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Author Topic: This might be the start of something big  (Read 1385 times)
ChrisSmolinski
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« on: August 11, 2017, 2304 UTC »

Perhaps too big.

Test fit of the PVC pipe for the 10 ft by 10 ft loop antenna.  That little patio umbrella stand, as heavy as it is, is no match for the loop frame. But that is just temporary, the loop is actually going to hang from a tree limb, at least for initial prototyping and testing.

The weight of the pipe itself is about 14 lbs, plus throw in the fittings, my guess is 16 or 17 lbs total.

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Chris Smolinski
Westminster, MD
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JRC-NRD 545 / RF Space netSDR / 670 ft horizontal loop / 500 ft beverage / 43mb sloping folded dipole
skeezix
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« Reply #1 on: August 11, 2017, 2341 UTC »

Be sure to paint it red & white and put a light on top.

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redhat
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« Reply #2 on: August 12, 2017, 0442 UTC »

Perhaps this will be incentive to get my MW TX running?

+-RH
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Somewhere under the stars...
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Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com
jFarley
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« Reply #3 on: August 12, 2017, 1530 UTC »

Nice!

When it's up in the tree, are you going to rotate the entire tree?  If so, Fanco makes a nice ultra heavy duty rotator which will do the job.  I assume you already have the required 480V 3 phase service to your shack?
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Joe Farley, Near Chicago
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« Reply #4 on: August 12, 2017, 1539 UTC »

These things are a sure fire wife pleaser!
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ChrisSmolinski
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« Reply #5 on: August 12, 2017, 1554 UTC »

Quote
Be sure to paint it red & white and put a light on top.

But then I gotta worry about getting one of the peeling paint NOVs.


Quote
Nice!

When it's up in the tree, are you going to rotate the entire tree?  If so, Fanco makes a nice ultra heavy duty rotator which will do the job.  I assume you already have the required 480V 3 phase service to your shack?

I got a surplus nuclear reactor from a Russian sub, so I should be all set.

As I mentioned earlier, this loop frame is a test bed vs a known path. I'll try both a resonant loop with a jFarley amplifier, as well as perhaps with a tuning cap and pickup loop. And maybe with the LZ1AQ amplifier in non-resonant mode.  I am somewhat torn as to use of resonant mode. While it has huge advantages, my DGPS data shows that the spectacular openings are inherently brief. Meaning you want to be looking at the entire band at once, not just a few channels. I guess I could run with a very low Q, so the entire DGPS band is passed, but I am not sure if that will be useful. Again why this is more of a journey than a destination.

Rather oppressive out today, but the dew points are supposed to be lower tomorrow, so maybe I can get back to it then. I'm going to set up a little table right next to the loop (more like under it I guess) with the AFE822 and laptop, so I can evaluate it in real time as I rotate it and fiddle with the settings and loop itself.
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Chris Smolinski
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JRC-NRD 545 / RF Space netSDR / 670 ft horizontal loop / 500 ft beverage / 43mb sloping folded dipole
John Poet
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« Reply #6 on: August 12, 2017, 1952 UTC »

Perhaps too big.

Test fit of the PVC pipe for the 10 ft by 10 ft loop antenna.  That little patio umbrella stand, as heavy as it is, is no match for the loop frame. But that is just temporary, the loop is actually going to hang from a tree limb, at least for initial prototyping and testing.

The weight of the pipe itself is about 14 lbs, plus throw in the fittings, my guess is 16 or 17 lbs total.



What size PVC pipe are you using there?

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John Poet

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ChrisSmolinski
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« Reply #7 on: August 12, 2017, 2041 UTC »

What size PVC pipe are you using there?

1 - 1/2" Schedule 40.  Some (hopefully all) of the sagging is because I did not completely insert the pipe into the fittings yet. The wire may help to tighten things up as well. No idea how many turns or what gauge I will end up with, that is part of the experimentation.
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Chris Smolinski
Westminster, MD
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JRC-NRD 545 / RF Space netSDR / 670 ft horizontal loop / 500 ft beverage / 43mb sloping folded dipole
redhat
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« Reply #8 on: August 12, 2017, 2317 UTC »

You will probably have to rely on the loop wire for support, as PVC has a tendency to snap under tension.  I would also paint it as the UV will cause the plastic to brittle over time.

