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Dave Williams

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  • Location
    South East QLD, Australia
  • About
    I'm a bit of a jack of all trades (master of some?) who has wide and varied interests in all things audio (and some things not).
  • Interested in Sound for Picture

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  1. Haha yeah only 67A at 12V... But that's what I love about batteries, you can keep adding more! Given suitable bus bars that is 😁. Plus 24 or 48V means less current for the same power out. I have a little fantasy of adding some sort of motor to my cart for going up hills / stairs. It could even incorporate some sort of regenerative braking for going back down again haha.
  2. I should clarify that this circuit wasn't necessarily intended specifically for bag/cart or even audio applications. I wanted it to be applicable to them, but also cover other scenarios as well. For example this is a really cool DC input ATX power supply - https://hdplex.com/hdplex-800w-dc-atx-with-12v-63vdc-input.html that could be used to build a server or other always-on computer setup, or some other sort of application where continuous operation was important.
  3. Yes I was originally considering a capacitor to cover any break-before-make situations, and it might still be a good idea to include one anyway to reduce operator error on the A/B select switch in 'run mode'. I simply just wanted options. Yes definitely the two batteries in parallel would last twice as long (or build a bigger battery in the first place), but I also wanted the flexibility to choose otherwise and also to bypass the diodes for integrated charger options.
  4. I've had batteries on the brain lately. Not just from a production audio point of view, but also for off-grid and house-scale solar applications. I'll be purchasing a spot welder and building various types of battery packs some time soon, and have also been thinking about setting up a decent cart power distro system for a big upcoming job, but the idea of seamless battery / power switching was giving me a bit of trouble. A simple diode arrangement is supposed to work well, but I wanted more manual control than that, while also keeping it as simple as possible. The other constraint I put on myself was to try and come up with a solution that could be scaled from small in-bag systems up to large high current applications (potentially with relays / contactors instead of switches). This is what I eventually came up with and I think it solves those issues elegantly (but I'm not an electronics expert by any means). As you can see, the switching circuit consists of 3 diodes and two SPDT switches (or relays / contactors). The idea is to have two modes (transfer & run). In 'transfer mode' it simply acts the same way as a regular diode power share circuit, where the current flows from the battery with the highest voltage, and cannot flow from one battery to the other. Once the preferred battery is selected, switching back to 'run mode' will then bypass the diodes and connect the selected battery directly to the load. So with this system you could have two batteries connected but preferentially drain one all the way down before switching to the full one (or leave it in transfer mode if you preferred). Previous iterations had a problem where there would be a break in power when using a break-before-make switch to change modes, but the diode across the mode switch should allow current flow for the brief interval of time that there is a break between contacts; this diode then gets fully bypassed once the contact is made. As far as I can tell this gives perfectly seamless switching (changes in output voltage notwithstanding) so long as you only select between the two batteries when in 'transfer mode'. If you attempt a switch between A & B while in 'run mode' the break-before-make switch should cause a very brief blackout. My thoughts are that this could easily be done with manual switches, or perhaps a microcontroller and relays would be a good upgrade because then some voltage sensing could be used to automatically switch batteries if one gets to a pre-set voltage level or similar. I've read that it's often fine to use Schottky diodes to minimise voltage drop in power sharing circuits, but I wanted to fully bypass them so that there would be the possibility of having some sort of charger option further down the chain (perhaps a charger / inverter?), and this way whichever battery is selected could also be charged by that. I need to research more about which types of charge controllers can also power a load at the same time without upsetting their charging algorithm. I figure if a solar charge controller can do it, then there must be some AC powered chargers that won't mind either. It also occurs to me that you could use this circuit as a UPS type of setup if left in 'transfer mode' and one of the inputs was from an external AC to DC power supply, so long as that voltage was higher than the battery, and if you're happy for the diodes to stay in circuit, the battery would take over the instant the external dc was interrupted. Another thought is that if uninterruptible power was important to you in a mobile bag context, while also saving weight, it might be possible to have a single 21700 cell connected to a boost converter to be a temporary power supply only while swapping the other battery over (I think a single 21700 could power a standard bag for over half an hour maybe?) Does anyone have any thoughts or feedback? Cheers! Dave.
  5. Thanks! Yep, they are 2A PTC Resettable Fuses, although I saw that in the data sheet that a Hirose connector is only rated at 2A anyway, so if you were at the stage of tripping one or more of those fuses, I guess the input connectors would be at or past their limit. I might change them out for smaller ones at some point, at least it gives some protection for a dead short!
