aerial diplexer

derekh

derekh

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I am using an M501 icom transciever with a DS100 icom dsc unit. They use two seperate aerials. I am adding ais and don't want another aerial. Icom don't recommend diplexing the existing units for obvious reasons ie sending 25 watts into the ds100. I think it should be ok to diplex the aerial feeding the ds100 and take a feed to the ais. Can anyone recommend a suitable diplexer and supplier.
Thanks.
Derek
 
What you are suggesting is not really a diplexer but a power divider or splitter. A diplexer is a filter with a high pass output and a low pass output and a combined input, given that outputs and inputs can be swapped. (similarly dividers are also combiners). Typical example combined aerial feeding tv and fm radio via diplexer.
Diplexers can be very low loss often <1dB.
Splitters are typically 3.8 to 4.5 dB, which may be a significant reduction in sensitivity, or not.
Personally I've bought them from www.minicircuits.com, ZFSC-2-W+ would do it, it's $42 but I expect there are cheaper sources in the amateur radio world. Try to get one with sensible connectors on it, like BNC, as some adaptors can be either unreliable, expensive or both!
Maplins do a wideband one for £4.99, but it has F connectors on it, so it's probably 75ohm not 50 and it's not waterproof.
Hope that helps?
 
Smart Radio is one, Comar AST-100 another. I can't make a recommendation because I wouldn't use a splitter but they are the most popular. Typically they draw 150Ma and the insertion loss is about 1dB, perhaps a bit less.
They are more expensive by far than another antenna and don't provide redundancy. If you have a sail boat this is of more concern - losing the rig loses your antennae so a good plan is to have a deck mounted AIS antenna which can be quickly hooked up to your radio in the event of the loss of your masthead antennae.
On a powerboat I'd also use a third antenna and save the money and complication.
 
The AST 100 appears to be a switch type device, whereas the combiners/splitters/diplexers I was going on about are passive devices. A passive device is OK if your AIS is receive only, if your AIS is a transponder, then additional switching would be required to give sufficient isolation between the transmit of the AIS and the receive of the DSC controller.
I tend to favour separate antennas, but can see that it's not always the most practical solution. An economical solution might be to replace the DSC and VHF with an integrated unit, requiring only one antenna, leaving the second for the AIS.
Hope my previous post wasn't misleading?
 
thanks everyone for your comments. It looks like a third aerial is the answer. I just don't want the boat looking like a christmas tree. I'll look at the option of a short aerial mounted as inconspiciously as possible.
Thanks
Derek
 
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