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Trapped Antenna Design & Build (008g1)
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- čas přidán 9. 05. 2022
- This video is about the stuff that goes into the successful design of a trapped antenna. I show what kind of effects the Resonant Frequency, Q and Capacitance Value associated with the traps have on the overall antenna system poerformance.
I show the three most common kinds of traps that are used:
* Discrete Inductor & Capacitor
* Coaxial
* Self-Resonant
I show how to tune your traps.
From some viewers ... I will add more as they trickle in.
* do not forget to pay attention to the voltage & current rating of the capacitor.
* adjust the L/C ratio so it resonates between the two bands and adjust the antenna to work for both bands. This reduces to voltage that will appear across the traps (and the trap capacitor).
I have provided all the files that you might need plus some extras ... see the links below.
=== PROMISED LINKS ===
Coaxial Trap Calculator Link
www.qsl.net/ve...
Self-Resonant Trap Calculator (spreadsheet)
drive.google.c...
I put it in a ZIP file so Google wouldn't try to open in in Google Sheets.
Self-Resoant Trap Website
squashpractice...
Coil Winding Spreadsheet that I created for myself and use
drive.google.c...
I put it in a ZIP file so Google wouldn't try to open in in Google Sheets.
Time Markers for Your Convenience
----------------------------
00:05 Introductions
01:35 The World of Antennas
02:23 DEFINITION: Antenna Bandwidth
03:32 A Symmetrical Dipole Antenna
03:48 Trapped Antenna Defined
04:15 Traps - the Multiband Magic
04:35 What are Traps???
05:30 What are Traps made of?
05:54 Trap Design Considerations
06:20 Resonant Frequency
06:51 The Experiment
07:20 Observations
07:22 Best SWR
07:28 Bandwidth
07:50 Quality Factor (Q) of the Trap
07:56 Q Defined
09:53 The Experiment
10:20 Observations
10:22 Best SWR
11:01 Bandwidth
11:25 Capacitor Value
11:47 The Experiment
12:27 Observations
12:28 Best SWR
12:38 Bandwidth
13:06 OVERALL
13:45 Types of Traps
13:53 Discrete Inductor & Capacitor
15:02 Coaxial Traps
16:03 Self-Resonant Traps
17:16 Choosing Your Trap Design
18:14 Modeling Requirements
18:44 A Leg Up on Building the Antenna
19:39 How to Tune a Trap
22:41 Final Comments and Toodle-Oots
-----------------------------
Excellent explanation Sir!
Thank you! 🙂
This is very interesting but to be honest some parts are way above my electronics/rf knowledge. But thank you for making it clear and informative.
You're welcome
Something that you didn't mention yet is the voltage that will appear across the trap. This also affects the choice of resonant frequency, since the voltage will reach its peak value when you transmit at the resonant frequency. I once built a 160/80m inverted L with a trap, which I tuned just below the 80m band. I managed to blow a 5kV doorknob to bits by operating full legal power close to the bottom of the band.
You are right. It didn't even occur to me. The trick is knowing how to definitively calculate that voltage; do you have a means to do this that you would like to share?
Then we run into higher voltage caps with MUCH lower Q and performance suffers. I suppose this is why so many traps are created as self-resonant because this elliminates the issue of capacitance voltage rating (??).
@@eie_for_you No, I don't know how to calculate it. I do know that the magnitude of the voltage is proportional to the Q and can be much greater than the source voltage. The shape of the frequency vs. voltage curve gets sharper as the Q increases.
You also need to consider the current rating of the capacitor.
I have a bunch of rg6 tv coax. Can I make antenna traps with it? If so how do I go about doing that with the aluminum foil that it is in it? Thank you for your videos!
Yes, you can use any coax to make these traps with. The RG6 is 75 Ohm characteristic impedance, but that wouldn't make any difference in this application. I've been doing some thinking about how to go about this. My first concern is that aluminum shield. Even if it has braid, that braid is probably aluminum, too. What if you terminated the coax ends with F connectors and then bought some mating F connectors (e.g. www.digikey.com/en/products/detail/amphenol-rf/222144/1989915) and made the needed connections to those? The coax would just plug into your connections. Of course, all of this adds weight, which is a concern.
My only other concern is the UV resistance of the outer sheath. if it is designed for outdoor use (e.g. cable T.V. coax), then you are probably ok.
I'm glad you appreciate my videos! 🙂
Choose the proper L/C ratio to resonate the trap between the two bands and make the antenna work both bands. This reduces the voltage rating. K5LYT
Good advice! Thank you for the input! Already I have seen how having the trap tuned lower than the high frequency band improves certain aspects of performance. This just gives more reason to do this.
@@eie_for_you If for instance a trap for an 80 / 40 dipole was resonant at 5 MHz, how different would that antenna perform at 40m compared with a trap resonant at say 6.8 MHz?
Well, it looks like the 80m band gets more and more useless as the frequency of the trap drops; the bandwidth suffers *badly*. On the other hand, the 40m band's bandwidth improves. I like what it does for the 40 meter and hate what it does to the 80m.
I put all the results of my simulations in a word file. I also put each of the simulations into their own file. You will find all of this (word files & nec files) in a ZIP file here:
drive.google.com/file/d/15_9LcnZKReVwLD2CyN4xy9EpIvriad6K/view?usp=sharing