jgthesoundguy

Awesome information, Glenn! It's nice to have it all consolidated in one location. I'd like to add a perspective from the live sound world that may be helpful as well. When deploying your LPDA style receiving antennas, polarization is an important consideration. In my field we use handheld RF mics very regularly and as you might imagine, the angle of the Tx varies quite a bit during a performance. As a result we need to be able to receive waves that can be in any orientation. The solution that is often employed is to place the two antenna 90º to each other and 45º to the ground plane. In other words they look like a V in the air. This allows either antenna the best chance at receiving waves in just about any orientation. The majority of waves aren't going to be coming in all fully horizontal or fully vertical. That being said, if most of your Tx's in the field are placed in the vertical position most of the time, then having your antennas placed vertically makes sense. However, if you have a mixed bag of vertically placed and horizontally placed Tx's in the field then I would encourage the V style setup if you're having issues with the fully vertical placement of the LPDA's. Another consideration for receiving antenna is to make sure they are not too close to flat, reflective surfaces like walls and especially corners in buildings. Radio waves are just light waves we cannot see and they will scatter just like any other light source on reflective surfaces. Placing an antenna array in a corner will create all kinds of standing waves, hot spots, and cancellations that will make for a bad time. I hope some of that is useful to someone! Jeremy Grodhaus

This is certainly outside of my wheelhouse as I’m not an RF or electrical engineer, but in my mind the following makes sense. The receiving antenna are tuned to a certain range of frequencies which it will happily chuck down the line to the receiver. If you have a very close transmitter that falls within that range, the antenna will happily send that down as well. Too much energy hitting the receiver can overwhelm it and it won’t be able to properly tune the desired frequency. So to me, having a filter earlier in the chain makes a lot of sense. It’s akin to getting a HPF early in your audio chain so that the extra low end doesn’t suck up available headroom on the headamps. The math behind these filters, I believe, is the same so that’s where my reasoning comes from. Continuing that line of thought, it also seems reasonable that additional filters down the line will stack and could potentially cause unwanted artifacts due to phase shifts and the like. So my view would be to filter early in the chain (with a quality filter) before the receiver and let it go after that unless there seems to be a problem that only additional filters can solve.

Not an electrical engineer so I may be mistaken, but I do not think this is correct. My understanding is that the filters stack and that is precisely how we achieve higher order filters. So if I put a 1st order filter of 3dB over octave with a corner freq of 80Hz, then place another 1st order filter at the same corner freq, I’ve made a second order filter of 6dB over octave. In the analog world this is true and I think once you get into digital the math is still true but now you’ve got other cool stuff (using FFT) that can take you farther. Time and frequency is akin to Heisenberg uncertainty principle in a way and it’s fascinating to learn about. Anyway, on to OP’s question: It has to do with headroom at the preamp stage. Subsonic freq’s take up a lot of energy and will suck up your available dynamic range in the headamp. Immediately following the headamp on a mixer is the HPF, so if you can get rid of it beforehand then all the better. It’s not such a huge deal with modern preamps, but that’s why the cut exists at the mic. Now it is a big deal when you get into the RF world because you only have so much dynamic range with which to modulate the signal. Unnecessary low end can trigger the compander which will broadband compresses everything and is not recoverable on the receiving end. Again, modern digital gets around this a bit because once the signal gets encoded into 1’s and 0’s it’s just a chunked data stream being sent. However you still need an analog front end before the ADC so the first part of all of this discussion still stands. In short, HPF everything at least a little bit and the earlier you can reasonably do it, generally the better off you are.

Not a doc, but I always see 8k-10k S’s on a vocal mic when I run my RTA on a live rig. And if I low pass and sweep down, I 100% notice a change well before I get to 6k. And this would be on a standard sm58 dynamic mic. That plastic capsule isn’t exactly known for its 20k reproduction. Hahaha

Disclaimer: Not an electrician; do your homework before messing with this stuff or better yet, hire a professional; seriously don’t listen to some random guy on the internet. In power generation the “earth” is the literal return path that the neutral is bonded to. So when you tie a building into the grid, each structure makes the connection back to the ground to complete this path. But with a portable generator the earth is not used as a return because the generator is the source of power and it has no connection to a power generation plant. Instead the neutral and ground lines are bonded together and are grounded to the frame of the genny. This makes the whole generator and anything attached to it a floating system which is totally fine and safe. But in a highly energized atmosphere a lightning strike that may hit the genny or any equipment attached to it has only this self contained system to dissipate the energy through. Eventually it will dissipate into the ground (just because of the huge potential difference between the earth and the atmosphere), but not without going through every single wire, chassis, and person in contact with it first. So it’s not like a hit will just take the genny out; it takes everything out, and that’s a lot of equipment and people all sharing a physical connection in one isolated network. And just like @documentarysoundguy said, any metallic, elevated, positively charged surface (looking at you aerial antennas) can attract a potential strike, especially in an open air situation. The whole idea is one of safety and an abundance of caution. It simply isn’t worth the risk. I work primarily as a live sound engineer and any time there is an energetic atmosphere and strikes within a mile of an outdoor event using portable power and an elevated stage, things get shutdown until it’s all clear. Rain is fine; lighting is no bueno. Even indoors isn’t totally immune to an energetic atmosphere. I once had a large, visible, and loud static discharge off of a sub stack into the air. The speakers were sitting on rubber shock pads to keep them from moving around and the constant moving of the speaker cones, that were coupled to the air, generated a sufficient enough potential difference that it arced. Outside was a very beautiful and active lighting storm with no rain. It was the most bizarre thing. Anyway, all that is to say it’s just a good and safe practice and there isn’t anything particular about the generator other than the entire network being electrically isolated which in and of itself has a higher probability of danger in an electrical storm. I should also add the caveat that I’m not an expert in this at all and this is just my best understanding of the subject.

I snagged up a couple of Gego GPS trackers for this season. Little flat rectangle devices that use Bluetooth when in close proximity and GPS for long range. You have to buy an annual service plan for the GPS part, but the Bluetooth part works all the time after you buy it. Not too expensive. Haven’t had the chance to extensively use them yet. My purpose is mostly for checked luggage not making it to destination and knowing which direction to send authorities to if someone walks off with my kit.

Hi all. First time posting here. I primarily do live sound and when I first learned about this technique, the RF tech also educated me on the fact that you shouldn’t fully enclose your Tx’s while the transmit circuit is on. All of that RF energy converts right into heat in an enclosed area and the units can get hot enough to catch fire or at the very least damage something. So if you hop on board with the bread tin trick, don’t stack them or otherwise cover all sides because you might be a sad panda.