  6. Just a quick showcase of an idea I've been toying with lately. I'm thinking of this as a sort of sub-distro and it will hang off the main BDS (or could easily be stand alone if need be). It's a pretty simple device; just a poly fuse on each output.
  7. I wonder if it's possible to get stereo transmission with ZHD modulation? (Or rather 2 x mono I suppose). And presumably that would mean mono only reception with a RX200 if using ZHD?
  8. How did you end up going with this? I did live sound production and some install work for years before I got into production audio. Happy to answer questions and provide some direction if you like.
  9. Excellent! That's a fairly minor caveat to worry about Thanks for all the info folks! Very exciting times, can't wait!
  10. Hi Rado, just to confirm; that will be a firmware update that will allow dual mode ZHD reception on the likes of QRX200 and the QRX212 modules? Oh and if so, is there a known timeline for its availability? I'm poised to start getting finance sorted for a wireless upgrade, but wanted to wait and see if I'd need to hold off for a new QRX model to come out. Cheers!
  11. Hi Mingo, that sounds like a connection issue to me, I had some similar problems when the pin of the SMA connector on one of my homemade whips wasn't protruding enough (but if it works on the RX, then the antenna is probably fine). Also carefully check that there are no loose connections or shorts in the TX; I accidentally created a tiny solder bridge to the little horseshoe shaped pad when I was modifying mine and this killed the RF entirely. I haven't modified my TXs as the stock antenna is softer than my 'memory wire' ones, and I didn't want to risk it being uncomfortable for talent. Yep, so long as the sleeve of the SMA connector has a connection to the case (ground) you can run an extension of any length (subject to cable losses of a couple of dB per metre) to a dipole or LPDA, or helical etc... You could also incorporate it into a RF management / amplification system. If anyone is interested in how to calculate the various lengths for antennas themselves, it uses my favourite formula that is also used in acoustics calculations: ƒ=v÷λ Where ƒ is frequency in Hz, v is velocity (speed of light in particular medium) in m/s, and λ is wavelength in metres. Rearranged as λ=v÷ƒ we can calculate a single wavelength, and from that 1/2 or 1/4 wave whips and dipoles etc... If you want to get super finicky the velocity factor (speed of light for) of copper is something like 0.95 so this will change the dimensions slightly - Speed of light in a vacuum is 299,792,458 m/s. So the speed that waves propagate in copper is 299792458 x 0.95 = 284,802,835 m/s. So for example, my G3s sit in the 'B' range 626 - 668MHz so to create an antenna that is most resonant in the centre of that band (647MHz) the calculation is a follows: λ = 284,802,835 ÷ 647,000,000 = 0.44m So a 1/4 wave whip antenna is 0.44 ÷ 4 = 0.11m or 11cm so a 1/2 wave dipole is just two elements that are each 11cm long. However! It's important to note the relative weighting of this information. Yes these are technically the 'correct' values, but will there be a noticeable or even measurable impact if you're a few mm out? Very unlikely. There are way too many other variables at work in a real-world situation.
  12. Yep I used heat shrink tubing, which actually ended up slipping off the wire, so I ended up using a cigarette lighter flame and some hot-glue sticks to pre-coat the wire in a thin layer of hot glue so that when the heat-shrink shrunk it also bonded onto the wire really well. You can get commercial glue lined heat shrink but it's considerably more expensive. Yes! By grounding the shield / sleeve of the second SMA to the case (any piece of copper or similar wire should do) you do allow the possibility of a remote dipole antenna. A whip is (kind of) the top half a dipole anyway with the metal enclosure being the other half. (Sort of anyway, haha... 'ground plane' or 'counterpoise' are probably more appropriate terms to use). It's super easy to make a simple (albeit missing a balun) dipole from just coax cable. There's various examples on this forum and out in youtube land. I also have made up a prototype that adapts a regular whip into a sleeve balun dipole design over on the DIY part of the forum if you wanna check it out. I haven't really had a chance to do many tests with it yet though...
  13. Hi Astro. I ordered mine from eBay - http://www.ebay.com.au/itm/120476274177?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT Just be aware that it won't tin if you try to solder it directly. I found that crimp connections worked ok, but ended up filling the little SMA centre pin receptacle with solder and then inserting the wire. So while it's not a properly soldered joint it was a reasonably strong mechanical connection (perhaps as the solder cools it contracts around the wire a little?), and you can also give the pin an extra bit of a crimp for good measure. It also pays to be aware of the difference between super-elastic wire (which is the one you want) and memory wire, which will bend quite easily but only springs back to it's original shape if heated to above a certain temperature. Cheers! Dave.
  14. 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.
  15. 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). 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? # - 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. 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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