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Very nice writeup Gary! I may have missed it, but curious about how using two FT240 cores stacked will behave vs total turns. I built one of these transformers with two FT240 type 43 cores stacked,

Mikek: Unless I am misunderstanding your test intentions, a network analyzer will not give you any signal strength indication. You would need a measuring receiver or a spectrum analyzer to check out

Here is a link that has all you need to know for 75 ohm NanoVna testing. https://volpefirm.com/nanovna-calibration-to-75-ohm-for-catv/ Larry, K4LED

The more windings, the more critical the parasitice become, and the less flat the transfer. Note that you can also buy ferrites that allow for half a winding, or even a quarter. Ferriet Varkensneus

MiniCircuits uses one inductor.? ?Common ground on the bottom, 75 Ohms at the top, and a tap for the 50 Ohm port.

Joe, yes you are correct. All he needs is a 75 ohm resistor or 75 ohm load to re-calibrate his NanoVna to 75 ohms. Thanks Joe. Larry, K4LED

Yes building or buying a 75 to 50 ohm matching transformer if that’s what you need (MiniCircuts sells them) is possible but it will cause a small insertion loss that needs to be accounted for if a

Or $2, plus shipping, from Minicircuits.

exactly. I'd do the cal at the end of the coax, too.

On 7/1/21 6:41 AM, Zack Widup wrote: I wouldn't sweat all these matching transformers, etc.? 75 isn't far from 50, so you're not going to have a "math and measurement" precision issue. What I would

I do not understand why a good 75 ohm calibration load would not make the thing be a 75 ohm test. Isn't that what the 50 ohm one is doing when you calibrate the dead short and the 50 ohms load? Joe

Zack, 12/10 turns is 2% off - certainly close enough as you say, but 11/9 turns is even better at 0.2% off. 73/72 John M0JBA

Normally the difference between 50 and 70 is neglectable. If you really know that the source/load is exactly 50 Ohm (that means you have measured that) and you really know the other side is exactly 70

I know. That's a problem in this application. Another possibility is a broadband impedance matching transformer with the appropriate ferrite toroid. I calculate 12 turns on the 75 ohm side to 10 turns

If your just making comparisons between antennas any mismatch would reduce the actual signal strength of both equally so a relative comparison could still be made. Larry, K4LED

Sorry, my mistake - I just detected that your picture shows already the H4, so I should change _from_ 5K to _1K_ But nevertheless it works well without the swap; the HI voltage is 2.2V - according to

thats all very interesting ... I'll need to read it a few times to 'digest' all your findings. thanks.

Quarter wave transformer for what frequency???? 54 MHz or 600 MHz.? ? ?Can't have both! 73? Kent WA5VJB Minicircuits does sell broad band 50-75 Ohm transformers.

The best way would be to use a quarter-wave section of 62 ohm cable. Lacking that, you may have to build some sort of antenna tuner. 73, Zack W9SZ

Good question, I'm sure part of it involves no 50-ohm cables, and probably calibration with a 75-ohm load termination, but there may be some other corrections to VSWR, etc. Let us know! 73, Willie