Build an End-Fed Halfwave antenna and bal-un

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vagrant

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@belvdr Unknown as prcguy sent it to me. The size of it is around 2.3 x 4.5 x 6 cm. I would not go any smaller on the box as those parts would not fit. Compact was the focus, but a slightly larger box would not hurt. The concern would be the thickness of the box as there will be stresses applied when taut.
 

Mikejo

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Until then, here's some detailed information from Palomar: Ferrite Mix Selection - Palomar Engineers®

Thanks AK9R, interestingly enough, that is where I had ordered the 31 mix FT-240's from.

Reading through the link you provided, I realize now the best use for the two Toroids I have coming will be for RFI suppression. I have a good deal of that to contend with anyway!

73's
K1MJC
 

wb4sqi

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How do you modify it to 49:1? I had a MyAntennas setup at one time at the house, but took it down and cannot find it. :/

The eBay seller provides information for changing ratios. I believe he told me to remove three turns from the core but to try it at 30:1 initially. The seller is convinced that 30:1 with 66' of wire provides three band coverage of 40, 20 and 10.

My only need at the moment is for a single band EF for 20M only so I bought this Unun for experimental purposes.
 

belvdr

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Thanks everyone for your patience. I'm gathering a parts list now. One question on the winding:

One guy on Youtube said to count the primary windings as part of the secondary. So 2 winds of primary and 5 winds of secondary for a total of 7, yet I see many (including here) using 2 winds primary and 7 winds of secondary and on the TRX side. I'm sure it matters, hence my asking.

For the first time in a long time, I'm excited to work on something within ham radio.
 

wb4sqi

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Thanks everyone for your patience. I'm gathering a parts list now. One question on the winding:

One guy on Youtube said to count the primary windings as part of the secondary. So 2 winds of primary and 5 winds of secondary for a total of 7, yet I see many (including here) using 2 winds primary and 7 winds of secondary and on the TRX side. I'm sure it matters, hence my asking.

For the first time in a long time, I'm excited to work on something within ham radio.
Here is my simplified understanding:

Depends on the ratio you need. Since people are finding success with 49:1 ratios that means you need to wind 1 turn on the primary to 7 turns on the secondary. Or, 2 turns on the primary and 14 turns on the secondary (14/2=7, 7 squared = 49) and so on.

In your example the turn count of 5/2 has a ratio of 6.25:1. (5/2=2.5 2.5 squared = 6.25) Make your secondary winging 14 turns will give you a ratio of 49:1. I'm certainly no expert on ununs but as I understand the theory of design you divide the secondary turn count by the primary turn count and then square the result to get your final ratio.

@prcguy, feel free to offer corrections or comments if my understanding is flawed.
 

belvdr

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This is the video I was referencing:


Skip to 9:15 where he says the secondary windings include the primary windings.
 

wa8pyr

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Well, this thread has got me fired up about trying something new. I've been using both the Comet HFJ-350M and the Yaesu ATAS-25 with my recently acquired IC705 (and my FT817ND before that), and results have been OK on digital modes, but so-so at best on SSB. So after reading this thread I decided to give it a whirl.

Found the eBay seller mentioned earlier; he's selling a 1:64 unun good for over 100w (not that I need that much) which can be converted to 1:49 if desired, with the necessary HV capacitor, for $8 and shipping. Also scored a 100ft spool of 22awg stranded Teflon wire (light green so I can see it), and a suitable project box. All-in price after tax and shipping was just a hair under $35.

This should be fun. . .
 

prcguy

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For a 49:1 or 64:1 transformer there is always two primary turns of twisted pair, do not make a single turn primary as there will not be enough inductance in the primary to work over most of the HF range.

For a single core, especially a small core I would make it a 64:1 with two primary turns and 14 secondary turns as shown in the link in post # 8 of this thread. For three stacked cores you definitely want to to make it a 49:1 due to the excessive inductance as shown in the Youtube video link in post # 27 of this thread. If in doubt on a single core you can always make it a 64:1, test on air then remove a turn or two and test again. You don't have to cut of the turns, just unwind them and test with an antenna analyzer to see if the overall match is better with 16 primary turns or 15 or 14. If it worked better with more turns then just wrap them back on.

