NVIS Dipole, Hybrid Balun Vs Nothing

Рет қаралды 6,450

Crazy Chekov

Күн бұрын

Real life measurements and comparison between a dipole antenna with an hybrid balun and one without.

Пікірлер: 54

@CrazyChekov Ай бұрын

Some forgotten infos. The antenna SWR was below 1.2 ( measured with Digirig Stick Pro ) The shown values are SNR in dB Transmit power was about 7W

@oasntet Ай бұрын

Yeah, it's easy to forget that baluns introduce their own losses, so they're only useful if they're fixing a worse problem than they are causing. Obviously vital in an antenna a long ways from 50Ω like an EFHW or an OCF dipole, but a normal dipole is close enough regardless of where you put it. Even the 'imbalance' from feeding it a dipole with coax is only a couple percentage points drop in effective radiated power, less than the typical loss in a current transformer...

@m0kov Ай бұрын

A very useful demonstration. The balun is there to stop common mode current on the outside of the coax especially on receive where we want to prevent any interference picked up on the coax outer from entering the receiver. Since noise levels when operating portable are low, a balun should not be needed. 73 de Steve

@chuckcarter7864 Ай бұрын

Thanks for the comparison. You’re the first one that I’ve seen. Cheers and 73 VK2SS .

@CrazyChekov Ай бұрын

thx. with digital modes we can make now more precise field tests. ...and a field test beats every lab test imho.

@survivalcomms Ай бұрын

Thank you for sharing . I stopped using a 1:1 balun on my antennas a couple years ago due to similar results. I do use a self built sleeve choke on my feedine to address common mode but to be honest I personally have not experienced problems with common mode on a center fed balanced antenna unless I loaded the antenna on a frequency below what I cut the antenna for. I feel the 1:1 balun just induces loss FWIW. Thanks again for sharing your data with us.

@N2YTA Ай бұрын

With a resonant antenna you don’t need any type of feed line choke.

@survivalcomms Ай бұрын

@@N2YTA Yes but I use a feedline with a choke because Its what I use as I said. Thanks for sharing your insight.

@N2YTA Ай бұрын

@@survivalcomms it's not likely that an antenna will be perfectly resonant everywhere in the band so using a choke is a good idea.

@VE9ASN Ай бұрын

A coax wound balun introduces no losses, yet still stops common mode, it's a win win with no negatives.

@N2YTA Ай бұрын

@@VE9ASN yes, good point

@mewrongway Ай бұрын

Pretty kool experiment. My 44 years in ham radio has taught me that just as soon ass your sure of something,You find out your wrong!!

@CrazyChekov Ай бұрын

😊

@batica81 Ай бұрын

Interesting. My guess is it would be even more noticeable on higher frequency.

@TheSmokinApe Ай бұрын

Interesting 👍

@BusDriverRFI Ай бұрын

Gotta love some signal loss.

@uploadJ Ай бұрын

I prefer isolation transformers. Nothing will provide the kind of isolation a flux-coupled transformer provides at like 475 kHz ... baluns become ungainly at that frequency, and I use one on a 1/2 sized K9AY loop to keep computer noise from swamping real signals picked up by the antenna.

@VE9ASN Ай бұрын

I challenge you to try again with a coax wound 1:1 choke. You definitely still want to keep the common mode current off the feedline. It's likely that the only reason you're not having issues is because of qrp power levels. Hybrid baluns are typically for ocfd anyway.

@CrazyChekov Ай бұрын

will make a comparison next time...coax choke vs nothing

@jesselannigan2300 Ай бұрын

I have to second this. When you are operating QRP your reflected power is so minimal that even a poorly matched antenna will have a low SWR and will typically not introduce "noticeable" common mode back into the feed line. Now try that same setup but with 700+ watts and see what happens. It's another reason I dislike QRP, besides the obvious futility at trying to accomplish something with a -10 to -20dB hindrance, but it also gives the illusion of a well matched system that truly isn't. No rule says you have to use a balun, but they're there for a reason.

@Richard-je4lt Ай бұрын

@@jesselannigan2300 700+ watts lol , WHY ?.

@jesselannigan2300 Ай бұрын

@@Richard-je4lt Why? Because I work DX. I'm working stations over 7,000 miles, not 3 blocks away.

@CrazyChekov Ай бұрын

@@jesselannigan2300in europe energy prices are too high to power a 700W amplifier. we can only go with QRP here 😁

@shanerorko8076 Ай бұрын

In my opinion, the only thing a CM choke will do on a dipole in the field is help keep the radiation pattern consistent. Without one the outer shield of the coax makes the antenna into a un-balanced T. If you get 7 beads of 41 mix or similar mixes with a 5mm inside diameter you can make up a lightweight choke cable that has no losses. When you're at home it's more about choking noise from the power lines.

@BusDriverRFI Ай бұрын

If that's worth worrying about with the far field loss being ~2.5dB.

@robduncan599 Ай бұрын

A field strength meter reading would have been a useful gauge as to sig going out ?

@CrazyChekov Ай бұрын

hmm not sure if you can read that meter precise enough if you are so close to it. just a feeling

@robduncan599 Ай бұрын

@@CrazyChekov possible. However the band going up and down ant a /b or in this case balun/ no balun is at best haphazard? Unless you conduct the experiment over a long period?

