Transformer test fixture

[brandon7861]

I tore apart a few relays to use the contacts to make a couple IF can test sockets. I plan to have sma connectors to feed signals from a sig gen into one side (50 shunt amd 10k series to tank to keep sig gen matched but limit tank loading) and a jfet source follower on the secondary.

Sockets seem to work good, now to add the rest of it.

I think having to be really careful when soldering SMD stuff has made me sloppy with the big iron lol

 

[19wrc333]

Cool.

Did you see this toko tester?

Toko tester v3.0

Website van on1bes

www.on1bes.be

 

[brandon7861]

Cool.

Did you see this toko tester?

Toko tester v3.0

Website van on1bes

www.on1bes.be

That's cool, but I don't think it will do what I want it to. That looks like an oscillator that uses a fixed capacitor to calculate inductance based on frequency.

I want to see the bandwidth of tuned transformers (ones with built in caps) under light loading conditions. I went with 10k source resistance so the tuned primary sees about the same loading as it might in a radio's IF, so hopefully the Q I see is close to what it would be in a typical circuit. The idea is to be able to compare coils and get a general idea how they might behave.

I plan to make another set of can sockets for a direct connect version for S11 measurements. If I measure inductance at a frequency so low the internal cap disappears, I should be able to figure out the turns ratios. Just trying to make evaluating unknown ones in detail a little easier.

 

[brandon7861]

I finally put the parts on the can tester. Initial results on two cans. The little can is 455kHz, the big can is 16MHz. I have a 10dB attenuator in line, and with the transformer ratio and nothing but a jfet for a load, it the overall amplitude probably doesn't mean much. At least it gives a good idea of bandwidth for similar loading. At the very least, I now have an internal cap tester.

 

[19wrc333]

Certainly understand better now that I see this on what you were after.
This looks very useful.

Great stuff, thanks for sharing.

 

[brandon7861]

It really taught me something. I have heard it here before (many times) that the inductance is highest with the slug flush with the top of the can. Seeing it on the SA really made me think about that. I have often felt that turning the slug in deeper than flush still increased the inductance, but seeing it visually made it click.

I made a short video of it on my channel yesterday.

 

[brandon7861]

Thinking I should do a better video on this so I can intentionally sacrifice the internal cap and see how the response changes to highlight the false peak that is said to occur when the cap is bad.

I imagine with max inductance, there would be max flux and max transfer to the secondary. I think watching the difference from the perspective of a fixed IF frequency would be interesting.