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Broadband HF Folded Dipole Antennas
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Broadband HF Folded Dipole Antennas at QRP power levels.......any experience with them out there ? The advantage of these is "no tuner required". I recall B&W selling these in the 60's and the military likes them because they don't require tuning and are good from 2-30MHz with a maximum SWR of about 2:1 and since they are wire antennas, you can roll them up and carry them easily.
73 Kees K5BCQ |
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Gordon Gibby
开云体育Kees --- I particularly DISLIKE those broadband tilted-folded-terminated?antennas because they ahve HUGE LOSSES on various? ferquencies, as much as 10 dB.
I much prefer something like a well-designed off center fed dipole with current/voltage baluns and the resullting abilaity to work reasonably well across wide swaths of the spectrum --- or an auto tuner and a balanced line fed random dipole.
10 dB losses jjust make me shudder inside.? ??
Gordon Gibby
From: [email protected] <[email protected]> on behalf of Kees T <windy10605@...>
Sent: Friday, May 11, 2018 10:47 AM To: [email protected] Subject: [BITX20] Broadband HF Folded Dipole Antennas ?
Broadband HF Folded Dipole Antennas at QRP power levels.......any experience with them out there ? The advantage of these is "no tuner required". I recall B&W selling these
in the 60's and the military likes them because they don't require tuning and are good from 2-30MHz with a maximum SWR of about 2:1 and since they are wire antennas, you can roll them up and carry them easily.
73 Kees K5BCQ |
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Hi, I have had a BW for twenty years. It's the 66feet version. It exceeded my expectations, you can use qrp levels at 1w as well or less with wjst sort of modes. Don't think these kind of antenna are for portable operation. First they are rather eavy. You should roll them very well. I just installed once and is surely easier to install compared to a av640. But for portable operation I would opt for a tuner and a wire, you betcha! Alternatively an endfed Zepp. BW are now extremely expensive, yes they are a durable good, but you can make a low power version that works similarly at a fraction of the cost and much more light and portable. So if you want one portable, just make it. Il 11/mag/2018 16:48, "Kees T" <windy10605@...> ha scritto: Broadband HF Folded Dipole Antennas at QRP power levels.......any experience with them out there ? The advantage of these is "no tuner required". I recall B&W selling these in the 60's and the military likes them because they don't require tuning and are good from 2-30MHz with a maximum SWR of about 2:1 and since they are wire antennas, you can roll them up and carry them easily. |
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I think your expected loss are a bit pessimist, 10db means 90 percent in heat. The resistor would have melt... Btw the 66 feet version or the 132 offer better radiation patterns than others and maybe better efficiency. IMHO. Il 11/mag/2018 17:07, "Gordon Gibby" <ggibby@...> ha scritto:
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Gordon Gibby
开云体育could be, hard to say, I've certainly not done a simulation of them --- but that is what i believe was measured or predicted by others in reviews etc that I've read elsewhere.? ?Without a solid measurement or simulation, of course, tough to say for sure.
Given that the SWR on a non resonant center fed folded dipole would be EXPECTED to go past 10:1 at various places, however, how ELSE can you explain that it would "present? < 2:1 SWR"??? ?I haven't run the numbers, but I would presume that means a heck of
a lot of power went into a resistor at those frequencies.??
The very very best way to get an extremely? broadband antenna (judging by SWR anyway)??.......is to use a resistor.? ?They call them "dummy loads".
If there isn't a matching system somewhere, and the thing is always under 2:1.....I'm going to believe there are a LOT of losses on some frequencies.....? We built knockoffs of Buckmasters over the weekend and my tests on my knockoff suggested I could keep
the SWR below 5:1 throughout 3-20 MHz using 100 feet of RG8X coax.....which has loss in itself --- and i would suspect that losses in my toroidial current- and voltage- baluns probably make that SWR look better than it really is.? ? The plots on the real buckmaster
site aren't nearly as nice as what I got so I suspect lower losses in THEIR design than our homebrew efforts using FT-140-61 and FT-140-43 toroids.? ? ? ?
