Tag Archives: Tufteln

Joshua explores Unun insertion loss (efficiency) comparison testing

Many thanks to Joshua (KO4AWH) who shares the following guest post:

Unun Insertion Loss (Efficiency) Testing

by Joshua (KO4AWH)

A simple “side-by-side’ method can be deployed with the use of a Calibrated NanoVNA to read back “S21 Gain” which is, in this case, signal loss from the output of S11 back into S21 through the identical windings. The gain (loss) reading in negative dB gives us the total signal loss through the windings. We can then divide by 2 to get the loss through one winding and then convert with a bit of math to an efficiency number.

p = 10^(x/10) * 100 where p = percentage 0-100% and x = loss in dB

Example: -2dB reading on “S21 Gain” on the NanoVNA divide by 2 for a loss of -1dB on each winding would be 10^(-1/10) * 100 = 79.4%

We have a 50 ohm signal coming out on S11 of the NanoVNA through the first winding to some unknown exact impedance but that is then converted back through the second unun into the S21 port where the signal is measured. It is therefore necessary to use identical windings for each test to ideally match the impedance change.

I like to run the signal test with the top and bottom of each band, take the average of the two, and then convert to efficiency, 100% being perfect. I record these values to then chart each band’s efficiency for the winding pairs. The goal here is to compare the different windings. For example, with a 9:1 used for a long/random wire, compare toroid sizes, number of toroids and in some cases the number of windings. One nice advantage to a 9:1 Trifilar winding is that you can increase or decrease the winding count in multiples of 3 while maintaining a 3:1 winding ratio. Take the square of the windings ratio (3) to find the impedance ratio of 9:1.

Here is one example of two different windings compared. Both are Trifilar but one with a single T80-2 toroid and 9 sets of turns and the second with a Double T80-2 and 12 sets of turns. 100% would be zero signal loss through the windings, 0% would be full signal loss. -3dB (loss) per winding would equate to a 50% efficiency in either single winding.

The difference between these two windings across the Amature Bands was quite surprising to me. I assume typical, often used windings will be decent across the bands. Here we saw a large improvement in access to the bands by adding several extra turns.

When each component of the station induces loss to the radiated signal, or the ability to receive, you have to improve each area for the best transmit and receive capability. This test is not foolproof, it is not the most accurate way to measure efficiency and maybe not the easiest but it gives me a comparative analysis of various windings with the tools available to me. If I can increase the performance of my windings, I can increase the performance of my station. Time to wind some more transformers!



Tufteln Antennas


The Elecraft T1 Protection Case by Tufteln

Long-time QRPer.com reader and supporter, Joshua (KO4AWH), runs an Etsy store with a wide range of products primarily designed for field operators. Over the past few months, Joshua has sent me various prototypes for feedback and also to test in the field. You’ll see some of his antennas in upcoming field reports and activation videos. I’m very impressed with his designs.

If you’re an Elecraft T1 owner, you should be especially interested in his T1 Protection Case.

Joshua sent me an early version of this clip-on case several months ago and it immediately replaced the simple cover I printed from a Thingiverse file. (To be clear, the Thingiverse case served me well for a couple years, but I prefer this one since it doesn’t require a rubber band to hold it on the T1.)

The Elecraft T1 is a hearty little ATU and I don’t worry about damaging it while tucked away in my SOTA pack, but the little buttons on the front are prone to be pushed with any amount of applied pressure. This can result in unintentional operation which can accidentally place it in bypass mode or at least shorten the life of your 9V cell.

The Elecraft T1 is not an inexpensive station accessory and, at the moment, they’re about as rare as hen’s teeth. The lead time on new T1s is counted in months rather than weeks (at time of posting, this is due to vendor board issues).

The Tufteln Protection Case simply snaps on the Elecraft T1 and protects the BNC connectors, ground point, and the front panel buttons.

The case material is durable and adds very little to the bulk of the T1.

Of course, you can’t operate the T1 with the case around it because the BNC connectors are covered, but I have propped up my T1 on the case while using it on rough concrete picnic tables. I’d rather the case be scratched than my T1!

If you own an Elecraft T1 and don’t have a protective cover, I’d encourage you to either print one, or buy Joshua’s T1 case. For years, I simply removed or reversed the 9V battery to keep the T1 from engaging while packed, but that doesn’t protect the buttons and (frankly) it’s a pain to pop the battery out and flip it for each use (then to remember to flip it back when packing away).

The Tufteln case is a simple and affordable ($16.50) solution!

Thanks for sending this to me, Joshua. I dropped my T1 while setting up my TX-500 for Field Day and it protected my favorite little ATU!

Click here to check out the Elecraft T1 Protective Case on Etsy.