[TowerTalk] Triplexer

[David Robbins]

on the other hand... if doing this for SO2R operation only one of the transmitters would be keyed at a time.  You 
would only have to worry about combined dissipation for multi-op stations or expeditions sharing multi band 
antennas.

Someone had a misconception on harmonics though a triplexer also.  a radio/amp say on 20m that generates
a 10m harmonic going into the 20m port of the triplexer would have that harmonic filtered out by the 20m bandpass
filter on it's port so it would not get to the 10m port at any significant level.  What WOULD be a problem is if the
antenna or something near it was rectifying and creating a harmonic, that would come back through the triplexer
to the 10m radio.


Apr 19, 2016 10:04:17 AM, jimlux at earthlink.net wrote:

On 4/19/16 6:19 AM, Jim Thomson wrote:
> Date: Mon, 18 Apr 2016 15:15:34 -0700
> From: jimlux 
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Triplexer
>
> On 4/18/16 8:06 AM, Jim Thomson wrote:
>
>
>> ## 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.
>
> &&& No, what I meant was say 3 amps, all running 1.5 kw RTTY.. simultaneously
> = 4.5 kw average power. Per Eimac, that would be the same as a 3 tone signal,
> with each tone having an average power of 1.5 kw.
> (Number of tones) squared, X 1.5 kw = 13.5 kw pep out.
> 13.5 kw pep out = 825V rms = 1166 V peak.


Summing three signals, the maximum voltage will be the sum of the peak 
voltages. at 1.5kW into 50 ohms, that's about 400V (387 actually). So 
three signals might combine at the peaks to 1200V, which is well below 
the voltage rating for most 0.405" coax (like RG-213/RG-8/etc)

However, the total power and loss dissipation is what will get you. The 
chart shows max power as 3700W for 7MHz and 2600W for 14 MHz. For such 
low frequencies, dielectric loss is negligible, so it's all IR loss, and 
will go as the square root of frequency (2600 = about 3700/sqrt(2))

what's really going on is that at 3700W for 7MHz, some amount of heat is 
being dissipated in each foot/meter of the coax, and that takes it to 
some predetermined maximum operating temperature, taking into account 
some (unstated) environment (is the coax immersed in water at 20C? fan 
cooled at 40C? or what).

You'd need to figure out the loss at each of your three frequencies, sum 
all the dissipations, and see if it works out.

I suspect it wouldn't, at least for the 3 transmitters at 1.5kW case.





>
> &&& 4.5 kw average, would be max worse case. Still, on CW, with all
> 3 on TX, it would still be aprx 2 – 2.25 kw average. So it may still work.
>
> &&& The other issue would be the tribander would be pointed in 1 direction,
> so all 3 bands would also be in one direction, which may not be what you want.
> But folks with rotating towers face the same dilemma.
>
> Jim VE7RF
>
>
>
>
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