Transformer T1-1T Output Impedance

Alfredo Mendiola Loyola

Dear All:

Does the Transformer T1:1T has an output impedance of 50 ohm through all the transformer bandwidth?

Does the transformer output impedance change on high frequencies?

Bandwidth: 0.08 to 200 Mhz

Branch. Mini Circuits

Regards

Alfredo Mendiola Loyola

Lima, Peru

K5ESS

Well I’ll take a shot at answering this and welcome any comments/corrections to my reply.  The T1-1T is a transformer with a one-to-one turns ratio, so within limits its output impedance should be equal to that of the source its connected to.  IF it were a perfect transformer which it isn’t.  The Input Return Loss gives a measure of how imperfect it is.  Let’s take the Return Loss figure for 80 Mhz.  and call it 10 dB.  So, if you connect the T1-1T to a device with a 50 ohm source impedance the output impedance of the T1-1T at 80 MHz. will be somewhere between purely resistive impedances of 96.2 and 26 ohms.  To see all the possible impedances presented for the 10 dB return loss you can draw a circle on a Smith Chart centered on 50 ohms normalized to one with a radius of 1.92.  See attached PDF.

Mike K5ESS

From: PHSNA@... [mailto:PHSNA@...]
Sent: Sunday, December 27, 2015 3:18 PM
To: PHSNA@...
Subject: [PHSNA] Transformer T1-1T Output Impedance

Dear All:

Does the Transformer T1:1T has an output impedance of 50 ohm through all the transformer bandwidth?

Does the transformer output impedance change on high frequencies?

Bandwidth: 0.08 to 200 Mhz

Branch. Mini Circuits

Regards

Alfredo Mendiola Loyola

Lima, Peru

Alfredo Mendiola Loyola

I understand that at 80 Mhz, I will not get an output impedance of 50 Ohm at the output of the T1-1T Transformer.

How Can I know the exact transformer output impedance at 80 mhz with a source with 50 ohm of output impedance.

How can I transform the 10db of return loss to impedances?

Thank you for the information.

Regards.
Alfredo Mendiola Loyola

K5ESS

Alfredo,

Well I don’t off-hand know of any way other than measuring it.  The T1-1T spec sheet gives the magnitude of the Return Loss but not the phase so the actual output impedance of the transformer at 80 MHz could lie at any point on the circle drawn on the attached Smith Chart.

Anyone out there want to chime in on this?

Mike K5ESS

From: PHSNA@... [mailto:PHSNA@...]
Sent: Monday, December 28, 2015 11:10 AM
To: PHSNA@...
Subject: RE: [PHSNA] Transformer T1-1T Output Impedance

I understand that at 80 Mhz, I will not get an output impedance of 50 Ohm at the output of the T1-1T Transformer.

How Can I know the exact transformer output impedance at 80 mhz with a source with 50 ohm of output impedance.

How can I transform the 10db of return loss to impedances?

Thank you for the information.

Regards.

Alfredo Mendiola Loyola

vasilyivanenko@...

Alfredo Mendiola Loyola

This is the link of the schematic,

73s
Alfredo

drmail377

* Alfredo Mendiola Loyola,

You asked: "How can I transform the 10db of return loss to impedances?"

You can easily calculate the minimum and maximum real (normalized) impedance limits for a given Zo and return-loss. (There are many references on the Web.) Here's one online calculator that may help as well as providing the equations:

http://chemandy.com/calculators/return-loss-and-mismatch-calculator.htm

The nice thing about the Smith-chart is that by plotting a circle normalized to Zo you can easily see how the real and imaginary parts change. Of-course you could also calculate the circle shown on the Smith-chart in a spreadsheet. Just be careful to handle the signs for the non-zero imaginary variables properly. Another (more rigorous method) is to plot and/or extract the complex (real and imaginary) data provided in the manufacturer's S-Parameter data for the transformer. But this is beyond the scope of my post, and I'm not sure if Mini-Circuits provides this data for the transformer in-question.

* Mike, K5ESS

What did you use to plot the nice Smith-chart circle?

Best 73's, David WB4ONA

K5ESS

David,

Well I cheated.  I pasted the Smith Chart .jpg image into Microsoft Visio, drew a line from R=0.52 to R=1.92 to determine the circle diameter needed.  Drew the circle, centered it on the line and deleted the line.  Not very elegant but OK for a quick response.

Best 73’s and have a great 2016

Mike K5ESS

From: PHSNA@... [mailto:PHSNA@...]
Sent: Saturday, January 02, 2016 9:47 AM
To: PHSNA@...
Subject: [PHSNA] Re: Transformer T1-1T Output Impedance

* Alfredo Mendiola Loyola,

You asked: "How can I transform the 10db of return loss to impedances?"

You can easily calculate the minimum and maximum real (normalized) impedance limits for a given Zo and return-loss. (There are many references on the Web.) Here's one online calculator that may help as well as providing the equations:

http://chemandy.com/calculators/return-loss-and-mismatch-calculator.htm

The nice thing about the Smith-chart is that by plotting a circle normalized to Zo you can easily see how the real and imaginary parts change. Of-course you could also calculate the circle shown on the Smith-chart in a spreadsheet. Just be careful to handle the signs for the non-zero imaginary variables properly. Another (more rigorous method) is to plot and/or extract the complex (real and imaginary) data provided in the manufacturer's S-Parameter data for the transformer. But this is beyond the scope of my post, and I'm not sure if Mini-Circuits provides this data for the transformer in-question.

* Mike, K5ESS

What did you use to plot the nice Smith-chart circle?

Best 73's, David WB4ONA