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Posted: 6/26/2015 10:26:49 PM EDT
[#1]
so with a few spools of wire lying around and actually having a couple of toroidal cores, I'm going to tackle building one of these from junk.
The balun designs pic has 10 wraps around the toroid, and I see other plans that say 12, some say 14. This is creating 2 1:1 baluns and wiring them together, so does the number of windings matter? Some plans specify the type of core to use, some don't. Does that matter in this application also? |
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Posted: 6/27/2015 1:07:46 AM EDT
[#2]
Quote HistoryQuoted:
A little digging on their website revealed a 4:1 designed for OCFD's that run close to a metal roof. It's like they looked in my back yard and built a balun for me. Got one on order, and if I get really motivated I can try it out side-by-side with my present Carolina Windom. Also ordered an unun for portable endfed use. 4114ocf, and 9130 if anyone's interested. LOL that their QRP units are rated to 300 W. These guys are serious. I and other OCFD builders still recommend the 4115 over the 4114. |
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Posted: 6/27/2015 10:27:24 AM EDT
[#3]
Quote HistoryQuoted:
I and other OCFD builders still recommend the 4115 over the 4114. Quote HistoryQuoted:
Quoted:
A little digging on their website revealed a 4:1 designed for OCFD's that run close to a metal roof. It's like they looked in my back yard and built a balun for me. Got one on order, and if I get really motivated I can try it out side-by-side with my present Carolina Windom. Also ordered an unun for portable endfed use. 4114ocf, and 9130 if anyone's interested. LOL that their QRP units are rated to 300 W. These guys are serious. I and other OCFD builders still recommend the 4115 over the 4114. Can you elaborate? It's not too late to call and change my order. |
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Posted: 6/27/2015 11:10:40 AM EDT
[#4]
Quote HistoryQuoted:
Can you elaborate? It's not too late to call and change my order. Quote HistoryQuoted:
Quoted:
Quoted:
A little digging on their website revealed a 4:1 designed for OCFD's that run close to a metal roof. It's like they looked in my back yard and built a balun for me. Got one on order, and if I get really motivated I can try it out side-by-side with my present Carolina Windom. Also ordered an unun for portable endfed use. 4114ocf, and 9130 if anyone's interested. LOL that their QRP units are rated to 300 W. These guys are serious. I and other OCFD builders still recommend the 4115 over the 4114. Can you elaborate? It's not too late to call and change my order. The 4114 is a single core. They can say it's two cores, but it is two toroids stacked together and wound as if one big fat toroid. It does not have enough common mode rejection, that is, ability to keep RF off the shield, and thus difficulties in tuning your OCFD. The 4115 series is dual core and will work as described. By suggesting this balan rather than others, or winding your own, is because I'm telling you what works and will give you the best chance of success. This is not just my opinion, but from many users world-wide, and measurements to back it up. Check out the Windom Antenna Yahoo Group at https://groups.yahoo.com/neo/groups/windom_antenna/info I've been a member for years, read all the literature, looked at the modeling, and listened to guys that know. If you have a chance, call and change to the 4115ET or 4115OCF. Do not try to "trim" individual bands. Use your tuner, that's what it's for. Get the lowest band to 3.500-3.550 mhz (or 7.050-7.100 mhz for the 40 m version) and let the tuner do the rest. |
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Posted: 6/27/2015 3:28:01 PM EDT
[#5]
Thanks for the advice!
I see the stacked core is intended to prevent saturation in the presence of severe imbalance. On closer inspection of the 4115 data sheet they recommend the 4114 for power levels over 700 W. Not likely in my near future, in fact I even noted how beefy they build these devices. (300 W is their QRP level; all my rigs combined don't add up to that!) One objective of this swap is to eliminate the big air core choke hanging in my back yard so I'll ask them to change to the 4115. Do you think there's any merit to using the coax shield with imbalanced currents as a vertical radiator to fill in the dipole's radiation pattern, with the choke at the bottom? That theory comes from the magazine article describing the Carolina Windom, and I've always thought it was a clever way of making lemonade out of lemons. Regarding lengths - My 2 trees are just a little too close to allow the full windom wire length. Probably about 2 feet shy of the full length. Right now I am tolerating a good bit of belly in the 2 wires, but is it preferable to pull them taut and let the extra length hang down? The thing is performing really well as it sits so I haven't bothered climbing up to work on optimizing it. |
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Posted: 6/27/2015 5:02:35 PM EDT
[#6]
I ordered the 4115ocf balun finally. Unfortunately, I think I only have room for the 40m version of the antenna. Although, I could make the 80m version if I want to run the long end across the street at 30' elevation. I have some serious concerns about doing that, even stealthily and at night only...
on another note, I was charged TX state sales tax so I assume they are operating here. Odd that they list NM as the contact address though. |
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Posted: 6/27/2015 8:54:27 PM EDT
[#7]
Quote HistoryDo you think there's any merit to using the coax shield with imbalanced currents as a vertical radiator to fill in the dipole's radiation pattern, with the choke at the bottom? Quote HistoryDo you think there's any merit to using the coax shield with imbalanced currents as a vertical radiator to fill in the dipole's radiation pattern, with the choke at the bottom? Any merit? None whatsoever. Regarding lengths - My 2 trees are just a little too close to allow the full windom wire length. Probably about 2 feet shy of the full length. Right now I am tolerating a good bit of belly in the 2 wires, but is it preferable to pull them taut and let the extra length hang down? The thing is performing really well as it sits so I haven't bothered climbing up to work on optimizing it. You can let the ends hang down, let it sag in the middle, zig-zag it a bit, it all works. Check out some of the variations here. http://www.packetradio.com/windom.htm |
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Posted: 6/28/2015 11:46:40 AM EDT
[#8]
What would be the correct lengths for a 160m OCFD that would work well with a tuner as discussed for the 80m version?
