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Author Topic: Calculate the impedance of a delta skyloop antenna  (Read 1791 times)

Offline bandarr3000

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Calculate the impedance of a delta skyloop antenna
« on: October 18, 2017, 0056 UTC »
I want to replace my long wire antenna with a horizontal delta skyloop and I only have about 100' total length to play with.  This is not optimal for 43 meters, so how do I calculate the impedance so that I make sure I get the right balun to match to my 50 ohm coax?  It would be just under 3/4 wavelength on our favorite pirate band.  Thanks in advance.
« Last Edit: October 18, 2017, 0102 UTC by bandarr3000 »
Yaesu FTDX3000D
SDRPlay RSP1A
W6LVP loop antenna
EFHW 40-10 as inverted L
Grand Rapids, MI

eQSL please to bandarr@gmail.com

Offline ChrisSmolinski

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #1 on: October 18, 2017, 1117 UTC »
You could use NEC or MININEC to model the antenna and expected impedance. And why yes, I have an app for that: http://www.blackcatsystems.com/software/mininec-antenna-analysis-modeling-software.html  ;D

I'll be honest and say that while it will give you a rough idea of how the impedance is going to vary over the HF bands, there's a lot of "known unknowns" as they say, such as the fact that the actual antenna geometry is not going to match what you put into the program (exact distances, heights, etc). Throw a few unknown unknowns into the mix, and it gets worse. You can tell how likely the model is to match reality by making small changes to your geometry (length, height etc) and see what happens to the output. If it varies a little, it is stable, and may be close to reality. But if you make small changes and the output varies wildly, then it's not stable, and probably just generating random numbers.

Yes, if you could make your loop a little longer and get to around a wavelength for 43 meters, that would be better, but 100 ft is probably not going to be to too bad for a receive only antenna. 

For reference, my sky loop is about 670 ft, or 206 meters. Down on the medium wave band, it does receive all the way down to 530 kHz, where it is only 0.36 wavelengths long. Sure, the signals are not as strong as up around 1500 kHz, but still quite good.

This is where I add a shameless plug for The Squid universal matching transformer http://blackcatsystems.com/rf-products/matching-transformer-unun-balun-beverage-longwire-k9ay-flag-ewe-dipole-antenna-shortwave-ham-radio.html   Try the various impedances and see which works best for the band(s) of interest. Plus if you ever change the antenna (add additional wire, re-route it, etc) you can re-try the impedances to see if there is a better match, without buying a new balun.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline bandarr3000

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #2 on: October 19, 2017, 1402 UTC »
Thank you.  The only other option is to get my loop out to about 170 feet, because of the location of the trees in my yard, which would actually be much closer to what I need.  Considering that I live in an urban area, I'm concerned that I may get a lot more noise with a longer antenna.  I'm strongly considering the Squid for this application if my impedance will be in the neighborhood of 253 ohms or 78 ohms (the two combinations that seem to be the only ones available for a loop).
Yaesu FTDX3000D
SDRPlay RSP1A
W6LVP loop antenna
EFHW 40-10 as inverted L
Grand Rapids, MI

eQSL please to bandarr@gmail.com

Offline Josh

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #3 on: October 19, 2017, 1650 UTC »
It'd be interesting to watch the unterminated leads of a squid attached to a large antenna during a tstorm or snow/dusty wind conditions, it may develop some high voltages ie plasma, wich is always welcome.
Conveniently located near Vincennes Indiana.

Offline jFarley

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #4 on: October 20, 2017, 1354 UTC »
It'd be interesting to watch the unterminated leads of a squid attached to a large antenna during a tstorm or snow/dusty wind conditions, it may develop some high voltages ie plasma, wich is always welcome.

Chris;

You may want to re-post the video in your "This is why you should disconnect your antenna during a storm" post in the RadioHobbyist blog.  It seems to be missing.
Joe Farley, Near Chicago
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QSLS appreciated to:    jfarley44@att.net

Offline ChrisSmolinski

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #5 on: October 20, 2017, 1536 UTC »
It'd be interesting to watch the unterminated leads of a squid attached to a large antenna during a tstorm or snow/dusty wind conditions, it may develop some high voltages ie plasma, wich is always welcome.

