Building a Direction Finding (DF) Portable Loop Antenna | Use this loop to Track Down RFI Noise!

[@TexasEngineer]

Back in 2008 I was working for CenterPoint Energy after Hurricane Ike on Galveston Island restoring power to the island. I found a quick and easy way to tell if a power line was hot or not. In my truck I would tune the AM radio to an off channel on the low end and drive under the power line. If there was static, the power was back on. No static meant the power was still out. It worked for both transmission and distribution lines. So the next hurricane you are empowered with a trick from an old engineer.

[@DarrenN4VFR]

Cool tip!

[@JamesEdwards780]

In the oil field we did a similar trick. If you tuned your truck radio off an AM station you could tell if the inverter was running the pump as soon as you drove onto the lease. More than once the green beacon lamp was latched on but the inverter had burnt itself up.

[@AlvinMcManus]

Your callsign is perfect for a pilot!

[@angelscomputers]

I agree 100%, that's why I thought for years he was a pilot every time he says "Captain Darren", then in another video recently is when found out about the Navy. Amazing call sign for a pilot

[@manyshnooks]

Unless you need to go into IMC :)

[@FocusedUpward]

@@manyshnooks lol.

[@normandavis6569]

To make even scoring on coax I find a small tubing cutter to work very well. When cutting through the outer jacket, you can feel the shield Jen you have cut through the outer jacket. The cut is clean and circular. No razor blades or box cutters needed and possibility of cutting your fingers is greatly reduced.

[@DarrenN4VFR]

Man, that's a good tip! Thank you.

[@AubsUK]

Nice video, thanks for sharing. I was frustrated when you didn't put the screw thread on and a few minutes later realised you could still do it from the other end 😁 One thing I would ask, at 16:30 you gave a demonstration with audio. It would be beneficial if you could cut the music that's playing while doing that kind of demonstration.

[@chrisst8922]

Always used to see those in films like Where Eagles Dare on the roof of a German truck when they're trying to triangulate the location of the resistance radio.

[@grumpy_ken]

just watched a demo of that WWII tech, and it is incredibly accurate kzbin.info/www/bejne/bJ62qmCfdp2laNk

[@grumpy_ken]

very cool antenna build, I will be experimenting with this

[@brentjohnson6654]

New subscriber here. Thanks for this video. I am wanting to use a loop antenna with my tiny SA to see if solar panel controllers are giving RFI. You mentioned being a pilot. I have my PPL which I earned as a 17 year old in 1975. Thought I would fly in retirement again but health had other ideas. So I took up another cheap hobby and was licensed in 2020 as a general. The VE’s talked me into taking all 3 tests. I was 3 questions away from passing extra. Funny thing - I couldn’t remember the RLC model of antennas from my engineering classes from the 70’s. Sorry for so much information. All the best from north Texas. 73 de KI5HXM

[@n1kkri]

What range of frequencies is that size loop good for?

[@kd5inm]

When Darren said "score", I could hear Beavis and Butthead chuckleing in the background... He's gonna score...😂

[@DarrenN4VFR]

@@kd5inm 😆

[@kd5inm]

@@DarrenN4VFR I subscribed to your channel. I saw you mentioned in QST. I did something similar to your apache case with my FT-897 w LDG 897 tuner. My 897 has the batteries and charging setup that are scarcer than hens teeth so it runs 20 watts and I have a home modded switching power supply good to 30 amps I can run it from as well. And I have some lovely Messi & Paoloni coax to go with it... hihi that Mr Messi personally sold to me... he's a great guy btw... continued good luck with your channel. I will be watching. De KD5INM

[@wd8dsb]

Hi Darren, very nice construction video. The design you used looks like the design I first saw published by the Radio Amateur Society of Australia in which they were using in on HF frequencies. A few years ago I built a DF loop based on their design and tested it using a preamp versus numerous other designs after I noticed it was really deaf below about 10 MHz compared with other comparable sized untuned shielded loops that I have used (really deaf down on the AM broadcast band as an example). Sure enough what I found was that between 14 MHz and 30 MHz the design identical to what you used worked well and provided gain similar to what I call the traditional shielded loop design but as I went lower in frequency from 14 MHz on down the gain dropped rapidly versus other comparable size untuned shielded loop designs. Just FYI in case you try and use it on MF/HF frequencies. 73, Don wd8dsb

[@RFeye]

18 inches circumference works well on VHF and 11 inches for UHF direction finding loops.