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Posted: 6/28/2015 3:18:05 PM EDT
[#9]
You notice the ratios are different for the 80 m and 40 m. Actually there are many good feedpoints, and some work better on
some bands than others. For example, for the 80 m OCFD, the 33.33% feedpoint leaves the OCFD unusable on 30 and 15 meters. A 33.33% feedpoint on a 40 m OCFD also leaves 15 m unusuable, and I consider 15 m an important band. Other feedpoints might sacrifice 17 meters, or 20 meters, etc. The 80 m version feedpoint I recommended will not work on 12 m, but works well on 15 m. That was acceptable to me. I have not experimented with the 36% feedpoint, that is supposed to work all the HF bands. Let me do a little research on 160 m OCFDs and get back to you. |
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Posted: 6/28/2015 6:30:28 PM EDT
[#10]
Quote HistoryQuoted:
Again, a balun with two toroids stacked and wound as if one big toroid is not a "dual core" balun. The Dual Core balun is a true current balun that will suppress RF on the shield. This is important because an OCDF is inherently unbalanced. I have built, successfully, OCFDs with simpler 4:1 baluns but had to add a 1:1 choke below the balun, that is, a series of ferrite beads. From the description at Radiowavz it sounds right. At the most, if you are getting certain indications, such as SWR changing if you touch the shield, or an SWR dip in the 75 meter range (when tuned properly down about 3.5 mhz) then add some snap on ferrites to the feedline just below the balun. I'd start with 10 beads. Quote HistoryQuoted:
Quoted:
Will a RadioWavz b14cf balun work ? It is a 1:4 farrite balun rated for 1500 watts ssb. Their website doesn't say if it is dual core or not but claims it is a guanella type. Again, a balun with two toroids stacked and wound as if one big toroid is not a "dual core" balun. The Dual Core balun is a true current balun that will suppress RF on the shield. This is important because an OCDF is inherently unbalanced. I have built, successfully, OCFDs with simpler 4:1 baluns but had to add a 1:1 choke below the balun, that is, a series of ferrite beads. From the description at Radiowavz it sounds right. At the most, if you are getting certain indications, such as SWR changing if you touch the shield, or an SWR dip in the 75 meter range (when tuned properly down about 3.5 mhz) then add some snap on ferrites to the feedline just below the balun. I'd start with 10 beads. I tested my antenna today with an analyzer and could not get the swr at 3.55mhz below 5.2. The feed point was only about 12' off the ground. I adjusted the lengths about 10 times to get to 5.2. Then I tried reversing the balun and the swr when to 13:1. Does this mean I have an incorrect or defective balun or is the antenna being to close to the ground messing up the readings ? It was raining all day as I was testing. |
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Posted: 6/28/2015 7:41:18 PM EDT
[#11]
Quote HistoryQuoted:
I tested my antenna today with an analyzer and could not get the swr at 3.55mhz below 5.2. The feed point was only about 12' off the ground. I adjusted the lengths about 10 times to get to 5.2. Then I tried reversing the balun and the swr when to 13:1. Does this mean I have an incorrect or defective balun or is the antenna being to close to the ground messing up the readings ? It was raining all day as I was testing. Quote HistoryQuoted:
Quoted:
Quoted:
Will a RadioWavz b14cf balun work ? It is a 1:4 farrite balun rated for 1500 watts ssb. Their website doesn't say if it is dual core or not but claims it is a guanella type. Again, a balun with two toroids stacked and wound as if one big toroid is not a "dual core" balun. The Dual Core balun is a true current balun that will suppress RF on the shield. This is important because an OCDF is inherently unbalanced. I have built, successfully, OCFDs with simpler 4:1 baluns but had to add a 1:1 choke below the balun, that is, a series of ferrite beads. From the description at Radiowavz it sounds right. At the most, if you are getting certain indications, such as SWR changing if you touch the shield, or an SWR dip in the 75 meter range (when tuned properly down about 3.5 mhz) then add some snap on ferrites to the feedline just below the balun. I'd start with 10 beads. I tested my antenna today with an analyzer and could not get the swr at 3.55mhz below 5.2. The feed point was only about 12' off the ground. I adjusted the lengths about 10 times to get to 5.2. Then I tried reversing the balun and the swr when to 13:1. Does this mean I have an incorrect or defective balun or is the antenna being to close to the ground messing up the readings ? It was raining all day as I was testing. What kind of balun? Did you have the coax connected directly to the analyzer, and was the analyzer or coax shield grounded? Is your analyzer metal cased (MFJ), or a plastic case (such as Rig Expert)? |
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Posted: 6/28/2015 8:41:49 PM EDT
[#12]
Quote HistoryQuoted:
so does the number of windings matter? So since nobody answered I went and did some reading. It seems that the number of windings in this case isn't going to batter as long as they are the same on each toroid. If I'm wrong, I'd appreciate a correction, and if available, an explanation. Thanks |
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Posted: 6/28/2015 9:06:14 PM EDT
[#13]
From what I've seen with my attempts, your best bet on a 2 core, bifilar wound, balun would be with a transmission line pair that have about a 100 ohm impedance. You can find calculators on line that will give you some guidance on your spacing depending on the wire you are using. FWIW, I found RCA two conductor 18 AWG speaker wire (like at Lowe's) has pretty much 100 ohm impedance as is and gave a pretty flat SWR for 1 Mhz out to past 30 Mhz when scanning a 2 core 4:1 current balun attached to a 200 ohm load ...