That's why I kept the leads short, to minimize that :)


Chris;

You may want to re-post the video in your "This is why you should disconnect your antenna during a storm" post in the RadioHobbyist blog.  It seems to be missing.

This one? The old URL is probably broken... http://www.radiohobbyist.org/blog/?p=1036

« Last Edit: October 20, 2017, 1539 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline jFarley

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #6 on: October 20, 2017, 1648 UTC »
TY Chris!

Love that video.
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

Offline ChrisSmolinski

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #7 on: October 20, 2017, 1726 UTC »
TY Chris!

Love that video.

Thanks. Next time a storm comes though, I will make a new one, using the beverage  ;D

I believe I correctly added a redirect to the old broken www.hfunderpants.com links, so they go to the new www.radiohobbyist.org/blog link. Thanks for reminding me that I needed to fix that.
« Last Edit: October 20, 2017, 1728 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline bandarr3000

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #8 on: November 09, 2017, 1835 UTC »
Thanks to a fast delivery from Black Cat Systems I'm using my Squid to tune my delta skyloop antenna just in time for pirate listening on long winter nights!  The wide variety of impedance options allows me to get the strongest signal for the frequencies I'm interested in. The Squid's heavy-duty construction is great for experimenting, since I don't have to worry about "wearing out" the connectors like I do with other transformers I've purchased in the past.  This is a great product and well worth the money. 
Yaesu FTDX3000D
SDRPlay RSP1A
W6LVP loop antenna
EFHW 40-10 as inverted L
Grand Rapids, MI

eQSL please to bandarr@gmail.com

Offline Finman

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #9 on: November 15, 2017, 1752 UTC »
For reference, my sky loop is about 670 ft, or 206 meters. Down on the medium wave band, it does receive all the way down to 530 kHz, where it is only 0.36 wavelengths long. Sure, the signals are not as strong as up around 1500 kHz, but still quite good.

Hey Chris, is that sky loop a horizontal loop? (laying flat with reference to the earth?) how high is it?. I have a very large wooded area to work with and I'm considering constructing one of these.

.......... and Bandarr...(or should I say Uncle Martin) do you own an antenna analyzer?.... these are EXTREMELY handy when experimenting with antennas.. I'm using an MFJ model but I'll be getting the "Rig Expert" soon because it covers the new 472khz amateur band.  8)


Offline ChrisSmolinski

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #10 on: November 15, 2017, 1914 UTC »
Hey Chris, is that sky loop a horizontal loop? (laying flat with reference to the earth?) how high is it?. I have a very large wooded area to work with and I'm considering constructing one of these.

Yes, it is horizontal. The height varies, but roughly 20 to 50 ft, depending on which trees were convenient.

It is a great performing antenna, as my logs suggest  ;D
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Finman

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #11 on: November 15, 2017, 1947 UTC »
Sounds good!. I would think an antenna at that low an elevation on the broadcast band would have a very high take off angle.
I'll be Installing a very long beverage this coming spring so I'll have to try and keep the loop antenna away from the beverage as much as possible to avoid interaction.


Hey Chris, is that sky loop a horizontal loop? (laying flat with reference to the earth?) how high is it?. I have a very large wooded area to work with and I'm considering constructing one of these.

Yes, it is horizontal. The height varies, but roughly 20 to 50 ft, depending on which trees were convenient.

It is a great performing antenna, as my logs suggest  ;D

Offline Josh

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #12 on: November 16, 2017, 1659 UTC »
Someone I know has a 500ft loop supported by phone poles. Out of hf beams atop a 75ft tower, professional (at least in price) active antennas, slopers, multiband vertials, the loop beats all of them from vlf to vhf. Loops are majikal.
Conveniently located near Vincennes Indiana.

Offline Finman

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Re: Calculate the impedance of a delta skyloop antenna
« Reply #13 on: November 16, 2017, 1727 UTC »
Someone I know has a 500ft loop supported by phone poles. Out of hf beams atop a 75ft tower, professional (at least in price) active antennas, slopers, multiband vertials, the loop beats all of them from vlf to vhf. Loops are majikal.

I highly doubt a 500ft loop is going to beat a Yagi on VHF freq's.  ;D