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Posted: 9/18/2020 12:47:21 PM EDT
Making this thread so as to stop hijacking Mach's thread
FEEL FREE TO ADD YOUR OWN HERE Quoted: Cool. I just made a 1/4 wave ground plane for 2m. Tomorrow I'm doing a coax dipole. Then I'll see what kind of SWR I have. decided to finish today. at 146.520 Coax dipole gets 2.70, ground plane is 7.50 time to do more reading and try to find out where I went wrong.I think I know Quoted: alrighty. The vertical dipole used these plans: link used 25' instead of 7 meters of RG58 Ground plane is this one 12 gauge solid copper. where i think i went wrong is, i left the insulation on and only stripped where a metal to metal contact is made. all 5 elements are 19.20"end to center of hole. all elements are a single 44" piece, bent in half then twisted together with drill, giving 2 12ga conductors. and I just had a thought, i dont think the radiator element legs are touching each other at the bottom, so it's seeing about 40" of copper wire instead of 19". @Nmbmxer asked for pics. None of the vertical dipole that would show anything. I think my problem there was not feeding the shieldinng back over the cable, but removing it as shown in my link above. I will try again in that one. As for the ground plane, it was tested while hung on a bunk bed. Pay no attention to the guard dog and oppossum.  Attached File Attached File Attached FileI think my fail on this one was not soldering the two ends of the radiating element together. Electrically it's closer to 38", not the 19 it should be |
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Posted: 9/18/2020 1:00:24 PM EDT
[#1]
get rid of all that twisted wire
just use regular wire, this isn’t a 1955 twisted pair telephone circuit  also, test the SWR out in the open, away from bed springs and stuff that will de-tune it  Attached File |
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Posted: 9/18/2020 1:09:09 PM EDT
[#2]
I agree on not needing twisted wire, mine is 1/16 brazing rod and it works fine. You could try soldering the wire together, or baring more insulation and making sure they are touching. The antenna in the video looked larger than 2m but it might have just been the camera angle, you want the radials bent down ~45. I'll upload a photo of my 1/4 wave ground plane j-pole thing in a minute with my phone.
 Attached File |
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Posted: 9/18/2020 1:40:27 PM EDT
[#3]
Looks like today I'll untwist my wires, use a single conductor, and verify the lengths.
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Posted: 9/18/2020 2:09:36 PM EDT
[#4]
Start too long.
It is somewhat easier to make it shorter than it is to make it longer. |
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Posted: 9/18/2020 4:21:03 PM EDT
[#5]
Twisting the wires makes it structurally stronger and should not change the resonance much except it will act longer than it is for a single wire. It will mostly act like a bigger wire which means it will need to be slightly shorter
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Posted: 9/18/2020 4:37:34 PM EDT
[#6]
Quote HistoryQuoted: Twisting the wires makes it structurally stronger and should not change the resonance much except it will act longer than it is for a single wire. It will mostly act like a bigger wire which means it will need to be slightly shorter I was going for strength. Lots of lessons learned here. I remade it with single bare conductors. 1.18:1 now according to my swr meter. Radiator is 19.25" from the surface of the SO-239, grounds are 20.25" from bend to end, about .25 from screw center to bend Does this mean need to trim, or too short already? More important than answer the question, teach me how to find it. |
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Posted: 9/18/2020 5:01:39 PM EDT
[#7]
Quote HistoryQuoted: I was going for strength. Lots of lessons learned here. I remade it with single bare conductors. 1.18:1 now according to my swr meter. Radiator is 19.25" from the surface of the SO-239, grounds are 20.25" from bend to end, about .25 from screw center to bend Does this mean need to trim, or too short already? More important than answer the question, teach me how to find it. I don't think the length of the radials is especially critical, but their angle affects the overall impedance. (which will affect the SWR) |
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Posted: 9/18/2020 5:28:52 PM EDT
[#8]
to be resonant on 144mhz it will be longer that 148mhz
so if they swr is better on 144 than 148, its a bit long (if you have an analyzer, make that 140 and 150) if the SWR is better on 150 than 140, it’s too short .  Attached File Attached File |
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Posted: 9/18/2020 6:37:30 PM EDT
[#9]
radials are at 45 degrees to the so-239, which puts them at 45 degrees to the main element.
I dont have an antenna analyzer. What I do have is this I'll check at 144 and 148, see where she's going. I appreciate the educations guys.. |
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Posted: 9/18/2020 8:01:04 PM EDT
[#10]
at SWR 1.18 i would just leave it as is.
you will loss 0.8% of the power which is nothing and at is after the loss in the cable. So if you have a 3 db (50%) loss in the cable and you lose 0.8% ( due to SWR 1.18 )at the antenna and your radio is 50 watts you will get 25 watts to the antenna and lose 0.2 watts ( due to SWR 1.18 )compared to a 1.0 SWR at this point what difference does it make? |
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Posted: 9/18/2020 8:17:20 PM EDT
[#11]
I just rechecked because the 1.18 didnt look familiar.