(this is used in the crawl space to transition from a ladder fed 80m FWL to coax) Nick |
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Posted: 6/28/2015 9:44:39 PM EDT
[#14]
Quote HistoryQuoted:
What kind of balun? Did you have the coax connected directly to the analyzer, and was the analyzer or coax shield grounded? Is your analyzer metal cased (MFJ), or a plastic case (such as Rig Expert)? Quote HistoryQuoted:
Quoted:
Quoted:
Quoted:
Will a RadioWavz b14cf balun work ? It is a 1:4 farrite balun rated for 1500 watts ssb. Their website doesn't say if it is dual core or not but claims it is a guanella type. Again, a balun with two toroids stacked and wound as if one big toroid is not a "dual core" balun. The Dual Core balun is a true current balun that will suppress RF on the shield. This is important because an OCDF is inherently unbalanced. I have built, successfully, OCFDs with simpler 4:1 baluns but had to add a 1:1 choke below the balun, that is, a series of ferrite beads. From the description at Radiowavz it sounds right. At the most, if you are getting certain indications, such as SWR changing if you touch the shield, or an SWR dip in the 75 meter range (when tuned properly down about 3.5 mhz) then add some snap on ferrites to the feedline just below the balun. I'd start with 10 beads. I tested my antenna today with an analyzer and could not get the swr at 3.55mhz below 5.2. The feed point was only about 12' off the ground. I adjusted the lengths about 10 times to get to 5.2. Then I tried reversing the balun and the swr when to 13:1. Does this mean I have an incorrect or defective balun or is the antenna being to close to the ground messing up the readings ? It was raining all day as I was testing. What kind of balun? Did you have the coax connected directly to the analyzer, and was the analyzer or coax shield grounded? Is your analyzer metal cased (MFJ), or a plastic case (such as Rig Expert)? A 4:1 current balun made be RadioWavz that in an earlier post you said would probably work. The coax was connected directly to the analyzer but it was not grounded. My analyzer is a metal cased MFJ 949d. |
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Posted: 6/29/2015 1:35:21 AM EDT
[#15]
Quote HistoryQuoted:
A 4:1 current balun made be RadioWavz that in an earlier post you said would probably work. The coax was connected directly to the analyzer but it was not grounded. My analyzer is a metal cased MFJ 949d. Quote HistoryQuoted:
Quoted:
Quoted:
Quoted:
Quoted:
Will a RadioWavz b14cf balun work ? It is a 1:4 farrite balun rated for 1500 watts ssb. Their website doesn't say if it is dual core or not but claims it is a guanella type. Again, a balun with two toroids stacked and wound as if one big toroid is not a "dual core" balun. The Dual Core balun is a true current balun that will suppress RF on the shield. This is important because an OCDF is inherently unbalanced. I have built, successfully, OCFDs with simpler 4:1 baluns but had to add a 1:1 choke below the balun, that is, a series of ferrite beads. From the description at Radiowavz it sounds right. At the most, if you are getting certain indications, such as SWR changing if you touch the shield, or an SWR dip in the 75 meter range (when tuned properly down about 3.5 mhz) then add some snap on ferrites to the feedline just below the balun. I'd start with 10 beads. I tested my antenna today with an analyzer and could not get the swr at 3.55mhz below 5.2. The feed point was only about 12' off the ground. I adjusted the lengths about 10 times to get to 5.2. Then I tried reversing the balun and the swr when to 13:1. Does this mean I have an incorrect or defective balun or is the antenna being to close to the ground messing up the readings ? It was raining all day as I was testing. What kind of balun? Did you have the coax connected directly to the analyzer, and was the analyzer or coax shield grounded? Is your analyzer metal cased (MFJ), or a plastic case (such as Rig Expert)? A 4:1 current balun made be RadioWavz that in an earlier post you said would probably work. The coax was connected directly to the analyzer but it was not grounded. My analyzer is a metal cased MFJ 949d. OK, you need to (1) add a 1:1 current balun right below the 4:1 balun. (2) ground the MFJ analyzer. Your measurements will change a lot. |
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Posted: 6/29/2015 2:11:28 PM EDT
[#16]
Quote HistoryQuoted:
Tehanks for the advice! (SNIP) Probably about 2 feet shy of the full length. Right now I am tolerating a good bit of belly in the 2 wires, but is it prferable to pull them taut and let the extra length hang down? The thing is performing really well as it sits so I haven't bothered climbing up to work on optimizing it. Sure, let the ends hang down, no problem. I'd suggest to wrap each length of wire through an insulator or at least make a corona loop. Hth 73, Rob |
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Posted: 6/29/2015 5:25:49 PM EDT
[#17]
Very nice write up!