The differences seen between a 49:1 and 64:1 can be subtitle on a single core version and it also might have something to do with how high you mount your antenna. In free space an end fed half wavelength of wire is very high impedance, probably over 3k ohms. Mount that antenna 20ft above ground and horizonal and the proximity to earth will lower its impedance. A 64:1 transformer will match 50 ohms to 3,200 ohms, closer to free space. A 49:1 will match 50 ohms to 2,450 ohms and maybe better for a lower mounted antenna.

BTW a turn is counted when the wire passes through the core, so count turns on the inside of the core not the outside.

On the capacitor, it only comes into play on the upper bands like 10m where it offsets some inductance of the transformer. For the voltage rating you don't have to go too crazy since its at the 50 ohm side of the transformer. Some companies like MyAntennas use huge voltage ratings and that might be to survive nearby lightning strikes where a lot of voltage can be induced onto the antenna. Otherwise at the 100 watt level and the antenna is resonant there will be about 70 volts at the input of the transformer. At 1500 watts there would be about 275 volts at the input of the transformer. If you go way out of resonance that voltage can go up so I would use something at least 4X the voltage expected for your power level, so for a 100w portable version a 200-250 volt rated cap should be ok. Personally I have been using 125pf dipped silver mica caps with a 500 volt rating since I had a bag of them. For a full legal limit permanently installed version I might upsize the cap even more due to potential nearby lightning strikes and that's up to you.

Here is my simplified understanding:

Depends on the ratio you need. Since people are finding success with 49:1 ratios that means you need to wind 1 turn on the primary to 7 turns on the secondary. Or, 2 turns on the primary and 14 turns on the secondary (14/2=7, 7 squared = 49) and so on.

In your example the turn count of 5/2 has a ratio of 6.25:1. (5/2=2.5 2.5 squared = 6.25) Make your secondary winging 14 turns will give you a ratio of 49:1. I'm certainly no expert on ununs but as I understand the theory of design you divide the secondary turn count by the primary turn count and then square the result to get your final ratio.

@prcguy, feel free to offer corrections or comments if my understanding is flawed.
 
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prcguy

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And another thing, when winding turns around a ferrite toroid, don't fish the wire through using the end like threading a needle, get the first turn on that way then push the middle of the wire closest to the last turn through with a finger then pull the rest of that turn through, it will make the wire hug the core better. When you see a sloppy core where the wires are all bent and puffed out away from the core, that was threaded like a needle. If all the wires hug the core tightly it was done the other way.
 

belvdr

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And another thing, when winding turns around a ferrite toroid, don't fish the wire through using the end like threading a needle, get the first turn on that way then push the middle of the wire closest to the last turn through with a finger then pull the rest of that turn through, it will make the wire hug the core better. When you see a sloppy core where the wires are all bent and puffed out away from the core, that was threaded like a needle. If all the wires hug the core tightly it was done the other way.
Thanks for that additional bit of info. I was wondering why some looked "loose".
 

belvdr

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Well, this thread has got me fired up about trying something new. I've been using both the Comet HFJ-350M and the Yaesu ATAS-25 with my recently acquired IC705 (and my FT817ND before that), and results have been OK on digital modes, but so-so at best on SSB. So after reading this thread I decided to give it a whirl.

Found the eBay seller mentioned earlier; he's selling a 1:64 unun good for over 100w (not that I need that much) which can be converted to 1:49 if desired, with the necessary HV capacitor, for $8 and shipping. Also scored a 100ft spool of 22awg stranded Teflon wire (light green so I can see it), and a suitable project box. All-in price after tax and shipping was just a hair under $35.

This should be fun. . .
I've ordered my parts too, except the screw for the antenna and eyelet. I figure I'll pick those up at the local hardware store this weekend.
 

prcguy

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Speaking of eyelets, I've found its best to put one at the upper rear side of the box and if its a low power transformer and tiny box you can usually get away without an eyelet and just have a #6 screw protruding from the box for wire attachment. Take a look at the picture in post #6 in this thread, which is a very old version of mine. Now I place the output screw or eyelet opposite the guying eyelet at the far upper corners of the box and the coax connector is at an opposite or lower corner of the box. This places all the stress at the stronger corners of the box instead of the middle. If there is no output eyelet to take the strain of the wire pull I always put the output screw at a right angle to the wire so its a straight pull on the wire lug. If you put the output screw sticking out the edge of the box in line with the wire then it folds the wire lug over and weakens it.

