Batboard

I have a friend who is setting up a small video production van (of a similar scenario as a pro television O.B. van but on a smaller scale).

Anyway he wants wireless comms from the van to his 2 camera positions.

His directors console talkback already has provision for wireless comms using a balanced line level audio input and output.

I have a ton of GM300's and want to set up one of those for him.

The remote keying of the simplex radio is easy, my thoughts on the balanced line audio are to get 2 x 600 ohm to 600 ohm transformers and connect one side up to Pin 5 and 7 for the tx audio and Pin 11 and 7 for the rx audio, and I think in theory that should give me the balanced line audio on the other side of the respective transformers.

Now the question is, how are these levels going to compare and handle the PROFESSIONAL LINE LEVEL audio from his directors console ?

Am I going to need a preamp for the RX audio going to his console and some sort of PAD coming back into the TX audio line ?

Has anyone done this ???

thanks
Mike

mrtor wrote:Has anyone done this ???

Should have a schematic around here that will help... will try and find it

Sundown wrote:

mrtor wrote:Has anyone done this ???

Should have a schematic around here that will help... will try and find it

that would be great thanks for the offer, I was intending this to be one of my new years day projects in the shed (once I wake up that is !!)

eagerly awaiting

regards
Michael

I was fishing for information on input and output levels a couple of weeks ago, and never got any answers.

Your idea for balancing the signals is on the right track, but I would look carefully at the impedences involved. A lot of pro audio gear has moved away from impedence matched 600 Ohm circuits, and towards high (10K-20K Ohm) impedence inputs.

As far as a com to radio interface goes, the hands-down best unit that I have ever seen is built by Production Radio Rentals, out of White Plains, NY. The owner is a member of this board under the screen name PRR.

The unit that PRR makes is built out of a GR1225 repeater and can be configured to send & receive straight audio, telco, ClearCom, or RTS.

Because it is built from a repeater chasis, it runs full duplex, with outbound audio on the air full-time and incoming audio received on a PTT basis. It also repeats the received radio audio out over the transmit side, so that radios in the field hear each other, in addition to personnel on the wireline side.

If you have the budget, their product is far superior to anything else that I have ever seen set up for that type of application.

Disclaimer: I did actually work directly for PRR on a show last year, but my impressions are strictly those of a duly impressed user, not someone trying to push a product.

HumHead wrote:I was fishing for information on input and output levels a couple of weeks ago, and never got any answers.

Your idea for balancing the signals is on the right track, but I would look carefully at the impedences involved. A lot of pro audio gear has moved away from impedence matched 600 Ohm circuits, and towards high (10K-20K Ohm) impedence inputs.

Typical, just when you think you have it nutted out, the buggers go and change the system...

Anyway, I know that this is 600 ohm balanced, but thanks for the heads up on that I shall not assume in the future.

HumHead wrote: As far as a com to radio interface goes, the hands-down best unit that I have ever seen is built by Production Radio Rentals, out of White Plains, NY. The owner is a member of this board under the screen name PRR.

The unit that PRR makes is built out of a GR1225 repeater and can be configured to send & receive straight audio, telco, ClearCom, or RTS.

Because it is built from a repeater chasis, it runs full duplex, with outbound audio on the air full-time and incoming audio received on a PTT basis. It also repeats the received radio audio out over the transmit side, so that radios in the field hear each other, in addition to personnel on the wireline side.

If you have the budget, their product is far superior to anything else that I have ever seen set up for that type of application.

Disclaimer: I did actually work directly for PRR on a show last year, but my impressions are strictly those of a duly impressed user, not someone trying to push a product.

That sounds good, but probably out of this guys budget, but I shall do a search on the net and see what I can find out about this for future reference. I am getting more and more involved in these sorts of things it would appear.

Cheers
Mike

Disclaimer: I did actually work directly for PRR on a show last year, but my impressions are strictly those of a duly impressed user, not someone trying to push a product.

Justin, do I send the check to the same place?

As for the GM300 interface, Mrtor basically has it figured out. The line level I/O of the GM300 is 600 ohms, though unbalanced, thus a simple 600/600 ohm line level isolation transformer will work fine. An IL-19 works well here. This is of course contingent on the output of the comms console having a source impedence of less than 600 ohms. If not, the appropriate transformer should be substituted. The HiQ series from Mouser works well, though if budget allows, I prefer either The Radio Design Labs or Sescom products for this application.