+-RH
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Somewhere under the stars...
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Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com
ChrisSmolinski
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« Reply #9 on: August 13, 2017, 1726 UTC »

First test. Using two pairs of turns (I happened to have some #16 scrap wire of that length) feeding the resonant amplifier, I get a useable range of about 900-2200 kHz. Fairly high Q even with the small gauge wire, I have to re-tune each time I switch to a different MW channel.

Now to add some more turns. Or one more turn perhaps for all of MW? Not sure I have enough capacitance range to cover the entire MW band, however.  A few more should get me down to DGPS, but I am not sure this will work well for decoding the entire band at once, as was my concern. I may be lucky to get a few channels.  Smiley
« Last Edit: August 13, 2017, 1731 UTC by ChrisSmolinski » Logged

Chris Smolinski
Westminster, MD
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JRC-NRD 545 / RF Space netSDR / 670 ft horizontal loop / 500 ft beverage / 43mb sloping folded dipole
skeezix
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« Reply #10 on: August 13, 2017, 1733 UTC »

Could you make multiple antennas on the same physical pipe covering a different part of the band, then combine the signals? If you need many, that wouldn't be feasible. But maybe several might?
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ChrisSmolinski
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« Reply #11 on: August 13, 2017, 1924 UTC »

Could you make multiple antennas on the same physical pipe covering a different part of the band, then combine the signals? If you need many, that wouldn't be feasible. But maybe several might?

I'm not sure how well a tapped resonant loop would work. Paging jFarley to the Electromagnetics Lounge.

Some more data:
Going up to 6 turns gives me a usable range of 350-700 kHz. Yeah. I just miss the DGPS band.

Going to 9 turns gives me a range of 250-530 kHz. In this case Murphy struck by my spool of wire being 3 ft too short to finish the last turn. Fortunately I found some scrap wire in the shed.   This is a nice range in that it gives me DGPS plus the NAVTEX channels. Also most of the NDB band. Another turn would probably give me all of the NDB band but then I'd lose NAVTEX. Decisions, decisions.

The useable bandwidth in the DGPS band seems to be about 2 kHz, I'll try taking a screenshot later. I guess that implies a fairly decent Q. Especially for something thrown together with some #16 hookup wire.

What I have ended up doing, for now anyway, is supporting most of the weight of the PVC frame with a rope over a branch. The bottom pipe then rests on the ground, and I can adjust the azimuth of the loop. Works pretty well.

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Chris Smolinski
Westminster, MD
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JRC-NRD 545 / RF Space netSDR / 670 ft horizontal loop / 500 ft beverage / 43mb sloping folded dipole
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« Reply #12 on: August 13, 2017, 1934 UTC »

Now that is one awesome radio room you got there in your backyard Chris!  Shocked
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« Reply #13 on: August 13, 2017, 2144 UTC »

That's much more graceful than that 8' x 8' loop built of 2"x4"s of Dick Pierce's that made it in to Pop 'Comm back in the '90's. Kudos!
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jFarley
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« Reply #14 on: August 14, 2017, 1341 UTC »

Just stuck my head in the door of the Electromagnetics Lounge, but the coffee wasn't ready yet.  Will be back...

In the meantime, the most important thing I look for in a loop design is the Effective Height, which is a measure of its signal collecting ability.  This is 2 * PI * N * A * Q / lambda, and if I have the following correct:

N = 9T
A ~ 9 M^2 For a loop with 10 foot sides
lambda = 1000M for 300 kHZ

then the He for the loop would be approximately 0.5 * Q Meters.

Knowing what the actual Q is would give a rough idea of what to expect from this loop in resonant mode.

I see that you are using the amp/supply from the HF loop.  This uses back to back tuning diodes such as NTE618.  These devices, IIRC, have a guaranteed minimum Q of ~ 100 at 1000 kHz.  In a tuning diode, the Q (at a given bias) is generally a close to linear  function of frequency.  My recollections of trying this type of tuning with the ferrite loop seemed to validate this, and that the diode Qs seemd to be significantly lower at NDB frequencies.  Even so, if the diode Qs were around 30, the the He would compute out to be around 15M, which would not be too shabby.

If you could actually measure the Q from a screenshot, that would be cool and helpful.

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Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
Active 60" Whip / PA0RDT
QSLS appreciated to:    jfarley44@att.net
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