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- เผยแพร่เมื่อ 4 ส.ค. 2024
- This video examines the effect of different vertical antenna lengths on the take-off angles that we would like to use to work DX. Do all antenna lengths have the same influence?
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Email: TimG5TM@icloud.com
Previous videos mentioned:
Video 1 - Introduction to Antenna Efficiency: • Vertical Antenna Effic...
Video 2 - Antenna Length and Efficiency: • HAM RADIO: Vertical An...
Video 3 - The Effect of Ground Radials: • HAM RADIO: How Many Gr... - วิทยาศาสตร์และเทคโนโลยี
Well done Tim! Thank you for showing this. I find that too many hams are fixated on SWR, and cut their antennas to give a good match. What they really should be doing is cutting the antenna for the desired angle or pattern of radiation, and THEN creating a matching network (at the antenna) to transfer maximum energy from the feedline. Most have the cart before the horse. 73 & stay safe.
I couldn’t agree more
Well said Greg
Very good point
I tend to tune out when you go modelling Tim as, sometimes, I find it complicated, but this one is brilliant, and I have it saved for future reference.👍☘️
Thank you Donal that’s very kind!
Great analysis Tim - exactly why 5 degrees is a good comparator for DX.
Diolch Tom!
Your point about longer verticals sometimes having excellent very low angle radiation (despite also developing high angle lobes) is well taken. But to work DX you have to hear them, as well as have them hear you. Those high angle lobes can mean you will be receiving lots of QRM from nearby stations, as well as QRN from nearby thunderstorms, both of which could be far less with a shorter antenna not having those high angle lobes. That receiving advantage with a shorter vertical might well be worth a few dB sacrificed in transmitted field strength.
David VE7EZM and AF7BZ
Good points 👍
Very Interesting!!! You gave me something to think about (and model). Thank you.
Thank you Paul
Perfectly well explained, thanks.
HF antenna is very counter-intuitive sometimes. Looking at graphs and numbers is convincing.
Thanks Olivier 73
Well done. Antenna designer here, I have been using NEC since the early 90’s.
Thank you!
Another great video. Thanks!
Thanks for watching! 73
I can't wait for next episode
Thank you!
Great info Tim
Thank you Pete
Another interesting analysis, and as WECB640 wrote we really should design for pattern and then figure out the matching. The models don't of course show every factor. In my small garden for instance a ground mounted quarterwave perhaps for 10m will by definition radiate all of the field from points less than 2.5m from the ground. Much of the low angle radiation will consequently be absorbed by fences, houses and foliage. A three quarter wave mounted at ground level will have a high current node centred at 5m off the ground. Way above the fences and much of the foliage and close to the height of the houses. This will lead to more low angle radiation escaping from the absorption by obstacles nearby. As another commenter mentioned the high angle lobes of the three quarterwave can be a problem with signal to noise. In my youth on CB in the early 1980s I used a Sigma 4 mounted at a good height over 100ft from any houses. It was very effective but at times the S/N was dreadful compared to a five eighth wave with the cleaner pattern. 73
Great points thank you
Great video Tim. More or less what I would expect based on what I’ve read elsewhere and heard others say but I really like the clear and concise way that present the information. I guess that’s your professional background showing!
With 1.25 & 1.5 wavelength antennas sending most of their RF skywards I have wondered how well these would work for chasing SOTA or WWFF (which is mostly short hop, high angle around the UK & Europe)?
Obviously there are some practical problems with building a vertical approximately 60m tall, assuming that I am chasing mostly on 40m but it might be possible with a kite antenna!
Obviously there are much easier & more sensible ways to achieve the same result with much less effort (such as using an inverted V) but it could be interesting as a purely educational exercise!
Love to see the 40m efhw with a kite - awesome!
Ive worked Japan, Indonesia, New Caledonia, Chile, Alaska, on ssb from UK using my trusty HORIZONTAL end fed piece of wire which is 20m long. Radio waves get their polarization all mixed up anyway due to hopping. Having the right propogation across the globe is far more important than whether you're using a 5/8 or 1/2 or 1/4 wave.
Thank you for your input, 73
Great introduction sir the key is ground it with multiple radials on the base ground part and height is key to👍⚛📻
Absolutely, check out my previous video on radials in the description. 73 👍
Great info Tim. As you know I only use resonant 1/4 wave verts which give me dx everyday zl to eu, and as we know there are many more important factors , apart from ant length , ground system, location, propagation etc, all of the factors including your info could alter takeoff and therefore db gain, but not really enough so the guy on the other end would know. The old set up of a simple 1/4 wave with radials will beat or be as good as most other ants.
Iam doing daily tests with a Swedish stn, he has a 40m loop and a 4 sqr, mmna puts the 4 sqr way ahead, but in real life it doesn't, 2 s points down on the loop working dx hi.
Look forward to your next video Tim, 73 mate zl3xdj
Cheers Brian !
@@timg5tm941 I've got a new ant video on my qrz if your interested, cheers mate.
Another interesting video Tim, many thanks. Mark, 2E0MSR
My pleasure Mark, thanks for watching and stopping by to say hello 73
Brilliant!
Thanks!
I would be very interested in how the random 41ft vertical wire antenna does. If there is an easy way to do all the calculations (as you did for the 36ft antenna) please share it and I'll do the calculations myself. This is really interesting for use home brew builders. I just started to build my own and I'm having a blast and this kind of information helps me a lot!!! Thanks for all your content!