A few things to consider and watch for:
- As Humhead mentioned, source and load impedence of the comms console must be confirmed and the appropriate transformers selected.
- Output level of the comms console: Can the transformer accept the voltage level (at least 8, and as much as 14 volts).
- Transformer must be a shielded design; Farady shield and mu metal construction strongly suggested.
- Keep the wire lengths between the transformers and radio as short as possible and use a shielded "coaxial" style wire (standard stereo interconnect wire).
- Use two separate shielded twisted pairs for the run between the comms console and the transformers.
- Use a double shielded antenna coax (double braid or braid and foil) and a high quality connector. Keep the antenna(s) away from the transformers.
- Use a completely separate shielded single conductor or twisted pair for the PTT trigger if using one radio in simplex mode.
- I strongly recommend using a compressor/limiter on the GM300's input (we use the RDL ST-CL1) so as to prevent overloading the radio's input and/or over deviation. The ST-CL1 also will act as the balancing/unbalancing transformer and give you precise gain control over the radio's input.
- Detune the transmit power of the radio to 2-3 watts, assuming a typical indoor studio/venue; 5-6 watts for stadiums or arenas where your interface will be in a different part of the complex from your camera positions.
- If using separate radios for TX and RX, and your TX radio is set to constant broadcast, be sure to force air cool it making sure the heat has an unobstructed path to rise.
- Using a GR300 housing makes for a nice compact package if the system doesn't have to be rack mounted: Plenty of room for the support electronics, built in fan and PSU, places to mount XLRs and room for a duplexer if you choose to.

Hope this helps.

Henry

PRR wrote:

As for the GM300 interface, Mrtor basically has it figured out. The line level I/O of the GM300 is 600 ohms, though unbalanced, thus a simple 600/600 ohm line level isolation transformer will work fine. An IL-19 works well here. This is of course contingent on the output of the comms console having a source impedence of less than 600 ohms. If not, the appropriate transformer should be substituted. The HiQ series from Mouser works well, though if budget allows, I prefer either The Radio Design Labs or Sescom products for this application.

A few things to consider and watch for:
- As Humhead mentioned, source and load impedence of the comms console must be confirmed and the appropriate transformers selected.
- Output level of the comms console: Can the transformer accept the voltage level (at least 8, and as much as 14 volts).
- Transformer must be a shielded design; Farady shield and mu metal construction strongly suggested.
- Keep the wire lengths between the transformers and radio as short as possible and use a shielded "coaxial" style wire (standard stereo interconnect wire).
- Use two separate shielded twisted pairs for the run between the comms console and the transformers.
- Use a double shielded antenna coax (double braid or braid and foil) and a high quality connector. Keep the antenna(s) away from the transformers.
- Use a completely separate shielded single conductor or twisted pair for the PTT trigger if using one radio in simplex mode.
- I strongly recommend using a compressor/limiter on the GM300's input (we use the RDL ST-CL1) so as to prevent overloading the radio's input and/or over deviation. The ST-CL1 also will act as the balancing/unbalancing transformer and give you precise gain control over the radio's input.
- Detune the transmit power of the radio to 2-3 watts, assuming a typical indoor studio/venue; 5-6 watts for stadiums or arenas where your interface will be in a different part of the complex from your camera positions.
- If using separate radios for TX and RX, and your TX radio is set to constant broadcast, be sure to force air cool it making sure the heat has an unobstructed path to rise.
- Using a GR300 housing makes for a nice compact package if the system doesn't have to be rack mounted: Plenty of room for the support electronics, built in fan and PSU, places to mount XLRs and room for a duplexer if you choose to.

Hope this helps.

Henry

Absolutely, thank you Henry.

A further question on the compressor/limiter you mention the RDL unit. Any more info on where I can get those, perhaps a web page ?

Thanks for the thorough explanation

Cheers
Mike

http://www.radiodesignlabs.com/stcl1.htm

Try Production Audio in Melbourne. 03-9878-1444.
http://www.productionaudio.com.au

Henry

PRR wrote:http://www.radiodesignlabs.com/stcl1.htm

Try Production Audio in Melbourne. 03-9878-1444.
http://www.productionaudio.com.au

Henry

Thanks for the quick response. I shall take a look at the web page and then give Production Audio a call

Cheers
Michael