We have an end-fed tower at my EOC.....with the tuner inexplicably postioned at the RIG end of the coax to the end-fed tower.....and when I spin the dials there I hear < 1/10th the number of literal stations that I could hear at my own house soon after in
time (had to drive between them).? ?Efforts at gateway connections (WINLINK) were virtually impossible at the EOC system....and easy at my home system....leading me to conclude there were huge huge losses in that system design on 80 and 40 meters.? ?Why else
would the band be so QUIET when my radios at home were JUMPING with stations unless there were a severe fault in the EOC transceiver?? ? By contrast we threw up random inverted vee's into their oak trees --- and made a TON of contacts.? ?
Cheers!
gordon gibby
From: [email protected] <[email protected]> on behalf of iz oos <and2oosiz2@...>
Sent: Friday, May 11, 2018 11:40 AM To: [email protected] Subject: Re: [BITX20] Broadband HF Folded Dipole Antennas ?
I think your expected loss are a bit pessimist, 10db means 90 percent in heat. The resistor would have melt... Btw the 66 feet version or the 132 offer better radiation patterns than others and maybe better efficiency. IMHO. Il 11/mag/2018 17:07, "Gordon Gibby" <ggibby@...> ha scritto:
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Loaded folded dipole have a corner frequency below with the load is doing the work.? This
is related to the length like any dipole.? Also as you hit various resonances? ithe resistor does some work.? Generally the losses are not horrific as sme may assume.? Some bands its about par with a dipole.? The other effect is the antennas patter is less subject to breaking into multiple lobes of unknown directionality (what NEC predicts vs what the field installations does). It would not be my first choice but it can be acceptable antenna for non-QRP operations. It would be far down the list as you have o carefully roll it up and it requires substantial height? at one end (if not both) to be useful.? They were popular for diplomatic missions as they made fewer demands on the radio operators skills in the deploy phase. A dipole fed with ladder line and a simple tuner is more efficient. and easier to install and likely transport.? If the band is limited to one the dipole can be coax fed and the whole thing fits in a plastic bag (25ft of RG174 and a 66ft 40M dipole). The other popular antenna for portable work is the end fed half wave which can be multiband LNR mades one the EF-QUAD for 40/02/15/10 that's 66ft long and also a shorter 40ft EF-40/20/10.? I have experience with those and they work.? You can make one or one of the many vendors sell them.? I know from use and also the manual the EF-40/20/10 can use a wire cut for most any band between 5 and 30mhz (468/f) and a handful of #22 wire is light.? Likely the easiest to deploy. The random length wire (53ft and 125 ft) with a counterpoise fed with 1:9 transformer and a tuner is also popular for field work.? The tuner is needed to insure the SWR is? low as some radios are fussy.? ? Its easy to deploy like the end fed half wave antennas as it can be Flat top, inverted V, L or sloping, even vertical depending on supports My favorite terrible antenna:? 134ft or wire 41ft and 93ft with a 1:4 balun between them? as an off center fed? wire about 1 ft (yes about 30cm) off the ground.? Its about -10db antenna but fairly easy to tune with an antenna matcher from 160 through 20M. If you like the B&K this is easier to install in a a flat area without any poles or structures. Three rules for better signals: 1. Put the wire up higher where possible. 2. If not higher, use more wire longer wires, vertical arrays, or wire yagi beams 3. Any wire can be an antenna, and likely better than a bucket of wire in the shed. The last one is most important, put something up!? Terrible antennas are still better than none at all. With even a poor antenna anything can be better or at least you have something you can compare to. Allison |
开云体育I have a Chinese copy of the old B&W folded dipole and have only used it on 2 ocassions, Kees. I saw considerable losses when compared to a G5RV that we used as a comparison at the same campsite, although I did not try it across all the HF bands to see if the loss varied, as Gordon reports.
Added to that, mine was obviously aimed at the military or commercial market and is therefore damned heavy! Not for QRP use methinks, at least not for portable use.
