Advice requested: Sennheiser Ch 70 and 38 from same remote antennas?

[alangeering]

Intro:

The church I help at has a mix of radio microphones but mostly relies on EW100 G1 and G2 mics in Channel 69. I'm going to re-tune these to Ch 70. To go beyond the 4 mic limit in Ch70 we're going to buy Ch 38 G3 equipment.

 

Our current set-up of our EW100 G1/G2 system:

Passive Directional Antennas - Narrowband (band E) Head Amps - Passive Split (ASP 2) - 4x Receivers

 

Problems:

The head amp/antenna booster isn't suitable for Ch 38. So adding another ASP2 and 4 x Ch38 Rx is not so simple.

 

Would the following work:

Antenna - Passive Split - Band E Amp - ASP 2 - Ch 70 Rx x4
              ¦
           Band GB Amp - ASP 2  - Ch 38 Rx x4

(or ASA instead of ASP2)

 

I'd rather have another solution that didn't mean 2 lots of Co-ax to each antenna!

 

Any advice appreciated - I'm guessing most of the pros here run entirely Band E or Band GB but don't mix.

 

Thanks,

Alan

[ramdram]

Must you use the paddles? It might be worth a punt to simply use the diversity pair aerials on the boxes themselves...assuming you have the room of course.

[chelgrian]

Any advice appreciated - I'm guessing most of the pros here run entirely Band E or Band GB but don't mix.

 

Do you actually need the head amps? It's highly likely that if you bought two ASA 1 and fed the antenna into them without head amps it would work fine. Don't forget the ASA 1 are unity gain where as the ASP2 are -3 db across.

[alangeering]

Don't forget the ASA 1 are unity gain where as the ASP2 are -3 db across.

 

Thanks for the suggestions. The ASA isn't on the UK sennheiser website (but is on the USA one) as it's still showing the ASP 2. This is probably the solution I'll have to go for... but buying two ASA is expensive. I might experiment with some different arrangements of ASA and ASP.

 

Must you use the paddles?

 

The congregation stand between the FOH receiver location and the platform. It's a long church. The directional paddle antennas are 3 meters up the walls so have clear LOS to the transmitters. Receivers are racked up and little antennas would be a squeeze. I'm still looking at the option of receivers on the platform - but I doubt the cost increase of getting EW300 gear with WSM can be justified. I like my team to be able to see the RM receiver screens (to check for mute/power/battery/problems).

 

Since we've got the antenna and the coax installed I'm just looking to make the best use of the previous investment.

 

Thanks again.

[paulears]

Efficient aerials for band 38 and band 69/70 are quite different physically - think back to TV aerials for the same bands. We had A,B and C/D and the performance of a band A in a C/D area was pretty well the same as having a random lump of metal in the sky! The Sennheisers for this reason use log-periodic designs and wide band amps - covering 450-866MHz. The boosters are frequency specific, but the splitters like the ASA3000 are wideband, as is the ASP2. So the only compromised part is the booster. I'm wondering why you needed the band specific booster? Could you not use the AB3700, which is wideband. I'm assuming you need a booster to overcome severe cable losses? Could be simpler to use lower loss feeder, and dump the pre-amp? Westflex-103 is popular but is pretty thick - 11mm(ish) diameter, and needs N types on the ends with short thinner jumpers to the paddles because it's pretty stiff.

[cedd]

I use a pair of log periodic paddles for exactly this purpose. I have a channel 70 rack and a channel 38 rack on the same pair of coaxes.

 

A slight word of warning - don't expect the same performance from the aerials in both bands. I see between 3 and 5 dB's lower signal in channel 70 compared to channel 38. I'd noticed poorer performance on my ch70 receivers but it was only when I got the aerial on a spectrum analyser with a tracking generator that I saw the peaks and troughs for myself.

 

I'm not saying don't use them (I'm still managing fine) but it's worth knowing about.

