Building a Random-Wire Antenna With a Choke, pt-1/2.
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- เผยแพร่เมื่อ 30 ก.ย. 2024
- For a shorter HF antenna the "Random Wire" antenna is a good option provided that you use an RF choke to get rid of troublesome common-mode currents. Here I combine both the 9:1 UNUN and the RF choke in the same box for a tidier installation. This antenna is typically used with a tuner and is multi-band. Max power? 50W, maybe... Check out part 2 for performances.
Watch Part-2: Working on it...
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9:1 UNUN non resonant end fed antenna is my favorite field antenna. I get coverage on every band from 70cm to either 80M or 160M depending on wire length. For me in the field it's the ultimate all band antenna. Is it the perfect radiator, no but it works perfectly well. I have several of them I have made to loan out to new HAMS. Again, it's a great all band antenna to get someone started on the HF bands.
Edited to add: Also they are not really "random wire". The length is quite critical to get all band coverage.
Absolutely, "random" is a misnomer..
Outstanding Gil! I absolutely love your antenna builds.
Thanks Julian!
La boîte jaune ou la trouvé faut t'il la fabriquer en 3 D. Merci d'avance Gilles. En français c'est mieux.
Of course putting the choke right next to the transformer prevents the coax shield from acting as a counterpoise.
EMP shield? So you turn your house into a Faraday Cage? That would be interesting as a radio ham! 🙂
No, it just grounds everything. Not 100% protection but better than nothing.
Je sort d'un opération.En retrant dans ma chambre j'ai vu ta reponse et ma mère m'a montré par téléphone les photos de mon yaesu fraîchement acheter donc je suis doublement content. Merci
Bon rétablissement!
Je prendrais une boîte à gâteau sinon. Merci encore de ta connaissance c'est grâce à des gens comme toi qu'on se dirigera vers le radio amateur. ( diplôme en main bien-sûr.
Merci, elle est ici: www.thingiverse.com/thing:5907022 sinon je peux vous l'imprimer pour 14 Euros, envoi inclus: gil@radiopreppers.com
Ben merci je vais me pencher sur la question. Je verrai bien ce que je ferai .73 comme on dit avec la CB. Et bonne continuation.
1. I like the idea of 2 in 1 - 9:1 resistance transformer and choke, but why does it seem that the windings of the transformer are not 9, but 8, or am I wrong?
2. From the studies I have seen about the two types of toroids - if they are exchanged, better results will be obtained. I'm sure. de LZ1MD 73
I just had this idea last night, seeing how most ununs need a RF choke I don't understand why they are not a popular commercial item. They shouldn't interfere with each other because toroids are self shielding.
If you used 550ohms instead of 450ohms for testing with VNA that is why you got a bit high SWR on 40.
J'ai juste besoin de savoir quelle est la grandeur de l'antenne est de l'autre fil banane merci.
Bonjour la.longueur du fil d'antenne peut être tout sauf une demi onde sur les fréquences utilisées, généralement 8m. Le fil de contrepoid, je mets environ la moitié du vertical. En mettre quatre aide beaucoup aussi..
Gil, nice design. Since your design includes an integrated choke, this in theory would eliminate the coaxial as a counterpoise. So a counterpoise should be required to make it work. I have had a good experience with random wire antennas, also random wire antennas provide you with more wire length options and access to WARC bands. 73s
I want to add that the use of a counterpoise and a choke is what may confuse people the most when setting up a random wire End Fed antenna. I prefer a separated 9:1 UNUN and Choke, because it gives me the option to either use the coax as a counterpoise or choke it out of the equation if the coax length is not working for me. 73s
Yes, good point.
HA HA HA! Not that finger... Then he switches hands and shows a defiant 'V'. Right. Lets get on with the video
J'ai bien aimé la demi-onde, sinon ! Bonne continuation.
Consider having the 2 toroids at right-angles, forming a T.
Your common mode choke stays the same, but you no longer have to worry about your antenna wire having to cross over.
I would love to have a coiled microphone logo displayed when printing the case. That would put it over the top! :)
We have been looking for an small HF antenna project for the kids 705, this is it.