I got 1.34, then a few minutes later 1.25 with it hanging nowhere near any metal, about 4 feet from ground. I'm done with this antenna! I'm still going to check it at 144 and 148, just to do the formula and see how it could be improved. Next I'll remake the coax vertical dipole. Maybe this weekend. Maybe. |
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Posted: 9/18/2020 9:21:24 PM EDT
[#12]
Quote HistoryQuoted: I just rechecked because the 1.18 didnt look familiar. I got 1.34, then a few minutes later 1.25 with it hanging nowhere near any metal, about 4 feet from ground. I'm done with this antenna! I'm still going to check it at 144 and 148, just to do the formula and see how it could be improved. Next I'll remake the coax vertical dipole. Maybe this weekend. Maybe. there is nothing wrong with 1.34 for an SWR. The VHF slimjim I built is 1.2-1.3 across the VHF band. I also wanted it to be good at the commercial VHF freqs so it was a bit of a compromise and is 1.3 there also, but still. Very minimal power loss. |
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Posted: 9/18/2020 10:10:40 PM EDT
[#13]
I'd agree,if you're below 1.5 SWR you're fine. If anything play with the angle of the radial to tweak it a bit and see if it improves a bit, but otherwise you should be fine.
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Posted: 9/18/2020 11:17:09 PM EDT
[#14]
Quote HistoryQuoted: I was going for strength. Lots of lessons learned here. I remade it with single bare conductors. 1.18:1 now according to my swr meter. Radiator is 19.25" from the surface of the SO-239, grounds are 20.25" from bend to end, about .25 from screw center to bend Does this mean need to trim, or too short already? More important than answer the question, teach me how to find it. Quote HistoryQuoted: I was going for strength. Lots of lessons learned here. I remade it with single bare conductors. 1.18:1 now according to my swr meter. Radiator is 19.25" from the surface of the SO-239, grounds are 20.25" from bend to end, about .25 from screw center to bend Does this mean need to trim, or too short already? More important than answer the question, teach me how to find it. 1.18, and you're asking to adjust?  Quoted: I dont have an antenna analyzer. Yeah you need one. With the price of Nano VNA's, its silly for folks to start antenna homebrewing / experimenting without one. |
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Posted: 9/18/2020 11:31:19 PM EDT
[#15]
Quote HistoryQuoted: 1.18, and you're asking to adjust? Yeah you need one. With the price of Nano VNA's, its silly for folks to start antenna homebrewing / experimenting without one. not going to adjust, but want to know how, for when I build one and it comes out at 11.80, etc. Had I known about NanoVNA i would have bought it instead of the one i did. |
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Posted: 9/19/2020 7:17:41 AM EDT
[#16]
Quote HistoryQuoted: I'd agree,if you're below 1.5 SWR you're fine. If anything play with the angle of the radial to tweak it a bit and see if it improves a bit, but otherwise you should be fine. Yeah that is a great point. A vertical antenna has a natural impedance of 75 ohms using buried or flat radials ( 90 degrees to the vertical ) at resonance. Elevating the antenna and then angling the radials down at about 45 degrees lowers the resistive impedance at resonance to 50 ohms or so. Without an antenna analyser there is no way to know if the less than perfect SWR is due to being off resonance, or being at resonance and the radials could still be angled some more, etc. |
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Posted: 9/19/2020 7:23:58 AM EDT
[#17]
Quote HistoryQuoted: not going to adjust, but want to know how, for when I build one and it comes out at 11.80, etc. Had I known about NanoVNA i would have bought it instead of the one i did. Quote HistoryQuoted: Quoted: 1.18, and you're asking to adjust? Yeah you need one. With the price of Nano VNA's, its silly for folks to start antenna homebrewing / experimenting without one. not going to adjust, but want to know how, for when I build one and it comes out at 11.80, etc. Had I known about NanoVNA i would have bought it instead of the one i did. Making antennas is one of the things I really like about the hobby. Get the NanoVNA when you can, it will make it much more enjoyable to make an antenna because you can actually see what is going on, where the resonance is and how it varies based on height, length, radials, angle of radials, and what the resistive impedance is at resonance or how much capacitance or inductance needs to be added to 'tune' the antenna if it is too short or too long etc for more complex antennas or mutliband antennas. Once you start seeing the actual impedance values of the antenna, it really comes into focus what it means when it is said that a short antenna is capacitive and a long antenna is inductive and what resonance really means. It is still magic, but with an analyser you get to be the magician. |
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Posted: 9/19/2020 10:35:06 AM EDT
[#18]