For those interested in modeling, below is the modeled SWR curve ----> 
http://i59.tinypic.com/24chzf4.jpg Resonance points and SWR (if fRes is in band, SWR is shown at that fRes - if fRes is out of band, SWR is shown for approx mid band): fRes = 3.55 MHz SWR(3.55) = 2.4 fRes = 7.05 MHz SWR(7.05) = 1.8 fRes = 10.6 MHz SWR(10.1) = 14.6 fRes = 14.1 MHz SWR(14.1) = 1.4 fRes = 17.7 MHz SWR(18.1) = 3.6 fRes = 21.2 MHz SWR(21.2) = 1.1 fRes = 24.7 MHz SWR(24.9) = 8.6 fRes = 28.3 MHz SWR(28.3) = 1.8 Antenna height = 50 ft. Would be interesting to see how this compares to actual measurement.... |
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Posted: 6/29/2015 8:25:07 PM EDT
[#18]
The modeling from KnowFear is just about what I measured with our club OCFD at about 40'.
80 m looks high, and it is higher up in the phone portion of the band. That is to be expected and NOT a problem. Your tuner will fix that, tuning right on down to 1.1:1 easily, with less than 1 db total loss even for 100' of RG-8X. The lower the frequency, the less coax loss. This antenna will work most all of the HF bands (but for 12 m) easily. It needs a tuner, but no big deal. |
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Posted: 7/1/2015 5:11:08 PM EDT
[#19]
Well, I built the 40m version of your OCFD almost exactly like you described. Exact same 4:1 current balun, the snap hooks, split bolts, anderson connectors, the works. The only thing different is I used a couple of white ceramic dogbone end insulators I had around. It went together pretty easily and quick. The son and I put it up last evening on the same supports my G5RV Jr was on. The end ropes are just thrown over a couple of trees at about 20'. I needed something to support the weight of the balun, so we rigged up a support with the BuddiPole long (18') mast and an insulated painter's pole lashed to the top to get the balun up about 22'. (We need to do something more stable than that.) Fed it with about 45' of RG-213 cable and ran it to my windowsill feedthru panel and into the shack.
IT WORKS GREAT! Checked the SWR with the MFJ analyzer and it's better than 1.5:1 across most of 20m. 40 and 15 m are between 2 and 3:1. 10m at 1.5:1 across the lower SSB portion, just where I want it. 17m and 12m are a bit higher, but I don't use those bands much at all. 30m it didn't like, about 8:1 SWR. Connected up to my old TS-450SAT and the internal tuner was happy to tune all bands other than 30m. I can even by-pass the internal tuner on 10, 20 and 40m. On 15m without the tuner I get some power limiting, but putting the internal tuner in-line makes the transmitter happy. This morning I made contacts on 10, 15, 17, 20 and 40m. All just using the internal TS-450SAT tuner. The antenna seems to hear better than the old G5RV Jr, and it tunes all the bands (except 30m) with a much better SWR than the G5RV, where I often had to use an external MFJ tuner to handle the 8.5:1 swr on 40 and 17m. Thanks for the great construction article and all the helpful replies and comments. |
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Posted: 7/1/2015 7:14:03 PM EDT
[#20]
You are very welcome!
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Posted: 7/1/2015 7:16:54 PM EDT
[#21]
I had posted this in another thread, but it should be here, too.
I've studied the OCFD for a number of years, and there are MANY possible feed points. Copied from a post on the Windom Yahoo Group: The following is related to a 80m OCF dipole (~135 feet total length): * If you feed it at 8.9%, you don't lose any ham band (80m-6m)(no in ham band sine nulls). Although the SWR will be higher on 80m. (Jup's note: Being fed closer to the end, unbalanced currents, that is, RF on the shield is worst with this feedpoint.) * If you feed it at 16.6%, you lose 15m band (sine equals zero). (Jup's note: I consider 15 m a very desirable DX band, so the 16.6% feedpoint is rejected.) * If you feed it at 20% (20/80), you lose 17m and 6m bands (sine equals zero). (Jup's note: I consider 17 m a desirable band, so the 20% feedpoint is rejected.) * If you feed it at 25%, you lose 20m and 10m bands (sine equals zero). (Jup's note: Oops! There go two bands we really want and part of the reason we built an OCFD in the first place.) * If you feed it at 28.89%, you lose 12m band (sine equals zero). (Jup's note: Not bad, I can live with this.) * If you feed it at 30%, you don't lose any ham band (80m-6m). Although the SWR will be a little higher on 12m. (Jup's note: 28.9% to 30%, 12 m is high SWR. The 29.5% feedpoint is my choice of good compromise feedpoint.) * If you feed it at 33% (1/3:2/3) you lose 30m, 15m, and 6m bands (sine equals zero). (Jup's note: I've built more than a few 1/3-2/3 or 33.3% OCFDs, and while they work well on the other bands, I miss not having what for me has been my best DX band, 15 meters.) * If you feed it at 36%, you don't lose any ham band (80m-6m). Although the SWR will be a little higher on 30m. (Jup's note: I can live with this, too.) * If you feed it at 41.6%, you don't lose any ham band (80m-6m). Although the SWR will be a little higher on 17m and 12m. (Jup's note: Nothing to be gained here over the 36% feedpoint.) * If you feed it at 50%, lose 40m, 20m, 15m, and 10m bands (sine equals zero), but should do very well on 80m, 30m, 17m, 12m, and 6m bands. This is a normal dipole, where you only get odd-harmonics. (Jup's note: Which reminds us of why we are building an OCFD in the first place.) By "lose," I mean the antenna will not be useable and will have very high impedance (Sine goes to zero). |
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Posted: 7/2/2015 4:26:39 PM EDT
[#22]
So, to be clear (for my rather simple mind), if I wanted to build a 40M OCFD, I could use the same ~30% feedpoint and get approximately the same results (30M ok, 12M lost)?