You don't need a choke if the secondary of the 49:1 transformer is NOT connected to the primary. Use a counterpoise on the low end of the secondary so there will not be any common mode current on the coax. Adjust length and position of the counterpoise for lowest SWR.
It's a 9:1, not a 49:1. No choke is necessary with a half-wave wire and a 49:1; it's just like a dipole. However this is a 9:1 with a random wire and the primary is connected to the secondary.
@@RadioPrepper Do not connect the primary and secondary. Use a real counterpoise on the secondary. No common mode current.
LOL! Gil you have great ideas and enthusiasm but you really must curb this need to smother solder joints with glue BEFORE testing! (And trying to hand drill holes in large boxes, without using at least a cheap table vise to hold them, is just an advert for Bandaids!). I'd be very interested to compare the on-air performance of this layout using the ferrite as the transformer and the powdered iron toroid as the choke. And of course magnetic coupling between the toroids can be minimised if they are set at 90 degrees to each other - a bigger box is easy if you are 3D printing them.
Guilty!
Fascinating I’ve been playing around with the position of the ATU with the 9:1 unun when the radio isn’t close to the antenna.
I keep the choke close to the ATU with generally a 1-3m patch to the UNUN
I see you’re loving the new knife (with new cut on the finger!)
I’ve built a QRP 9:1 unun using three strands of twisted multi strand wire from an Ethernet cable - I’ve had good results and wonder why it’s suggested to use solid wire, other than the chaos of flexible wire compared to enameled wire. Any ideas?
The original document shows insulated multi-strand wires with colored insulation but I think solid wire stays in place better..
The original document shows insulated multi-strand wires with colored insulation but I think solid wire stays in place better..
That's a very elegant case design!
I never really built a random wire antenna until now. Ok... time to have fun and watch now 😀. 73 Gil.
I would love to see a video with one of EMP Shield's antenna units installed in a ham radio antenna, then retuned.
Don't use a powdered iron core for the 9:1, us an FT140-61 core and it gives you a little more CMI. Powdered iron cores are designed to be used as inductors in tuned circuits in things like tuners and harmonic filters, they are not designed to be used as baluns and ununs for HF work.
Did you watch the video? I explain...
Great vid Gil, I use various EFRW with 9:1 ununs and occasionally with terminating resistors, especially if you use ALE.
I want to share some Military secrets with you on the favorite ratio of the military (the 9:1) in its antennas.....
The secret is ; in order to be able to operate in the lower HF bands (especially for NVIS) you must reduce from 9 turns to 7 ! this will provide the proper inductance below 7 mhz up to 1.5mhz providing of course you have the magic lengths that do not fall into the 1/2λ formulas of the radiating wire. this will also work with the various T2FD antennas and the BBTDs as well as in vertical configs (over 6m height and never at 6 or below) be aware though that with 7 turns instead of 9 you gain efficiency lower HF band but loose more efficiency above 14 mhz. but as all compromise antennas, they are designed for specific purpose's.
in all cases though, try to never cross over the ant. feed wire over the transformer. remember though that ununs radiate the coax and rightfully you use a choke, in some freq. though the counterpoise should be as short as possible but direct ground to the dirt this will give better results. noted dearly that in your video part 2. that beautiful Mediterranean beach with pebbles gives a bad ground, I'd love to see you work the same config. in a redder dirt area like a nice French park. I'm sure you will have better results.
73's from an N2 in SV0 land!
Great info thanks! I will try it on my boat with the counterpoise in the water..
I like it! Are you going to put the STL on Thingiverse when you're ready?
It's on!
@@RadioPrepper awesome!
✋73's🎙 KD9OAM🎧📻📡
Does EMP protect from lightening?
Hi, EMP what?
Amazing stuff Gil!
Good video 73 KV5P
Maybe try the 5:1 former from G8JNJ. 6 toroids with copper tubing inserts and wire wrapped. Similar make to the Alpha Antenna balun but cheaper.
I have a kit for it, need to build it..
Sounds interesting. Looking forward to the video on that one. Maybe I should search for the original...
