[Lowfer] Lowfer JH Loop Experiment

John Hamer wilbur0611 at gmail.com
Thu Dec 2 18:02:19 EST 2021 

Hey Guys,

I found something kind of interesting and I wanted to run it by yall and
see what yall thought. I don't have a way to monitor the current in my loop
for peak current yet, but I will have something soon. So, what I have been
doing is tuning it with either my Nano VNA or my Rig Expert AA-30, then
connecting my transmitter to it. After I connect it, the current to my
final starts off exactly where I would expect it for a 50 Ohm resistive
load, but then slowly drops down suggesting the antenna is coming out of
tune. It is not an issue with my transmitter, because I can connect an
actual 50 Ohm load to the transmitter and it behaves as it should. So, I
have been blaming this on the film capacitors I have been using to tune the
loop. I know this does not make the most sense since they should be stable,
but I have ordered some Mica's and they should be here tomorrow.

So, tonight I retune the antenna and connect it as usual, watch the current
fall off slightly, adjust the variable cap to get the current back where it
should be, and I notice the current is slightly increasing and decreasing
at about a 2Hz rate. First I am thinking there is something wrong with my
transmitter, but then I notice the vertical loop wires are slowly swaying
with the wind. I grab the loop and pull the wire towards the center of the
loop a few inches and the current changes a surprisingly large amount
suggesting I'm bringing it pretty far out of resonance. I guess since the
loop is so small, it is really sensitive to movement. I tightened the guy
wires up a bit to try and help with this, but I'm now wondering if when I
cut the transmitter on, the loop is magnetically repelling itself just a
little bit and this is causing that initial difference in tuning. The loop
sides are 12 feet and only supported at the corners. What do yall think?
Have yall seen this? Is this normal and I just missed it? It would explain
not seeing this on my Nano VNA and Antenna Analyzer since they would be
much less current.

Here is a video of me demonstrating what I saw.
https://youtu.be/mqJqFakwmmk

John Hamer

On Tue, Nov 30, 2021 at 7:54 PM N8OOU <n8oou at meekfarm.us> wrote:

