UHF Antenna Splitting/Distribution

[timtheenchanteruk]

I have 2 trantec S4.5 UHF radiomics, I would like to mount them together, and use just one pair of antenna.

I am sure I have read somewhere that using passive for 2 is fine, but anymore needs active, is this true, and if so how reliable is it, or is it worth going the whole hog and getting an active splitter/distro.

 

Thanks in advance

[Bobbsy]

For only two receivers you're most likely better off with a good quality passive splitter (coupled, of course, with good, low loss cable, proper connectors and so on).

 

However, the equation is not nearly as simple as "2 good, more than 2 bad". Each component you add in the RF path will introduce a loss; the antenna will provide some gain. Putting together a link budget will tell you if the inclusion of several ways of splitter will still leave you with an acceptable signal.

 

Going for an active splitter is not always the panacea either. Unless designed well, an active splitter can introduce phase errors in the signal that can cause many problems. Similarly, depending on where in the chain the active splitter is placed, it can also raise the noise floor or increase the potential of interference from more distant TV transmitters. Some years back I bought the very expensive Sony active splitter and this has served me well with no problems. However, standard "domestic" UHF splitters have frequently been the cause of problems on systems I've been asked to look at.

 

Anyway, back to your initial query, for only two receivers a good passive splitter is probably your best choice; beyond two takes some maths rather than a hard and fast rule.

 

Bob

[badger]

as far as memory serves, Canford Audio flog a Trantec Active Antenna / Power splitter for about £350, but specifically for the S4000 range. It may be compatable with the S4.5.

[timtheenchanteruk]

£350 is a bit steep for my budget right now, I already have a pair of Tratec (not a typo) 2 way splitters, rated for 5-1000MHz, but the outputs are labled as 3.7dB, would these be suitable??

[Bobbsy]

I had a look on the Maplins web site and the tech details for the Tratec unit are fairly sketchy. They do mention that the insertion loss up around the frequencies you will be using is approaching 4dB. Only experimenting will tell if your link budget can afford a 4dB loss but in many radio mic applications this could be a factor. If going to remote antennas with a splitter lets you get the antennas signifcantly closer to the stage, you may well make up for the insertion loss.

 

On the positive side, Maplins claim that the splitter is suitable for digital TV so that implies that it won't introduce any nasty phase jitter (something DTB is susceptible to) so that bodes well.

 

Best I can say is that, at £4.99, try it and see.

 

Bob

[timtheenchanteruk]

Cheers, the spliters I have came from a cable installer (ie cable TV) so cost me nowt, ill just get some cable and give it a go then.

[Bobbsy]

Sounds like a plan. FYI, if you need more (or if you report to the Blue Room they work perfectly and everybody wants them!) when I googled the details, they came up as a Maplins product at the £4.99 price I mentioned.

 

Bob

[paulears]

I've had really good success with a batch of passive splitters I got from offshore RF equipment at a radio rally a few years ago. pretty decent loss figures, TNC connectors and solid construction. I agree with Bob - give them a try.

[dbuckley]

The Tratec units on the Maplin's web site look like perfectly ordinary CATV splitters, widely stocked and available, and with any name you like printed on the front if you buy enough. Never tried them on radio mics, but, as stated earlier, if the losses are acceptable they should work fine.

 

You can also get them with more than two outputs. there are also active variants available, which, if the received frequency is within the range of the unit should work adequately well, with the proviso that they are wideband, and thus any out-of-band (from the radio mic perspective) signal will also be amplified, which could end up crushing the front end of the receivers.

[StevieR]

I think you may have a problem with impedance matching with the Maplin units. These are designed for TV signals as, as such, are likely to have an impedance of 75 ohms (although there is nothing in the spec on the Maplin site). Radio microphone systems have an impedance of 50 ohms and so all connections, cabling and electronics should match this.

 

Additionally, wide-band splitters like this are more-lossy than a narrower band splitter. Personally, I would spend the money and get the correct widget for the job.

 

Steve

[Alec]

I spent a long time deliberating cheapy options for my 4 JTS radio mics. In the end I was fairly confident that I'd get *acceptable* for me results with TV technology, despite the impedence mismatch.

 

But, in the end, I couldn't be bothered with the messy setup that would leave me in the rack, and the risk of problems, and the time spent making up cables and mountings. My time is not chargeable, but is ultimately of value to me!

 

So, in the end, I just spent GBP250 and bought the tool designed for the job. The JTS active splitter is just perfect, comes with all the cables, and provides DC power to all receivers, allowing me to get rid of the 4 separate PSUs. Took moments to install, and makes for a neat rack - no complaints.