I’ll check out the 41 feet version soon
Another really good video, have you considered writing these up for Radcom?
Thanks Liam, no but I have written a few times for PW. 73
Good video as always, I've been experimenting with a 1/4 wave vertical on 20m using 32 x 5m radials and it works well but I don't think it's as good as my vertical end fed 1/2 wave on 20m from UK Antennas plus no radials and easier to deploy!!
Nick
2E0PDN
Agree!
5:53 There's something funny about the graph, the blue 3/4 Wave antenna has higher gain EVERYWHERE, which means that this graph CANNOT be a 'Directivity' graph, as directivity must always integrate to precisely unity. Therefore, this must be a 'Gain' graph which combines directivity and losses. So the information is incomplete, in that our host isn't even mentioning loss here. Not sure why, but this information glitch instantly jumped out at me. Directivity plots always integrate to unity, so all antennas have the exact same average directivity. Gain includes also loss, but you need to discuss loss to understand where and why.
Good practice calls for a table's columns to be labelled with the units. So if you put (dB) under or beside the headings 2 DEGs and 5 DEGs none of us would be confused.
Ah I see…. Very nice
Thanks 7 3
Pleasure!
Recently I went down a rabbit hole in wikipedia about antennas. The article was talking about vertical antennas and wavelengths, and after a point there was no benefit in going bigger. From memory I thought it was 5/8 wave, but of course, now I can't find my way back to that rabbit hole! Anyway, from what you've shown, perhaps I'll try build a 3/4 wave 10M antenna. And maybe 15M.
I'd also been pondering, what would happen if I could somehow make my efhw a vertical ? (I'd need a bloody long squid pole!!)
73
3/4 wave is good .. it will need matching to a 50 ohm feed. However, I will cover this in a forthcoming video
Hi Tim. Question . Just theory. So i have a yagi beam tuned for 20m. I have it up in the air say 5 to 10m above ground with no building near. So using you findings, would i angle the beam at say around 4 to 5 degrees from earth . Would this give me a better DX than having it parallel to earth. ???. Just curious as to your idea's on this. Thanks for the great video.
Steve. M7DOZ.
Hi Steve being a yagi it will radiate at low angles but to make it sing it still needs to be closer to half a wavelength in the air. 73
@@timg5tm941 Slightly confused Tim. Do you mean if it was for 20 metre band , then it would need to be 20 metres above ground. ????
Steve
Hi Tim, Looking for a non resonant vertical length that would work well on 10 down thru 17M. Would a 23foot vertical and a tuner work well on just those Bands?
Yes should do
I’ve always wondered if a roof ground plain would be better for dx compared to a hood fender mount ground plain.
More metal and higher away from lossy ground probably gives the edge to the roof
Thanks Tim. Only transmit when out in the motor, 20 & 40 Ampros. I'm thinking about the "slide winder" coil with the "Mil whip" on a magnetic base. Would you (or anyone one else) recommend it, or is there something better that I could use? Obviously I could throw poles out & about with dipoles & wires and whatnot but, you know -> convenience , and I'm a little self conscious about mounting erections out in public etc.
The Slidewinder has a wider coil and the mil whip is longer than the Ampro so a little more efficient also once you learn the points to tune to it’s a little more convenient than swapping a whole antenna to change bands. That said, Ampro whips at 20m and above represent very good value for money and work very well 73
@@timg5tm941 Thank you.
So it looks like .70 WL for any band is optimum for a monobander? How high is base above ground? Z at optimum height AGL? Much appreciation Tim!
Hi Mark you’ll need a tuner although a 3/4 wave should present a decent match. The antenna is ground mounted. 73
I'm confused by this. Can someone maybe explain? How can the antenna radiate more power in all directions. My understanding was, that an antenna can only redirect, or "focus" power in certain directions. This would implicate for gains at 5° of elevation you would lose some power on say 45° of elevation. The plots here show a gain from one antenna to the next over all elevations. This feels odd to me and i wonder if theres something wrong with MMANA. Maybe SWR does impact far field plots in MMANA after all, at least the absolute values.🤷♂
A vertical is omni directional with a 360 degree coverage of ground radials such as those modelled here 73
@@timg5tm941 Thanks for the response :). Maybe the meaning of my question got lost in translation. The antennas you modelled and compared were all verticals, but e.g. the 0.7*lambda did perform better than the 0.25*lambda over all take-off-angles. I would have thought that to gain at one take-off-angle one would need to lose at another. 73 DD4AB
And dont get me wrong, i veriefied your results in MMANA. I just dont understand how one vertical can be better than another at all take-off-angles if the power is the same and everything is radiated. Having one antennas far field plot completely contained within anothers far field plot is what puzzles me.
Can only be loss (to ground) with real antennas. The volume of the „bubble“ that is deformed should always be the same (1) with ideal antennas.
Really wish I could put up a 40m 1/2 wave as a vertical.
You and me both!
655.2/frequency = 70% vertical using stranded wire. Easy math!
Indeed!
200 ft.
Indeed
Very confusing when you were “ pointing” things out. Finally discovered in the last 2 minutes that you actually had a cursor. Needs to be bigger.
Righto I’ll get the pump
All information provided is not an inducement to buy or invest in antennas and is for educational purposes only. Tim does not accept or imply any liability for any money lost in pursuit of optimal DX. 73 M7BLC
I’m copying that for my small print!
Excellent information as usual, Tim! Thanks!! de W5ODP
Thank you Dave! 73