Best wireless at higher cost to avoid RF hits

L

lasikdenver

Well-known member
I am fairly happy with my Sennheiser G3's with Sanken COS 11 microphone but am frustrated with the occasional RF hit in an otherwise perfect recording. I have read that the Selectronic 400 series does not have this issue but there are so many models/frequency blocks to choose from that it is confusing. I want a small transmitter, a range of 50 feet, and no RF hits. I am willing to spend up to $2000+ and wonder if Selectronic, a better line of Sennheiser, or something else would be better. Yes, I scan for clear channels at each site with the G3, but I believe that this does not find the intermittent transmissions that hit my receiver. Also, my batteries are fine.
 
I've used $600/channel G2 and G3 and Sony UWP-V1 and Audio Technica U101 systems, and I've used $2k/channel Lectros. At some point, they will all fail. This is the risk of using radio mics. The airways are clogged, and with the 700MHz range now off-limits in the US there are more people operating in the 500MHz and 600MHz ranges. Plus, with everyone being a producer these days thanks to miniDV, HDV, DSLR, etc., there are more systems running.

There is absolutely no amount of money you can throw at a wireless system that will guarantee no RF hits. Minimized? Perhaps, but not eliminated. Diversity is your best bet (which the G3 offers), and ensuring that the transmission path is unhindered by C-stands and other metal obstacles.

The G3 is the least expensive system you can buy that's reliable. Above that, you only gain so much in signal stability simply because wireless is, by nature, unpredictable. But what does the increased investment buy? Smoother companders with less artifacting, better frequency response (audio frequencies, not transmission frequencies), more robust construction with more metal and less plastic.
 
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I don't know what the Selectronic 400 is - and can't find any internet info, but occasional RF issues are a problem with all RF equipment - if it's analogue or digital doesn't matter if another source of RF appears at much higher signal strength to your transmitter. Digital systems can have error correction, but are not immune - no signal is no signal. Signal strength isn't the real issue - because transient bursts of RF are unpredictable, and scanning for channels is probably a pretty useless feature. All it tells you is a frequency is unoccupied at the time of the scan, it can't tell you who is about to power up a system next door! My own technique is simply to have a number of channels that I favour and for bigger jobs, I often use a main powered system that has 8, 12 or 16 receivers in it - and turning the rack on and observing it for a few minutes is a better way of determining which channels 'may' be ok. The reality is that here in the UK, many users are going to get nasty surprises as a result of the analogue TV switch off and the 'digital dividend' - and many more channels will suddenly be busy. Interference from other radio equipment is also impossible to predict as many problems are caused by mixing - when two transmitters mix with each other and produce spurious outputs at combinations of their frequencies - so one is ok, so is the other - but if both appear at the same time - your RF link gets compromised. The only almost foolproof system is a spectrum monitor of some kind that lets you see what is happening in your locality, but even this can't predict interference in advance of it happening.

For what it's worth, the Sennheisers seem to have better filtering than many others I see, but you can never guarantee RF performance. Just watch the broadcasters to show how common it is. The only practical solution is double miking - with two transmitters on each person. This is quite common where absolute signal integrity is important - the first RF burst might ruin channel 1, but channel 2 on another frequency might (not will be) be ok. In permanent set-ups you can do clever things with antennae to minimise the interfering RF, once you track it down, but in set up and go systems, doubling up is the only practical solution.
 
I have two Lectro 411 systems, they are not 100% reliable either. Due diligence in set-up.. frequency selection, receiver / transmitter and antenna placement can help reception, but still not as good as a $20 cable.
 
Alex and others,

Great points! I have my G3 receiver mounted at the rear of my rig and sometimes there is a lot of metal between the antenna of the receiver and the transmitter (camera, EVF, etc.) It is mounted on a Sennheiser holder that is attached to a rear battery plate. I notice that sometimes when I move in to look at the EVF and I am in the path that the RF spikes are more likely. I also notice that when the receiver is on the back of the talent, this is more frequent. For some reason, when using the handheld mic with attached transmitter that came with the kit, there is rarely RF spikes, more common on the body pack transmitter. I also notice that when the talent moves quickly that RF spikes are more common, but maybe this is just coincidence. You probably saved me some serious money, so thanks! I am fairly happy with the quality of the audio on the G3's but realize it is not nearly as good as a wire.
 
