[TowerTalk] Triplexer

[jimlux]

On 4/18/16 8:06 AM, Jim Thomson wrote:
> Date: Mon, 18 Apr 2016 10:13:00 -0400
> From: "Douglas Ruz / CO8DM" <co8dm at frcuba.co.cu>
> To: <john at kk9a.com>, <towertalk at contesting.com>
> Subject: Re: [TowerTalk] 6 x 2 unit...
>
> I have been thinking about a Triplexer to share my Tribander with both
> radios...what Triplexers do you suggest ?
>
> ##  I cant even begin to fathom the concept of a triplexer.   It must be
> pretty complex, to be able to stuff  1.5 kw into  say 20 + 10M , and RX
> on 15M !


Not necessarily, they're basically a bunch of filters.

The devil is in the details: what sort of bandwidth do you need, what 
are the terminating impedances (and how stable are they), what's the 
port to port attenuation needed (if you're putting 63 dBm into one port, 
and you want no more than -50 dBm coming out the adjacent port, that 113 
dB isolation requirement is non-trivial).

This is the kind of thing where you also need to pay attention to 
harmonic output from transmitters.  A 40m transmitter with -30dB third 
harmonic may be putting watts into the 15m port.




>
> ##  do they actually work good ?   Can you stuff 4.5 kw up through  213 U..
> or do you use bigger coax ?   They must be some serious coin.

0.405" coax can handle 3700V, so your practical limit is going to be 
current/heating.  On 40m, 3700W is the rating, on 20, 2600W.  So 4500W 
would be a lot.




>
> ##  can u get em to handle 40m as well, like on a 40-20-15-10m yagi ?

You can, but it can be tricky with harmonically related frequencies, not 
because of the filter, but because you have to worry about harmonic 
outputs of the transmitters.


There's also some passive intermod issues that come up.