lug #1.
* Optionally add your own additional ferrite choking and/or galvanic isolator transformer to the feedline.

The convenience of their grounding setup makes me happy. Perhaps I'll get one just to prove it.
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