Quote HistoryQuoted: A vertical antenna has a natural impedance of 75 ohms using buried or flat radials ( 90 degrees to the vertical ) at resonance. Quote HistoryQuoted: A vertical antenna has a natural impedance of 75 ohms using buried or flat radials ( 90 degrees to the vertical ) at resonance. No. A vertical has a natural impedance of something like 36 ohms. Elevating the antenna and then angling the radials down at about 45 degrees lowers the resistive impedance at resonance to 50 ohms or so. A dipole has a natural impedance of like 72 ohms (imagine that). In between the flat ground plane and a dipole you will find 50 ohms, yes. |
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Posted: 9/19/2020 11:27:12 AM EDT
[#19]
Quote HistoryQuoted: No. A vertical has a natural impedance of something like 36 ohms. A dipole has a natural impedance of like 72 ohms (imagine that). In between the flat ground plane and a dipole you will find 50 ohms, yes. Quote HistoryQuoted: Quoted: A vertical antenna has a natural impedance of 75 ohms using buried or flat radials ( 90 degrees to the vertical ) at resonance. No. A vertical has a natural impedance of something like 36 ohms. Elevating the antenna and then angling the radials down at about 45 degrees lowers the resistive impedance at resonance to 50 ohms or so. A dipole has a natural impedance of like 72 ohms (imagine that). In between the flat ground plane and a dipole you will find 50 ohms, yes. you are absolutely right. My mistake, had a brain fart. It is angling the dipole toward the ground that you get closer to 50 ohms depending on height above ground. Thanks for the correction. I never noticed that the vertical is half the impedance of a dipole ,makes sense. All antennas are dipoles anyway 
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Posted: 9/19/2020 3:31:17 PM EDT
[#20]
Nano version 1 added to the amazon cart. $50 is doable. I'll just have to suffer the smaller screen, though the v2.2 with bigger screen is nice, not twice the price nice.
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Posted: 9/19/2020 3:33:32 PM EDT
[#21]
Quote HistoryQuoted: Nano version 1 added to the amazon cart. $50 is doable. I'll just have to suffer the smaller screen, though the v2.2 with bigger screen is nice, not twice the price nice. You can hook up the nano to a computer and get a big screen. That is what I do, otherwise I can't read it, it is too small. |
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Posted: 9/19/2020 3:39:58 PM EDT
[#22]
Quote HistoryQuoted: You can hook up the nano to a computer and get a big screen. That is what I do, otherwise I can't read it, it is too small. That is great info, now I can be cheap too! Thanks! |
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Posted: 9/19/2020 3:46:36 PM EDT
[#23]
It works way better on a computer. The screen shows 101 data points. If the sweep is large (say 144-446 for a dual band) then your lucky to get two points in the 2m band. VNASaver will you make, for example, 25 sweeps that cover the same range - each with 101 pts.
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Posted: 9/19/2020 6:33:55 PM EDT
[#24]
Using my meter, I tested from 140 to 150 Mhz, at 1 MHz intervals.
What the heck does this mean?????  Attached File |
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Posted: 9/19/2020 7:03:27 PM EDT
[#25]
Quote HistoryQuoted: Using my meter, I tested from 140 to 150 Mhz, at 1 MHz intervals. What the heck does this mean????? https://www.AR15.Com/media/mediaFiles/32438/VSWR_test_jpg-1598972.JPG hard to tell without seeing more of both sides. It might, might be a little long, maybe. but it will work fine with that SWR as is |
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Posted: 9/19/2020 7:14:25 PM EDT
[#26]
Quote HistoryQuoted: Using my meter, I tested from 140 to 150 Mhz, at 1 MHz intervals. What the heck does this mean????? https://www.AR15.Com/media/mediaFiles/32438/VSWR_test_jpg-1598972.JPG Usually it means you have a long piece of coax between meter and antenna. |
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Posted: 9/19/2020 7:39:47 PM EDT
[#27]
In an ideal world you would have an even multiple of 1/2 wave lengths of the coax between the analyzer and the antenna. This would theoretically repeat the impedance seen at the antenna connector, at the input of the analyzer or VSWR meter. Trim the antenna to match up with a VSWR meter at 146 MHz and run the sweep again.
73, Rob |
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Posted: 9/19/2020 7:44:06 PM EDT
[#28]
Quote HistoryQuoted: 1.18, and you're asking to adjust? Yeah you need one. With the price of Nano VNA's, its silly for folks to start antenna homebrewing / experimenting without one. This |
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Posted: 9/19/2020 7:59:03 PM EDT
[#29]
again, not changing the antenna, trying to learn.
I do have about 24.5' of RG58, with a self applied PL259 (I need a hotter soldering iron) between the high dollar, high quality Baofeng HT. |
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Posted: 9/19/2020 8:34:09 PM EDT
[#30]
Quote HistoryQuoted: self applied PL259 (I need a hotter soldering iron) save your money on the soldering gun and buy a crimp tool instead. |
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