[@sleeve8651]

I think you should do a review of the proper way to install this type connector ! As I believe the shield is supposed to be under the crimping sleeve ! ☝️🤨

[@z3r0c00l2]

Amazing

[@bill-2018]

A similar loop was made by an amateur in the 1980's to track a C.B.'er coming on 10m causing a nuisance. A small value capacitor to tune it. He was knocking on the guys door in ten minutes saying if he didn't stop he'd contact the authorities. He stopped. G4GHB.

[@jhonsiders6077]

Not a good idea now days you may get shot ! My gate has phone number beginning of driveway there is close to 1/4 mile then up a hill to my front door that’s a threat .sounds like a sad ham to me .

[@bill-2018]

@@jhonsiders6077 I'd have just told the authorities and let them deal with it. Why should we let our hobby be interfered with. Jealousy? We don't do it to them, we have far more interesting things to do with radio and more frequencies.

[@jhonsiders6077]

@@bill-2018 I have had my general since a teen my uncle fitz was a ham that got me interested in the hobby he was always the guy that said why do so many think they should police the airways ? I am the same way it’s not hurting me . When he passed away I inherited his shack of gear my kid was never interested in it but was into radio . I put together a low power FM transmitter for him and his buddy’s to play with they fooled with that for years until he went to collage kept them out of trouble and off the streets . Just ten watts and being out in the country never bothered a commercial station but there was one guy that threatened to turn me in over it I said if that is your way to make brownie points do so . That was the end of it a guy on here coined the term Sad Ham I have to agree with him . Even as a teen the older operators when they heard me talking would break in and demand my letters I would ID my station I got good with MC and could do 15 WPM just so my voice was not used . That is what is turning off young people to it and we are loosing parts of the spectrum being sold off for other uses .

[@bill-2018]

Why? Because they interfered with our communications playing music and noises over the top of us! What is difficult to understand about that? They have 27 MHz to do that on. Stay off 28 MHz is all we ask of them. If you see me as a Sad Ham then so be it! I'm not having my hobby ruined by some idiot and neither did the amateur concerned. You might like it but most don't. G4GHB.

[@jhonsiders6077]

@@bill-2018 We have so many more places to go is why it does not bother me spin the knob on my old Viking . plus really how many of us did sneak to the CB bands and have some fun with over a KW of power ?? no ones a saint .

[@RFeye]

If you actually short the inner conductor to the braid at the end of the cable where the centre of the PL259 plug is not connected, you will find the loop is a lot more sensitive and the null sharper.

[@sfrahm1]

Yep, I saw that too, that's the way I made my own, with the inner wire shorted to ground on one end. I used a piece of some old 19mm CATV hardline 1/10 of a wavelength in diameter to make the loop out of, put a trimmer capacitor across it and mounted it to a dowel rod for a handle. I could actually even use it to transmit on when using only a couple watts. I was the target when we were doing some fox hunting & whenever I saw my friends were getting close I switched over to the loop to transmit on & pointed the null at them, which made the reflections stronger than the direct signal. They finally gave up & I had to explain the trick to them.

[@hubercats]

How did you settle on a 90 cm loop circumference? Was it simply to keep the antenna small for ease of handling? - Thanks!