On higher power transformers with heavier boxes I always use an output eyelet to take the strain and have a small loop of wire from an output screw to the eyelet as shown in this picture. This one is a repackaged MyAntennas 2kW version in a better box. These boxes are available at Home Depot or Lowes for about $7.

EFHW box.JPG

Here is the inside of the box with the three core transformer that just barely fits. This core is made by MyAntennas, probably the best available and I would take careful note of how the windings are placed and spaced. Danny at MyAntennas knows what he is doing.

2kw transformer.JPG




I've ordered my parts too, except the screw for the antenna and eyelet. I figure I'll pick those up at the local hardware store this weekend.
 

palmerjrusa

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I've never really done the mobile thing and am interested in a PAR quad band resonant EFHW for the IC-705.

Appreciate learning how folks here set such an antenna up in an outdoors/mobile situation?
 

wa8pyr

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I've never really done the mobile thing and am interested in a PAR quad band resonant EFHW for the IC-705.

Appreciate learning how folks here set such an antenna up in an outdoors/mobile situation?

I have a 9:1 unun I've used in the past; main element is about 53 feet long and the counterpoise about 14 feet long. I just fling the main element over a tree limb, and tie the end of the counterpoise to a bush or something 180 degrees away from the main element to keep it about a foot or so off the ground. Works decently. This thread has got me fired up to try something new so I've got the parts coming for a 64:1 unun which supposedly needs no counterpoise; looking forward to giving that a shot but the setup won't be too much different except for wire length.

Experimentation is half the fun.
 
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vagrant

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@wa8pyr The coaxial cable can/would act as the counterpoise eliminating the need for a separate "counterpoise" wire. I recommend you experiment with 25', 50' or whatever lengths of coax and review your results. To handle RFI I use a 1:1 RF choke about 3' from my radio. This allows the coax to work as the counterpoise and keep things friendly.
 

palmerjrusa

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I have a 9:1 unun I've used in the past; main element is about 53 feet long and the counterpoise about 14 feet long. I just fling the main element over a tree limb, and tie the end of the counterpoise to a bush or something 180 degrees away from the main element to keep it about a foot or so off the ground. Works decently. This thread has got me fired up to try something new so I've got the parts coming for a 64:1 unun which supposedly needs no counterpoise; looking forward to giving that a shot but the setup won't be too much different except for wire length.

Experimentation is half the fun.

Thanks!
I have a 9:1 unun I've used in the past; main element is about 53 feet long and the counterpoise about 14 feet long. I just fling the main element over a tree limb, and tie the end of the counterpoise to a bush or something 180 degrees away from the main element to keep it about a foot or so off the ground. Works decently. This thread has got me fired up to try something new so I've got the parts coming for a 64:1 unun which supposedly needs no counterpoise; looking forward to giving that a shot but the setup won't be too much different except for wire length.

Experimentation is half the fun.

Thanks!

Do you use some catapult arrangement to get the antenna high up in a tree branch or limb?
 

prcguy

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For the PAR and home made versions I like to get the entire length of wire horizonal and as high as possible but thats limited to about 15-25ft due to available trees, etc. On the home made versions with chalk line reel the empty chalk line reel is your throw weight to get the far end up in a tree. I usually carry a second chalk line reel with about 80ft of miniature parachute cord to toss over another tree and pull up the transformer end. If a second tree is not available I will sometimes use the antenna with the transformer lower and the wire sloping up to the only tree or high point.

In all cases I get signal reports similar to other 100 watt stations on the band and I'm usually running about 10 watts into the end fed.

I've never really done the mobile thing and am interested in a PAR quad band resonant EFHW for the IC-705.

Appreciate learning how folks here set such an antenna up in an outdoors/mobile situation?
 

prcguy

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And another thing....
The 49:1 or 64:1 transformer is broad band and will work anywhere from about 60m to 10m for the tiny 100w version or down to 80m and even 160m for some larger high power versions. You simply attach 1/2 wavelength of wire at the lowest frequency you want to use and it will resonate on just about all odd and even harmonics.

You can also use it as a mono band antenna like attach about 88ft of wire and use it on 60m, which might also work on 30m. Or you can attach about 32ft of wire and run that up a 33ft telescoping fiberglass mast for a 20m vertical. Or attach about 16.5ft of wire for a mono band 10m vertical, etc.
 
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