Bill, VK7MX On 12/05/2018 1:07 AM, Gordon Gibby
wrote:
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Yeah, usually are heavy as they are meant to withstand quite some power. If you build one with a 9:1 unun plus a choke and a 560ohm non inductive resistor you won't have the same of a BW but close and much more light. In any case other antennas may be more adequate for portable use, the G5RV is a good performer. Still a tuner and a wire is also good as a dipole with ladder line. I would never use RG174 or similar size cables, I checked its real losses and is really bad. I use RG174 only for audio, PTT and other interfaces with the PC. Use instead Messi Paoloni same size of RG58 cable. That is light and low loss. Il 12/mag/2018 01:13, "William R Maxwell" <wrmaxwell@...> ha scritto:
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RG8X is also fine for HF. Btw where can I see the Chinese copy of the BW? Il 12/mag/2018 08:06, "iz oos" <and2oosiz2@...> ha scritto:
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L.B. Cebik, W4RNL (SK) did a lot of documentation on these antennas.? His conclusion was that up to 35% in losses depending on the frequency.? However, it IS frequency agile and it DOES radiate.? You DO need an antenna matcher because it is not all that flat.? A lot depends on what length of the antenna and the operating frequency is.? Several folks and companies have experimented with different load resistor values and different wire spacings and claim improvements.? Some have even made it a 3 wire folded dipole and claim improvement.? I ran one for years until the elements got to it.? It was "OK".? Not great.
I have friends who operate ALE and must be frequency agile.? The TFTD is ok for that.? They claim that what they lose in transmitter power they make up with lower receive noise.? I guess the resistor swamps the noise too. I did a lot of research before planning my next antenna system and I concluded that the best antenna system I could come up with was a dipole as long as possible, not necessarily cut to a frequency, fed with parallel line and use a good antenna matcher.? There are few frequencies you cannot use because of excessive SWR and it WILL radiate, usually quite well.? Best to use an automatic tuner located outside the shack.? You can use an LDG tuner with a 4:1 balun (even a 1:1 or other ratio) and bring the signal from the matcher with coax.? Use a good 1:1 choke balun and a good ground to keep RF out of the shack.? You might not know what the pattern will be without simulation because it may (will?) radiate from the feedline and the antenna at the same time depending on the frequency. My two cents for what it's worth. K4TQL |
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35percent in loss means less than 2db, a value quite far from 10 db. The actual shape, the balun and the resistor can make different models to have slightly different characteristics. Do you need a tuner? It depends on whether how much power your radio can give at an SWR between 1.3 and 2. If you have an internal tuner you surely don't need another one. The 66feet offers better radiation patterns above 5 mhz then others. It should be low noise but don't think it kills all the noise. It probably has a slight lower noise because it is a closed antenna, dc grounded etc. Its signal/noise ratio seems fine to me. When I use the club station with an efficient yagi I can clearly notice the statics rain, something not imaginable with the T2FD. Also consider the lobes of radiaton, so 10db difference may well be found on an A-B comparison but depends on where A and B and their antennas are located. This does not mean that 90 percent of the energy is dissipated into the resistor. Having said this, other antennas like doublet, G5RV, fan dipole, endfed, wire and tuner are at least as good and cheaper antennas. Il 12/mag/2018 17:20, "BruceN" <k4tql@...> ha scritto: By the way, a 10 db loss would be represented by a loss of 1 1/2 S units figuring an S unit is 6 S-units as usually measured. |
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Gordon Gibby
开云体育Think through what is being said.?A Loss of only 30% would be somewhere in the range of one dB—-unnoticeable.
But Almost everyone notices losses with these antennas. ?Even on receive!?
The primary reason you have a “quiet antenna”, is because losses are so high that it can’t even present your receiver with a strong signal from the normal ionosphere static!
Such lossy and wideband antennas have their place, but I agree with one of the writers , give me a low loss feed line and Antenna ?and I’ll use an auto tuner. ?Last thing I want to add to my Antenna is a dummy load resistor! ? Unless I’m truly forced to.
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Gordon Gibby
开云体育Here’s the page showing the extraordinary losses in a simulation: ? Up to 950 out of 1000 watts ?dissipated in the resister! ?That’s even worse than 10 DB. ?
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Bo Barry
Probably worth a LOT more than two cents.
