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[Justin Goodman]

Video: https://www.dropbox.com/s/vznr6jla7hz37ju/IMG_2976.MOV?dl=0

Working on learning as much as I can about wireless - fun stuff.  So looking for an explanation here... why does an antenna with a listed gain of 6db show essentially no gain in this outdoor line of sight test.  UR3 at 50mw and ~300ft (exactly 305 according to Google Maps) away with direct line of sight up the street from my house ... first with LPDA and then with 1/4 wave whip.  Hanging in there like a hair on a biscuit at -80db +/- 1db regardless of which antenna I'm using.  Why not a stronger signal with LPDA?

Is it:

A) At my location I'm actually getting a stronger signal reflected off another house than directly from the transmitter (why?) and therefore the omni whip is better able to capture the signal as hot as possible vs directional LPDA.  This suggests I could probably get -7x by differently orienting the LPDA but that wasn't possible in my extremely limited test (I tried after recording).

B) The 12" of RG58 vs direct connection to 1/4 wave whip (seems like that can't be it since it should be 0.1db of loss over 1')

C) Weird luck ... multiple tests at different locations of the same distance would reveal an average of 6db increase, and this is an outlier. 

D) 300ft is nothing for 50mw tx power -- it's essentially as strong of a signal as it's going to get -- and you wouldn't start to see gains unless you turned down the tx to 10mw and/or moved farther away.  (Though again this doesn't seem like it because it was -10db before I walked the hundred yards away, so clearly the scale "goes higher")

E) Something else

Leaning toward that it must be C or E.  Thanks for the help. Hopefully others are finding these newbie questions valuable as well. 

Edited to add: I saw this video and then cleaned my screen. Not embarassed enough to re-shoot. 

[Pete Erskine]

Video: https://www.dropbox.com/s/vznr6jla7hz37ju/IMG_2976.MOV?dl=0

Working on learning as much as I can about wireless - fun stuff.  So looking for an explanation here... why does an antenna with a listed gain of 6db show essentially no gain in this outdoor line of sight test.  UR3 at 50mw and ~300ft (exactly 305 according to Google Maps) away with direct line of sight up the street from my house ... first with LPDA and then with 1/4 wave whip.  Hanging in there like a hair on a biscuit at -80db +/- 1db regardless of which antenna I'm using.  Why not a stronger signal with LPDA?

for wireless reception An antenna with GAIN doesn't actually make the RF "louder"  if you are 20' from an omni and 20' from a paddle front the rf level will be the same.  The difference is the back of the paddle has almost no reception so technically the front has gain... or more specifically the back has loss.

As a TX antenna more power is directed out the front side than you would get using an omni.

[Justin Goodman]

for wireless reception An antenna with GAIN doesn't actually make the RF "louder"  if you are 20' from an omni and 20' from a paddle front the rf level will be the same.  The difference is the back of the paddle has almost no reception so technically the front has gain...

As a TX antenna more power is directed out the front side than you would get using an omni.

Can you expand on that some? So you wouldn't see any increase in distance of usable signal with an LPDA vs omni whip? What's everyone doing with LPDA's if whips that come free with the RX's are just as good--just lowering the noise floor? 

[Pete Erskine]

Can you expand on that some? So you wouldn't see any increase in distance of usable signal with an LPDA vs omni whip? What's everyone doing with LPDA's if whips that come free with the RX's are just as good--just lowering the noise floor?

rejection of unwanted signal makes the RX more sensitive with lower noise floor.  maybe Henry can explain it better.

Other types of antennas do have gain like parabolas.

[Scott Holtzman]

rejection of unwanted signal makes the RX more sensitive with lower noise floor.  maybe Henry can explain it better.

Other types of antennas do have gain like parabolas.

It does make a difference on transmit too.  Much like a horn on a loudspeaker, gain only applies to a directional signal.  The gain is not free, basically by reducing the pattern of the antenna energy is directed the way you want it to go and not wasted.



