Ham Radio: HF Mobile - Base-Loaded or Centre-Loaded?
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- Опубликовано: 9 апр 2023
- You often read-/hear recommendations to use a centre, rather than a base-loaded whip for mobile HF.
Why is this? To what extent does centre-loading beat base-loading?
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Excellent, thanks Tim
73
Robert G3RCE
Darn good film this one.. Well researched and presented. Bigger is better as usual...
Thank you! Yes more metal in the air
Great video Tim, this is actually a topic with a couple questions on the US Extra exam.
Ah nice one Walt. 73
very good explanation. I think im going to try a center load next time working portable
I have the super antenna. I love it. You can get the swr perfect on it adjusting the coil.
Wonderful video Tim! I would add the mechanical constraints of each type in the comparison. Base loading puts the weight and wind drag at a minimal position while the center loading increases both wind drag and weight AND also the torque on the mount due to the lever effect. In the end, a proper capacitance hat (stationary vehicle) seems to offer the best radiation resistance and lowest loss. We often use part of the top radial wires on our broadcast towers as a cap hat for towers that are a bit short for the frequency of the station. This can happen when a station (say 1500KHz) is sold and the license goes to a new owner at frequency (800KHz). It is a good way to increase effeciency while the engineer works on the GM for a real operating budget or quits. LOL! 73, and keep up the great work.
Ah yes I totally agree about cap hats .. now they ARE silver bullets on 40-160 for sure! 73
Hey Tim, greetings from Silicon Valley! This is the best analysis I've seen yet on this topic - thanks so much for putting it together. You approached this messy subject with clarity and logic which made it easy to understand. I would be VERY interested in a similar discussion about the Cap Hat. I know it makes the best physics to place it at the top of the antenna but so many operators can't do that for whatever reason(s) and place it above the loading coil, or halfway up, etc. That would be a great video, too 😀 73 KJ6ER
Thank you Greg! Placing the cap hat say above a centre or base coil will work in the sense it will make the antenna broader banded but the price is it’ll be less efficient
Very good video, many thanks!! Robert K5TPC
Glad you enjoyed it 73
Very interesting video. So it sounds like it doesn’t really matter which you go with. I don’t operate mobile HF only POTA. I do it outside my car and don’t use the car for the antenna. I have a 17’ Chameleon whip I use for 20-10m and a couple of choices for coils. The BuddiStick and the Super Antenna and both of those are center loaded. The WRC coil I believe is a base loaded setup but I’ve never tried one. Thank you for the explanation.
No problem! Sounds like you are having lots of fun
Great video Tim! One of your bests so far. Thanks! 👍
Thank you my friend 73
Great stuff Tim, thanks!!
Thanks!
Great information and great show thanks Tim bro
Well said
Thanks Andy !
Cleared that up for me. Thank you.
Cheers!
Great explanations, Tim. I always learn a lot from your videos but they also get me thinking, which is an important part of the hobby.
Thanks Mike!
Oh brilliant, what a great description to a question I’ve not even thought of . But of course it makes sense. Thanks man.
No worries Chris 73
Great video something I've learned from you Tim.
Cheers!
Thanks for the video, so well explained it has become much clearer to me... I would love you to reprise and talk about Q in the same way. It's still a bit of a mystery to me.
I've concluded that a lot of the people I work with are "Centre Loaded"... they are good but not as good as they would like you to believe! LOL 😆🤣
Very good analogy!!!
Great Video Tim. I just feel that any mobile whip be it centre or base loaded is always going to be a compromise at and around 40m. Conditions play a big part as does what you want to do at the end of the day. I prefer 10m, 12m, 15, 17, 20m for mobile 73 - G0LQP
100% Steve. I’ll be looking at 40m in more detail, mobile, in a future video 73
Thanks Tim
You’re welcome
Interesting Tim. Thanks.
I've not done any mobile operating on HF for probably 50+ years!
In those days as a teenager, it was 160M that was of interest -- and Base loading was the ONLY chance you had to get something fixed to the car that wouldn't break streetlamps with the whip section as you drove past 🙂 (or pull the wing off your car if you caught the antenna on a tree or bush!)
I've also run centre loaded verticals at the home QTH in 'postage stamp' gardens with a capacity hat above the coil to 'drag the current' further up the antenna. I always made contacts -- which was the main objective.
There was very little maths involved back then -- just 'emprical' methods -- but we did at least have fun trying!
73
Bruce G4ABX
Sounds like proper fun Bruce! 73
Hi Tim great words. Well above my pay grade. Mind blown. 😵💫
Motters M7TRS 73
Hey no worries 73
My answer to those experiments is 5 meter (17ft) long telescopic whip on a magnet base on a metal roof of the car. I don't use any coils to avoid losses. That's important. I just keep the telescopic length as a quarter wave length on every band 20-17-15-12-10 meter. And it works perfectly. No problems with establishing contacts with VKs. Recently had a contact with this setup with Hawaii. I use bottom loaded coil on 40 meters and the antenna is still efficient as actual radiating length of the whip is 1/8 of the wavelength for this band.