Or, more to the point, so that I learn something - where would I got to find the results that you listed above and also how would I ascertain the results if I made the change I suggested (40M ocfd/66', 30% feedpoint instead of 80M ocfd/135') |
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Posted: 7/2/2015 7:54:50 PM EDT
[#23]
Quote HistoryQuoted:
So, to be clear (for my rather simple mind), if I wanted to build a 40M OCFD, I could use the same ~30% feedpoint and get approximately the same results (30M ok, 12M lost)? Or, more to the point, so that I learn something - where would I got to find the results that you listed above and also how would I ascertain the results if I made the change I suggested (40M ocfd/66', 30% feedpoint instead of 80M ocfd/135') No, don't use the same feedpoint for a 40 m OCFD. This is because the relationship of the ham bands and OCFD harmonics above 40 m are not the same ratios, etc, as the harmonics above an 80 m OCFD. For a 40 m OCFD use the 40.5% feedpoint, 27'-2" and 39'-10". The results regarding various feedpoints has been posted a few times on the Windom Yahoo Group. It has been confirmed mathematically, graphically, etc, several times and ways. Harmonics are whole number ratios of the fundamental. 80 m OCFD 3.5 x 1 = 3.5 mhz (fundamental) 3.5 x 2 = 7.0 mhz (40 m) 3.5 x 3 = 10.5 mhz (30 m is 10.1) 3.5 x 4 = 14 mhz (20 m) 3.5 x 5 = 17.5 mhz (just below 17 m, but it works) 3.5 x 6 = 21 mhz (15 m) 3.5 x 7 = 24.5 mhz (12 m) etc But a 40 m OCFD 7 x 1 = 7 mhz (40 m) 7 x 2 = 14 mhz (20 m) 7 x 3 = 21 mhz (15 m) 7 x 4 = 28 mhx (10 m) There is no 1.5 x harmonic, so it is not going to work on 30 m. Etc. You can see that the relationship between the whole number harmonics and the ham bands are different. And which feedpoints work, which don't for various bands is different, too. You can use a tuner and for 17 m from a 67' OCFD with a 38% feedpoint. 12 m does not seem to work. 15 m works only because the feedpoint is not at 33.3% (location of a node for that frequency). Another feedpoint that works for a 40 m OCFD is the 19.5% feedpoint (or 20%). RF on the shield is greater, unless suppressed by a choke. |
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Posted: 7/4/2015 9:14:39 AM EDT
[#24]
Time to start building.
 The first lines I make will be 25' and 41'. Not enough room at the QTH for the 93' line.
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Posted: 7/4/2015 11:37:16 AM EDT
[#25]
Quote HistoryQuoted:
Time to start building. The first lines I make will be 25' and 41'. Not enough room at the QTH for the 93' line.
<a href="http://s228.photobucket.com/user/tangotag_bucket/media/058C782B-224E-40D7-8D73-41F784D8BE9F_zpsqgx59zow.jpg.html" target="_blank">http://i228.photobucket.com/albums/ee73/tangotag_bucket/058C782B-224E-40D7-8D73-41F784D8BE9F_zpsqgx59zow.jpg</a> Wire and end insulators. You forgot wire and end insulators. It'll work better with wire. 
All kidding aside, if you are making a permanent installation, no need for the Anderson Powerpoles. Those assist in assembling dipoles and OCFDs used for portable operations. The snap hooks are handy, and let you make more than one set of legs for experimentation. |
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Posted: 7/4/2015 12:51:11 PM EDT
[#26]
I bought 1/4" hole ring terminals too so I could swap out the short power pole lines I use on my Balun Designs 1:1 Current Dipole box. Still working with THHN wire until I can source MTW for a better portable setup. My insulators are on the cheap too cheap to put in a pic.
But I think I might order some black plastic dog bone insulators eventually. |
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Posted: 7/4/2015 1:15:17 PM EDT
[#27]
Quote HistoryQuoted:
... My insulators are on the cheap too cheap to put in a pic.
