Loop and random wire combination

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Robertkoa

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Question:
1)Receive Only with Indoor Antenna/ Longwire for AM thru full Shortwave:

Has anyone tried a Passive Tuned Loop at the END of the longwire then placed in a window?
This would have a tuner like used on AM Passive Loops but be Shortwave Tuneable (with a Bypass )-possibly with multiple taps on the Coils or Concentric ?

It could be used at the End of the Longwire in a Window-
OR as the final stage right before Receiver fed from the Longwire and plugged directly into the Ext Antenna ...

Both above ways would be plugged in to Ext Antenna of Receiver
'Tuner' would have a bypass also.

Theoretically the Preselector Tuning Freq would have more effect placed right before Receiver...BUT may be better at opposite end...Window Placement or 'Tuner OFF '.
Since these work well for AM Broadcast- using a larger loop for SW / All Bands might work also IF there are Harmonics of the ' Waves ' [ frequencies ] you are trying to catch.
Does the Active 'Magnetic' Effect increase the Resonance more ( like a Wellbrook ?)

Could a Passive Version work well also ?

Possible that this would increase Antenna Gain without increasing noise ?

Could it be only 2 feet or so in diameter ?

What do you Antenna Wizards think ?
 
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ka3jjz

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The MW only Select-A-Tenna had this kind of a setup, but it's coverage is MW only. I'd be a little sanguine about this, due to the fact that you are using an unshielded wire that could potentially act as a noise magnet - something a loop is supposed to be resistant to. And the overall effect of the MW loop at the end of the wire would be a little hard to project across such a wide bandwidth.

Hams do something very similar to this with mobile antennas, but the bandwidth such antennas cover is quite narrow.

I don't think your idea would work very well, frankly.

Mike
 

Robertkoa

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Mike - I appreciate your thoughts on this.

Forgetting about the 'tuning' aspect - because the long random wire would influence/ limit/ eliminate the tuned resonance-

BUT does a passive loop in a window at the end of a longwire ADD to the reception on Shortwave more than just the end of the wire.

Using an AM Loop at the end this way increases Gain slightly but obviously a larger loop possibly with concentric coils could take this further...but enough to get 2 or 3 DB more gain with negligible noise increase would be the question.

The Active Magnetic Loops are expensive and I wonder if anyone has tried passive shortwave loops..and if they are effective at all ....
OR do they need to be huge to work in a Passive way for no noise ?

The Principle of Magnetic Loops like Wellbrook do not apply well to Passive Loops ?
 

ka3jjz

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No, loops are loops - whether they are active (that is to say, amplified like the Wellbrook or Pixel) or passive (no amplification). The amps are intended to compensate for the relatively small capture area of a small loop. They work on precisely the same basic principles (their design and matching can have a big impact on this- keep in mind the difference between the Wellbrook and Pixel). There are several such passive loop designs and even a kit or two out there; I've never tried them, to be honest, but I would suspect their signal levels would be much lower - but with a lot less noise.

Here is some examples of a passive loop from our wiki;

Review of the DoxyTronics 8020CA magnetic loop antenna | The SWLing Post

http://www.angelfire.com/mb/amandx/loop.html

Dave's Homemade Loop Antennas at MAKEARADIO.COM

Loop Antenna Index -- antenna special on hard-core-dx.com

I will admit that I've never tried to put a MW loop at the end of a random wire, so my speculation is purely based on theory and not actual practice. I don't know how that jack on the Select-A-Tenna is wired, so it's a little hard to have hard science on this. I suspect that as you go further away from the design frequency, the coil would start acting like a choke, limiting the frequency response and reducing the signal levels.

Mike
 
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WA8ZTZ

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One of the advantages of a loop is the ability to rotate it and null/peak certain signals. If my understanding of the OP's intentions are correct, he mentioned mounting the loop in a window but it seems that would limit being able to rotate it. Otherwise, my advice would be to experiment with various arrangements, that is part of the fun. btw... Joe Carr's Loop Antenna Handbook is a good resource.
 

Robertkoa

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Thanks Ka3jjz- I need to read those References.

Also WA8 and Mike - good points also.

My Novice experiments are I have the Eton E1 with 2 cheapo wind up Antenna Wires clipped to base of Whip going to 2 different windows.

And I have two RCA side by side 24 foot Radio Shack Speaker ( side by side positive and negative thin wire so not shielded) on the EXT jack at ceiling corner then ending at a window with an AM Loop ( too small a Loop for broadband but does increase the 'length ' a little of the longwire NOT intended to be tunable ).
So there is 48 foot total at ceiling line but can switch to 24 feet via quick unplug 2nd section.

Question -I suspect that the really thin wire on the Wind up Antennas is not as good as slightly heavier gauge wire - is this correct ?

So I can switch from Internal to External and compare the two on different Bands and Frequencies and Conditions.

The External [ switch only - all Antennas are INSIDE ] is sometimes really really quiet on 41 Meter Ham signals although lower gain than the Internal - a ' cleaner ' flatter freq response signal sometimes almost Zero hiss - but not because of the loop at end- maybe the length ?

So the idea of a 2 or 3 foot Passive Loop with a lot of wire with different 'Taps' which can be selected for different Bands might ...might increase gain with little noise penalty and the Coil Effect may lower RF Noise somewhat...and it can go in front of a window on a longwire to add to longwire RF Pickup or in noisy environments could go at end of sheilded Coax.

That's the idea...but very vague because I know little about this Subject lol - I do have 'recording studio ' ears but still Novice with Antenna Theory etc.

Of course if something works extremely well - it trumps Theory ...or the Theory comes afterward.

So because a passive longwire is fairly quiet- IF 2 or 3 db of clean gain could be added to it with a 2 or 3 foot Loop - that could be very significant/ good.

One thing is on a strong AM Station the Loop at Longwire End - can kill the slight background hum / line noise when plugged in at end ....kind of like a Hum Cancelling ( humbucking ) Guitar Pickup does versus a Single Coil Pickup.

I need to make or get a bigger coil with 'taps' every 40 feet maybe ?
 
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