Why Won't My 80-Meter Dipole Cover the Whole Band? (
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- Опубликовано: 2 фев 2021
- A dipole covers some entire bands, like 20 and 40, very nicely. But no simple wire dipole can cover all of 80 meters. Let's find out why. BTW, I mention West Mountain Radio. Their URL is www.westmountainradio.com/.
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Dave,
The 30 meter band is only 50KHz wide. (correction might be needed.)
Good catch! That's what I get for doing things from memory.
obviously a no coder :)
I don't know if I've even seen that explanation laid out like that before.
Thank you very much for that!
Glad it was helpful!
Cage dipoles for the win. I built a vertical Marconi T antenna for 160 that covers about half the band under 2:1 and all of 80 if you move a tap on the base loading coil.
You've sent me on a search to learn about caged dipoles. Thanks! :LOL
I know that this video is several months old, but I happened upon it and it really opened my eyes to something new about this hobby which is truly helpful. Thanks Dave.
Thank you Dave. Your channel provides a year service to the ham community. There are basically two ways to deal with the 80 m bandwidth issue. One is the way you suggested, having a fan dipole or similar design to broaden out the bandwidth. The other us to invest in a remote autotuner and connect it at or near the feedpoint to tune out reactances and match the line as close as possible to keep the swr along the feed line close to 1:1. I have a lot of experience with the latter and find it most convenient.
Excellent video and very timely. Thank you.
Well done, David!
Great video Dave - that's why I use a DX Commander with an 80 m element - less than 2:1 across the whole band with no tuner needed. Better take-off angle for DX and all the other bands too.
Excellent video Dave. I was considering putting up an 80 meter Dipole for local rag chewing to compliment my vertical, you convinced me to put up a 40 meter Dipole instead, Thanks and 73! , Tom, K2BEW
Awesome explanation, thanks very much.
What a Great explanation! Thank you.
Thanks Dave. Good Data. I need to get a 80 m wire up soon for the band.
Good explanation, Dave! I learned something.
Helpful. Thanks.
Well stated Dave!
thank you that was very interesting information.
You could have a type of vertical capacitance hat to broaden the band. At each end of the dipole you could have thin pvc tube hanging down with a counterweight allowing a stainless whip to stick up into the air at each end.
And that’s why I have 40/80 Ultimax bazooka at 35 ft.
All of 40 and most of 80 with my IC7300 with my internal tuner. If I want the of 80 the other parts of 80 I turn on my MFJ939 external tuner.
Once again another super helpful video Dave
73
wd4dda
Hi Dave,
After about 400+ videos from you have finally stumped me.
I have no idea what the ratio between the band size and the median frequency is.
It's just a number to me. (With no meaning.)
Then again it might just be me.
If it wasn't for the "numbers", from the ratio of the two statistics, I would have completely
'understood' the video.
Could you do a deeper dive into this or am I at the point of my Ham Radio journey that I need to start reading Antenna Theory books? (Serious statement.)
Thanks for everything you contribute to the hobby.
Take Care and 73.
Everything scales, so looking at the size of the band as a percentage lets us compare. From wherever you tune an antenna, things get worse the farther away from the tuned frequency. All things being equal, 10% away from tuned center of 10M is as bad as 10% away from tuned center of 80M, but the frequency allocation of 10M (only 6%) isn't wide enough to have the same problems as 80M (more than twice the relative frequency allocation at 13.3%).
Maybe that's a better way of looking at it. 80M has a frequency allocation that's more than double the relative frequency allocation for 10M, so it's going to have more than twice the problems getting everything in the band tuned up.
If the 80M allocation where cut in half, we wouldn't have the problem, but who'd want to give up allocation?!? LOL
Thanks for the excellent comment. You said it better than I did!
@@davecasler You're too kind. Thanks. 73 de KF4UCQ
Love your shirt! I ran the race in 2000 but dropped before going over Handies Peak at around 30 miles.
It didn't run in 2019 because of too much snow, and in 2020 because of Covid. I've helped with the race five or six times and enjoyed it every time.
Thank you.
Outstanding info, especially the chart from West Mountain Radio. Do you know if there is a similar chart that exists for EFHW antennas?
Actually, the lengths are about the same.
To defend Alpha Delta (ref #263): I literally threw their monoband 40m dipole (DX40) into my trees at 30 ft up. When I swept it it looked exactly like West Mountain’s 40m curve. No adjustment needed. I could have bought the parts and cut it, but buying premade was definitely worth it.