.... Hey! I resemble that remark! (I routinely use chunks of cutting board for center & end insulators) Nick |
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Posted: 7/4/2015 1:57:48 PM EDT
[#28]
Insulators - see p1, 4th post, there is an Update. I just bought a bag of 25 insulators, $13 with shipping. These are the
exact same C150 insulators I get from Universal Radio. Being plastic, they don't get chipped when banged around for portable antennas. MTW wire 13 cents per foot, $32.50 for a 250' reel. http://www.wireandcabletogo.com/Copper-Building-Wire/14-AWG-Type-MTW-Wire-41-Strand-250-or-500-Spool.html?_vsrefdom=GAW&gclid=CPa865WFwsYCFRCqaQodO6gFYw Also, on the terminals, put some dielectric grease there, too, both sides of the ring terminal, before snugging down the nut and star washer. On Powerpoles, since they should only be used on portable antennas, no dielectric grease. But if you did use Powerpoles, and intend to leave it out in the weather, squirt them full of dielectric grease, wrap with tape. |
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Posted: 7/4/2015 3:33:27 PM EDT
[#29]
Jup do you use 19 or 41 strand for your wire? I'll probably get a 500ft spool. I ordered the insulators but they didn't have the 25 pack deal now it's 10 for $4.95. They had 6 (60) so I bought 4 (40).
Some of the wires I'm making will be permanent and others will be temporary (fair weather) when the power poles are in use. Right now for testing everything comes down at the end of the day. I'm running everything right now up my non-conductive 35ft mast like a flag pole. Easy up - easy down forming an inverted V for the dipole lines. Here is my dipole setup. Now i can quick swap out my lines with the power poles and dog lead clips trick. I normally have a G5RV at home but these baluns add options that are much more portable too. The dipole lets me have a great standard to evaluate the performance of my other options. I also have a Earchi for an additional portable option. The wires for my OCFD 40m will not use power poles just come straight from the terminals. 
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Posted: 7/4/2015 4:22:16 PM EDT
[#30]
I have a 500' spool of MTW out in the shop now. I don't know the strand count, nor on what I've used in the past.
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Posted: 7/4/2015 4:24:12 PM EDT
[#31]
Quote HistoryQuoted:
Hey! I resemble that remark! (I routinely use chunks of cutting board for center & end insulators) Nick Quote HistoryQuoted:
Quoted:
... My insulators are on the cheap too cheap to put in a pic.
.... Hey! I resemble that remark! (I routinely use chunks of cutting board for center & end insulators) Nick On my fan dipole I still have the 1/4" Plexiglas insulators a friend made me 8 or 9 years ago for my SWL antenna, since converted to ham use. |
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Posted: 7/6/2015 9:04:22 AM EDT
[#32]
Quote HistoryQuoted:
No, don't use the same feedpoint for a 40 m OCFD. This is because the relationship of the ham bands and OCFD harmonics above 40 m are not the same ratios, etc, as the harmonics above an 80 m OCFD. For a 40 m OCFD use the 38% feedpoint, 25' and 41'. The results regarding various feedpoints has been posted a few times on the Windom Yahoo Group. It has been confirmed mathematically, graphically, etc, several times and ways. Harmonics are whole number ratios of the fundamental. 80 m OCFD 3.5 x 1 = 3.5 mhz (fundamental) 3.5 x 2 = 7.0 mhz (40 m) 3.5 x 3 = 10.5 mhz (30 m is 10.1) 3.5 x 4 = 14 mhz (20 m) 3.5 x 5 = 17.5 mhz (just below 17 m, but it works) 3.5 x 6 = 21 mhz (15 m) 3.5 x 7 = 24.5 mhz (12 m) etc But a 40 m OCFD 7 x 1 = 7 mhz (40 m) 7 x 2 = 14 mhz (20 m) 7 x 3 = 21 mhz (15 m) 7 x 4 = 28 mhx (10 m) There is no 1.5 x harmonic, so it is not going to work on 30 m. Etc. You can see that the relationship between the whole number harmonics and the ham bands are different. And which feedpoints work, which don't for various bands is different, too. You can use a tuner and for 17 m from a 66' OCFD with a 38% feedpoint. 12 m does not seem to work. 15 m works only because the feedpoint is not at 33.3% (location of a node for that frequency). Another feedpoint that works for a 40 m OCFD is the 19.5% feedpoint (or 20%). RF on the shield is greater, unless suppressed by a choke. Quote HistoryQuoted:
Quoted:
