Jump to content

lectro smv question


jwill

Recommended Posts

I was on a shoot where the "Talent" wanted to do a standup in the endzone and wanted the camera out at the 40 yd line, her idea was to start tight as the camera could get and zoom out to show the distance and her point was this team had not had a passing td from that distance all season. Ok i puy my 2700mah rechargeables in my lectro hm and mate it to my re-50..."no I want a lav"...so out comes my smv windscreen put it on her and off she goes....as soon as she gets into the endzone I start getting dropouts, b4 we even attempt a take I realize the smv is on 50mw, a quick reset to 100mw did the trick. My question is this, I understand that for most applications the 50mw setting is more than ample, at what distance does it become untenable. I looked in lectros website, i searched here on JW Sound and cannot find an answer. I know there are all sorts of variables, this scenario was a direct line of site I had let all of my 25 ft snake out and went closer to the talent,(no metal poles nearby) 40 yds or roughly 120 ft and 50mw was breaking up! I have left my one smv set to the 100mw setting anticipating another such standup. What do JW Soundies set their smvs to? Has anyone ever used the 250mw setting, what kind of range does that give? Thanks for your input/thoughts and advice JHW

Link to comment
Share on other sites

Hi John. As you say, there are many variables. Putting an SNA600 antenna on my receiver has helped improve distance. Also putting the transmitter on the front of the person rather than on their back can certainly help (flesh absorbs RF signals). if you don't have the SNA antenna, getting your receiver higher up can help, as can putting the receiver closer to the talent with a long XLR cable (if possible).

Link to comment
Share on other sites

I'm not sure why you would be operating at 50 mW in the first place.

Actual battery savings from using the lower output with the variable Lectro transmitters are either nonexistent or quite minimal.

The lower output is primarily for operation in places where 100 mW may not be permitted. The Broadway stages, for instance, have an agreement not to use more than 50 mW to avoid stepping on each other since the theaters are so close, one to another. It might also be useful in situations where the transmitter is so close to receivers that there is some potential to overwhelm the front end. Camera hops used in a bag with talent receivers would be an example.

But I would expect you to be at least twenty feet from a stand-up announcer so you wouldn't ordinarily be concerned that RF would swamp your receiver at 100 mW.

As to what range you might expect, I've run distance tests with radios in a moderately dense urban environment with clear line of sight. The results varied somewhat with each iteration but I could usually get at least 500 feet at 100 mW using 1/4-wave whips. For the tests, the transmitters were attached to a short pole and held, waist high, so there would be minimal absorption from the body of the "walker." With the talent wearing the transmitter, the results are likely to be a bit less.

Test results are available online at:

http://695quarterly.com/previous-issues/

The initial run of tests is in the Spring 2010 issue. Follow-ups are in the Fall 2010 edition, Summer 2011 and Winter 2011 editions.

David

Link to comment
Share on other sites

[snip]

My question is this, I understand that for most applications the 50mw setting is more than ample, at what distance does it become untenable. I looked in lectros website, i searched here on JW Sound and cannot find an answer. [snip]

JHW

To quote a frequent poster, "It depends." The reason there are no answers is there are none that manufacturers are willing to put in print, without major weasel words. The amount of RF noise at a given location can change the range by a factor of 20 (and much more). The type of receiver antenna can change the range by a factor of 3. The location of the antennas on the talent and in the bag (cart) can change the range by a factor of 5. The digital noise from other items in a bag can alter the range by a factor of 5. And so on and so forth. When you consider that I am just making best guesses on these factors, you can see that "It depends."

If Lectrosonics said 100 mW will give you 300 feet of range, imagine the argument when the user only got 298.6 feet and crashed an expensive shoot. We'd be claiming that the summer weather caused his tape measure to stretch.

Let's try some numbers at this site: http://pa2ohh.com/jsffield.htm and get some theoretical distances. I assure you, you will quickly realize the distances are not reproducible on a movie set.

Frequency 600 MHz

A transmitter's 100 mW output is 20 dBm

A good receiver's sensitivity is -107 dBm

The maximum path loss we can stand is the difference in the two above numbers or 127 dB (20 -(-107))= 127

The transmitter antenna has 2.1 dBi of gain out in the open.

The receiver antenna has 2.1 dBi of gain for a dipole (SNA600)

Plug the numbers in and what's the possible range? 144.5 km or 90 miles

This is a touch more than most wireless manufacturers will claim, even us. Is there something wrong with the formula? Not at all and those kinds of distances can be done with good antennas, line of sight transmission and good receivers. Hams do it some of the time. Conditions just have to be perfect. In the imperfect world you deal with every day, "It depends."

Best Regards,

Larry Fisher

Lectrosonics

Link to comment
Share on other sites

" for most applications the 50mw setting is more than ample, at what distance does it become untenable "

it depends

well, I would have said it first...

as noted, the power setting is not really the most important factor

BTW, the handheld probably would have worked better, other things being about the same, because the antenna would be clear towards the RX, and the TX would be a bit away from the talent's body....

Edited by studiomprd
Link to comment
Share on other sites

My preference is for 100mw for wireless lavs all the time, but there are many parts of the world where that's illegal (particularly parts of Europe and Asia), and other areas where the venues have voluntarily agreed to a 50mw standard (like Broadway) to minimize RFI.

I use my SMQV's at 250mw for camera hops and for boom op IFB, just "because" of the possibility they get in a weird position where they get a momentary hit. In both those cases, the SMQV's are being powered by external batteries, so there's no chance of running out of juice. I'd be reluctant to use those on a person except in unusual conditions. In truth, I think running in 100mw for 10 hours+ is a better incentive on the SMD/SMQV models.

I'd be curious to know what kind of receiver and antenna JWill is using, because that absolutely has a big effect on reception. I'd also be curious how clean the RF spectrum was at the stadium -- I've seen some weird RF issues during football games or in arenas. If I get hits, I just move closer or break out the sharkfins (if I'm not using them already).

Link to comment
Share on other sites

  • 1 year later...

Everyone has said it well.  "It depends".  I have a few random examples.  I've experienced range consistant to 1/4 mile while sometimes going to 1/2 mile with at 250mW when using powered antennas.  This was in the desert near the Hoover Dam and when I scanned my Lectros they come up clean as a whistle.  While using the whip antennas it seems like you can easily get 300 feet at 250mW, although I've experienced much better range in desolate areas and they can even in urban ones.  I run mine at 100mW generally and adjust when necessary.  I'll save batteries and drop to 50mW if I know the tx's will be close by. Sometimes certain individuals absorb a ton of rf compared to others so I'll boost them to 250mW.  

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...