Inductive Coupling And A Loop

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ridgescan

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If you have the inclination, some 300 ohm twinlead, a 9:1 balun and a Wellbrook loop outside, you can use that Wellbrook on any regular radio in your house with inductive coupling.
I discovered this by accident.
My old tube table radio is on the far side of the radio room. I was running a feed for it from my antenna switch that goes up to the loop on my roof. I ran 50 ohm coax off that switch to my PAR 9:1 box, then to 300 ohm twinlead which was on my floor in a looped pile waiting to be cut down to the length needed for the feedrun. I had the radio on tuned to a MW station, and the loop's power was already on. As I connected that feed system onto the loop's switch, that radio came alive!
I doubletaked at that 300 ohm bunch setting on the floor about 8' from the radio and immediately realized major inductance. Picked up that pile off the floor and shoved it behind the radio and boy talk about potent reception. Tuned around a bit and it was getting distant stuff as I would if it was directly connected to the loop.
But I wound up direct connecting anyway because that old radio has shortwave:) inductance won't work there.
Just thought I'd throw that out there for some to try.
 

Ed_Seedhouse

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I
But I wound up direct connecting anyway because that old radio has shortwave:) inductance won't work there.
Just thought I'd throw that out there for some to try.
Stuff and nonsense. Every radio on the planet, no matter what the receive frequency, relies on inductors.
Lots of hams use also baluns to help match their transmitters to their antennas. A balun is a transformer that uses, guess what, inductance!
 

ridgescan

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No need to be arrogant. I barely post here anymore. When I do I try to help. This post was based on MY experience here as tried, which is mostly all I ever post.
I was sharing something I happened to discover here. There was no response on SW with this. You were saying?
 

Boombox

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I've done similar. I'm not sure how much of it is inductance, or the radio picking up RF from the field surrounding the antenna feedline.

I've heard it referred to as the "proximity effect".

Some years ago I placed the whip from a portable SW radio near my 100 ft wire antenna's feedline. The whip picked up a lot of stations that way. At the time I used it as a method of listening to SW stations with less QRM from the local powerline buzz that was happening at that time.

For some reason, the powerline buzz didn't overpower the reception of SW stations. I suppose the distance between the whip antenna and the wire from the antenna was acting as a sort of minor attenuator. SW station strengths were a bit less, but more QRM free.

Either way, it does work..
 

Ed_Seedhouse

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No need to be arrogant. I barely post here anymore. When I do I try to help. This post was based on MY experience here as tried, which is mostly all I ever post.
I was sharing something I happened to discover here. There was no response on SW with this. You were saying?
I don't see where pointing out that you were wrong is "arrogant", sorry.

You drew conclusions that were wrong, based on insufficient evidence, and gave incorrect advice to another user of the forum based on your ignorance. Who then is being arrogant?
 

ridgescan

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Thank God and RR for the edit feature. I posted like never before in my time here.
Hey Ed-lighten up. Instead of being arrogant and curt with your "pointing out" my ignorance, you could have corrected me where you saw an error within the same bandwidth. No need to be stuck up about it. There's enough bad stuff going on in this world you don't need to be mean to another member here who made an error. If the tables were turned I'd have picked a better attitude when "pointing out" your ignorance.
 
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ridgescan

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I've done similar. I'm not sure how much of it is inductance, or the radio picking up RF from the field surrounding the antenna feedline.

I've heard it referred to as the "proximity effect".

Some years ago I placed the whip from a portable SW radio near my 100 ft wire antenna's feedline. The whip picked up a lot of stations that way. At the time I used it as a method of listening to SW stations with less QRM from the local powerline buzz that was happening at that time.

For some reason, the powerline buzz didn't overpower the reception of SW stations. I suppose the distance between the whip antenna and the wire from the antenna was acting as a sort of minor attenuator. SW station strengths were a bit less, but more QRM free.

Either way, it does work..
I thank you for the education Bbox:) this is very similar to my experience. This is how we gain knowledge.
 

corbintechboy

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I shot a quick video to illustrate to those who might be interested in actually seeing what I was talking about in post 1. You will see inductive coupling of the feedline with the internal loop of the radio (by the way-nice old radio aint it?)
http://vid739.photobucket.com/albums/xx34/ridgerocker2001/MVI_0506_zps27dacd44.mp4
Nice video Ridge.

I would not let people get you down with their "must be facts" stuff.

People seem to forget when they first started the hobby and were doing all sorts of strange things and were excited when those strange things worked. Those days were the best days I can remember. No science, no facts just a man on a mission to make something work and when it did a ton of excitement.

I sense the excitement in your video :D. Those Ridge are the parts of this hobby that mean something. Those bits of excitement are what it's all about and those that have to insert fact and logic when we don't want fact and logic are the people that ruin it for the people that just want to have fun.

Enjoy what you do! Don't worry about the facts and have a load of fun. If wrapping wires around your arms and flinging them in the air is fun to you or I let's do it. That is what the hobby is to me. Knowledge goes a long way but sometimes we require no method to our madness :D.

