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[keven mcdonald]

Hi folks

I'm looking to create a wide area system akin to wisycom reportage systems using an Axient digital quad RX, with a beltpack attached to a 1W booster. We've used similar kits with wisycom and other analogue modulating transmitters really successfully. The attraction with Axient is quadversity receive, where we can have receiving antenna in 2 different locations. I've mentioned this more generally on the forum before but a potential flaw has been mentioned in my plan...

I'm in the UK, and it has been mentioned that we may have trouble licensing digitally modulated transmitters at 1W regardless of band, apparently to do with how the sidebands mask other TX. Anyone here with any experience of such a thing, particularly with regards to licensing such a system through PMSE?

Cheers,

Kev

[Henry Cohen]

Hi folks

I'm looking to create a wide area system akin to wisycom reportage systems using an Axient digital quad RX, with a beltpack attached to a 1W booster. We've used similar kits with wisycom and other analogue modulating transmitters really successfully. The attraction with Axient is quadversity receive, where we can have receiving antenna in 2 different locations. I've mentioned this more generally on the forum before but a potential flaw has been mentioned in my plan...

I'm in the UK, and it has been mentioned that we may have trouble licensing digitally modulated transmitters at 1W regardless of band, apparently to do with how the sidebands mask other TX. Anyone here with any experience of such a thing, particularly with regards to licensing such a system through PMSE?

I can't address the Ofcom regulations, but in order to amplify the digital signal properly - and keep the emissions within regulatory compliance - you'll need a very linear amplifier, either specifically designed for wideband digital signals, or a unit with a CW P1 of at least 10dB more (10W in this case) than your target output power. Don't forget to consider the amplifier's gain and the subsequent input required to achieve a stable +30dBm output, which you'll need to measure with a true RMS RF power meter or a spectrum analyzer that can do channelized power measurements.

Then remember power supply considerations: An amplifier of this RF power level will need lots of current at the rated voltage. In general try to get an amplifier that operates on 12VDC, this way you can use common RF camera batteries (IDX or Anton Bauer) with everything mounted on a utility belt. If you think your talent can handle the weight of two batteries, you can use a 24V amp.

[keven mcdonald]

I can't address the Ofcom regulations, but in order to amplify the digital signal properly - and keep the emissions within regulatory compliance - you'll need a very linear amplifier, either specifically designed for wideband digital signals, or a unit with a CW P1 of at least 10dB more (10W in this case) than your target output power. Don't forget to consider the amplifier's gain and the subsequent input required to achieve a stable +30dBm output, which you'll need to measure with a true RMS RF power meter or a spectrum analyzer that can do channelized power measurements.

Then remember power supply considerations: An amplifier of this RF power level will need lots of current at the rated voltage. In general try to get an amplifier that operates on 12VDC, this way you can use common RF camera batteries (IDX or Anton Bauer) with everything mounted on a utility belt. If you think your talent can handle the weight of two batteries, you can use a 24V amp.

Cheers for this Henry. For info this was the unit I was looking at:

https://osjdc3i0amq1yt5xh4ckyyj1-wpengine.netdna-ssl.com/wp-content/uploads/2018/05/spa001_datasheet-2.pdf

Indeed - the idea is to use a V-lock battery and mount in a shoulder carry type arrangement. So pardon my ignorance - this unit will provide 1W output with a 30mW TX on the pack with analogue transmission. My (wrong) assumption was that I'd get the same performance with digital modulation. I think it may be time for a good read up on RF theory!

Kev

[Henry Cohen]

Cheers for this Henry. For info this was the unit I was looking at:

https://osjdc3i0amq1yt5xh4ckyyj1-wpengine.netdna-ssl.com/wp-content/uploads/2018/05/spa001_datasheet-2.pdf

Indeed - the idea is to use a V-lock battery and mount in a shoulder carry type arrangement. So pardon my ignorance - this unit will provide 1W output with a 30mW TX on the pack with analogue transmission. My (wrong) assumption was that I'd get the same performance with digital modulation. I think it may be time for a good read up on RF theory!

That amp will not work for a 1W output of a digital transmission scheme. 100mW will be about the maximum linear output that amp will be able to deliver. Ask them if they can change the frequency range of the http://www.sarastech.co.uk/images/pdf/spa1014-11-37_datasheet.pdf or see if they have a spec sheet on the http://www.sarastech.co.uk/index.php?option=com_content&task=view&id=70.

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