RF transformer test

Thread Starter

DaniKowa

Joined Jul 1, 2021
41
Hi,

I bought some RF transformers for study and test purposes by mounting them on a breadboard and connecting them as in the image then:

+ and - is the primary where the input signal generated by a signal generator arrives, which in this case I used 100mV at 10Mhz.

Scope Probe 1 and Scope Probe 2 are the two outputs connected to the two channels of the oscilloscope.

Common GND is the GND used for the two probe grounds.

I expected to see an output voltage on the two probes, but it didn't happen. I know it's a really simple thing, but obviously I'm wrong in something. The voltages and frequencies used are within those compatible with the coils. COIL RATIO 1:2 in this case.

Thank you


ef.jpg
 

LesJones

Joined Jan 8, 2017
3,506
Does the frequency that you are using match the design frequency of the IF transformer ? IF transformers are designed to filter out frequencies away from the design frequency. 10.0 Mhz is not a normal frequency for IF transformers. 10.7 Mhz is a much more common. Another frequency that was common in medium and long wave receivers id 465 Khz.

Les.
 

Thread Starter

DaniKowa

Joined Jul 1, 2021
41
Can you get a waveform with the scope connected to the primary?

Bob
Sure. So i think the coil and and the signal gen it works.

Does the frequency that you are using match the design frequency of the IF transformer ? IF transformers are designed to filter out frequencies away from the design frequency. 10.0 Mhz is not a normal frequency for IF transformers. 10.7 Mhz is a much more common. Another frequency that was common in medium and long wave receivers id 465 Khz.

Les.
In this case i used this coil and i seem there's on range i think. The only doubt I have is a breadboard problem but it seems strange to me. However, I do some other tests. Can you confirm that the connection is still correct? Because I already have another one already on pcb and connectors even if with different package but it works.
 

ronsimpson

Joined Oct 7, 2019
1,533
Please (using a ohm meter) confirm you have a CT on one side of the transformer. There are 3 different types of transformers in the data sheet.
 

LesJones

Joined Jan 8, 2017
3,506
Please ignore my post #3 For some reason I was thinking about IF transformers rather than RF transformers in general.
When I saw the picture in your link in post #4 I realised you were talking about wide band RT transformers.
I can't see any reason why you can't see an output on the secondary. As the 38 uH primary will have a reactance of about 2.4 K at 10 Mhz it will not have any significant loading effect on the output of your signal generator. (Which I assume will be 50 ohm output impedance.)

Les.
 

Thread Starter

DaniKowa

Joined Jul 1, 2021
41
Hi sorry for late,

the problem is solved. A hole in the breadboard used for coil is worn out so do not guarantee a perfect component contact . Now it's ok but I expected the two outputs to be reversed 180 ° between them instead they are both with the same phase. It is probably the coil model that used the same winding for both secondaries.

forum_CC.jpg
 

ronsimpson

Joined Oct 7, 2019
1,533
On all of my Scopes. when 1=+ and 2=- that indicates I have "invert" channel 2 on. Please move probe 2 so it see the same thing as probe 1.
1630591596648.png
 

Thread Starter

DaniKowa

Joined Jul 1, 2021
41
Hi @ronsimpson

furthermore, I've done a measurement in this way:

Image 1 show both probe on one of the secondary output coil. I've swapped the probe channel, but the result is the same.

Image 2 is one probe each one secondary coil Also in this case swapping the channel nothing change about the phase.

Both the image have the signal overlapped because.

1.jpg2.jpg
 

Thread Starter

DaniKowa

Joined Jul 1, 2021
41
Hi Eric,
it's the same idea as I said in post 9. Probably the two secondaries are wrapped in the same direction. What confused me was that if I look at this schematic, I should expect a type of winding that allows reversed phase on the two secondaries at pins 1 and 3. Am I wrong? . I will ask the manufacturer for confirmation, but I believe it is. I don't see any other possibilities.

3.JPG
 
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