1.8 GHz Wireless Microphones

[Lamplighter]

Has anyone used any of the cheaper offerings in the 1.8 GHz band. I am looking for any practical experiences.

I am trying to sort out a local theatre group with some additional channels and 1.8 GHz seemed a possible solution.  I have found one model with 16 channels and a statement that up to 6 simultaneous channels can be used. I enquired of the supplier what were the 16 channels, what was the minimum frequency separation and also maximum Tx deviation. This seemed to me the basic information required to have 6 channels co-exist. The reply was "usually the available channels in a single back are the channels with the less interferences" so no help there.

The second unit claims 8 banks of 12 channels so I assumed I would be ok to use 12 channels together. I enquired if this was so, no it's a maximum of 4 channels. The same questions as before Frequency separation and deviation gave me "400 Minimum" and then "

Please understand, I just can offer you official Data from us. 

U518 // 1785 – 1800 MHz // four systems can be used simultaneously "

To be clear I wasn't expecting miracles at sub £300 channel  but 4 channels in a 19 MHz bandwidth seems ridiculous when quoting a minimum separation. I did a quick calculation and easily fitted 12 intermod free channels in the band using 100 kHz as the TX deviation. 

Any real world observations welcome.

[DavePallant]

I was thinking you were trying to find more unlicensed wireless channels but it looks like 1.8GHz is one of the licensed bands under a standard Ofcom license.

I would ask if you had used up all available licensed channels in the GB band 606.5-613.5MHz and the E band 823-832 before looking at the 1.8GHz band. I reckon there are about 24 channels available in GB and E with the Sennheiser systems I use and they have the XSW2 units for about £300 a channel which are perfect for theatre groups if you cannot afford their G4 system. (Other manufacturers are also available!)

Dave

[Lamplighter]

Hi Dave

To clarify, the group already has maxed out on channel 38s, 64/65 and 70, largely due to using older, fixed channel systems. There are plans afoot to replace this but funds are currently very limited due to investments in building infrastructure. I am looking for a cost effective way to increase their channel count whilst not blocking the future improvements in the existing bands. 1.8 GHz seems to meet this requirement. Sadly the current price of the XSW 2 seems to be around £400 per channel.

Brian

[DavePallant]

Hi Brian,

Had not realised everything else was full. There is no 1800MHz (1G8) in the XSW range either it appears. I looked at the Sennheiser and Shure digital systems thinking that they might give me more channels in the GB range but although there are other improvements going digital, extra channels is not really one of them. I ended up simply buying more channels in the 823-832 E band which you have already done. 

The U518 system info you quote there does seem to be strange that it only offers 4 channels when Sennheiser seem confident they can put 12 in the same frequency space albeit at a higher price with the G4.

Dave

[Lamplighter]

Hi Dave

I have a couple of the T-Bone 1.8 GHz units on order. They claim 6 channels in the band out of 16 preset frequencies. When they arrive I will put them through their paces and report back. 

[sandall]

10 hours ago, DavePallant said:

The U518 system info you quote there does seem to be strange that it only offers 4 channels when Sennheiser seem confident they can put 12 in the same frequency space albeit at a higher price with the G4.

Iffy filtering on the receivers?

[DavePallant]

19 hours ago, Lamplighter said:

Hi Dave

I have a couple of the T-Bone 1.8 GHz units on order. They claim 6 channels in the band out of 16 preset frequencies. When they arrive I will put them through their paces and report back. 

I would wonder how to know which 6 from the 16 to use?! There is an auto button on the receiver to find an "unused" channel but it would be nice to know how it worked out which channel of the 16 to use next!

[Lamplighter]

The official answer pre purchase

"usually the available channels in a single back are the channels with the less interferences. 

Unfortunately one unit was damaged on arrival, the other works. They have actually got 16 banks of 12 channels. I checked bank 1.

