Tuning Antenna Traps (026)

[@acestudioscouk-Ace-G0ACE]

Really useful Ralph, thank-you. Certainly a good addition to the toolkit.

[@eie_for_you]

Thank you! I'm glad that you found this helpful! 🙂

[@SpirosAmpatielos]

Very nice to know all this staff. very helpfull. I like to ask you if you know how to measure the traps of a mosley cl-33. Do i take each coil out from the aluminium tube or there is a differend way?

[@eie_for_you]

Hmmmmm...I honestly do not know the answer to that question. I have never had to do that. The aluminum is non-magnetic, so it *should* not (?) have an effect on the resonant frequency. With that said, I am not sure if the shielding effect of the alluminum would prevent this method from working. If it were me ... I'd *try* it without disassembling the trap and see if it works. If it is inconclusive or doesn't work at all, I'd disassemble it and try again. Sorry that I cannot be more help.

[@PD0G]

@@eie_for_you I would like to continue on this topic, but I had sent you a message today that I had not yet succeeded. Now I'm sitting here reading and I have that too. With an aluminum bus it is an LC circuit so you cannot remove the bus otherwise the LC circuit is no longer correct. PD0G

[@eie_for_you]

@@PD0GInteresting. I can potentially see the aluminum affecting the capacitance. Being that is is non-Ferris, it should affect the inductance. I haven't tried this with a trap from a Yagi ... yet

[@smellthecoffee5314]

Interesting video - thanks. How would you tune a small toriod based trap using a nanonva ? Can you still use a the wire loop method ?

[@eie_for_you]

I have not had the pleasure of doing that ... yet, BUT, a tuned circuit is a tuned circuit. I am assuming that it should work the same.

[@TheTransam4350]

how do you get to that test screen on the nanovna? could you reply with a quick instruction on that part? i can only find the swr option that I tune my antenna with and that reads 90 something, I am pretty sure I am not that far off, I would like to see the mHZ like you have in the video here, any suggestions?

[@eie_for_you]

I have to admit, I used my high end VNA for the video ... its easier. BUT, here is how to get what you need on your nanoVNA. What you are looking for is "S11 Return Loss". 1. Set your frequency extents (STIMULUS->START & STOP) 2. Turn off all unnecessary traces. (DISPLAY->TRACE, then double tap TRACE 2 through 4) 3. Set return loss in dB format (DISPLAY->FORMAT->LOGMAG) 4. You will likely need to set the scale to make it more visible. (DISPLAY->SCALE->SCALE/DIV) I just did (1->x1). You might have to use something different depending on your test setup. If you are using the nanoVNA software with your PC, then set your start and stop frequencies. Click on the Display Setup button. Choose "S11 Return Loss" for one of the displays. If it were me, I'd set all of the rest to "none." Then your are good to go. Hope this helps! 🙂

[@TheTransam4350]

@@eie_for_you thanks for the response

[@eie_for_you]

No problem! :-)

[@roy-wn3f]

Thanks - nice succinct video.

[@eie_for_you]

Thanks, man!

[@reedreamer9518]

It would have been useful to tell us how you set up your VNA - e.g. what format/scale are you using?

[@eie_for_you]

Aaaaah... well, based on the fact that this was also done with the Antenna Analyzer which is looking at SWR, the measurement was done with S11/Reflection with the VNA (what they call it depends on the particular VNA - S11 is the standard VNA nomenclature - Reflection as seen by port 1 at port 1). Format-wise, this depends on your preference. dB or SWR doesn't make much difference. dB (return loss) will show a much narrower point of resonance than SWR just because of the math associated with it. Scale ... this depends on the coupling with your loop. This is so very variable, there is no way for me to give some sort of definitive number to it. I position the loop for what looks like the response I will get and then just tell the VNA to do an "auto-scale." Hope this helps.

[@PD0G]

I watched the film with admiration, I also tried this with the Comet CAA 500 Mark II, but it was not successful yet. I don't know if it is possible with the Comet CAA 500 Mark II?

[@eie_for_you]

I am so glad you found the video helpful. To answer your question, it should work with any antenna analyzer. The idea is that at the frequency of resonance, the trap "sucks" energy out of the loosely coupled loop and, thus, the apparent SWR will dip on the antenna analyzer. You are not looking for a specific SWR reading, just the frequency where the SWR dips to its lowest point. Hope this helps. :-)

[@wechselrichterschaltungen]

@@eie_for_you super erklärt.

[@garrykraemer8993]

Ralph, which side of the 20m band should the trap be tuned? 13.9 or 14.4? Current at the resonant freq will be max. What is best practice? TNX. WD0DUD

[@eie_for_you]

Goooooooood question. I tuned my own 20 meter traps for 14.3, the top end of the band. My reasoning is that I wanted my antenna to look longer and longer as I went down in frequency, thus giving me the flattest response that I could get for the 20 meter band. I honestly didn't give much thought to current. I was concerned a bit with the voltage across the trap, though. I also discovered that the higher the voltage rating of the capacitor, the lower its Q. 🙂

[@victoryfirst2878]

HOW would I make a 75 ohm to 300 ohm balun for my TV antenna ??? I am making my own gray-hoverman TV antenna and would like to make my own transformer without buying one made in CHINA. Thanks vf

[@eie_for_you]

My initial thought was one made out of coax, but this type is frequency specific. Such as making one for the 144-148 MHz Amateur Radio band. TV covers a very wide frequency range that this may or may not work well with. It is a 1/2 wavelength piece of coax (electrically speaking, including the velocity factor ... thus, the frequency dependence)feedline connects to it and one side of the antenna. The other end of the 1/2 wave coax connects to the other side of the antenna. The shield of the feedline and both ends of the 1/2 wavelength coax are all connected together. Otherwise, you are looking at more of a traditional Guanella 4:1 Balun. The trouble you are going to have is finding the right toroidal core for the frequencies you are looking to cover. I suggest checking out Amidon, Kemet, and Fair-Rite Products.

[@victoryfirst2878]

@@eie_for_you Thank you for the advice Sir.