Trivia - Do you know why they put the little ball on the top of a whip?  So all the RF doesn't leak off the top. <<g>>

[Ray Aberle]

Can you expand on that some? So you wouldn't see any increase in distance of usable signal with an LPDA vs omni whip? What's everyone doing with LPDA's if whips that come free with the RX's are just as good--just lowering the noise floor?

Shure explains it well: Their UA874US / PA805SWB don't boost the RF signal, rather they "increase off-axis RF rejection." So, the directional antenna are focusing their attention in a 70° wide zone, and ignoring more of the other 290°. If there's a strong interfering signal in the area, using the antenna to put that strong source in its rejection zone can help you achieve a more reliable RF signal.

The active (UA874US) antenna has an RF gain on it, which is useful if the antenna is mounted some distance away from your receivers, but again, that doesn't increase the TX power from the microphones; it just boosts the signal from the antenna to the receivers. The UA874US actually does the full spread- -6dB, 0dB, +6dB and +12dB, so you can also pad it with the -6dB if you are overloading the RX circuits. [The PA805SWB is a passive antenna- it doesn't need power to operate, but also doesn't have those gain adjustment settings.]

Bonus Points: Shure sells the WA874ZP zippered pouch for the PA805SWB/UA874US antenna. Not only is it padded to protect your $200-$300 antenna, it's also weather-resistant AND RF-transparent. So, when working outdoors, keep your expensive antenna in that pouch, and deploy as normal. It'll help prevent failures from rain, etc, but still do its antenna job like you need it to!

-Ray

Disclaimer: Kelcema Audio is a Shure Authorized dealer in the United States, and sells the products mentioned.

[Jason Glass]

for wireless reception An antenna with GAIN doesn't actually make the RF "louder"  if you are 20' from an omni and 20' from a paddle front the rf level will be the same.

Sorry to disagree, Pete, but that part is incorrect.  Any antenna with axial gain should show a difference in received power on axis equal to the antenna's gain specification in dBi or dBd.  Those terms are by definition gain vs. isotropic and gain vs. dipole, and gain refers to signal amplitude which does mean louder.

Justin, there are several issues with your test setup.  As with all things RF, a bit of A, B, C, D, and E are all significant factors.

First, measurements like these should be made with an analyzer in "channel power" mode, where it's not just the peak being measured but rather an average power across the entire channel bandwidth.  In the case of typical RF mics that would be 200kHz wide.  Alternatively, you would place a measurement marker on the peak that shows a precise readout of RSS.

Second, measurements of this kind are best conducted inside an anechoic chamber or at the very least in a wide open outdoor space.  Reflected signals cause enormous variation in received signal strength because both constructive and destructive interference can occur.

Third, 50mW is indeed too much power at 300ft. for this kind of measurement.  If you were to attempt again at 1mW power, or if you were to insert a sizeable precision attenuator into your signal path, you'll most likely see differences more clearly.  Especially with an SA of such dubious measurement precision (compared to legit lab instruments of 100x the $) in your setup.

Fourth, your RBW should be set narrower.  With such a wide RBW, there is a good chance that much of the RSS is spread out into an adjacent FFT bin and not being accurately attributed to the peak's displayed amplitude.  When using RF Explorer, setting your span to 400KHz or 500KHz should automatically narrow its RBW.

Fifth, even a short 12" RG58 will introduce losses from connectors and adapters, and there's no guarantee that your cable is actually performing to spec if it's not a VNA certified assembly, although the Shure cables are admittedly pretty darned good when in new condition.

[Pete Erskine]

Sorry to disagree, Pete, but that part is incorrect.  Any antenna with axial gain should show a difference in received power on axis equal to the antenna's gain specification in dBi or dBd.  Those terms are by definition gain vs. isotropic and gain vs. dipole, and gain refers to signal amplitude which does mean louder.

that was my experience in actual use which was not free field and using regular power.  thanks for the clarification.

[Justin Goodman]

Sorry to disagree, Pete, but that part is incorrect.  Any antenna with axial gain should show a difference in received power on axis equal to the antenna's gain specification in dBi or dBd.  Those terms are by definition gain vs. isotropic and gain vs. dipole, and gain refers to signal amplitude which does mean louder.