> John and the list;
>
> I put a high res image of the simple LED RF Detector on my qsl page.
> The components are one LED, and 1 or 2 diodes. I think the ones in the
> picture are schottky diodes. In the loop tuner that I used on the three
> LF bands, I used only 1 diode.
>
> The pictured unit lights brightly a number of feet away from my 2m
> handheld.
>
> http://qsl.net/n8oou/ledrfdetector.jpg
>
> 73   de   N8OOU - Mike Meek
>
> On 11/30/21 2:38 PM, John Hamer wrote:
> > Mike,
> >
> > My mica's should be in this week and I think that will solve the tuning
> > issue. I bought some old 4ls style ones and some standard through hole
> > ones. They range from 500V to 5KV.
> >
> > I will try the led trick tonight. That will be really cool if it works
> for
> > me. I have never heard of that. I think I have some pretty high turn CT's
> > somewhere, so I will build a current meter when I come across them. I
> need
> > one for this type of stuff anyways.
> >
> > Yes, Your capture does seem to match up. I used the same frequency
> counter
> > to tune it, so it should be at the same place.
> >
> > John Hamer
> >
> > On Tue, Nov 30, 2021 at 3:04 PM N8OOU <n8oou at meekfarm.us> wrote:
> >
> >> John,
> >>
> >> I have used Mylar and polystyrene caps for determining the values needed
> >> to tune the loops. They seem to do ok, but after getting pfff's needed I
> >> have always put Mica HV caps and Air variables on the air.
> >>
> >> I use a simple LED - Diode as an rf detector with one lead connected to
> >> a loop end. The other hanging in free air. Tune for max brightness.
> >>
> >> I also put up this 2020 capture of JH. I was comparing the frequency
> >> from it to last night. Last night the noise level was a lot higher.
> >>
> >> qsl.net/n8oou/JHbeaconJan152020.jpg
> >>
> >> 73   de   N8OOU - Mike Meek
> >>
> >> On 11/30/21 9:11 AM, John Hamer wrote:
> >>> Mike,
> >>>
> >>> Thanks for looking last night. There is definitely something there.
> It's
> >>> hard to tell if there is a JH in there, but it definitely looks like it
> >>> could be.
> >>>
> >>> I am using some met poly capacitors I had right now for tuning the
> loop,
> >>> but I have some mica's on order. I also have a 900pF tuning cap for
> fine
> >>> tuning. Do you have any experience with Met Poly caps with something
> like
> >>> this? They claim to be pretty stable. Something is changing after the
> >>> transmitter cuts on. I am tuning the antenna using a nanoVNA. The
> current
> >>> on my final looks exactly correct for the 50Ohm load every time the
> >>> transmission starts, but over the next 30 seconds to 1 min the current
> >>> slowly drops. I'm not sure if the capacitors are warming and changing
> >> value
> >>> or if there is just a connection issue with them in a breadboard. I
> will
> >>> remove one of those possibilities when I solder everything together,
> but
> >> it
> >>> kinda looks like it's just coming out of tune. I also need to build
> >>> something to measure antenna current. I should have it all next week
> >>> sometime.
> >>>
> >>> Finals are staying cool and frequency is stable.
> >>>
> >>> The link below has some pictures.
> >>> http://jwhamer.me/lowferJH/Loop2021/
> >>>
> >>> John Hamer
> >>>
> >>> On Tue, Nov 30, 2021 at 7:55 AM N8OOU <n8oou at meekfarm.us> wrote:
> >>>
> >>>> John,
> >>>>
> >>>> Thanks for the info, I can relate your results to the tests I made
> using
> >>>> Quad Shield RG6 and RG8.
> >>>>
> >>>> I shut down WM to listen overnight. Nothing seen until Gray Line this
> >>>> morning. See the first capture at;
> >>>> http://qsl.net/n8oou/nov29210006.jpg
> >>>>
> >>>> I have a second screen comming, it looks like you went qrt at 06:30
> CST.
> >>>> The filename will be nov29210007.jpg when it's ready.
> >>>>
> >>>> 73   de   N8OOU - Mike Meek
> >>>>
> >>>> On 11/29/21 8:58 PM, John Hamer wrote:
> >>>>> Mike,
> >>>>>
> >>>>> I actually have some pretty good size litz wire. It looks to be
> around
> >> 3
> >>>> or
> >>>>> 4mm diameter.  Ill see if there is a label on spool with more
> >>>> information.
> >>>>> I'm not sure if the spool came with the wire.  I got it from my last
> >> job
> >>>>> years ago when they were trashing it.
> >>>>>
> >>>>> I still have everything breadboarded, so I'm not sure if that is
> >> causing
> >>>>> any issues,  but I will solder it all together in the next few days
> >>>>>
> >>>>> John
> >>>>>
> >>>>>
> >>>>> On Mon, Nov 29, 2021, 9:52 PM N8OOU <n8oou at meekfarm.us> wrote:
> >>>>>
> >>>>>> John,
> >>>>>>
> >>>>>> Good to have another loop experimenter. I am curious about what you
> >> are
> >>>>>> using for the loop conductor. My experiments have shown the larger
> the
> >>>>>> conductor, the better.
> >>>>>>
> >>>>>> Good Luck
> >>>>>>
> >>>>>> 73   de   N8OOU - Mike Meek
> >>>>>>
> >>>>>> On 11/29/21 5:17 PM, John Hamer wrote:
> >>>>>>> I have a 12'x12' square loop setup. I am transmitting my usual mode
> >> of
> >>>>>>> qrss60 and a graphic on 181.818KHz. I just got it going tonight and
> >>>> still
> >>>>>>> have some work to do, but if you are looking for a challenge, give
> >> it a
> >>>>>>> shot! It is aimed in the N/S direction.
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