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Zaxcom QRX "dual mode" real-world performance?


Derek H

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Hey group,

I'd like to start a thread to consolidate information on using the "dual mode" of the new Zaxcom QRX receiver.

Specifically, I'd love to hear reports from users who are using the QRX in the bag or on the cart as a dual receiver, that is, using the unit to receive two different transmitters simultaneously. As in the situation where you have one QRX receiving two talent mics.

Currently I've only used the QRX in single mode as a stereo camera hop. For that it has been perfect. But I have not been able to test out how robust the dual receive mode is.

For example:

One of my concerns is that occasionally I will see the indicator LEDs show a receive error (red light). In single mode this is not a problem as the unit will just switch to the other receiver seamlessly.. However, I worry that in dual mode where the unit cannot flip to the other receiver these errors will result in audio drop outs, furthermore the red light errors seem to pop up now and then regardless of distance from the Tx, at least on my unit, and I believe they are inherent to the digital design of the system. Though with the current firmware version they are less frequent. For reference, my understanding is that the red LED indicates that a receive error has occurred that was not correctable by the built-in error correction system.

That said, I would love to hear from users who have actually logged some working time with the QRX receiving 2x LTs or TRXs.

Looking for any and all feedback!!

Thanks!

-Dh

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Nice topic Derek. The idea to sum it all up right here.

I don't own a QRX (yet) but we all love range. Lots of range (as far as can be electronically and legally done).

:-)

What would be nice is people specify if they're cart (shark finned/dipoled) or bag (whipped) users in the answers.

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I too am using the QRX as a hop but have entertained the idea of using it in the bag to. I have noticed great range with the QRX in Single mode, but every now and then I also notice the red LED pop up indicating an error sometimes even when in close vicinity to the Tx. I would be hesitant to use the QRX in dual mode if a red LED indication would mean an audio dropout since there is no backup antenna to pick up the signal.

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So I did some tests with the QRX in 'Dual' mode and found that the range decreases a little bit, but not a ton. The one thing that worries me is that it looks like (and correct me if I'm wrong) one freq is used by antenna A and the other freq by antenna B, so basically there is only one antenna per receiver. If there is an error received at one of them, then there is no backup antennae to correct the error as there would be in single mode. I believe a receiver like the Lectro SR still uses both antennae for each freq, which is nice.

I have given a lot of thought to how a QRX would be in the bag. With some simple walking tests, I was extremely pleased with how it compared to a 411. Audio quality was superb, I thought, compared to my 411 especially when the RF was low. Range was better too. If I could get the QRX to do the same in dual mode, I would definitely get a bunch for the bag. I currently don't have enough Zax hardware to test out the QRX in dual mode in a reality TV type gig, but I'm definitely interested due to how it has already stacked up to a 411.

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Subscribe to this thread as I expect to receive QRX with IFB board and LTS with a 'Y' input cable for two independent lavs within a couple of weeks.

Will test QRX/LTS on receipt and report back.

Would be amenable for someone to join the faux car rig setup and test afternoon. Could be interesting since I've got full guns antenna/amp setup to try next to the comes-with 1/4 waves. Lemme know.

My ultimate nefarious sound plan is to use 'em in conjunction with the pre-ordered Nomad for car and remote rigs come August...or thereabouts, at which time will test that setup too.

-- Jan

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I have a QRX with 2 Trx900lt's in the bag only (I don't have a cart). The range in dual mode does decrease slightly. The part that you luck out on is the type of diversity. In single mode, both antennas are connected to both receivers. In dual mode, both antennas are connected to a single receiver each. This means it can (and does, p-did) swap antenna for better reception, and because it is digital there is no switching noise. Afaik, it does not combine antennas, but I may be incorrect on that. It cannot though, swap receiver and if you lose a block (.5ms) of audio in dual mode, you dont have the option to possibly salvage that block from the other receiver. It's gone. So...record at the tx!

Again, because it's digital, you can have a very low signal displaying on the rx, and still get great sound. It is all or nothing though - get a full signal loss in dual mode and it'll cut out entirely.

Out of the bag, I'm yet to see a full (audible) drop out while recording, but I've also generally been within 15-25m of the talent. The signal strength bar did get very low at one point, during a public address from a gov advisor, and I saw the little led turn red for a split second. I couldn't hear the dropout, so it must have been very brief. I later found out the speaker had moved his mobile phone to rest on top of the tx...

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I have a QRX100/ TRX900 wireless hop system and am also looking to buying a second QRX with 2 TRX 900LTH's for the talent mic's. What worries me is the fact that there is mention of a drop in range in dual mode. With the new transmitters outputting 125mW, wouldn't there now be an improvement in the range and therefore a better signal? Added to that question, would one need a 2 block separation between the hop and talent mic's or is that a Zaxcom/ Lectro issue. In other words could the hop AND talent mic's be in the same block?

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I have a QRX100/ TRX900 wireless hop system and am also looking to buying a second QRX with 2 TRX 900LTH's for the talent mic's. What worries me is the fact that there is mention of a drop in range in dual mode. With the new transmitters outputting 125mW, wouldn't there now be an improvement in the range and therefore a better signal? Added to that question, would one need a 2 block separation between the hop and talent mic's or is that a Zaxcom/ Lectro issue. In other words could the hop AND talent mic's be in the same block?

