I started writing this post on my phone while on an airplane. (LAX to Pittsburgh) I also started to draw my charts while on that same shaky long flight. Lets just say these charts look like a 4th Grade Science Fair project but not the kid who wins, those charts always looked good. So in the spirit of the 4th Grade I will write this post like Science Fair project. Enjoy.

And if you aren’t sure what the Sennheiser G2/G3 EW100/EW300/EW500 SMA mod is check out this post.

https://holdforsound.wordpress.com/2016/10/27/sennheiser-g2g3-sma-mod/

 

Thesis Statement:

The Sennheiser G3 SMA Mod will increase usable range and give better stability of the signal overall.

The Constant Control Subjects:

Stock Sennheiser G3 Reciever tuned to 516.150MHZ after running a scan

Stock Sennheiser G3 Transmitter synced to RX

The Variables:

Sennheiser G3 SMA Reciever

RCA Dipole Antenna

PSC Log Periodic UHF Antenna

Remote Audio Miracle Whip Antenna (sometimes branded as the “Stiff Antenna”)

The Test:

I drove an hour outside of LA to the La Verne California. There we found a empty baseball field and setup in left field (or was it right field… is it like stage left where its all about the peopling performing for the audience… IDK) and we had the transmitter placed in our subjects pocket. We used a Sanken Cos-11D with the extra cable wrapped around the transmitter. Audio input levels were set so that the peaks are just bumping up against the Sennheiser’s limits for the best signal to noise ratio. The subject walked from Left/Right Field across the outfield and into a neighboring ball field. No metal fences came between the TX and either RX used in the test. See the diagrapm below.

baseball-field

With each antenna change we repeated the yellow path of the transmitter. We used the following parameters to determine what we’d call “usable range and give better stability of the signal overall.”

The understanding of what is “Usable RF” and what “Some RF Hits”  was based on if  the editor of a cheap MTV docu-follow would have to use subtitles in order for the audience to understand what the dialog was suppose to be. “Some RF Hits” is acceptable on these shows. For what qualified as “Usable RF” was based on the standard a post audio supervisor would use on if the audio was audible enough for a feature film.

The Results:

Here is a poorly drawn chart of the results.

2016-11-10-12-30-32

The results are shocking and very interesting. Some things to note is the stock antenna’s RF signal to distance felt very much like a linear scale. For every foot you away from the receiver, the RF signal diminished equally. The other 3 all had far less overall declines in RF signal but eventually all of them felt like they a hit a cliff that resulted in a steep drop off in RF. The distances between the 3 also was remarkably similar despite the RCA UHF Dipole being a 1/2 wave and the Log Periodic adding the most dB gain.

The Log Periodic did reject the most outside RF interference. Second was the Remote Audio Stiff SMA Antenna, and the Dipole and stock really tieing when it came to rejecting outside interference. This shouldn’t really be any surprise, the LP and the Stiff Antenna are positioned to recieve RF waves on the vertical, TV UHF signals are broadcasted on the horizontal. The stock antenna is bent limp anf the RCA UHF Dipole is very floppy because its a thin strip of metal in a Dipole antenna pattern printed on flexible plastic. An antenna that is stiff and on the vertical pickup instead of on the horizontal gives you a 6dB in separation between your transmitter and surrounding UHF TV signals in the same spectrum.

The other thing we noticed was the lack of RF Hiss in the signal within zero feet to max usable range. So often the G3 is said to have terrible sound quality. That is no longer the case. The audio was more than usable in for most productions.

 

 

The Science:

 

So what’s the science at play and why do 3 of the antennas have similar results. Simple, the Inverse Square Law.

The further the receiver is from the transmitter the less “RF waves” each square gets. Each square in this chart can be thought of as an antenna. The further you get back the signal gets cut in half, and in half, and in half again. Here is a chart that shows the diminishing return of a 30mw transmitter.

 

Now different antennas do help recieve these smaller fractions of a signal and add dB gain so receivers can read that signal BUT there is a limit. Here is a simple way to understand that.

RF Signal = Base_Signal + dB_Gain where Base_Signal > 0

(Base_Signal + dB_Gain) > RF Squelch

dB_Gain= postive/negative numbers based on boosters and cable length

So at around 150-200ft we noticed the G3 RF Signal < UHF_Interference  depending on which antenna we used. And just beyond this range we noticed a dramatic spike in RF static and RF Hiss. This can be thought of as the fraction of the 30mw was too close to zero even with dB gain added and no longer greater than atmospheric RF. Adding gain does not help pickup fractions of a signal, it just moves the signal further down longer cables while trying to overcome the cable's natural resistance. 75 Ohm cables offer too much resistance and will kill your signal. 50 Ohms hurts your signal less and doesn't need a boost over short runs.

So, no matter what antenna you use after the mod, it can be said that 30mw can only go so far according to physics and that's what we've proven today. I think personally the cost/size/results of the Remote Audio SMA Stiff Antenna really show that its the best choice. Plus with a simple right angle adapter can still be used when you tip your bag on its side when you place it on a cart. This also means you can set the squelch on your G3 to low and really enjoy your new found range.


profile-picAbout the Author

Andrew Jones is a location sound mixer based in Los Angeles. He started in the TV and Film industry in 2004. You can email him at  Andrew@HoldForSound.com

www.HoldForSound.com

Advertisements