Justin, there are several issues with your test setup.  As with all things RF, a bit of A, B, C, D, and E are all significant factors.

First, measurements like these should be made with an analyzer in "channel power" mode, where it's not just the peak being measured but rather an average power across the entire channel bandwidth.  In the case of typical RF mics that would be 200kHz wide.  Alternatively, you would place a measurement marker on the peak that shows a precise readout of RSS.

Second, measurements of this kind are best conducted inside an anechoic chamber or at the very least in a wide open outdoor space.  Reflected signals cause enormous variation in received signal strength because both constructive and destructive interference can occur.

Third, 50mW is indeed too much power at 300ft. for this kind of measurement.  If you were to attempt again at 1mW power, or if you were to insert a sizeable precision attenuator into your signal path, you'll most likely see differences more clearly.  Especially with an SA of such dubious measurement precision (compared to legit lab instruments of 100x the $) in your setup.

Fourth, your RBW should be set narrower.  With such a wide RBW, there is a good chance that much of the RSS is spread out into an adjacent FFT bin and not being accurately attributed to the peak's displayed amplitude.  When using RF Explorer, setting your span to 400KHz or 500KHz should automatically narrow its RBW.

Fifth, even a short 12" RG58 will introduce losses from connectors and adapters, and there's no guarantee that your cable is actually performing to spec if it's not a VNA certified assembly, although the Shure cables are admittedly pretty darned good when in new condition.

This makes a lot of sense.

In terms of testing in an anechoic chamber, part of me wants to say it's disingenous to make empirical claims about a product (in this case 6db of gain) to be used in the real world (hotel ballrooms, football stadiums, etc) when the results are only replicable or closely realized in an anechoic chamber ... though I guess one could say the same about Ferrari claiming a 180mph top speed on a production car.  You can't drive that fast on the highway but that doesn't make it less true...

I'll try again at 10mw with a 200khz view and see what happens.

[Lyle Williams]

Reception is normally a signal-to-noise game, rather than being dependent on the ultimate sensitivity of the receiver.

When a receiver stops working it is often because there is too much noise (relative to a weakening-with-distance received signal from the transmitter.) 

[Henry Cohen]

Reception is normally a signal-to-noise game, rather than being dependent on the ultimate sensitivity of the receiver.

When a receiver stops working it is often because there is too much noise (relative to a weakening-with-distance received signal from the transmitter.)

It's always about the CNR (carrier to noise ratio; "signal" to noise is generally applied to non-EM applications).

[Henry Cohen]

This makes a lot of sense.

In terms of testing in an anechoic chamber, part of me wants to say it's disingenous [sic] to make empirical claims about a product (in this case 6db of gain) to be used in the real world (hotel ballrooms, football stadiums, etc) when the results are only replicable or closely realized in an anechoic chamber ... though I guess one could say the same about Ferrari claiming a 180mph top speed on a production car.  You can't drive that fast on the highway but that doesn't make it less true...

Your Ferrari analogy, although a correct statement, is not really analogous here: In this case of RF level observation, your measuring equipment and configuration is not up to the task of seeing what's really happening (as well as there being too much "traffic" - reflections and other external interference - to provide a proper measuring environment).

[Justin Goodman]

Your Ferrari analogy, although a correct statement, is not really analogous here: In this case of RF level observation, your measuring equipment and configuration is not up to the task of seeing what's really happening (as well as there being too much "traffic" - reflections and other external interference - to provide a proper measuring environment).

[Bolding mine]

That's where to me, the disingenuousness comes from ... If anyone here lands a gig in a zero reflection environment, it will be the first such gig.  The measuring equipment concern is fair enough -- I don't expect $250 worth of gear to be accurate to within a decimal place -- though the signal strength is remarkably consistent both in comparison to each other and while measuring on their own.  I think it's a reasonable assumption that if anywhere near 6db of signal gain were being realized, that some indication of that would be shown -- even if not exactly 6db. 

That said, if AT wants to claim their LPDA's get 6db of gain only in such an ideal environment, while perhaps misleading, they'd still be lightyears ahead of speaker manufacturers in honesty given the SPL figures they like to throw around.

