[time-nuts] Re: WWVB Loopstick Antenna Project

[paul swed]

Well Glen as you say tradeoffs. Always. Thats why the Loops are 162' away
from the house with some woods around. The 10' loop is shielded and the 5'
not. They are directive. Which helps reduce local noise. Boy does it exist.
My noise floor today on the 5' loop is 20 uv. I do hear lots of crud/noise.

I remember when the only thing you needed to worry about was a leaking
power line insulator. Power company got tired of fixing them so they
invented CFL, LED lights, and switching power supplies. Now they never get
calls.......
The 5' loop is actually tuned for 100 KHz not 60 KHz.

Anyhow go big or go home. Chuckle.
Regards
Paul
WB8TSL





On Sun, Sep 11, 2022 at 4:06 PM glenlist <glenlist at cortexrf.com.au> wrote:

> Good stuff Paul
>
> What needs to be determined is the required Signal to Noise for the
> application, since its about using the signal for analytical purposes. That
> will drive the design and requirements. Higher SNR for indoor antennas will
> certainly be got with electrostatic (ES)  shields -
>
> But the trap  is that you cannot just use a very low efficiency antenna in
> a high noise environment-  with very low efficiency antennas this leaves
> very small signal values which can easily get drowned out by any common
> mode noise getting on the cable, which means you have to work VERY hard on
> common mode rejection / suppression and balance,  and also  garbage getting
> onto the cable in the shack, if the coax is not choked where it leaves the
> shack, will take noise to the near field of the antenna !
>
> So, careful thought is required- balanced input preamp on the antenna
> terminals is recommended- not because there is a lack of signal, but to
> give it a boost above everything else.  Either that or tale great care,
> perhaps twincoax balanced feed and resonant common mode chokes to get Zcm >
> 10,000.
>
> Well I am getting off topic, there are a thousand ways to skin this cat.
>
> A 5' loop with ES shield  in the attic can work well, as long as you dont
> have LED lightning wires criss-crossing under your antenna.
>
> I'd suggest a smaller loop with more turns FURTHER away from the house.
> Why? because noise will dominate close to the house.  The near field pickup
> region will be smaller for a smaller antenna.
>
> Perhaps a 2' loop up on a piece of pipe, or a rod.. You can likely
> dispense with the ES shield if it is a mile away from any noise source and
> structure.
>
>
> On 12/09/2022 1:13 am, paul swed wrote:
>
> The header seems to say the application. A wwvb antenna.
> If you look in any of the simple cheap atomic clocks you will find a rod
> about 2-3" long.
> Typically a resonating cap right on the antenna for 60 KHz. These work
> well enough to receive wwvb at night when the signals much stronger than
> during the day.
> As insight near Boston 60 uv day and last night 1500 uv on a 5' loop tuned
> for 100 KHz not wwvb. The 10' square loop is something like 200/10,000 uv.
> Honest. Not every night but many of them. I have used bundled rods for a
> number of years but the square loops are better. More importantly no
> ferrite was ever harmed in building them.... So that must mean the square
> loops are more green. Right?
> OK sorry went of topic.
> all things are a tradeoff. Large loops are hard to install and then manage
> over time. Especially when a large branch crashes through the loop after 5
> years. Thats why at 100 KHz I went to a 5' loop. Less of a target.
> Whats nice about the rods are they really are pretty small.
> Regards
> Paul
> WB8TSL
>
> On Sun, Sep 11, 2022 at 12:08 AM glen english LIST via time-nuts <
> time-nuts at lists.febo.com> wrote:
>
>> The referred article by Richard Q. Marris is a good one but liekly mass
>> overkill for this application.
>>
>> Seek a rod that is good at the 125kHz RFID frequency. Type material 78
>> comes to mind,  but almost any Manganese Zinc Ferrite is going to work.
>>
>> Although they'll probably be fairly small . All the higher frequency
>> rods will be fine on losses but have low perm and need lots of turns.
>> Something with an initial permeability of at least 2000 will be suitable.
>>
>> greater Length/Diameter will increase mu-rod. 6" x 3/8" sounds good.
>>
>> You might not need that much rod, I dont know what the field strengths
>> are (does anyone know) but something like this might be suitable  :
>>
>> https://www.fair-rite.com/product/antennarfid-rods-3078990901/
>>
>> a ferrite rod is not necessary if you have space... if this is a fixed
>> application,  many turns around a foot square will be just as
>> effective.  No need for a ferrite rod.
>>
>> Suggest electrostatic shield and balanced  feed for the wire , coreless
>> loop.
>>
>> For a small ferrite  rod, put the rod length wise in a deep aluminium
>> channel section.
>>
>> It's certainly easier to build a ES shielded small rod than a loop.
>>
>> -glen
>>
>>
>>
>> On 11/09/2022 12:38 pm, Lux, Jim via time-nuts wrote:
>> > On 9/10/22 7:59 AM, D. Resor via time-nuts wrote:
>> >> I exploring the parts needed to construct this particular VLF Loop
>> Stick
>> >> Antenna by Richard Q. Marris G2BZQ.
>> >>
>> >> I have uploaded the article to my DropBox Account here:
>> >>
>> >>
>> https://www.dropbox.com/s/niv64xqmghu76z3/1_1201157_4_Ultima_loopstick_VLF_a
>> >>
>> >> ntenna.pdf?dl=0
>> >>
>> >> The project explains you should use 9.5mm (3/8") Diameter X 15cm (6")
>> >> Length
>> >> Ferrite rods.
>> >>
>> >> The closest I have been able to find are 10mm (0.393") Diameter X 160mm
>> >> (6.299) Length.
>> >>
>> >> Will it make much of a difference?
>> >>
>> >> Thank You
>> >>
>> >> Don Resor
>> >
>> >
>> > Not much difference.. the diameter 0.375 vs 0.393 isn't much. Length
>> > doesn't much matter, as long as the windings fit.
>> >
>> > A bigger issue might be the permeability of the rod.
>> >
>> > _______________________________________________
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>>
>> --
>> Glen English
>> RF Communications and Electronics Engineer
>>
>> CORTEX RF
>>
>> Pacific Media Technologies Pty Ltd trading as Cortex RF
>>
>> ABN 40 075 532 008
>>
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>
>