Definitely can’t beat a straight QW.. just need a location to use the 17ft
Hello Tim, do you have an idea what the efficiency numbers on an HF20FX or CL could be ?
Tim, great video. Literally have just been playing with this same topic. I have two quick questions that either you or someone else might be able to guide me on.
1) Does the centre loaded coil have to be exactly in the centre? I have used K7MEM calculator which allows you to put it anywhere but I am unsure what that would do to its radiation efficiency. I know the further away the coil is from the feed point the inductance required goes up...this leads to question 2
2) what would happen if we swap out the air cored wound coil for a ferrite wound coil of the same value? As this shrinks its size and there fore allows for a longer top radiator or longer overall radiator. I am thinking there could be bandwidth implications? or is this a no-no?
One thing I hate about this hobby...so many variables!!!! . I have made a 40m centre loaded that approx 3.8m tall. Also a 80m off centre loaded 3/4 1/4 at about 5.7m. I am getting some contacts, but the QRM at home is a killer. I am in ZL land but I can hear VK's and occasional JA. Next builds are Mag Loop and LOG to kill some noise.
Anyway next experiment is the ferrite inductor. I might be back with more questions.
Thanks again, 73 ZL2DEW
Super questions! On a vertical, the coil can be anywhere, funnily enough as you move it nearer the end further than centre, it’s argued that efficiency suffers. Please report back about the ferrite loading. 73
Hi Tim. Great video and learnt a lot!
I've just bought an Ft857d and borrowed some AM PRO baseloaded whips from a friend onto a magmount just to try them out. I may get a Diamond K400 mount or use a separate earth strap at the base of the antenna. I was only able to use the 20m due to 10m being flat. I worked Italy, Bulgaria and Lithuania in about 10 mins during a contest that was going on.
I only intend to use HF static mobile and thinking about a more efficient antenna system for 40 20 and 10m. You mentioned a 9 foot antenna you use. Can you tell me who make this or if its homebrew and recommendations for base loaded coils. Many thanks Simon M0SCS
Hi Tim Just found all your vids on Sidewinder M1EEC coil and Chameleon MIL whip. Looks ideal for my use. Great videos as always! Simon M0SCS
Thanks Simon they work great!
Hi Simon I think you have already found this information - its a 9ft tank whip antenna (about 20 quid) and the slidewinder coil or my LDG RT100 ATU near the feedpoint. 73
Would all of these theory/calculations also apply to a portable vertical antenna base vs center loaded vs mobile?
Yes absolutely.
Hi Tim, another very interesting video, though I wonder if you were testing both of those ants in a qso with me, if i would hear any difference . 73.
I agree Brian. I think lots of folk believe centre loaded is vastly superior. But in most cases who is going to notice 1.5dB? 73
@@timg5tm941 absolutely correct.
Center loaded whips have a radiation pattern like a 5/8 wave out to the horizon, Where as the base loaded 1/4 wave gives you low angle radiation pattern for dx. So for example on 40m the center loaded is great for inter G, The based loaded great for dx. So if dx is your thing Base loaded should be your choice.
Good points. I think in practice given the minimal difference in efficiency, we’d struggle to notice any on air difference between them.
Great video Tim. I can see this being used for training by clubs on antennas. Are the spreadsheets available anywhere for download? 73 G0JLF
Thanks John. Not yet but I can tidy them up a bit and maybe post up.
Hi Tim, avid viewer and reader of your work. Do you have a complete citation for the ARRL work yiu used here? I scanned the latest Antenna Handbook and did not see what looked to be your source material. 73 de K4FMH
Is this what you are looking for ? m.qrz.ru/schemes/contribute/arrl/chap16.pdf
FOO is using a PAC12 at the top of a 28 storey building in Sth Korea
Works a treat. 😅
Great take off!! I bet you enjoy it. 73
@@timg5tm941 bit chilly at night, but we'll worth it. 10 to 40 at the right time is gang busters, funnily except for Sth Africa, all the the rest are +1 - +18 on 15 watts FT8 Ft891 and Pac 12.Cheers mate from FOO on the move Unseo Sth Korea for a mth. H7/VK4FOO
Buy a Tank whip, That works well on 10, 20 and 40 meters
I have and I do! 73
@@timg5tm941 Video link?
So it’s sort of like splitting hairs.
Your analysis seems to ignore I²R at any given point along the antenna. Too bad.
Loving your Videos Mate.
Very Thorough & Clear.
Keep up the great work mate ⚡🙏⚡
That’s very kind! 73