@CrazyChekov Ай бұрын

the longer the better for sure. feel free to join testing. the more results we get the better.

@haraldlonn898 Ай бұрын

What I wonder should the current choke be at the antenna side or to the radio. As I see it the current choke should be to the radio side. I may be wrong but think about it.

@CrazyChekov Ай бұрын

not sure too. I found both versions in the internet .

@uploadJ Ай бұрын

re: " current choke " I am looking for a "voltage choke" ... un-obtainium? /sarc

@youtubeaccount931 Ай бұрын

is it what is called a guanella balun or is that something else? I have not found the need for a balun with my dipoles but I have also not run over 60 watts or so out of it, perhaps with stronger power I would need to worry about return currents etc

@CrazyChekov Ай бұрын

not sure about guanella balun. its a current balun and a voltage balun what I used.

@jesselannigan2300 Ай бұрын

60 watts max? Try it with a kilowatt and tell me what you discover.

@uploadJ Ай бұрын

@@jesselannigan2300 I could light 4 ft fluorescent bulbs leaning against the shack wall at one point running a few hundred watts carrier for AM on 80 meters ...

@jesselannigan2300 Ай бұрын

I believe it.

@jesselannigan2300 Ай бұрын

@@uploadJ on 80 meters at anything over about 180 watts keying up will cause one of my battery chargers to reset. 40 meters causes one security cam to distort. 15 meters around 21 275 will trigger the remote control to the LED strip lights my daughter has in her office. That's why there's safe distance RF exposure protocols.

@F_Tim1961 Ай бұрын

What would be even more interesting would be to use the Hybrid balun with the shield of the Coax grounded to a proper say one mtr in copper coated steel ground rod , or equivalent buried wire in damp soil to simulate what a mains powered transceiver sends to the coax when running. In the case of a low hung antenna which sees a non true differential signal at the feed point but with the coax tied to the ground plane I think you may see better relative performance of the hybrid balun in S/N on transmit. It 's not relevant to your transceiver when run off a battery pack but one day you may want to run it off a 4 A mains DC supply which will likely have the secondary of the transformer earthed to the case and then back to the ground stake of the house supply. The frequency at which you run the test is relevant too, because as the antenna rises up a more significant fraction of the transmitted wavelength, the existence of the ground underneath, in particular with respect to the E field is less significant.

@F_Tim1961 Ай бұрын

Further comment. I'm not sure why the lower voltage balun has four turns and not three. I'd be interested in any references to the design file - though Ytube comments often stop direct UR_Ls being sent. I notice that the top balun, the current balun of the hybrid seems to have four wires. I wonder why it has not been implemented with a cross over of a single pair similar to the Balun Designs 1171 (nb their design uses well separated Cu so it does not give a 50 ohm internal transmission line - I am not suggesting this is what you want). The cross over at turn number five changes the winding sense half way through the winding and thus the gross circulating flux is zero. This clearly reduces losses over a conventional non cross over current balun design. There is still local ferrite linkage between the individual pairs. It's very cunning and produces an non radiating or minimally radiating parallel transmission line. You may be familiar with this implementation and have rejected it for some reason. TEF

@CrazyChekov Ай бұрын

hi TEF, I used this wiring layout for the voltage balun/transformer.... images.app.goo.gl/4JuRFtMux5j5NTEM9

@CrazyChekov Ай бұрын

the current choke design is from DG0SA --> kzfaq.info/get/bejne/f7ajkrV6ytCXcpc.htmlsi=jIYh4DAXms9yVhin

@F_Tim1961 Ай бұрын

I had a look at the DF1BT design and there's a lot unsaid. Firstly on the Strombalun it appears that vinyl insulated figure 8 cable is used - at least in some of the designs . PVC insulation is death to RF above about 10 Mhz. The only reason it can be used on the outer jacket of RG58 is there is an assumption that there is no E - field at the surface of the braid. The PVC molecule is excited electrically not magnetically . The other point is that twin ax is around 80-85 ohms impendance normally. If it is wrapped as you have done it then you get "two coax wires " in parallel. This would drop the input inpedance of the current transformer down to a nominal 50 ohms. It seems gimmicy. The known good way to make the current balun for minimal loss is to use RG188 and provide the cross over so there is no net flux in the main core but there is magnetic coupling between the individual turns if there inbalance from shield to core caused by an differential current in the load. It seems as if a current choke is "required" after a voltage balun because though the VB converts a single ended signal to a differential one, it can't discipline the RF if the load is not electrically symmetrical. That's my take on it.

@F_Tim1961 Ай бұрын

@@CrazyChekov The five Wire voltage BN/transformer is new to me. It goes schematically Blue Red, Green , blue, Red in parallel with a green wire as a DC short in the centre of the wound set. It seems that there is an attempt to get a better approximation of a non radiating transmission line this way . I have never seen a test comparison between the five wire version and the three wire version of this design. BTW if you look at the Balun Design webpage you will see that wherever they do an impedance conversion they always follow up by a current balun. It therefore seems that voltage baluns cannot cope with driving what might not be a physically symmetrical antenna. I've never seen that explained.