Extending wireless antennas w/o distribution system

[jkowtko]

Last night I tried the 6' RG58 cable extensions on the rabbit ears on one of our problem channels, and I'm happy to say that there was a noticable improvement in RF strength on that channel. It increased maybe an average of 10db on the RF meter, and from maybe 70% to 95% "solid" as far as intelligible RF noise ... so this does help. Does it give me the same comfort level as a powered antenna would? No, but for roughly $20/channel if you don't absolutely need the solid signal strength of a full antenna distribution system (for me, ~$150/channel) it's a good first step to help make things better.

But yes, I hear your argument on moving the receiver rack. It's an almost no-cost adjustment if you have access to a snake. And if you don't have a snake, the cost of a 16-channel snake is far less than the cost of a 16-channel antenna distribution system. I'm doing Gypsy in May so I may try it then. I'm a little paranoid not being able to see the receiver displays ... I'll see if our house tech mgr can set me up with a camera.

Thanks. John

 

[mixmaster]

Last night I tried the 6' RG58 cable extensions on the rabbit ears on one of our problem channels, and I'm happy to say that there was a noticable improvement in RF strength on that channel. It increased maybe an average of 10db on the RF meter, and from maybe 70% to 95% "solid" as far as intelligible RF noise ... so this does help. Does it give me the same comfort level as a powered antenna would? No, but for roughly $20/channel if you don't absolutely need the solid signal strength of a full antenna distribution system (for me, ~$150/channel) it's a good first step to help make things better.


Thanks. John

I am certainly not an RF junkie but Your mention of a six foot increase in distance making a significant improvement popped a thought in my mind. Seems like I read somewhere that antennas in a diversity system needed to be mounted a certain distance away from each other as well as surrounding RF reflective surfaces. IIRC the distance is a multiple (or fraction?) of the wavelength of the primary frequency. Anyway, what I was reading was that remoting at least one antenna was almost a necessity because there was no way to get enough distance between the antennas in a 19 inch rack, let alone a half rack space like most wireless receivers. Perhaps 6 feet just gave you enough separation.

All this being said, I've often wondered about the practicality of mounting one antenna on each side of the stage for maximum separation...

 

[SHARYNF]

What you are seeing is the issue with just getting a whole stack of wireless and trying to get it to all work well.

A 10db improvement is a HUGE improvement and with the 6 foot extension I would also surmise that what is really going on here is the interference from one antenna to another in the system.

Here is a link for some of Shure's guidelines

If you read thru it it points out that the antenna's should be at least 4 inches apart (1/4 wavelength UHF) and that up to 16 inches will probably see an improvement. it also talks about Oscillator interference from the receivers being mounted close together

http://www.shure.com/stellent/group...ents/web_resource/us_pro_antenna_setup_ea.pdf


The high end wireless system designed and installed using a sophisticated antenna system tend to minimize these problems. I you are using the lower end units, again in my experience with 16 of these all close together you going to run into problems. And again IMO this is why the 6 foot extension is having such dramatic improvement.

Sharyn

 

[jkowtko]

Thanks for the link Sharyn -- this is a great primer. Lots of good info that I didn' know.

So to sum up, the benefits I gained by moving the antennas out:
- I increased spacing between the two diversity antennas by > 1 wavelength
- I increased vertical spacing above/below other receiver antennas by > 1/4 wavelength
- I removed antenna crossovers, which I have inside the rack on the inside antennas from each side

However:
- I lost the ground plane, which is supposedly required for the 1/4 wave whips. So why is it still working?

Fyi, the AKG tech explained the vertical stacking effect on the antennas, and the reason for increasing the splay angle within a stack:

"Stacking identical antennas on a common vertical mast will narrow the vertical beam-width angle. Vertically stacked antennas more effectively reject signals arriving from above or below their horizontal plane than a single antenna. So by fanning vertically stacked antennas you are increasing each antennas range. "

So I wonder if placing the rack backstage is going to solve all the problems ... it sounds like it will definitely increase RF strength, but will I still encounter interference and limited angle of reception until I separate the receivers more from each other?

 

[SHARYNF]

Typically since space is less an issue backstage you would place the receivers with more space between them to avoid some of these problems. In a rack you are very restricted but I have seen where you could use two shelves that allow for both vertical and horizontal separation

I know this is typically WAY OUT of a small theater budget but it gives an indication of where the high end thinking is going, basically that there is an ethernet link from FOH to the receivers, this lets you place them back stage and still monitor and control from foh


http://www.audio-technica.com/cms/wls_systems/12b16c15b118e2ca/index.html

Sharyn

 

[jkowtko]

It's been a while but just an FYI on what the tech director at the theater has done since I left ... I had moved the receiver rack to stage right and still had some issues ... but now all antennas are moved out out of the receiver rack and connected with 25' cables so they can be located on either side of the stage (above). I've been to a few shows since and I haven't heard any RF interference ...