Loop Calculators

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rocky28965

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nanZor

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Make sure that this is really what you want for an RX antenna. The tuned types, usually used for transmitting, have a very narrow bandwidth, meaning you are limited to having the tuner within arm's reach or remote and constantly fiddling with it, as opposed to a broadband untuned loop.

I have never built a tuned loop myself, so I will admit ignorance as to why the difference between the two programs.

Be sure to visit probably the freshest STL (or ostensibly a very narrow manually tuned loop project) from KK5JY - maybe the values he is using might help suss this out.

KK5JY Small Transmitting Loop Project

I know you probably want to look at the AA5TB loop calculator online too - perhaps this might help show the discrepency...
 

majoco

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Here's a couple of pics of a loop I lashed up last week for a trial - the sides of the diamond are 600mm/24inches and the coupling loop is about 200mm/8inches diameter - the tuning cap goes from about 30pf to 400pf +/- a bit for stray capacitance and according to my little meter it has an inductance of about 250uH which seems a bit high to me but the meter digital scale is on 20mH so I wouldn't put too much faith in that. It seems to tune from about 4MHz to just over 15MHz - I'll give it a try outside this evening and see how well it works - it seemed pretty good inside the garage!
 

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rocky28965

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Make sure that this is really what you want for an RX antenna. The tuned types, usually used for transmitting, have a very narrow bandwidth, meaning you are limited to having the tuner within arm's reach or remote and constantly fiddling with it, as opposed to a broadband untuned loop.

I have never built a tuned loop myself, so I will admit ignorance as to why the difference between the two programs.

Be sure to visit probably the freshest STL (or ostensibly a very narrow manually tuned loop project) from KK5JY - maybe the values he is using might help suss this out.

KK5JY Small Transmitting Loop Project

I know you probably want to look at the AA5TB loop calculator online too - perhaps this might help show the discrepency...

Strangely enough the aa5tb calculator gives values hallway between the other two.
 

majoco

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Right, here's some results - my main aerial is an OCFD 45/15ft up about 20ft running east/west through a 9:1 unun to a multicoupler to 5 HF receivers - I used the Kenwood R2000 turned up loud so I could hear it outside but a G33DDC SDR to measure the peaks of the signals. The loop was just outside my shack window and only 5ft off the ground at the centre. I orientated the loop for best signals from WWVH on 5, 10 and 15MHz, the local time was between 1930 and 2000local, 0630/0700UTC. Tuning the signal was quite tricky at all frequencies - difficult looking for a peak when the signal is fading and the receiver AGC is trying to level the audio.

WWVH 5MHz, OCFD -90dBm, Loop -95dBm, noise -130dBm.
WWVH 10MHz, OCFD -80dBm, loop -85dBm, noise -120dBm.
WWVH 15MHz, OCFD -85dBm, noise -120dBm, loop -105dBm, noise - 140dBm.
CRI on 15.135kHz in Spanish, 0700 UTC - very little difference between the two antennas in readability, S9+ on the Kenwood both signals.

I'll leave you to draw your own conclusions! If I didn't have to get up early in the morning I'd do some late-night tests but my bed calls...... baby sitting tomorrow!
 

rocky28965

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I'm slowly getting the bits together to build a small indoor loop antenna similar to this one.


I need some advice re connecting the variable capacitor.
I'm not sure of the exact capacitance but comparing it visually with others on the nett, I am assuming it to be around 3x300pF
I would like to be able to progressively select 1, 2 or all 3 gangs.
I'm thinking I will need a 3 position switch but would appreciate if someone could show a suitable wiring circuit.
 

majoco

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Not so easy to find a rotary switch that will connect the three gangs sequentially - you don't need to select "1", it can be permanently wired, but I would go for the KISS principle - Jaycar have two-pole three-way toggle switches.


Loop Selector.jpg

Have you actually sent for that capacitor? GBpounds 18 looks awfully expensive - I can send you one for postage.

Chhers - Martin
 

rocky28965

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Not so easy to find a rotary switch that will connect the three gangs sequentially - you don't need to select "1", it can be permanently wired, but I would go for the KISS principle - Jaycar have two-pole three-way toggle switches.


View attachment 68260

Have you actually sent for that capacitor? GBpounds 18 looks awfully expensive - I can send you one for postage.

Chhers - Martin

Thanks Martin.
I found one in an old radio at our local recycle centre.
 

majoco

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That looks like it will do the job - the centre position will be the "1" with "2" up and "3" down - whatever takes your fancy - I can draw a physical diagram on how to wire the switch if you have a problem.
 

rocky28965

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Thanks, I get one on the way.
Just making up a copper tube roller atm
Gotta get those curves right.
 

rocky28965

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Slowly getting this project together.

Using the design in post #7, pros & cons of having the main loop inside a pvc flexible tube?
 

rocky28965

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Finally got this project completed & ran a few quick tests yesterday.
Middle of the day picked up Auckland MWARA on 8.867MHz from inside my garage.
Thats over 1000k's from my location, so I'm happy with that.
Main loop is 3.4M x 10mm copper tube.
Small loop is 680mm x 6mm copper tube.
It's tuneable from 2.075MHz - 15.220MHz
 

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