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Is there much benefit to the Sennheiser 2000 over the G3, I noticed it can be changed in transmit power to up to 100 mw (I understand that for a strong RF spike this will not help, but can it help in certain cases?) I also noted that the 2000 has balanced XLR outputs, is that helpful for the XLR inputs in the Sony F3 (it does not mention if they are balanced in the specs)?
 
Hello Lasik,

I think you mean Lectrosonics. As mentioned, most wireless will fail, usually when you don't want them to. Frequency selection, antenna positioning, use of directional receive antennae, moving the receiver closer to the transmitter, will all mitigate dropout, but expecting 50 in most metropolitan areas is chancy at best.

The best range I have gotten with wireless is with Audio Ltd. systems from the UK. They run about $5k a set. On the east coast of the US, Vark AUdio in Cabin John Maryland carries them. You can download my trial recordings with them and the Sanken COS11 here: https://www.dropbox.com/sh/0pjmdcb8u2wcc1t/Q-hsPVTpnY

Is there a particular reason you need 50 feet?

Regards,

Ty Ford
 
50 ft. is not far, even for a G2, there are probably other issues at play. You would likely get fewer 'hits' with a Lectro or other $2k+ wireless, but that's significantly more expensive than a G2/3 100 series... and as I stated, even the top dollar systems are not totally interference free, even less so for a switch-it-on-and-shoot user.
A balanced output is really not that necessary as long as your cable run is short. (a few feet)
 
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Rick R said:
50 ft. is not far, even for a G2, there are probably other issues at play.
Click to expand...

From your own description, it sounds like you aren't very careful with either the transmit or the receive antennas. You can't take them so casually if you want good performance. With ANY wireless system of ANY price.
 
any wireless system can get hits. The higher end wireless systems are the Lectrosonics 400 series and the Zaxcom digital wireless. The one thing the Zaxcom units do that no other wireless system does is the transmitter has a built in recorder that records to SD card, so if there is a hit, or the transmitter gets out of range, you can have the transmitter recording, and you can get to those audio files later. I know lots of people that have used this feature, and it has saved them. There is a big list of other features of the Zaxcom digital wireless as well that I won't get into here. I also really like the Lectro 411 wireless and the Venue system. Really solid wireless system. The receivers can scan easily for available channels, so set up is a breeze. The advantage to the Lectros is that most rental houses carry them, so if you have some sort of failure, you can rent one in a pinch to fill the gap. The Zaxcom wireless is great, but they are expensive, so most rental houses don't carry a big stock of them.
 
"The one thing the Zaxcom units do that no other wireless system does is the transmitter has a built in recorder that records to SD card, so if there is a hit, or the transmitter gets out of range, you can have the transmitter recording, and you can get to those audio files later. I know lots of people that have used this feature, and it has saved them."

An excellent point Mr. Fisk!

Regards,

Ty Ford
 
lasikdenver said:
I am fairly happy with my Sennheiser G3's with Sanken COS 11 microphone but am frustrated with the occasional RF hit in an otherwise perfect recording. I have read that the Selectronic 400 series does not have this issue but there are so many models/frequency blocks to choose from that it is confusing. I want a small transmitter, a range of 50 feet, and no RF hits. I am willing to spend up to $2000+ and wonder if Selectronic, a better line of Sennheiser, or something else would be better. Yes, I scan for clear channels at each site with the G3, but I believe that this does not find the intermittent transmissions that hit my receiver. Also, my batteries are fine.
Click to expand...

From an RF standpoint, any 'wireless' communication should be considered to be unreliable. There are setups that can make things 'better', such as 'line of sight', and the mentioned 'diversity', but in it's essence RF is just unreliable.

RF 'waves' behave in some way like 'sound waves', and as such such things as 'echo', aka 'multipath', are problematic. Since we can't 'hear' or 'see' RF energy, it's perhaps not as obvious as seeing a light reflection, or hearing an echo... but all this adds up to 'crummy reception'... a technical term...

Just as with sound a number of things contribute to RF problems. The construction of the 'space' were the RF is used... steel used in construction, or used as pillars, will cause RF reflections. The human body will attenuate the signal so, placement of the transmitter, relative to the receiver will introduce attenuation dependent on the movement of the actor.

I think most RF mics use FM, which is less sensitive to certain types of noise, but still not immune.