Can someone tell me why my 80 meter dipole lowest dip in the SWR is 1.5. I have never been able to get it lower than 1.5. Should I put it higher to get the dip in the SWR lower? Or has it to do with something else?
Higher may actually make it worse. 1.5 is fine. Let the tuner in your rig tune it down to 1:1.
Great explanation, tnx es 73 de KT1R
Nice job on this explanation. Isn't the difference at 10 MHz (9:27 video time) 0.25 FOOT instead of 0.25 inch?
Yes
the Mosley TW-3X covers the whole 80 band. I am going to buy one soon.
If the diameter of the wire affects bandwidth, how big a pipe would you need suspended in the air to cover the bandwidth? LoL
I remember pictures of ships with multiple wires, and doesn't the ARRL have that antenna on its badge?
Giving band width numbers is doomed to invite corrections, as the different regions have different allocations. My understanding is that the US allocations are more generous than for example the European ones. Which still does not refute the basic message that the 80 meter band can not be covered with a single dipole -- not in any region.
Probably, my theory is all wrong, but taking into mind the idea of a FAN dipole? If we just consider 80/75 meters as two real bands and stretch out two elements one for each edge of each band of course using 2.1 or whatever number attainable for the band edge most of the frequencies with a usable loss might be available? I can't remember reading this idea being shot down or any of the forums, but no one else has suggested it. Just dropping a second element a few inches lower shouldn't be too hard if someone desires the bandwidth?
Thank you. I like 80 M, so I guess I will live with the problem.
So could you increase the bandwidth if you built something like a fan dipole or butterfly? Ok I didn't wait long enough
I’ve done the same thing. Lol
What would happen if we made fan dipole with 2 elements cut with one for the upper half and one for lower
Nvm you answered my question
Really liked this video. My 2 cents is ... An 80 meter dipole at the end of a transmission line is like any other network element. If you hit it with some excitation it will respond..... In this case the 80 meter dipole has a high Q....... Am I wrong ?
A standard 80m dipole has the same Q as any other standard dipole (all things being equal). It's just that the 80 meter band is so wide compared to its center frequency that it just can't cover the whole band.
Will you ever do a review on that Isotron antenna you mentioned a few times?
Yes. I need to get outside (or have someone else do it) and get it mounted. We have maybe six inches of snow on the ground--that's why I haven't done it yet. (Not to mention the broken ankle.)
@@davecasler Glad you still plan to do that one, might be very useful for us with difficult antenna situation. But above all else, get well soon! :)
Dave
Good stuff on 80M, but please define how you get your percentages; I.e., SWR
CALCULATION: "Total Band Width divided by Center Frequency" (TBW/CF)
Kind of annoying how he measures in feet while talking about metres too.
@@garrysekelli6776 - It's fairly common in the good ol' USA. ;-)
You can convert meters to feet by multiplying Meters x 3.28. (Mtrs x 3.28) (1 mtr=3.28 ft.)
Convert Feet to Meters: Feet divided by 3.28 (Ft/3.28) (EX. 6ft /3.28=1.83 meters)
You can calculate the length of a half wave Dipole in Feet: 468/Freq in Megahertz
Example CB Antenna (chnl 20 27.205MHz): 468/27.205=17.2 feet. (8.6 Ft. each side of dipole)
Where it DOES get stupid is converting a metric fraction of a foot back to inches, because you are cutting up 12 inches into 10 parts.
Cutting an 8 foot length of wire is easy, but what is 0.6 feet in inches? LOL
Each 1/10th of a foot=1.2 inches. (12/10) -So 0.6 ft.=7.2 inches. (6x1.2)
Now to get even more stupid, you have to divide an inch (sixteen 16ths) into 10 parts to get that fraction.
16/10=1.6 16ths of an inch....you could go on endlessly.
If you want to work in Meters, simply divide 300/Freq in MHZ
CB Ch. 20 Example: 300/27.205=11.02 meters.
Cheers & '73
\m/ ô¿ô \m/
@@greglawrencemusic that's a lot to soak up. I'll stick to measuring in cubits and furlongs.
@@garrysekelli6776 Using the above example of 27.205 MHz 11.02 meters would equate to 24.49 cubits. ;-)
Dumb question, could you cover the entire 80m band by adding traps? I know traps are usually used to make a multiband antenna but could traps be used within one band to increase the amount of available bandwidth?