[Henry Cohen]

That's where to me, the disingenuousness comes from ... If anyone here lands a gig in a zero reflection environment, it will be the first such gig.  The measuring equipment concern is fair enough -- I don't expect $250 worth of gear to be accurate to within a decimal place -- though the signal strength is remarkably consistent both in comparison to each other and while measuring on their own.  I think it's a reasonable assumption that if anywhere near 6db of signal gain were being realized, that some indication of that would be shown -- even if not exactly 6db.

Note I said ". . . there being too much "traffic" - reflections and other external interference - to provide a proper measuring environment". The RF Explorer has too poor selectivity to discern the desired carrier. But the gain is in fact present in the antenna, and if the carrier is within the main lobe, there is a 3-6dB greater signal strength at the antenna connector, along with all the other RF energy present within the antenna's 3dB beamwidth and bandwidth.

[Jason Glass]

[Bolding mine]

That's where to me, the disingenuousness comes from ... If anyone here lands a gig in a zero reflection environment, it will be the first such gig.  The measuring equipment concern is fair enough -- I don't expect $250 worth of gear to be accurate to within a decimal place -- though the signal strength is remarkably consistent both in comparison to each other and while measuring on their own.  I think it's a reasonable assumption that if anywhere near 6db of signal gain were being realized, that some indication of that would be shown -- even if not exactly 6db. 

That said, if AT wants to claim their LPDA's get 6db of gain only in such an ideal environment, while perhaps misleading, they'd still be lightyears ahead of speaker manufacturers in honesty given the SPL figures they like to throw around.

It's not disingenous, though, and absolutely not misleading. It's dead-on accurate and measured precisely under ideal laboratory conditions as generally accepted by the RF engineering community. Just because average users don't understand all the hows and whys and don't see commensurate measurements with substandard equipment in an utterly unacceptable measurement environment doesn't impugne the specifications one bit. Not to mention that even cursory modeling using the numerical electromagnetic code (worldwide accepted as legitimate) concurs for PCB LPDA designs of this kind and provides compelling verification.

The thing that every world class RF tech intimately understands is that we must utilize EVERY seemingly miniscule advantage that we can for every component in our signal path, to the point of OCD hypersanity. It's the best known way to build a system robust enough to be acceptably reliable in the face of maddeningly harmful, unpredictable, and constantly dynamic real world environments. Theoretical free space and laboratory conditions are the great equalizers that allow us to subjectively judge individual component performance on a level playing field.  Without them our science is reduced to the Voodoo that too many users still believe that we practice.  Kinda like loudspeaker manufacturers.

Sent from my SM-G950U using Tapatalk

[Scott Helmke]

That's where to me, the disingenuousness comes from ... If anyone here lands a gig in a zero reflection environment, it will be the first such gig.

There *is* actually such a gig - it's in the space program.

[Frank Koenig]

Sorry to disagree, Pete, but that part is incorrect.  Any antenna with axial gain should show a difference in received power on axis equal to the antenna's gain specification in dBi or dBd.  Those terms are by definition gain vs. isotropic and gain vs. dipole, and gain refers to signal amplitude which does mean louder.

Jason is spot on. Antennas behave identically for transmission and reception with respect to pattern and directivity (gain). Reciprocity applies. Transmission and reception are not entirely equivalent however. The shape of the wave in the near field of a transmitting antenna, and the corresponding voltage distribution in its elements, is different from that of the same antenna used for reception in the far field of a transmitting antenna. Transmitting antennas may also need to handle the currents and voltages encountered at higher power levels -- generally not an issue for wireless audio.

I remember someone who got their hands on a high-power FM transmitting antenna (made from beautiful, heavy copper tubing) and repurposed it for their home FM receiver. Of course it worked just fine. But then a coat hanger often works pretty well, too

--Frank

[Don Boomer]

I think you have to remeber that engineering specs are just that. They are for engineers to make comparisons and were not intended (at least by the engineers that ran them) to be a sales tool. There's just no way to use “real world” measurements in the specs as everyone’s real world is different.

[ProSoundWeb Community]