In terms of signal detection for the FM receiver, I've monitored the Sennheiser, I think it was the G2 as it was several years ago... to about 200-300 yards, line of sight. However, I was not interested in 'audio quality', just detecting the pilot tone the Sennheisers have.

I believe the FCC has allocated specific frequencies for wireless mics, elimiating some above 700 MHz, and those frequencies are potentially 'shared' with other licensed transmissions. I believe those frequencies are off limits to the so called 'white space devices'.

However, this only 'works' if one has properly allocated devices for a given area.

For a given area, there can be transmitters operating on an intermittent basis, so one day the 'channel' will appear 'clear', on other days there will be something there... whether the 'interferer' relative to one's audio RF devices is 'licensed' or operating outside of a licensed band, is unknown... unless one consults the FCC database. And in terms of use of the channel makes no difference...

Also, on 'fringe' areas, again the channel may seem ok today... but due to atmospheric conditions... tomorrow it's 'occupied'... perhaps by transmissions emanating.

I'll give you an example... at about 'sunrise' on many days, I can receive an AM band radio station that is about 300 miles away. I believe it operates at about 50KW, which is called a 'clear channel', by the time the sun has risen off the horizon, the signal has decayed to 'noise'.

The 'object lesson' here is, if I tried to use that band for some reason were I live... I would have interference, quite 'licensed', during that period.

The 500-700 Mhz band that the the FM Wireless audio devices operate in, may have 'less' interference at such distances... but with in 90-100 miles of a 'powerful' transmitter, depending, one can still have problems.

Cable connected devices have some problems, but none mounting to those one finds in RF... well until the cable lengths become 'large'...

Another thought that occurs to me is the mutual interference that two, or more, mic transmitters may cause each other... If the actors are 'close' together there could be 'problems' due to how antennas 'work'. Again to use the 'audio analogy'... look at some of the effects (usually bad) of intermodulation.
 
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We're in danger of increasing confusion. UHF radio waves behave very differently from MF/LF radio - the phenomena of evening long distance reception is well known amongst the DX brigade, but apart from a few unusual things like ducts and troposcatter, UHF is pretty safe to be considered line of sight. We didn't quite get to the problem here. The OP refers to what we're now calling RF hits, but I wonder if what he's really getting are RF dropouts, and not interference at all? The aerial systems used for radio mics are pretty basic - often a simple 1/4 wave with rather poor ground plane - making efficiency poor to start with. If you ever spend time watching RF meters, they seem to indicate full or near full most of the time, then as the person steps us into a null area, the signal strength takes a dive. It's not even really output power - subject to licensing, some systems can up the output power, but it makes little difference because the constantly changing path still has deep nulls. Some users use log periodic aerials to give some directional properties and a bit of gain, and there are some that combine vertically polarised directional with horizontally polarised dipoles to give some assistance when the aerial alignment changes polarisation.

Human bodies, being mostly water, act like a sponge and UHF RF doesn't go through them very well - so I wonder if in this example, the real problem is lack of signal in the nulls and NOT interference. The nasty burst of white noise revealed as somebody drops out (if not squelched) can easily be thought to be interference, when it isn't? I can't speak for the US, but the kind of RF issues we have here in the UK are co-channel interference from other radio systems. Real RF interference is quite rare - although I do know a few popular locations where data interference from a high power paging system does get through and cause a bit of a problem. As bands get crowded, we're going to get much more co-channel interference than we've been used to before.
 
A lot has already been said and *any* radio system can get random RF hits, whatever the price.

You should be fine with your G3 system, if you take care.

Firstly, the antennas should be in free air and definitely not blocked by any metal.

If the antenna of a pocket transmitter/receiver touches the body, you will have about a 70dB reduction in signal strength - the antenna should be, ideally, about 1cm or more away from the body. At this distance you will get most of that 70dB loss back again.

Body absorption will affect UHF signals more than VHF - so try to avoid getting a body between the antennas.

If the receiving antenna on the camera is high and in free space it helps a lot.

If you are in the USA, RF hits tend to be worse than in the UK where there is a lot more regulation about what frequencies radiomicrophones can use.

I know people complain about regulation, but the one thing it does really well is to keep the RF spectrum a lot cleaner.

By the way - it *is* a good idea to have all mobile phones in the vicinity turned *off* or put to *airplane mode* and NOT just to silent. Mobile phones looking for the cell transmitter can cause splats, especially if they are ramping up the power if you are on the edge of a cell. Blackberries and some smart phones can be particularly bad at causing interference.