I've thought of that too but after looking into it. I think a cage dipole is better
Traps actually raise an antenna's Q, making it more narrowband. Maybe you could do something to at least add some coverage lower in the band.
@@davecasler Ah ok. Please disregard the emailed question I sent about this.
I don't understand why people won't use balanced feed line. You sure can cover the whole 80 meters band and any band higher in frequency and do a fine job of it. Hello.....
Jeff ke4fwe
If you have a wide-range tuner and use ladder or window line, you can indeed cover the entire band.
Has anyone ever attempted to electrically adjust a dipole with low-current relays? I know that would be a little "overhead" with two-conductor dc supply lines. Maybe a good experiment for an attic setup? :)
Yes, you could do this.
Finally.i asked myself this very question. Also what äbout 160 metres and 320 metres?
160 Meter is 1.81-2 MHz. Nearly 10%. I don't believe we have an allocation in 320 meters, but under some strict conditions, 600/640 meters is allocated. From Wikipedia: "In the United States, the Federal Communications Commission approved allocating 472-479 kHz on a secondary basis to the amateur service, in a report and order released on 29 March 2017.[19] Amateurs wishing to operate on the band will need to notify the Utilities Technology Council (UTC) and be separated at least 1 km from electric transmission lines that carry Power line Communication (PLC) signals that use the same band. The maximum EIRP is 5 watts with the transmitter output power not exceeding 500 watts PEP. CW, RTTY, data, phone, and image emissions are allowed. The first US amateur stations activated the band on Friday 13 October 2017."
@@berkeleygang1834 cool. Ima use the 10,000 meter Ör 10 km bandwidth.
My mobile hustler 80 meter antenna covers very little of 80 meters! It will cover more with the larger ‘super hustler’ loading coil, but it’s still a narrow banded antenna. I wonder how much of 80 meters can be covered by a full wave loop?
With a full wave loop you will need to feed it with ladder line and use a wide-range tuner. With that in mind, you can cover all of 80 meters.
Outstanding job. It all comes down to math!!!!!!Rock On
Yes, when cut for the center frequency, a simple wire dipole cannot cover the entire 80m band at/close to resonance.
However, an antenna does not have to be resonant to be an efficient radiator. Even with an SWR as shown in the graph at 3.5Mhz and 3.9Mhz, a good wide range antenna tuner will easily transform the impedance to 50 ohms for the radio.
Unbalanced (coaxial) transmission line is subject to losses at high SWR. Balanced transmission line would be indicated for feeding an 80m dipole cut for half way through the band or cut for the lowest frequency of interest.
I won't attempt the math, but the losses with balanced line feeding it would be insignificant.
Sir! Take a litttle time to contemplate using a Loop-antenna (loop skywire) 273,1feet total length and fed with 450 Ohm Ladderline 76 fet long (or 900Ohm=2x450Ohm) to a 2:1 (4:1 not critcal) into a MFJ969/962 Antennatuner. Then You c a n cover 160-6M!160M will be v e r y narrow!
80-10M varying 15kHz-500kHz
6M You'll cover all 50-52MHz
(even up to 54MHz)
Dipoles aren't sufficient, but loopantennas a r e and they
don't pickup noise that easy!
Midpoint earthed = You DO NOT RISC that You blow Your rig on BUILD..UP STATIC!
73s de Gunnar sm6oer >>\
Loops are great. I had a loop skywire cut for 80m for quite awhile. Then I renovated my Butternut HF-9V and gave it lots of radials. It worked so much better than the skywire that I took it down and cut it up into more radials for the vertical!
Or just 8.2% "spread" if you live in the #1 region in the world of radio;-) (300/3650) Good job "we" only get a miserable 300kHz of band.
1337
Comment
A doublet can easily cover all of 80m, and all HF bands for that matter. You are just feeding your dipole the wrong way. A balanced antenna deserves a balanced feedline.
I run a doublet. It's great if you ignore the manual tuning all the time.
@@BobDarlington I run a remote auto-tuner on my doublet. I press one button on my radio for two seconds when I change bands and I’m ready to operate. I’ve also got a 160m loop with the same type setup.
On 80m, I am only needing coverage from 3.6 MHz to 4.0 MHz. My dipole seems to cover that range pretty well (at least, from an SWR standpoint).
Dipole antenna's seem to be pretty good for the voice portion of 80m.....my antenna is under 2.1:1 in that range and reaches a minimum of 1.1:1 at 3.8 Mhz.