What...The...F....Unun?

 

Hi, Yesterday I decided to test a long wire antenna I got cheap last year. It came with a 9:1 Balun...Or so it was advertised. Anyhow, I decided after first test that it worked, but I wanted to open it up and have a look inside to see what was going on.

 Opening her up there seemed to be a spare loose wire. So I posted a quick question about it over to the nice bunch at rtl-sdr group on facebook. It quickly turned heavy, and we all debated Balun vs Unun until the sun came up.

But some great information was given, and we decided that this cheap WTFun must in fact be (possibly) a type of unun. It is still ongoing lol. Balun/Unun/Autotransformer Balun. You tell me in the comments.

So anyway, today I decided to do a simple test to see if any of the suggested alterations help with signal noise or performance.

To test, I soldered some dupont connections to quickly allow me to change through the ideas.

Pin 1) dupont pin soldered to original loose wire which we think should be counterpoise/GND or to pin 2

Pin 2) Another dupont pin to test the connection that Watcharapong Chuginda did

Pin 3) Another dupont pin which runs a few metres of wire to a crocodile clip to connect to a good ground source.

Pin 4) Another dupont pin to connect to Ground/Counterpoise on pin 3

Now to test (p.s i don't have an antenna tester yet, so I have to just compare in SDR software sorry for my amateurishness haha)

So onto the quick test.

Test number one) - in original format

 

Connecting up the long wire to the WTFun Red connector, and connecting RTL-SDR device to BNC connector at the base.

Picking up some signals on 19Mhz. It seems to be a good day to get HF signals, yesterday was stormy and things were dropping in and out a lot. from 1Mhz-30Mhz I can receive some stations.

I am however getting quite a lot of static and what seems to be POCSAG interference/overloading as I am in between two hospitals. There must be a lot of pagers going off.

Test number two) Pin 1 to Pin 3

Ok. Looking at the same 19Mhz station, it seems to be a little bit stronger, clearer, less noisy.

A marked improvement. The POCSAG interference seems to still be there. But stations which were inaudible before are now listenable. I can pick up stations at 7Mhz. 9Mhz is much more strong than before.

Test number three) Pin 1 to 2

 

 

This connection was described by Watcharapong on the RTL-SDR group.

 

Seems to be between the factory wiring and setup two. There is a signal improvement, however it does not improve as much as test two. It feels a bit different does test three.

Test number four) Pin 1 to Pin 2 - and - Pin 3 to Pin 4

This setup was suggested by Harold over at RTL-SDR facebook group. It seems to work similarly as test two and three.

The same 19MHz station comes through well. I'm starting to struggle to hear any major differences to the tests apart from the original wiring as that was definitely worst of all.

Bonus test five) - Pin 3 to Pin 4
For some strange reason... I don't know why, this wiring setup seemed to be best of all.

Things just seemed least statically noisy, stations seemed clearest. I have no idea how or what the maths onvolved is, but it's just an observation. It is a narrow margin but I think this might be the best. Correct me if I am wrong.

Conclusion
It seems for now I am choosing test 5 setup. it is all about personal preference, but at the time i did this test it seemed to give the clearest sound.

The test shows that connecting a ground or counterpoise is the most important thing to add to this 9:1 WTfun (balun or unun?) to obtain a much improved signal compared to how it arrives from the store. I would say it is junk as it comes from the store. However making a simple ground connection will significantly improve it to the point that I feel I already have made progress with my HF reception.

I would like to thank all the RTL-SDR contributors over at the Facebook group for making suggestions and providing feedback. I hope this provides some answers to this device for others.

Thanks for reading.

Update:

For comparison to the wtfunun from china, this morning I made a true 9:1 Unun using a micrometals toroid and It provides significantly stronger cleaner HF reception. So there you go
Thanks again for helping. I plan on later removing the insides of the wtfunun and placing the micrometals unun inside.

Reference Circuit:

Update 2:
I rewired the Wtfunun. I learned that if we follow the above unun schematic then the wtfunun is wired backwards. I did not have to rewind the wiring just change the connections to the above image.

rewired to match the wiring of the micrometals unun i made. Now testing it with gqrx

 

rewired wtfunun to 9:1 unun top, micrometals 9:1 unun bottom

 

It is similar. But different if we look around 1Mhz the radio stations are much higher peaks.

Now, I must work on reducing overall RF noise
- setup long wire outside instead of attic
- Try SDR HF using battery power instead of household mains
- Go out to the countryside and test
- Try a different HF adapter such as Airspy spyverter.

I read that most RTL SDR devices use a 1.2v switching power supply and that it is a source of harmonics and RF noise. I could modify the pcb, but I may just search for a better noise-free device.

Thanks.