I hope this helps.
 
Paul -- as I think about it you may be right, it might be white noise coming through in a short burst, since the "static" always sounds the same and like the noise when the transmitter is not turned on yet but the receiver is. I have the squelch set to low, maybe medium would be better? I know this is a "no-no" but when I take the antenna of the reciever and poke it into the cheeseplate on the opposite side of the brick battery, it seems to greatly reduce this interference, whatever it is. I wonder if this somehow is making the metal frame of the camera part of the antenna?
 
Good point Dave, if it's impossible to recreate a line of other audio the Zaxcam recording transmitter is invaluable.
 
Which model transmitter is the Zaxcam that has this capability, and does this tie one in to Zaxcom in the future if I want to add a mixer? Approximately what is the cost?
 
I realize this thread is already a little old, but I had to think about a response for a few days before typing it out.

First of all, much of the information here is not only accurate, but important to understand. True, wireless communication links in general are not as reliable as wired links.

That said, I think it is important to understand that when decent wireless mic equipment is used properly, it should NOT cause problems. And cables aren't perfect either. First off, in many cases, the use of cables is either not possible or not pracitcal. Furthermore, I have personally seen cables fail and then wireless mics came to the rescue as backup.

Thousands of users every day are mixing theater sound, touring sound, conferences, videos, films, TV shows, etc. with zero or negligible RF problems. I just had Adam Day, a top-tier guitar tech (worked with G&R, Slash) working for Neal Schon of Journey in here at the factory for a tour last week. He told me that in the 5+ years he has used Lectrosonics wireless for guitar players, he has NEVER had one single RF problem. How is this possible?

1. Decent gear. Anything from the level of Sennheiser G2/G3 and Shure ULX Pro on up should provide many users with solid, dropout free audio if used properly. That said, better/more expensive systems do provide some benefits to some users.
2. Using wireless properly requires a certain amount of understanding. Frequency coordination is important, and perhaps critical. Wireless systems interact with each other and with other external signals. Gain structure is also important so that the units modulate properly.

I think the idea of intermittent external RF signals is overblown here. Again, Thousands of users with millions of channels of wireless mics operate daily with vanishingly few issues.

OK, let me say this also: the recording feature on the Zaxcom units is very cool. Lots of people are using those units successfully. It is a great way to have a backup copy of the audio if RF problems crop up.

But let me say this also: as mentioned above, there ARE differences between lower-cost units and those that cost more. What are the differences?

1. Tighter tolerances in terms of RF and audio performance.
2. The ability to use more channels at once. Although this may not be of importance to the OP, it does indicate the RF "robustness" of the more expensive systems.
3. In general, greater operating range. Better systems have better RF filtering and again tighter tolerances. This translates to higher performance and greater range. This is taking into account proper use, i.e. frequency coordination.
4. Robust physical characteristics. In general, the more expensive units are designed and made to hold up to more abuse. Some units are splashproof, some are even waterproof.

When the OP is talking about getting hits at 50 ft, I think it is clear that this should not be happening, even with the system he has. 50 ft. is not far at all, and ANY decent quality system should be providing rock-solid RF performance at that distance. This brings up several possibilities:

1. Frequency issues. Again, I think the "intermittent RF signals" issue is overblown. However, intermods can cause this condition. Most likely, he is too close to a strong RF source, even though his receiver scans provide him with "clean" channels. Strong RF signals that are in band (within the frequency band of the unit) can cause a loss of sensitivity/range.
2. The transmitter is on the talent's body in a way that absorbs most of the RF. Be careful with transmitter placement. Try to position the transmitter so that the antenna points down and away from the body, instead of touching skin. A nice feature of the G2/G3 transmitters is the reversible wire clip.
3. Do you have line of sight between transmitter and receiver? This is tremendously helpful.
4. Is your receiver antenna vertical or horizontal? The receiver antenna should be oriented vertically, to match the orientation of the transmitter.
5. Is the gain structure optimized? In general, it's a good idea to have as much modulation as possible before clipping/limiting. A good rule of thumb is to push the audio gain until the peaks are bumping the limiter. This will extend your range and solidify the RF signal.
6. Clean frequencies are great, but intermittent RF CAN come from intermods. This gets back to frequency coordination.

/rant
 
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