So, to be clear (for my rather simple mind), if I wanted to build a 40M OCFD, I could use the same ~30% feedpoint and get approximately the same results (30M ok, 12M lost)? Or, more to the point, so that I learn something - where would I got to find the results that you listed above and also how would I ascertain the results if I made the change I suggested (40M ocfd/66', 30% feedpoint instead of 80M ocfd/135') No, don't use the same feedpoint for a 40 m OCFD. This is because the relationship of the ham bands and OCFD harmonics above 40 m are not the same ratios, etc, as the harmonics above an 80 m OCFD. For a 40 m OCFD use the 38% feedpoint, 25' and 41'. The results regarding various feedpoints has been posted a few times on the Windom Yahoo Group. It has been confirmed mathematically, graphically, etc, several times and ways. Harmonics are whole number ratios of the fundamental. 80 m OCFD 3.5 x 1 = 3.5 mhz (fundamental) 3.5 x 2 = 7.0 mhz (40 m) 3.5 x 3 = 10.5 mhz (30 m is 10.1) 3.5 x 4 = 14 mhz (20 m) 3.5 x 5 = 17.5 mhz (just below 17 m, but it works) 3.5 x 6 = 21 mhz (15 m) 3.5 x 7 = 24.5 mhz (12 m) etc But a 40 m OCFD 7 x 1 = 7 mhz (40 m) 7 x 2 = 14 mhz (20 m) 7 x 3 = 21 mhz (15 m) 7 x 4 = 28 mhx (10 m) There is no 1.5 x harmonic, so it is not going to work on 30 m. Etc. You can see that the relationship between the whole number harmonics and the ham bands are different. And which feedpoints work, which don't for various bands is different, too. You can use a tuner and for 17 m from a 66' OCFD with a 38% feedpoint. 12 m does not seem to work. 15 m works only because the feedpoint is not at 33.3% (location of a node for that frequency). Another feedpoint that works for a 40 m OCFD is the 19.5% feedpoint (or 20%). RF on the shield is greater, unless suppressed by a choke. Thanks for this, I think I'm going to have to buck up and do the 80M then, I can't do without 30M. Except....... Maybe I'll do a single feed fan dipole, 40M OCFD and 30M dipole? Will that work? The reason I suggest this is lack of space for a 135' antenna. P.S> I was going to snip all your results but liked them too much to do so. |
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Posted: 7/6/2015 10:59:04 AM EDT
[#33]
Quote HistoryQuoted:
Maybe I'll do a single feed fan dipole, 40M OCFD and 30M dipole? Will that work? The reason I suggest this is lack of space for a 135' antenna. If you have a tuner, and if not, why not?, you can get all the bands from a 3-band fan dipole. Legs cut for 75 meters (120' overall), 40 meters (65' overall), and 20 meters (33' overall), with a tuner will give you 75, 60, 40, 30, 20, 17, 15, maybe 12, and 10 meters. If you try to shorten the lowest band on an OCFD to 120' (75 meters) then all of the higher bands will be out of resonant range. Another possibility, use a short section of coax to go just outside, and there connect to a 4:1 balun. From the balun to antenna use 450 window line. Make the antenna a plain dipole 120' - 130' overall span. Connect the window line directly to the dipole, no balun at that end. This is called a "doublet". It is not resonant and does not have to be. |
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Posted: 7/6/2015 11:48:12 AM EDT
[#34]
For sure I have a tuner!!!!!!
I'm still limited by length, 40M (66ft) maximum - that's why I thought of the 40M OCFD and 30M dipole. As I understand it, the OCFD will not be resonant on 30M and so will be 'invisible' to 30M. Then, the 30M dipole will be 'active'. Tell me why I'm wrong
One thing I am concerned about is that the 30M dipole will be resonant on a frequency that the OCFD is resonant on also - what affect will this have? |
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Posted: 7/12/2015 8:55:41 AM EDT
[#35]
According to one of my expert friends on this subject Rick at Spiderbeam, the most common problems
with OCFDs is by far balun related. In this thread I suggested a balun that is known to work well, a true dual core Guanella type balun (Balun Designs 4115), but numerous people ask, "Can I use brand X" or "I'll just wind my own balun." Fine, but you may have problems. Often a balun will need more choking of RF on the shield, and that is about the cost of another balun. Just understand, I specified the balun that you will most likely achieve success, have good performance, and reduce problems. |
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Posted: 7/12/2015 11:59:13 AM EDT
[#36]
I am steadily convincing myself I need to try one of these. I guess it's time to walk off the distances involved.
Without getting overly complex, what kind of radiation pattern would I expect at 15'-20' height, long leg pointing due north and short leg pointing east? |
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Posted: 7/12/2015 2:37:40 PM EDT
[#37]
Same as a 1/2 wavelength centerfed dipole. It is still a 1/2 wave dipole, it is not fed in the middle.
