How to determine the frequecy rage limits of a line tuner. 1

[powereng1]

How can I determine the frequency range limits of a line tuner to make sure that the low and high frequencies I picked will work for a power line carrier application?

The line tuner is Trench, model A9508, bandpass, the frequencies I would like to use are:
DCB 129kHz
TTR 74kHz and 74.5kHz
TTT 133kHz and 133.5kHz

If I know the capacitance of the CCVT, how can I figure out if the frequencies I picked will work?

Thanks for the help.

 

[scottf]

You will need the Trench literature to be able to make a precise calculation.

If memory serves,

BW = 2*pi*(GMF^2)*Rl*CC'*k

BW = bandwidth
GMF = geometric mean frequency = for simplicity it normally works just to take the middle frequency between your lowest and highest frequencies used. So in your case GMF~104kHz.
Rl = characteristic impedance of the transmission line
CC' = effective coupling capacitance in uF = coupling capacitance of the CCVT in series with the blocking capacitor of the line tuner (normally this is 10 or 15 uF for a 2nd order BP line tuner).
k = is a factor based on the maximum return loss limit for defining the band-width. This would be in the Trench literature too. I believe a 10 dB return loss limit is close to k = 1 (something like 0.97).

 

[cranky108]

I rage at line tuners all the time.

The roll off of a line tuner is defined by the expected impedance loss. And how sharp the roll off is will depend on the designed Q.
Better to look it up in the manual.

Since the line tuner works with the Coupling capacitor, that will also make a difference.

 

[scottf]

I forgot to mention.... you've checked the line trap too?

 

[powereng1]

Thanks Scotff and Cranky108, looking at the manual and talking to the manufacturer the low end frequencies will not work with this type of tuner model. We tried using a different model (3rd order filter) line tuner and this type of tuner will only work with 10 dB return loss (10% reflected power) for the frequency we need. I am not sure if we can get it to work with the 10 dB return losses, the standard is 12dB reflected power min.

Thanks,

 

[cranky108]

There are tuners that are called high pass tuners that work well as long as your frequencies are high enough.

 

[scottf]

For those frequency sets, I would look at using a 2-frequency line tuner. Only question is whether you can cover 129-133.5 kHz on f2. It will come down to if your coupling capacitance is high enough, but I bet you can make it work.