EDIT: And yes, that was a nice radio and it sounded great.
 

Boombox

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I can't see the video here, but I'm guessing the tube radio in question has a MW loop antenna. It's probably still active in the circuit when the radio is switched to SW, and that would explain how the RF from the loops of antenna cable is being picked up by the radio -- by the RF field being picked up through the radio's loop antenna.

I know some guys attach a length of wire to the end of an antenna feedline and wrap it around their portable radios to get better signal without a lot of overload. I think it's because the SW whip antenna in a lot of SW radios is inductively coupled to the radio's ferrite bar in the antenna circuit (especially older style multiband transistor radios -- and probably tube multibanders also).

I have a transistor with SW capability that is wired that way. The wire from the whip goes several turns around the ferrite bar, and then to ground. So it stands to reason that any strong enough SW RF field seen by the radio's loopstick will be amplified and then received by the radio.

In Ridge's case, it may be the radio's air loop (?) working the same way.

I think in the case of my digital portable's loopstick being placed near the field of the longwire's feedline, it was capacitive coupling.

Either way, it's a good trick to know.
 

jackj

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Yes!!

Stuff and nonsense. Every radio on the planet, no matter what the receive frequency, relies on inductors.
Lots of hams use also baluns to help match their transmitters to their antennas. A balun is a transformer that uses, guess what, inductance!
What's your point, Ed? Everyone here knows what a balun is and what it is used for. I have a radio that doesn't use inductors, it's a Software Defined Radio or SDR. All solid state with IC's and stuff but no inductors so your statement about inductors being universally used in radios is wrong.

Jack
 

jackj

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Ridge, Boombox's statement about why this works with MW and not SW is right on. And you are correct, the signal is inductively coupled to the loop. But inductance is what makes antennas work to start with. Your receive antenna is inductively coupled to the transmitting antenna. You can think of it as a air-core transformer with several miles spacing between the primary (transmit antenna) and secondary (receive antenna). School is out now and I'm sorry to have ruined your thrill of discovery. I've had a lot of those thrills myself.
 

E-Man

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I always enjoy your video's Ridgescan. Thanks for sharing.
 

ridgescan

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jackj-excellent explanation, thanks. And nothing is ruined when people like you add their knowledge like you did and turn a crap thread into a good one with good information. This is what makes a joint like RR valuable.
I sure appreciate Boombox's explanation affirming the "phenomenon" I accidentally discovered-thanks again Boombox-and thank you RadioTuner for the support! After all, for me anyway, experimenting and discovery are the fun aspects of the radio hobby, but knowing the reasons why are the icing on the cake:)
 

corbintechboy

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I sure appreciate Boombox's explanation affirming the "phenomenon" I accidentally discovered-thanks again Boombox-and thank you RadioTuner for the support! After all, for me anyway, experimenting and discovery are the fun aspects of the radio hobby, but knowing the reasons why are the icing on the cake:)
I agree. When we want to know we want to know, when we don't we are inwardly ecstatic it works ;).
 

nanZor

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It could just be that once the loop amp is powered up, one combination of the antenna switches makes the short output cable a transmit antenna of sorts, using the common mode of the coax.

But that is a distraction at this point, after seeing the video of the setup.

What I would recommend is that ANY loop user who does use a common antenna switch to other antennas, is to first get a BASELINE of loop performance going from the loop DIRECTLY to the radio in use.

Get a handle on your null directions, and depth, killing various local noise sources. Take note of signal strengths and general performance as you swing it around.

NOW, attach it to your common switch(es), and see if there are any differences in null direction, depth, or signal strength.

What you may find, is that the loop may be affected or swamped by the other feedline common mode, even if switched away, by long runs of alternate antenna coax braid, and in some cases even the side of say dipoles which are connected to that braid, skewing the loop performance.

Most importantly, get your baseline of operations first without any sort of switching or possible ground-sharing setups. Disconnect all other antennas to make sure you don't have any ground loops that can be overlooked when getting this baseline.

When building my own loops years ago, I had FANTASTIC results when tested out in the backyard on a receiver with a battery. (A Yaesu FRG7 to be exact). But when I brought it all into the house, and attached it to my antenna switches, the results were not what I expected. What the loop saw was the common mode of all my other antenna feedlines as if it was surrounded by metal weeds. :)

Anyway, that is what I'd concentrate on, not the infighting. :)
 
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Turbo68

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Hi ridgescan well done if we dont experiment in our hobby we wouldnt know how to get the best of the antennas and radios we use.I do have lots of receivers but at times one receiver will work better than another one with the same antenna oh well try a different antenna thats what makes this hobby so great.
I always wonder why some people really need to get a life because all they do is try put others down instead of helping and explaining..

Regards Lino..
 

ridgescan

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Thanks for adding in Lino-I agree about experimenting. Due to my high RFI environment, I've had to make many trips to the roof in the past trying to get that old wire antenna system right with it. Without all that trial and error it would've been a lousy listening experience. Luckily, since I got that Wellbrook, I haven't gone near that roof (and my disability is one that I shouldn't be up there at all)
73s-Frank
 
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