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Author Topic: IC706 on 630m band using four turn magnetic loop antenna  (Read 2545 times)

G0OQX

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IC706 on 630m band using four turn magnetic loop antenna
« on: November 10, 2018, 12:31:24 AM »

I've been playing around with home brew mag loops over the last few months, and I've achieved excellent results on 160m with a 6ft dia four turn loop. When setting up this loop with a 250pF vacuum capacitor I found that it would tune down to 1MHz which got me thinking that it might work on 630m with a bit more capacitance thrown in. Plotting capacitance versus resonant frequency suggests another 1000pF should do it which would be easy to add if I decide to try this out.
However, before going any further into the 630m world I would be interested if anyone has any views or personal experience of mag loops on 630m, particularly as I've not come across any online discussions concerning mag loops on this band. Is it worth me persevering?
Also, when googling transmitters for 630m the other day I came across a thread (sorry, forgot to record the link) that discussed HF rigs on 630m, and it was said that the only HF rig that will transmit on 630m unmodified is the IC706, although it only claimed this with the power turned down to 2W. I'm not sure if the power restriction was mentioned for driving an amplifier or because the IC706 would not be happy running more power on this frequency. Any input here would be appreciated. I've got two of these wonderful cheap and cheerful rigs, and I wouldn't want to blow either of them up trying to use them on this band if they are unsuitable.
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WA4JNX

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #1 on: November 10, 2018, 05:15:20 AM »

Hello,

Loops are for many the only way to go in Longwave reception because
in general:
-they only respond to the magnetic part of the e/m wave (most
noise is in the electrical part)
-they are directional (you can null out the noise),
-they are polarized (vertical or horizontal).

(Yes,dealing with The Infernal Noise is a big deal for many of us.)

My efforts went nowhere until viewing NG9D's "Hula Hoop Longwave Loop"
Youtube video...when a one turn pickup loop was added to feed a converter the
results were outstanding:

https://www.bing.com/videos/search?q=ng9d+youtube+longwave+loop&view=detail&mid=19754959942898A294A919754959942898A294A9&FORM=VIRE

I'm sure the advanced members will offer additional suggestions but
"this works for me".

For transmit info please see John Langridge's site:

http://njdtechnologies.net/category/630-meters/

Used to think loops were so old-timey,wouldn't use anything else now.






« Last Edit: November 10, 2018, 05:19:20 AM by WA4JNX »
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W9IQ

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #2 on: November 10, 2018, 05:42:28 AM »

Quote
-they only respond to the magnetic part of the e/m wave (most
noise is in the electrical part) 

I know that this is constantly repeated on the Internet but both of the assertions are wrong.

Noise arriving in the far field of the antenna is an EM (electromagnetic) wave just as any other signal is an EM wave. They contain both an electric and magnetic component and the signal and noise is contained in both parts of the EM wave. The ratio of the magnitudes of the electric wave to magnetic wave in free space is ~377 which is also the impedance of free space, ~377 ohms

The primary reasons a loop antenna seems to be quieter is that is has very low gain (often -10 dBi or lower) so all signals including noise are attenuated and it is directional so it can be turned away from the source of the noise.

The small loop antenna is called a magnetic loop because the effervescent near field is primarily inductive. It has nothing to do with receiving only the magnetic part of the EM wave.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9IQ

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #3 on: November 10, 2018, 06:12:41 AM »

I should add a third reason for noise rejection by the loop: If the offending signal is arriving in the far field of the loop via ground wave, the polarity of the loop may help to attenuate the noise in a cross polarity case.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

G0OQX

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #4 on: November 10, 2018, 07:30:27 AM »

Quote
For transmit info please see John Langridge's site:
http://njdtechnologies.net/category/630-meters/

Thanks for this link, after a quick look at John's site I can see I've got months of reading and a lot to learn about 630m operation. At least this will give me plenty to do through the winter.
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WA4JNX

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #5 on: November 10, 2018, 07:42:12 AM »

Thanks for your comments,Glenn...always wondered
how some noise managed to get thru the "magnetic"
loop.
73...ron
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K0OD

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #6 on: November 10, 2018, 10:07:34 AM »

Quote
"Loops are for many the only way to go in Longwave reception..."

I only receive on 630. Have no transmitting ability, yet. But I observe who "hears" the best around me in the midwest on WSPR. E-probes do very well. And even a simple random wire can pick up plenty of WSPR DX. Many of the stations with the best ears are in deep rural areas.

BTW, WSPR long-haul DX is starting to come in for the season. Some midwest reporters are printing VK/ZL and there have been a very few reports of EU. Note that LU1DOW is now on 630 WSPR from Argentina.

K0OD, Saint Louis
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VK6HP

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #7 on: December 02, 2018, 02:55:19 AM »

Glenn is right to draw attention to a couple of pieces of the nonsense that seem to make up the ham folklore surrounding small loops.  A number of antenna engineering books have good descriptions of the antenna but I like Kraus' (W8JK, SK) "Antennas for All Applications" as a solid, readable reference.

But, Glenn, I think you mean "evanescent" near-field rather than "effervescent"; maybe a wayward Berocca insinuated itself into your thinking :)

73, Peter.
« Last Edit: December 02, 2018, 03:01:02 AM by VK6HP »
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G8HQP

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #8 on: December 02, 2018, 06:29:35 AM »

Local near-field noise need not be a transverse EM wave. It could be primarily longitudinal electric field, which would not be picked up by a shielded 'magnetic' loop.
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KM1H

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #9 on: December 02, 2018, 06:38:30 AM »

Quote
My efforts went nowhere until viewing NG9D's "Hula Hoop Longwave Loop"
Youtube video...when a one turn pickup loop was added to feed a converter the
results were outstanding:

Is that loop split and the cap connected to each side or is it more involved?  Hard to see any detail.

Carl
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W9IQ

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RE: IC706 on 630m band using four turn magnetic loop antenna
« Reply #10 on: December 02, 2018, 08:26:00 AM »

Glenn is right to draw attention to a couple of pieces of the nonsense that seem to make up the ham folklore surrounding small loops.  A number of antenna engineering books have good descriptions of the antenna but I like Kraus' (W8JK, SK) "Antennas for All Applications" as a solid, readable reference.

But, Glenn, I think you mean "evanescent" near-field rather than "effervescent"; maybe a wayward Berocca insinuated itself into your thinking :)

73, Peter.

Thanks for catching that, Peter. Maybe I am low on some vitamins...

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.
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