Sony Freedom Radio Microphones

[simon-carter]

Hi All

 

I'm hoping someone can help. We've hired a Sony freedom radio microphone system for an amateur musical prduction and are having problems with reception drop-outs. We have 9 channels split over 2 receiver racks, with 4 active aerials in total. Initially we had these near the sound desk at the back of the auditorium (approx 15m to stage) were the receivers are located but got poor reception with mics dropping out on-stage and going completely out of range off-stage. We have moved the aerials nearer the stage, placing 2 in the orchestra pit (i.e. ant. input A from each rack) and the other 2 (ant. B) at the side of the auditorium. The distance from transmitters to anternnae is now probably 5m at most. The problem appears worse when the transmitter pack is clipped to a costume and the actor gets between it and the antennae; holding the pack out at arms length improves matters. All transmitters are showing full battery display.

 

Has anyone got any ideas how to solve the problems? We are going to contact the hire company but as we open tonight we need to solve this fast.

 

Thanks

 

Simon

[Andrew C]

1st question... The hire company did supply them all, with frequencies set so that they don't inter-modulate?

2nd question...Is there anything else radiating nearby? Turn everything else off and see if it clears. Years back I had problems caused by the colour modulator in a BBC micro. (Someone much smarter than me found it!)

[simon-carter]

Hi Andrew

 

Thanks for the reply. Yes, all supplied by the hire company. They cam with the frequencies set up so I assume they should be set to avoid inter-modulation. There are operating on licensed frequencies (with the appropriate license) so presumably this was checked. The only unknown factor is how far apart the aerials from the 2 separate racks should be. We've tried them a reasonable distance apart with no improvement.

 

I can't immediately think of anything else near the aerials to radiate interference, the equipment in the pit was off at the time, I'll try turning all other sound / lighting equipment (and anything else I can think of) off and see what happens.

 

Simon

[back_ache]

I assume

A great detective once said "Emliminate all that is probable and whatever is left, however improbable, is the truth".

 

I would power each pack and reciever one by one and monitor the results, I have hired sony freedom racks from a supplier specialising in the amateur sector before and I had to re-program the entire rack, which was made even difficult as on the on we had, as the packs used channel numbers and the receivers used frequencys (make your mind up Sony!).

 

You can't assume how the rack is set up.

[Shez]

Definately something wrong there...

 

I had a rack of six of those for a musical a fortnight ago; antennae were mounted on the front of the balcony, 10 - 15m to the stage. Whilst on stage, none of the signal strength bars dropped below the maximum. Very occasional drop-outs from the dressing room but generally fine there too.

 

What kind of cable is used to connect the aerials to the receiver racks? Chunky ~1/2" coax or something weedier? How long are they?

 

I assume the green LEDs on the bottom of the antennae are lit up to say they're getting power?

 

Hope you get it sorted - they're fantastic mics :)

 

Shez

[bruce]

I assume

A great detective once said "Emliminate all that is probable and whatever is left, however improbable, is the truth".

 

Agree with all of the above. You need a methodical approach. Does the problem occur when you have only one mic active? If so, is it only that mic, or do you get the same problem when only one different mic is active.

 

If one is OK, how about 2? Simplify things as much as possible, to try to isolate the problem. If the simple setup is OK, then build things up, but only make one change at a time.

 

And change the batteries, even if the display says they're OK! Just in case.

You can't assume how the rack is set up.

 

As the saying goes, never assume, as you will make an ass of u and me.

[Bobbsy]

I frequently use a rack of 12 "Freedom" series mics with the antennae at the back/side of the auditorium with reception problems being rare to non-existant.

 

All the previous suggestions are good:

 

-make sure the frequencies used are intermod free

 

-make sure they've given you proper "chunky" antennae cable.

 

And a few other things:

 

-if you're using the Sony "shark fin" antennae, make sure the switch providing power for them is on and the green LED on the antennae light up

 

-make sure any spare outputs on the Sony antenna divider are terminated with BNC resitor loads.

 

-the very original "Freedom" transmitters came with quarter wave "stubby" antennae which performed poorly. Sony soon replaced these with half wave flexible antennae which more or less doubled the range. If you have stubbies, ask for these to be changed.

 

Bob

[simon-carter]

Thanks for all the suggestions. To answer a few questions:

 

We've tried just one mic, 2 mics and every other combination, with the rack not covering the mic being tested turned off. The cable is RG58 coax with BNC connectors, approx 10m, doesn't look very thick though. We had to extend them with some (chunkier) RG59 of our own to try them nearer the stage, but the origional configuration only used the supplied cables. The aerials are the 'shark fin' type, and have the green LED lit.