Bent 90* it will skew the pattern, but I don't know how exactly. |
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Posted: 7/13/2015 8:39:37 AM EDT
[#38]
Quote HistoryQuoted:
What would be the correct lengths for a 160m OCFD that would work well with a tuner as discussed for the 80m version? OK, After hearing back from one of my OCFD expert friends I think I have a good answer for you. 1 - Unless you can get it somewhat higher than 45 ft. or so they are fairly useless, except for local NVIS work. The ground losses are just too high and so is the take-off angle. 2 - The 160m OCFD is also pretty useless on the higher bands because its lobes split up into so many minor lobes. |
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Posted: 8/30/2015 10:51:21 PM EDT
[#39]
Quote HistoryQuoted:
on another note, I was charged TX state sales tax so I assume they are operating here. Odd that they list NM as the contact address though. That is strange. I'm in NM and they didn't charge me any tax at all. And I tracked the package after it shipped and it was shipped from NM. That's not how it's supposed to work but this NM GRT is such a crappy deal I'm happy when they get stiffed. |
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Posted: 9/18/2015 1:43:10 PM EDT
[#40]
Edit to add underscores between columns
I made 2 of these, one in N-S and the other E-W. The SWR is listed below. Do you have any tuning wisdom. I do not know the correct equation to calculate the required length changes of a OCFD. OCFD 85' & 48' w/Balun Designs Model 4115ocf @ Fence Line w 200' coax You Kits FG-01A Freq_SWR_Z 160m 1.800_9+_350 2.000_9+_350 80m 3.380_3.2_64 3.500_2.6_33 3.550_2.4_24 4.000_3.1_105 6.580 MHz_1_47 40m 7.000_2.6_16 7.300_3.5_48 30m 10.100_3.9_149 10.150_3.9_109 20m 14.000_1.7_39 14.350_2.3_100 17m 18.068_2.6_83 18.168_2.5_66 15m 21.000_2.2_39 21.450_1.8_20 12m 24.890_2.1_80 24.990_2_60 10m 28.000_2.3_49 29.700_2.4_62 OCFD 85' & 48' w/Balun Designs Model 4115ocf @ Stump to Fence Post w 150' coax You Kits FG-01A Freq_SWR_Z 160m 1.800_3.2_102 2.000_2_89 80m 3.380_1.8_32 3.500_1.9_70 3.550_2.1_92 4.000_5_36 40m 7.000_1.1_44 7.300239 30m 10.100_4.8_186 10.150_5_210 20m 14.000_1.2_54 14.350_1.6_48 17m 18.068_2.4_109 18.168_2.6_127 15m 21.000_2.6_109 21.450_2_50 12m 24.890_1.1_50 24.990_1.1_50 10m 28.000_2.3_56 29.700_2.3_26 Thanks in advance, Double-Zero |
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Posted: 9/18/2015 3:03:56 PM EDT
[#41]
Edit your post using an underline where the spaces between columns should be, it will be easier to read.
Then let's take a look at it and see if it needs trimming or not. Jup |
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Posted: 9/21/2015 12:37:36 PM EDT
[#42]
Edited above post for readability.
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Posted: 9/21/2015 4:08:40 PM EDT
[#43]
The basic way that you tune an OCFD is as follows:
1. Adjust the overall length to obtain a minimum VSWR at the lowest frequency of operation, typically 3.5 or 3.6MHz for an 80M OCFD (you don't want to go higher than that because then it will be difficult to get good performance on the higher bands). 2. Move the feed point to put the VSWR minimas on the higher bands where you want them. You must keep the overall length the same, so if you lengthen one end the other end must be shortened. Do not expect to be able to get all bands to perform well. Do not expect it to work on 160M at all (you have an 80M OCFD). Do not expect results to match up perfectly with the various formulas and guidelines you will find online or even in our most excellent ham forum. OCFDs are very picky about your particular ground conductivity, height above ground, surrounding objects, etc. Each one is very much an individual, although you might get lucky! Do expect to have to use a tuner to get the best performance. There is a slightly more detailed way to figure out where to put the feed point based on observed measurements. It may have been posted earlier in this thread (can't remember). It has been posted somewhere in this forum before, though. |
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Posted: 9/22/2015 11:29:51 AM EDT
[#44]
Double Zero. Leave it alone. Don't touch a thing. Nail it down. Run what you brung. Don't fix what ain't broke.
36% feedpoint (which you have) is an excellent split, working on the most bands. 48' / (48' + 85') = 48' / 133' = 0.36 or 36%. One of the tips on tuning an 80 m OCFD is to look at 12 meters, and adjust for best SWR there. Then you will have the best compromise. You do. Let the tuner do its job and go play radio. |
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Posted: 11/18/2015 9:31:42 AM EDT
[#45]
Tractor Supply http://www.tractorsupply.com/ has 10-packs of plastic corner egg insulators at a reasonable price:
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Posted: 11/18/2015 3:12:23 PM EDT
[#46]
Quote HistoryQuoted:
Tractor Supply http://www.tractorsupply.com/ has 10-packs of plastic corner egg insulators at a reasonable price: http://i.imgur.com/Mx2c1dH.jpg I think they were $8.99. I just bought a package last week. |
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Posted: 11/18/2015 11:19:13 PM EDT
[#47]
I just got a box with my 2, 4:1 baluns from balundesigns. I suppose I should go redo my antenna now
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Posted: 11/20/2015 12:17:30 AM EDT
[#48]
Built one with suggested balun and suggested 36% feedpoint-85' and 48' between the split bolts.
Freq SWR 3.500 2.1 3.550 2.0 (lowest dip on 80 meters) 3.800 2.8 7.200 1.37 (7.135 lowest dip) 14.250 1.6 (14.110 lowest dip) 18.140 3.7 21.325 2.0 (21.150 lowest dip) 24.960 1.5 (lowest swr at lower band edge) 28.500 4.5 (lowest dip at 28.050) The short leg is at about a 45 degree angle, I'm going to get it a little flatter check it again then add an 1" at a time to each side. I didn't expect 10 meters to come out that high. Been happy with antenna as it sits though. |
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Posted: 11/20/2015 10:49:17 PM EDT
[#49]
then add an 1" at a time to each side. No, for each 1" you add to the short side, you need to add 1.78" to the long side. |
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Posted: 11/21/2015 1:29:22 AM EDT
[#50]
Quote HistoryQuoted:
No, for each 1" you add to the short side, you need to add 1.78" to the long side. Quote HistoryQuoted:
then add an 1" at a time to each side. No, for each 1" you add to the short side, you need to add 1.78" to the long side. Thanks! |
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