Especially for those with long coax lines. Having a true matched coax and the impedance corrections done at the antenna make the most sense. Unfortunately an economical outside tuner isn't around. I'm gonna research them anyway. I'd love to experiment with Smith Charts again. I studied them in '65 &'70 in grad school. The EZNEC program looks interesting but I haven't figured it out yet. 73 Bo W4GHV since '54 |
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That is a model based on assumptions. The only way to establish how much power is dissipated into the resistor is to measure the heat produced. By the way it is true that at low frequencies, it dissipates much more. It behaves like a high pass filter. The 66feet version was sold by BW with a 5Mhz lowest frequently. Il 12/mag/2018 19:44, "Bo Barry" <bobarr@...> ha scritto: Probably worth a LOT more than two cents. |
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Any time you include a resistor you loose some efficiency.? ? Having designed mil antennas usually
the source tolerates some maximum SWR without a tuner typical is 2.5:1? some its 3:1.? However where you put the resistor and how you construct the system as a whole is important.? The B&W is simple and does work and generally for various bands its not bad for the long version.? Like all antennas the short version does NOT have the same low frequency capability and will be lossy there. As to modeling it, beware dragons may lie beyond.? The most common error is that NEC (V2) does not alway shandle two parallel wires correctly if they are close.? The result then is invalid. I've done an eval using the NEC4 engine and even then you have to pay attention to wires close spaced though it handles it better.? Folded dipoles are tricky to model. There are resistor loaded antennas that offer gain and are considered wideband as well. One that comes to mind is the Rhombic. Allison |
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Gordon Gibby
开云体育Yes, it is a model.1. One could measure the power sent to the antenna and then measure the RF voltage across the load resistor, and compute the power dissipated on the load resistor presuming that it is somewhat noninductive. ? ? Repeat every quarter megahertz or so, from
3 MHz to 30 MHz. ?
2. For somebody a little brighter than me, Open the antenna where that resistor is, measure the SWR with an antenna analyzer at every frequency; repeat with the resister connected back in, do you some fancy math and tell us exactly what the loss in the
resister was to make the SWR looks so wonderful.
3. For a rough estimate, one could take a normal non-lossy antenna, and measure the background static on a receiver without automatic gain control. ?Replace with the tilted folded dipole and see how much softer the background static is. ?Although the patterns
will not be identical, atmospheric noise ?is probably somewhat Homogeneous. ?
4. If one had a calibrated S meter they could do the same there.
5. We know from many many observations that it is considered a quiet antenna, giving experimental evidence to suggest the losses are quite noticeable. A 3DB loss would probably not be so noticeable. ?
The problem for me is that I need an antenna at work on many frequencies, not just the ham radio frequencies, so wide ranging losses aren’t ?my best goal.
Perfect application: Give me a platoon of Marines who need to get antennas to work for ALE? I’ll send them out with the tilted folded terminated antenna every single time. ?it is a perfect antenna for that kind of mission, absolutely perfect. ?No muss
no fuss, it works. ?And since the military has money to burn, it fits perfectly. ? Give me a government installation in the shares ?system, perfect match also. ? ?Give me a emergency operations center wanting to run shares and ham, with a bunch of hams with
a little less experience, perfect application also.
Every antenna just like every boat, and every airplane, every ship, is a compromise.
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Gordon Gibby
开云体育Thanks Alyson for that information!I guess if you take any antenna with 15 dB ?of gain and then throw in 3DB of loss, you still have 12 DB of gain!
In order to make my non-resonant dipoles tune with an MFJ auto tuner on?just about any frequency, I almost always end up with a problem at one particular band, usually where the antenna is a full wavelength long.
I gave up, and just put in simple traps made out of RG 58 coax. ?Undoubtedly, that adds some loss & ?I think it’s worse near there resonant frequency I’m told, but I still think I’m probably better off than having an actual big resistor ?somewhere. ? The
compromise of coarse is I have to spend a couple hundred dollars on a fallible auto antenna tuner. ?So that’s a compromise!
But I think I have lower loss most of the time. ?My gateway station get plenty of use, so it must be doing something right.
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