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Dave Williams

Dave's DIY Dipole 'dapter - and other RF thoughts and questions

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Hi folks!

I'm a bit of a hardcore lurker here, and while I read much, I post little. I'd first like to commend everyone for maintaining such a fantastic community and resource for soundies everywhere! I've learnt (and continue to learn) so much from here. One thing that someone said (can't remember who) but it really stuck with me, was that in this day and age a good production mixer needs to be as knowledgable as possible about RF, and so I've been researching as much as possible and trying to come up with ways to improve my professional practice. One day soon I'll own a full Zaxcom rig to go with my Nomad, but for the time being I'm trying to hone my skills, and get the most out of what I have (G3s).

I think one of the most important purchases to further this ethos was an RF explorer, which immediately gave me invaluable real-time feedback on what was happening in the spectrum nearby. I also use the FreqFinder app to help coordinate frequencies and avoid intermodulation issues, and finally have been modding my G3s with SMA connectors to use external antennas / distribution (details are in the topic about this also in the DIY group). I also purchased a bunch of Nitinol super-elastic wire and SMA male crimp connectors and have been making my own whips. 

So finally to the dipole adapter! I was thinking for a long time about a versatile and easily made dipole antenna (plenty of people make them quickly and easily from coax), but I wanted it to be relatively sturdy as well as compact, and I also wanted to try and have some sort of integrated Balun. I finally discovered the sleeve dipole (which uses a 1/4 wavelength sleeve around the feeder coax as both the lower half of the dipole and also acts as an integrated balun of sorts). So with a few plumbing fittings, some copper pipe and end caps and couple of SMA connecters the 4D mk1 was born! (Dave's DIY Dipole 'dapter).

56d7da6e2993b_Dipoledapter.thumb.jpg.8ee

Key points:

# - I wanted something that could be mounted almost anywhere easily so there is a 1/4" 20 mounting point epoxy'd into the bottom which fits a squillion different common mounting thingies (pic below shows it attached to a little ball head and 1/3" thread adapter on to a mic stand).

# - I made it so that it is an adapter not a complete dipole - you simply screw a whip on the top and suddenly you have a dipole! I've yet to discover the effect of 'tuning' a dipole with only one half of it changing length though... However the parts are so cheap that having several for different 'blocks' would be no trouble - and maybe the thickness of the sleeve half of the dipole would increase the bandwidth a bit?

56d7da79dca46_DipoledapterMounted.thumb.

# - It is also pretty easy to attach to a harness (as shown) and the top whip sits above the shoulder for a good LOS to the TXs if they are behind.

56d7da8514f84_Dipoledapteronharness.thum

 

Finally, I also have heaps of questions and ideas about RF and antennas that I'd like to discuss and share so perhaps this topic could also be a place where people can talk about the sort of things that aren't normally found in HAM radio texts?

Cheers!

 

 

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11 hours ago, resonate said:

Dave, check my design, it works and it's a bit safer for the eyes : 

 

Yes this was one of the many examples that I took as inspiration thanks! Do you have some sort of balun or choke in there to help keep RF off the outside of the coax? Although for reception it possibly doesn't make enough of a difference to care about...

 It was never really the original intention to attach mine to a harness (just a happy coincidence that it works), and also as a glasses wearer, I guess I'm accustomed to the extra eye protection so danger to eyes didn't really occur to me at all! (Good thinking though!) I did also find that when attaching high up on my harness it actually angles backwards a bit so was away from my face / eyes, even when turning my head. Also it only takes a few seconds to unscrew the whip if it's in the way when not shooting.

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the design does not use a balun, it's very easy  - and works well - range is enough for 95% of the shoots i've been doing. I like the pvc build because i can attach it to the any kind of harness (even just a strap) with bongo ties, and the pvc protects the antenna from bending, so it's always straight inside the tube. Of course, it's not always vertical, but i found it does not matter as much as long it's near my shoulders.

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