Amazing job.
Cool desing.
Very cool!
Excellent Job, Gill. I cannot confirm of ever had Common Mode Issues with my 9:1UNUN's but I fully agree with you that the 49:1 Transformer is more effective than a 9:1UNUN. Happy Sunday & 73 de Uncle Guenter💯👍🙋♂
Thanks! Some radios are more sensitive than others..
Thanks!
Thank you!
I really like the dual enclosure. I'm not sure about the iron core but if it works well, that's all that counts. Now I must add a 3D printer to my wish list. Haha
The T106-2 works, I have a couple UNUNs using it, and better than an FT-140-43.
I may be confused, but if you are going to use a tuner anyway, why is it not good on 40 meters (15:10)?
80 not 40... It will work but won't be as efficient..
4:10
You disprove Kirchhoff's first law ))
Counterpoise is always there. Explicit or implicit. Current simply doesn't flow into single wire, there must be second. If you don't have wire your counterpoise are the coax, your radio, your hand.
Yes! But I don't want it to be the coax in this case so I add a wire...
@@RadioPrepper I wrote about EFHW ))
Nice project, Gil. May I ask, what instrument are you using to measure the SWR? Is it a nanoVNA installed in a custom box, or perhaps something else? Thanks
Hi, no, it's an EU1KY analyser..
@@RadioPrepper Thanks!
Hi Gill, I've made up a random wire with a couple of short lengths of ~25mm diameter PVC tube sections. The first has the 9:1 with optional terminal for a counter poise wire, then a second tube with 1:1 choke balun.. I normally use a length of coax between the transformer and the choke as my combined cp and feed line back to my operating position works well for me!
Great, I am curious to see if it will work with the toroids so close..
@@RadioPrepper yes will be interesting! It should work great, especially with a counterpoise terminal between transformer and choke. Thanks for the videos, Gil!
can the choke be wound with two wires instead of coax?
Hi, certainly.
Gil, Gil, Gil...still testing AFTER epoxying? 🙂
I epoxied them as to not need a case..
I know right!
Why no glue around the torroids ? Be kind I'm a newbie.
Hi, I did not say no glue on the toroids, I said no epoxy. I once potted two transformers in epoxy, neither worked. Hot glue, however, has no effect..
Hi, I did not say no glue on the toroids, I said no epoxy. I once potted two transformers in epoxy, neither worked. Hot glue, however, has no effect.. I wish newbies did not have to ask OMs to be kind. Those who aren't are assholes..
@@RadioPrepper Thanks mate, 73 VK2LA
i dont understand why it doesnt work at 80m. is there a modification you could do to make it better on the lower bands?
It just isn't good at 80m... Using a different toroid is the solution.
@@RadioPrepper Next project, doing the same with FT240-43 and um, whatever the equivalent size of powdered iron core is! I built a 9:1 using an FT240-43 for my untuned EFHW. Since it was wet and windy and I hadn't put it up properly yet, I didn't want to go out and tune my EFHW, so I built a 9:1 transformer instead. On some bands the built in tuner in my 991 tunes with the 49:1, on other bands it tunes with my 9:1! 🙂
Well, I have no need for a higher power rating though..
@@RadioPrepper
It looks, that on the left
transformer (thumbnail photo),
the one turn is missing.
Which turn? Not important in any case..
Should be symmetrical :
six to six or five to five,
Not six to five as your photo
shows.
73 from Voytek
If it was a bifilar symmetrical design, but it isn't.. Whether it's an odd or even number of turns makes no difference. I did not even need to cross over.
Really ?
What is the function of this
transformer ? I hope, you know.
We need to block the RF signal
on the Coax Cable at this point
(the Coax Shield). This is a
reason to use of this
transformer.
The turns (both direction)
must be the same, to neutralize
magnetic field
(the magnetic trap).
@@voytekfid7734the current on the shield gets attenuated everytime it passes through the torrid.
The number of turns is completely irrelevant to this function.
The more turns the higher the CM attenuation.
This W1JR "balun" is no transformer in any way, it's just a common mode choke.