 

We could do with somebody building a nice passive bandpass filter for specific radio mic channels. I'd really like to have a channel 38 filter after my split in my ch38 rack, so there's no other rubbish getting to my receivers and contributing to RX desense. Similarly in my ch70 rack.

 

C

[chelgrian]

The congregation stand between the FOH receiver location and the platform. It's a long church. The directional paddle antennas are 3 meters up the walls so have clear LOS to the transmitters. Receivers are racked up and little antennas would be a squeeze. I'm still looking at the option of receivers on the platform - but I doubt the cost increase of getting EW300 gear with WSM can be justified. I like my team to be able to see the RM receiver screens (to check for mute/power/battery/problems).

 

Ah does this church have large stone pillars? If so you may be getting fresnel effects. There was a whole thread about this recently on this forum. RF is quite tricky and just putting bigger antenna and boosters in doesn't always help.

[ramdram]

Amen to that Chelgrian.

 

I did a bit of reading long after "that" thread faded out and, for a permanent installation, it might be an idea to experiment with all the options ref placement of stuff, for optimum performance that is. This is as opposed to trying to get a result AFTER you have found a convenient little nook in which to hide the kit. Almost as though you are actually engineering problems into the system...then trying to resolve said problems...

 

It does seem as though "you/we/us" are making a rod for our own backs if we have to faff around with log periodics (far from optimum solution in anyone's money) or buffer amps, etc, etc.

 

I appreciate having the rx very close to the tx (on your platform) is not ideal for monitoring the signal parameters so to speak, but, what is better, having the af on a multi to wherever with excellent audio results or being able to monitor the possibly lesser rf performance because it is more convenient to see how how poor the rf is in actual fact?

 

The fact you can't see the readouts is hardly a worry really...if something was detected going bad you can't do a lot about it mid sermon or address anyway.

 

If you have a multi you could at least have a wired mic to the pulpit or a hanging condenser over the sanctuary as your insurance.

 

However, I daresay you have a budget and you have to get on with it as best you can.

[alangeering]

Some more details on our situation:

 

Previous to my arrival the church had installed radio mics but had reception issues. They then paid a company to solve the problem - which they did by installing directional antennas, boosters and an ASP 2. Total cost was in the region of £1500.

 

The current G2 and G1 recievers work very well in channel ch69/ch70 with this set-up so I'm not too worried about fresnel effects etc. We have a system that works well it's just limited to 4 channels come 2013.

 

I'm new to the sound team but come with previous installation and theatrical experience and in my day job I'm an avionic engineer. My aim is to help the church get the best vaule out of what they have, and make good choices for the future. Currently there is very little to no budget.

 

If money were not a problem I'd go with EW300/EW500 side of stage with WSM to control. Unfortunatly this would mean expensive receivers and a new multicore (we don't have the channels free).

 

The fact you can't see the readouts is hardly a worry really...if something was detected going bad you can't do a lot about it mid sermon or address anyway.

 

Partially true in our case... but preachers/speakers have a habit of misusing the mute switch so we've implemented a big sign we can hold up to say "UNMUTE" when they forget. Should there be a more serious problem we can raise the "CHANGE MIC" sign. It's certainly helped us in the past. Unless you have receivers at FOH or a monitoring solution (WSM) then this isn't possible.

 

Thanks again. This is a great forum.

[alangeering]

Having slept and re-read advice I've come up with the folowing scheme for the addition of 3 receivers in ch38 to our currently ch69/70 system. Please let me know if you think there are any issues with this.

 

Broadband directional antennas --- ASA 1 (unity gain) --- 3 x Ch 38 Rx
                                     ¦
                                  AB 3-E Booster (Sennheiser recommend this to make up gain lost in ASP 2)
                                     ¦
                                  ASP 2 (passive split) --- 4 x Ch 70 Rx

 

In this scenario I only need to buy one ASA 1 but am limited to three new receivers (this might be enough) for a total of 7 channels.

 

Thanks,

Alan