Thank you, thank you, thank you! I have been searching the Internet for WHERE to make a trap resonant and you finally explained it. Lots of folks say "at the bottom of the band" but they don't say why or what the result is. You've gotten me over that hump! 72, Jim / K7TXA
What a great video. Watched it twice. What about the rf power? If I use a small capacitor, will I melt it with a 100 watt transmitter? Don’t have an antenna analyzer. What one should I get?
Thanks! Yes, R.F. power does, indeed, affect the choice of capacitors. The voltage rating of the capacitor is the important specification. The higher the power, the higher the voltage rating of the capacitor. The issue I found with the high voltage capacitors was that they had a lower Q, meaning the trap wouldn't trap as much even squarely at its resonant frequency. There is a lot of debate and great dearth of information about choosing the right voltage rating for a trap capacitor given a particular power being used. This is, in part, due to the fact that the actual maximum voltage that will appear across the capacitor depends on the frequency that the trap is tuned to. I **THINK** 1.5 KV capacitor should be sufficient for 100 watts. Nonetheless, I built my own capacitor to use for my traps (see the video here: ruclips.net/video/VIMhfX9quac/видео.html). Antenna Analyzer: There are some good ones like the RigExpert ($$-rigexpert.com/products/antenna-analyzers/#) and some not so good like the MFJ-259. If I were in your shoes, I'd much rather spend the money on a good nanoVNA (nanorfe.com/nanovna-v2.html). I say this because it will do soooooo much more for you that an antenna analyzer. It takes more work to use and learn to use (see my Play List on the the whole VNA thing), but it will open experimentation doors for you. I hope all of this helps! 🙂
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.
Ok Love this I work 40/20 phone area. Since space is messy where do I set the frequency to optimize the performance in the region of 7.15-7.3 and 14.15-14.3. Hi end, middle range, low end? That is only question remaining. My design is 14.1 but I am getting argued this will not correspond to best swr on 40-meter area. Also, Hi Q means less Band Width on 40?
First, the trap is tuned for the 14 MHz band so as to "hide" the extra wire required for 40 m while on 20 m. There is the forever debate where you want the trap tuned by a lot of people; each of these have their "good reasons" for tuning it there. My personal preference is near the top of the frequencies I want for the 20 m band. Why? Again, my reasoning ... It hides the extra wire best where I need it hidden the most. Then, as I move away from the resonant frequency of the trap, it becomes less effective in hiding that extra wire. Thus, as I move away from the higher end of the band, the antenna will "look" somewhat longer, widening the good SWR on the 20 m band. The trap Q will not affect the tuning on 40m because it becomes "invisible" to it. We are far away from the resonant frequency of the trap. Be sure to take in the video on how to create your own capacitors for the trap: ruclips.net/video/VIMhfX9quac/видео.html I hope this helps! 🙂
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! 🙂
So, I come back to you to get more information. A trapped antenna allows the same antenna to be used on two or more bands. So, I ask, What two (or more) bands is this antenna going to be used on? 🙂
@@geirha75 Aaaaah! 12 m CW 24.89-24.93 MHz (U.S. allocation). There are a LOT of opinions out there regarding the frequency traps should be tuned to. If it were me, I'd be shooting for 24.9 MHz. This way the trap truly, really "hides" the rest of the antenna for the 12 m band. 🙂
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
Thank you, thank you, thank you! I have been searching the Internet for WHERE to make a trap resonant and you finally explained it. Lots of folks say "at the bottom of the band" but they don't say why or what the result is. You've gotten me over that hump! 72, Jim / K7TXA
You are welcome! I ran into the same problem when trying to get definitive answers. I'm glad you found this helpful. 🙂
This is the best description of traps I've heard. Thanks for explaining this so well. Take care and 73!
Thanks, man! ... and you are very welcome! 73 🙂
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
What a great video. Watched it twice. What about the rf power? If I use a small capacitor, will I melt it with a 100 watt transmitter? Don’t have an antenna analyzer. What one should I get?
Thanks!
Yes, R.F. power does, indeed, affect the choice of capacitors. The voltage rating of the capacitor is the important specification. The higher the power, the higher the voltage rating of the capacitor. The issue I found with the high voltage capacitors was that they had a lower Q, meaning the trap wouldn't trap as much even squarely at its resonant frequency. There is a lot of debate and great dearth of information about choosing the right voltage rating for a trap capacitor given a particular power being used. This is, in part, due to the fact that the actual maximum voltage that will appear across the capacitor depends on the frequency that the trap is tuned to.
I **THINK** 1.5 KV capacitor should be sufficient for 100 watts. Nonetheless, I built my own capacitor to use for my traps (see the video here: ruclips.net/video/VIMhfX9quac/видео.html).
Antenna Analyzer: There are some good ones like the RigExpert ($$-rigexpert.com/products/antenna-analyzers/#) and some not so good like the MFJ-259. If I were in your shoes, I'd much rather spend the money on a good nanoVNA (nanorfe.com/nanovna-v2.html). I say this because it will do soooooo much more for you that an antenna analyzer. It takes more work to use and learn to use (see my Play List on the the whole VNA thing), but it will open experimentation doors for you.
I hope all of this helps! 🙂
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.
Excellent explanation Sir!
Thank you! 🙂
Ok Love this I work 40/20 phone area. Since space is messy where do I set the frequency to optimize the performance in the region of 7.15-7.3 and 14.15-14.3. Hi end, middle range, low end? That is only question remaining. My design is 14.1 but I am getting argued this will not correspond to best swr on 40-meter area. Also, Hi Q means less Band Width on 40?
First, the trap is tuned for the 14 MHz band so as to "hide" the extra wire required for 40 m while on 20 m.
There is the forever debate where you want the trap tuned by a lot of people; each of these have their "good reasons" for tuning it there. My personal preference is near the top of the frequencies I want for the 20 m band.
Why? Again, my reasoning ...
It hides the extra wire best where I need it hidden the most. Then, as I move away from the resonant frequency of the trap, it becomes less effective in hiding that extra wire. Thus, as I move away from the higher end of the band, the antenna will "look" somewhat longer, widening the good SWR on the 20 m band.
The trap Q will not affect the tuning on 40m because it becomes "invisible" to it. We are far away from the resonant frequency of the trap.
Be sure to take in the video on how to create your own capacitors for the trap: ruclips.net/video/VIMhfX9quac/видео.html
I hope this helps! 🙂
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! 🙂
I plan to make a trap for 12m band cw portion only. what resonance frequency should I design for. exactly 24 mhz?
So, I come back to you to get more information. A trapped antenna allows the same antenna to be used on two or more bands. So, I ask, What two (or more) bands is this antenna going to be used on? 🙂
@@eie_for_you 2 band vertical ant, only for CW portion. Vertical efhw 12m/17m with coax trap for 12m.
@@geirha75 Aaaaah! 12 m CW 24.89-24.93 MHz (U.S. allocation). There are a LOT of opinions out there regarding the frequency traps should be tuned to. If it were me, I'd be shooting for 24.9 MHz. This way the trap truly, really "hides" the rest of the antenna for the 12 m band. 🙂
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