Electrically short antenna, base load or center load?? - Page 1
Forum section: electronics / rf-microwave

author: CaptDon
author_rank: Super Contributor
timestamp: April 30, 2021, 01:23:25 pm
content: Because of my long daily commute on a bad piece of interstate I am still one of those folks who relies on the U.S. 27mhz citizens band radio for traffic information. My regular antenna is about 4 feet long and is base loaded and works well, 5 miles mobile to mobile is typical. The antenna is too tall to get my car into the garage. I have been looking at shorter antennas and in the 18" long category I find both base loaded and center loaded models. Is one better than the other or is there really no difference when the antenna is so short?? All of my 'hamstick' amateur radio antennas are base loaded.

author: M0HZH
author_rank: Regular Contributor
timestamp: April 30, 2021, 02:14:08 pm
content: In theory, you want the loading to be as close to the end as possible, as the losses are lower. However, because of mechanical challenges the middle loaded antenna will probably use a physically small inductor with thin wire, which adds losses.Bottom line, the only real rule with shortened antennas is "bigger is better".

author: A.Z.
author_rank: Super Contributor
timestamp: April 30, 2021, 02:46:23 pm
content: Given that either antennas will be short, I'd go for a base loaded one, at least it should be a bit more robust; an old trick used by truckers to increase range was to install two antennas and change the phase to obtain a bit more gain either perpendicularly or longitudinally to the vehicle (usually the second option is preferred and the antennas are placed to the two sides of the vehicle)

author: coppercone2
author_rank: Super Contributor
timestamp: April 30, 2021, 06:50:49 pm
content: how about some kind of hinge or something to lower it or change the angle when going into your garageI have seen a youtuber experiment with a slinky antenna and it offered good performance so there might be something you can do with springs and a pullya little ridiculous but it seems like you can get into a real bad situation if your communications dont work given your situationand telescoping, i think I figured out how to make telescoping things, theoretically you can use concentric tubes and hydroforming in the middle tube with plenty of lube between them and then cut them both to release the pressure point formed and have things that nest very well, so you get a stack of tubes and the most inner tube is capped and connected to a forming pump. something i need to work out but it seems like a good ideaas you can see, despite the fact that it looks like an inductor, at some frequency ranges.. you can do some creative stuff with an antenna

author: tkamiya
author_rank: Super Contributor
timestamp: May 03, 2021, 12:07:29 am
content: If it's going to be 19" only (50cm?), I don't think it will make any difference. But traditional wisdom says middle loaded antenna is more efficient radiator than base loaded. I would prefer continuously loaded, helical wound for ease of construction. Either way, performance will be minimal.The most efficient short antenna will be capacitive loaded at the top. There were some intensive experiment done by now deceased ham, Dr. Jerry Sevick in the 60s. I recall he achieved almost full size performance with 1 meter long antenna at 7MHz. This type of antenna will be impractical for mobile use though.

author: A.Z.
author_rank: Super Contributor
timestamp: May 05, 2021, 08:18:32 am
content: Quote from: coppercone2 on April 30, 2021, 06:50:49 pmHi "coppercone", while a slinky isn't suitable for mobile uselooking at the vertical in the video you posted, I started wondering if it may be possible to use a slinky as the vertical section of a "T" antenna; I mean somethinglike thisbut with the vertical section made using a slinky and the top hat made using some telescopic whips, with such an approach, by adjusting the hat arms length and the vertical support length, it may be possible to adjust the antenna to work on different bands; what do you think ?