 

Other mics we've used in the venue before (Sennheiser / Trantec / even Gemini) have all worked flawlessly from the back of the auditorium to the stage, even through to our green room / other parts of building, although these have been 2 mics at most on de-regulated frequencies. Everything I've read here and elsewhere suggests the Sony's are very good kit and should easily work from the back of the auditorium.

 

I'll try the suggestions when I'm at the theatre later.

 

Simon

[Lamplighter]

The cable is RG58 coax with BNC connectors, approx 10m, doesn't look very thick though. We had to extend them with some (chunkier) RG59 of our own

 

Simon

RG 58 is 50 Ohm cable, RG 59 is 75 Ohm, not compatible especially at UHF. I wouldn't run more than 5m whichever you try, you really need RG213 as a minimum.

 

Having been negative, try one channel on its own aerial, bypassing the distribution system completely, if that is feasible. If that works check each channel on its own then look at the distribution system, it should work without any dropouts at that short range.

 

Brian

[Shez]

Stupid question, but you are pointing the antennae at the stage aren't you? Hearing them referred to as "shark fin" brings up imagery of them pointing at the ceiling...

[mackerr]

The cable is RG58 coax with BNC connectors, approx 10m, doesn't look very thick though. We had to extend them with some (chunkier) RG59 of our own to try them nearer the stage, but the origional configuration only used the supplied cables. The aerials are the 'shark fin' type, and have the green LED lit.

The cable youare using is one problem. You do not want to mix cable types, and you should be using 50 ohm cable, although there is anecdotal evidence that RG59 works well. The cable you should be using would be an RG8 type, or RG213 or LM400. These are all low loss 50 ohm antenna cable, RG58 is 50 ohm, but not low loss, and RG59 is 75 ohm video cable. You may be better off moving the receivers to the stage to get the antenna closer, and using short low loss antenna cables.

 

Mac

 

I need to type faster, Brian got my points in first. :) Also a good point from Shez about pointing the antenna at the stage.

[Bobbsy]

I'm wondering a bit more about the provide antenna cables.

 

RG58 is nominally 50 ohm cable (which is officially a match for the Sony system) but is getting reasonably lossy up at the frequencies you're using. Losses over 100 feet at 900 MHz vary between 9 and over 14 dB depending on the quality of cable supplied.

 

RG59 is nominally 75 ohm which is technically wrong for the Sony stuff. I've seen a mathematical justification as to why this can actually be more efficient than using 50 ohm cable, but this was based on having lower losses in the cable. However, at 900 MHz, losses in "average" RG59 can be around 11dB per hundred feet.

 

I know that when I've used the Freedom mics I also use a Sony-provided antenna cable. This is about a half inch in diameter and is proper 50 ohm stuff. I don't have the spec in front of me, but by memory, the losses are a bit under 4dB per 100 feet. This is a significant difference to the losses in RG58/59. I realise you're using a shorter length (or, rather, a choice of more loss on a shorter cable or slightly less on a longer one) but I suspect this might be part of the problem. I'd talk to the hire company and see if they can provide a more appropriate cable.

 

Bob

 

Edit: Wow! Three posts in the time it took me to type this! We're all coming at it from the same direction though. I was about to edit to add a reference to RG8 but Mac got there first. One thought...the Sony receivers usually come with a right angle half wave antenna that can go straight on the back of the splitter...if you have these (and can't get better cable) since you're in the auditiorium you might almost be better off to try these.

[soundo26]

We have three Sony freedom 6 way racks here and have never had any problems even in some fairly large venues.

all I can suggest is that you make sure that you are using 50 Ohm cable NOT 75 Ohm video cable.

 

Might also be worth checking that the mics are not over-attenuated (use the set button to scroll through the menu)

 

One other thing to check is there is not too much steelwork aroun dthe venua as this will affect any radio mic system (investigate the faraday cage effect).

 

Also for the guy who posted that he had a system where transmitters were showing channel numbers and receivers were showing frequencies, both units are capable of showing either by using the set button to select (RTFM).

[audio]

Hmmm,

 

We had problems with drop outs with some freedoms we hired, on two different shows within about a month of eachother. Tried everything I could think of, including all suggestions above, and the packs worked fine a few cm from the aerials, but from the distance from onstage to the wings they were dropping out regularly.

Flew the aerials, didn't help.

Still don't know why.

Now we hire in shiny new Mipro packs and the problems have gone away. Very odd

 

John

[Bobbsy]

Hmmmm...I'd love to check out the faulty systems with a spectrum analyser and see what was happening.....

 

Bob