1795.650

1796.050

1796.750

1797.250

1797.650

1799.000

1799.400

1775.700

1786.100

1786.950

1787.450

1788.300

Life is too short to read the remaining 15 banks!

looking at the separation between channels we have 400, 700, 500, 400, 1350,

400,  miss the gap between channels 7 and 8, then 400, 850, 500, 850 all in KHz, then 7. 5 MHz between channels 12 and 1.

so a very strange combination. Taking the first 7 channels we have very obvious 3 transmitter 3rd order intermods.  However taking all 6 even numbered channels we have good spacing and free from 3rd order intermods. 

I set a transmitter to channel 1 and receiver to channel 2, the minimum spacing in the bank and even with Rx and Tx aerials touching and Tx audio driven did not get breakthrough on the receiver. A crude test but seems to indicate a reasonable adjacent channel performance. The accompanying booklet gives the deviation as +/- 55KHz. It is frustrating that all my test gear only goes to 1500 MHz so I am not able to do any precise measurements. 

I cannot fathom the logic of the preprogrammed channel/ banks and the 6 channel recommended limit. I can easily arrange 12 channels in the available bandwidth with a minimum separation of 400KHz and 100Khz deviation, clear of 3rd order 3 transmitter intermods. It's as though there is a hidden trap somewhere.

It will be some time before I can fully explore the practical limitations on some real world site, so anyone actually used 1.8 G in the real world?

Brian

 

 

[Simon Lewis]

I've not used the 1.8GHz band radios but do remember from a training session that the Sennheiser G4 1.8GHz units had a better designed front end filtering that allowed linear spacing of adjacent frequencies, something that has carried over to their new(ish) EW-D range. Their gear may be pricey but seems well designed. Hopefully you can get your new purchases co-existing happily?!

[Lamplighter]

Hi Simon

Improving the receiver front end is always a good thing, however it cannot sort out the intermods caused by linear frequency spacing  in analogue systems (assuming that means that each channel is spaced the same from its adjacent channel). This only works in the digital realm. In the world of radio microphones most intermods are transmitter related, so intermods generated by equally spaced transmitters will still fall in the centre of the receiver passband. Improved receiver filtering will certainly assist with adjacent channel problems and possibly allow more channels in a given spectrum.

Currently I am only purchasing 2 channels of 1.8 GHz equipment, until I have gained enough experience to see if larger numbers are viable. The EW-D range looks interesting, but are currently beyond any foreseen budget. 

Brian

 

[DavePallant]

The 12 channels in that list are only the lower part of the 1785 - 1804.8MHz bandwidth available for beltpacks (50mW max). That would indicate there is plenty of bandwidth available to spread just 6 channels around in...?

Dave

[Simon Lewis]

On 1/25/2023 at 8:41 PM, Lamplighter said:

Hi Simon

Improving the receiver front end is always a good thing, however it cannot sort out the intermods caused by linear frequency spacing  in analogue systems (assuming that means that each channel is spaced the same from its adjacent channel). This only works in the digital realm. In the world of radio microphones most intermods are transmitter related, so intermods generated by equally spaced transmitters will still fall in the centre of the receiver passband. Improved receiver filtering will certainly assist with adjacent channel problems and possibly allow more channels in a given spectrum.

Hi, Brian,

I found this quote from a report "Technology Evolution in the PMSE Sector":
 

Quote

Sennheiser Evolution 100G3-1.8GHz range tunes only 1785-1800MHz, and includes ferrite directional couplers: this equipment offers 400kHz spacing without intermodulation planning

Perhaps it is just improved receiver filtering?

[Lamplighter]

Possibly referring to IEM transmitters?

 

[cedd]

I had a long chat with Sennheiser about this at Plasa. They have circulators on their antenna inputs (that'll be the ferrite directional couplers) which they said means they're essentially intermod-free. Just space the channels correctly and get on with it. I was really quite amazed by the claim, but am not an RF circuit design expert, so can only take them at their word. 

[Lamplighter]

That makes sense, fitting circulators in the transmitters will drastically reduce the intermods between them, the major source of the problem. It is interesting that they have developed them to be small enough to do this.