[@brandonporter4227]

Watched this video a couple times through and liked the design. This is the only thing that bothers me though. He doesn't explain where the 90cm circumference comes from and why the gap in the shield is 20mm. I'd like to use the design for a 2m foxhunt antenna since I have a couple small scraps of LMR400 laying around, but without the details, it's difficult to figure out. I see another commenter said for 2m to make the circumference 18 inches, which would be about a quarter wavelength. Makes sense. As best I can tell, his 90cm antenna isn't made for a specific amateur radio wavelength and is just a noise detector.

[@DL5LC]

Many thanks for the very interesting projekct and your great execution! vy 73, Andy, DL5LC

[@staceyward777]

I love the way you call the cable jacket everything BUT "jacket"...."sheath" "outer black protection"

[@DarrenN4VFR]

Hahahaha, your right.

[@zukjeff]

is the 900mm the 1/2 or 1/4 wave ( what frequency is it made for ) ?

[@gobstoppa1633]

topman.

[@ericb.3580]

Did you ever have a chance to test this outdoors with aerial powerlines ?

[@DarrenN4VFR]

No, I haven't tried to use it with powerline noise yet. I've been busy with work and family.

[@hubercats]

Hi Darren - I’m interested in having a DF receive-only system that covers as much of the spectrum as possible. I don’t need to transmit. Are you able to recommend any hand-held radios that I might consider? - Thank you!

[@azarellediaz4892]

Well made and explained. Thanks. Can this be used for a “Fox Hunt” in 2m or 70cm bands?

[@RFeye]

If you make the loop 18 inches in circumference it will work on VHF and for UHF 11 inches works fine. If you short the braid to the centre conductor of the coax at the end where the centre of the PL259 plug is not connected to the coax centre conductor, you will find the loop is more sensitive and has a sharper null.

[@CrucesNomad1]

Subscribed

[@DM-fz3ly]

Any chance you can provide an electrical drawing of the antenna? or a link to resources describing the electrical/RF theory? Thanks

[@DarrenN4VFR]

Sorry, I don't have any drawings. I was emulating the process from another person.

[@sammas7440]

will this work for 40 meter band to find RFI?

[@corradoQC]

I wonder how much of a difference cutting the shield in the middle section makes. I've been using the inner loop of my mag loop antenna with good success to find RFI.

[@JayN4GO]

A lot for me

[@mrtonicsvls3624]

Altrimenti diventerebbe un tappo e non un'antenna, come un circuito chiuso su se stesso.

[@BLACKHEAT1028]

Would it make it more sensitive if you cut the away the foam for the middle section and just had the copper? Nice video

[@epedja]

Nope.

[@BarefootBeekeeper]

Why 90cm?

[@sparkybluefox]

Do you have to have an AM receiver , or could an FM handheld scanner work as well ?

[@jimeppright7862]

Noise is AM - there is no FM component to it. So, if you are looking for noise, and FM receiver will not work.

[@jansmejkal7650]

Co to pijete?😀

[@swartzautoman2]

My nephew is an active Seabee radioman

[@DarrenN4VFR]

I was a Radioman too for 24 years.

[@swartzautoman2]

@DarrenN4VFR I saw that in your information. My nephew has only been in a few years now but he is absolutely loving it. I hope to learn as much as I can from him

[@actsrio]

73 from Brazil PY1TS! Work fine tô fox hound???

[@abdellahreda2760]

Good job . 73 QRO, CN8RED

[@alessioschiavone3898]

ON5ALE my callsign

[@glyn1]

WATCH YOUR FINGERS One slip could be a TENDON Seen that two fingers ULESS ZL BP

[@DarrenN4VFR]

Thank you. That's dangerous.

[@KB1UIF]

Hi, to prove the directional property of your loop, your demonstration would be more effective if you turned off the apple computer that was on your desk. The RFI could have been stronger from the direction of the apple computer than the LED lamp. As you turned the loop it was broad-side on to the screen/computer. Having a more obvious source of RFI would have been better proof to convince viewers of the directional properties of your loop. I was not convinced that the thin side of the loop was the direction of the noise. 73.

[@GregoryFenton_UK]

Thanks de M0ODZ Greg