Recently I decided to use some of my vast amounts of spare time (as if I have any of that...) to hang a dipole for 6m in a tree.
I have it tuned and can hear some beacons.
I don't yet have a balun for the dipole. Although I have toroids, coax, connectors, a NanoVNA and have worked out how to S21 sweep a balun, I do not have a starting point recipe for a balun on 6m.
Now I guess I could start from scratch, pick a toroid, wind some coax on it and test it, then rinse and repeat until I suss it out but I am, on the whole, lazy.
I have both 31 and 61 material ferrites.
Does anyone have a starting point recipe?
This is going to sound like a stupid question (it sounds stupid to me
) but if the antenna is tuned, why or what function do you want the balun to perform?
If its just to stop stray RF coming back down the coax, 6 (ish*) turns, 3-4" in dia, of the coax feed at the antenna should sort that.
* Depending on where you look, the # turns varies between 3 and 11.
Hey Terry,
I would like to use a balun as it is a balanced antenna fed by an unbalanced feed line.
Additionally, I have brand spanking new NanoVNA and wanted to have some fun with that too.
(I am not a fan of air core/ugly baluns. I have not been very successful with them as common mode chokes.)
Ok, have fun.
Not having (yet) any 6m gear, I don't have any direct experience but a quick troll with Google shows almost as many options as stars in the night sky
With a bit of luck, one of the 6m regulars will pop in with a practical idea or two.
(30-05-2024, 12:43 PM)VK5TM Wrote: [ -> ]With a bit of luck, one of the 6m regulars will pop in with a practical idea or two.
That's what I was hoping for
Colin
Unless you have a fairly significant coupling factor between one leg (or both) to the coaxial feeder then the nanoVNA will not really show any significant difference between the no-balun or a balun fed dipole. It is showing the effective load impedance (R/L/C) at the test end of the cable, not how that impedance is achieved at the far end.
The style of balun is unimportant in your case.
It could be an approx 1.5 metre sleeve of conductor (eg 1/4 wave of RG213 braid) over the outside of your existing coax feeder, finishing just short of the feed point and insulated from the braid from that point and connected to the feeder braid outer that 1/4 wavelength away. Messy to achieve but would do what you need.
A 1/4 wavelength of the main feeder coiled up as an air-cored coil just before the feed point is just as effective and easier to achieve. Use a bit of 40-50mm PVC plumbing pipe as a former if you need to get the shape and hot glue to its adjacent turn then heatshrink the whole lot to maintain shape and the PVC former can be removed - or left in place.. Your choice.
The same criteria applies though - minimise the coupling between either arm of the dipole to the coax feeder by perpendicular positioning of the feeder, balun or no balun.
Coupling between the feeder and the dipole will tend to skew the polar pattern more than anything else, but with a dipole that is not a major concern.
73 Doug
Thanks Doug.
When I said having fun with the NanoVNA, I should clarify that as it is getting down to low single digit temperatures here in the evenings, I was envisioning sitting near the wood fire, playing about with the balun/s and keeping warm, rather than playing with the antenna per se...
Colin
I might be nearly a couple of thousand KMs north of you but our overnight temp this morning was 6.4C, so that puts a similar lump in doing things outside too.
Tonight I am sitting near our wood heater (/fireplace) in our lounge room just short of 9PM, 22C inside and < 10C outside and still dropping... Similar minimum expected in the morning, and hopefully better than yesterday's 5C at 7AM.
The thought of trying to use my nanoVNA inside on a 6M dipole had not occurred to me, balun or no balun. It really would have to wait until the temp was a little more desirable - like midday-ish - and be ouside in a nominal free-space environment to make any sense !
73 Doug
Next morning PS : 5.4C at 7AM today !
It's a funny thing. For the first time in my adult life, I finally have a couple of large sheds where I can set up a couple of workbenches and do the things that one does at workbenches.
However, to get the sheds we had to move to regional SA.
So when the temperature is hovering around 0° and below or 40° and above the last place you want to be is in a big metal shed.
Recently I have been pondering just how much it would cost to build an enclosed room in one of the sheds that I could heat and cool...
Yep, haven't been in the shed to do anything serious workbench wise in a looong time.
I too investigated doing the small room in the shed and decided it was cheaper to commandeer a spare bedroom and fit a reverse cycle aircon.
Trouble is, the get up and go to get up and do it has got up and left
I managed to get a small amount of time this afternoon to rug up and get out to the shed (before the firewood delivery turned up).
I grabbed a FT140-61 and wound ~12 bifillar turns of 1.25mm diameter enamelled wire.
Across the 6m band it shows a pretty much flat S21 LOGMAG through map of between -20 and -21dB.
This seems adequate to me.
Across the HF band the minimum was about -15dB at 80m then better than -30dB from 7 to 30MHz.
I have more wire and different cores, so once I have split and stacked the tonne and a half of firewood, I may try a FT240-31 core.
(this assumes I can muster any energy after doing the firewood
)
(08-06-2024, 08:25 AM)VK2CSW Wrote: [ -> ]It's a funny thing. For the first time in my adult life, I finally have a couple of large sheds where I can set up a couple of workbenches and do the things that one does at workbenches.
However, to get the sheds we had to move to regional SA.
So when the temperature is hovering around 0° and below or 40° and above the last place you want to be is in a big metal shed.
Recently I have been pondering just how much it would cost to build an enclosed room in one of the sheds that I could heat and cool...
Why not insulate the shed itself ?
I did that with mine using Foilboard from Bunnings and its made all the difference. I had the ceiling insulated by the shed builder as it was being constructed but it shouldn't be too hard to add insulation to the ceiling after the fact.
See pic attached of my shed with the insulation nearly complete.
cheers
Tim
Hi Tim,
I had considered that but the effort would be large - it is a 12x7m four bay shed that I have installed shelving pretty much right around.
The roof is insulated, the walls aren't.
Also the big sliding doors do not seal in any way, shape or form...