Depending on the age of your QRX, there may or may not be a decrease in range. Zaxcom made a few changes to the QRX recently (<4 months ago) and this has reportedly resulted in very little difference between operating in single or dual mode. Some users, including myself, are trying to find out what version of hardware is inside their QRX. I don't find a huge decrease in range in dual mode, but the QRX is unable to swap/combine( does it do this anyway?) receivers to get a better signal. So you may or may not notice more instances of dropout...as always YMMV.

With the transmitters putting out 125mW, you may see an increase in range, you may not, it depends more on how and where on the body the pack is mounted, interference in the area you're shooting in, the kind of building you're in, the alignment of the planets etc etc. What you definitely will get is reduced battery life, though this may be partly improved by the new 'Power Roll' feature (only if you have a Zax recorder).

Technically, hops and talent mics COULD be in the same block, as there's little to no problem with intermodulation (that you can hear) with the digital nature of the Zaxcom system. BUT. There should always be separation between hops transmitters and talent transmitters anyway, if for nothing more than good practice. If it was not a big deal and you could do it, I'm sure Zax would tout it as a fantastic feature, but instead, when using a product like their MicPlexer, they ask for 2-3 blocks separation between hops and talent blocks. And, as per standard practice, as much physical separation between talent RX and hops TX (including their associated antennas) as possible should be implemented.

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  • 4 weeks later...

Hello,

I use 2 TRX 900 with my QRX. Strange thing, I place the two TX at the same place and when I look on the QRX, I see a difference between the 2 received signals on the transmitter display. I also have this difference in the range, one of the transmitter (always the same) is less efficient than the other. I try to swap the frequencies, I swap the antennas on the TX and on the RX, nothing changes.

The 2 TX have the new firmware and they are both set on 50 MW power.

Do you have an idea how to fix the problem? Is it better to have a low frequency on the TX 1 and a higher on the second one?

Thanks

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  • 2 weeks later...

The quality of the transmission is exactly the same with each Zaxcom receiver when both are in analog output mode. Because the QRX100 has AES outputs it eliminates a D-A conversion in the receiver and an A-D conversion in the camera. If a camera has AES inputs this will provide a small increase in audio quality. The important difference is the elimination of level mismatch between the wireless receiver and the camera. This alone will improve camera audio quality more than any other factor as the dynamic range of the receiver and the camera audio system are always matched. Set up time is also eliminated.

With the upcoming STA042 digital input adaptor for our stereo transmitter and Nomad mixer/recorder, talent mic audio will go through only 1 analog to digital conversion at the transmitter. This is very advantageous as compaired to the 8 analog/digital conversions necessary for 2 channels of analog wireless with digital companders when used in typical ENG/EFP applications.

Glenn

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Speaking of QRX100 and AES, tried (under some time pressure) to connect the QRX --> 788t via AES. Had 110-ohm cables between 'em. The machines are not in front of me at the moment, but I had the settings where I thought they should be, and was unable to get the two units to speak to each other digitally in the hour I had to dedicate to the exercise.

Any suggestions?

-- Jan

[sorry for the thread hijack.]

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Speaking of QRX100 and AES, tried (under some time pressure) to connect the QRX --> 788t via AES. Had 110-ohm cables between 'em. The machines are not in front of me at the moment, but I had the settings where I thought they should be, and was unable to get the two units to speak to each other digitally in the hour I had to dedicate to the exercise.

Any suggestions?

-- Jan

[sorry for the thread hijack.]

had no issues when i tried.

but at the risk of asking an insultingly obvious question, you were using the digital inputs on the base of the 788 werent you? as the xlr/ta3 connectors on the side only accept analogue inputs - unlike the 744 where the xlr would take analogue or digital.

if you were using an XL88 cable, did you take apart an xlr to make sure that it was wired correctly as there was a batch in the uk that had the ground wired to the shell only and not pin 1.

also note that i found that using the digital input added 2ms of delay compared to the analogue input - it was suggested that this was due to the sample rate converter in the 788.

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had no issues when i tried.

but at the risk of asking an insultingly obvious question, you were using the digital inputs on the base of the 788 werent you? as the xlr/ta3 connectors on the side only accept analogue inputs - unlike the 744 where the xlr would take analogue or digital.

if you were using an XL88 cable, did you take apart an xlr to make sure that it was wired correctly as there was a batch in the uk that had the ground wired to the shell only and not pin 1.

also note that i found that using the digital input added 2ms of delay compared to the analogue input - it was suggested that this was due to the sample rate converter in the 788.

Yes, I used the DB AES input on the back with XL88. Thanks for asking :)

Will look at the TA3/XLR cables in the morning. The folks who made the cables said they spoke to the manufacturers relative to wiring, but...you know...

-- Jan

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  • 1 year later...

I am hoping to get some Zax for the bag relatively soon so I am reviving this topic. I hope to report back soon with my findings with my QRX in dual mode with just the whips.

In the meantime, any new user reports of the QRX in dual mode with the whips are welcome!

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Nope, they're comparable to the performance of a SRa without it.

If I find this to be true, I'll be happy. Many times my SRs have outperformed my 411s due to whatever voodoo RF was out there, and if the QRX in dual is like the SR, I'll be a happy camper.

On the other hand, if I need a MicPlexer to make the QRX in dual mode usable for run and gun, I won't be very excited.

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