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Author Topic: Distance with 10W on A.M. (M.W.)  (Read 932 times)

Offline Stretchyman

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Distance with 10W on A.M. (M.W.)
« on: December 30, 2023, 1826 UTC »
Just had some feedback from a customer running a 10W carrier tx with a simple 8' base loaded antenna and moderate earth system.

5 miles with radio able to auto detect, 15 miles with manual tuning with signal detectable upto 35 miles.

Not bad!

Thought it best to put this up for reference as do get asked this question a lot!

Cheers

Stretchy.
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline Charlie_Dont_Surf

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Re: Distance with 10W on A.M. (M.W.)
« Reply #1 on: January 01, 2024, 0128 UTC »
Assuming that they aren't planning to boost output power significantly, the best things that this person could do is 1) make the earth/ground radial system as extensive as possible and 2) add a capacity hat to the top of the (presumed) vertical antenna. Both can have dramatic effects upon antenna radiation resistance and thus antenna efficiency.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Kage

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Re: Distance with 10W on A.M. (M.W.)
« Reply #2 on: February 13, 2024, 2019 UTC »
I prefer top loading with a coil or even a combo of that and a T top hat or inverted L configuration, inductor at the 90 degree bend. Only drawback is the added top weight and the coil being much higher inductance compared to having it near the bottom tuning section when using a shortened antenna. Also getting the inductor turns right can be a pain since you have to take down and put up the contraption until it's tuned. This can be used as a single vertical antenna this way without needing to tie off wires at the top to a structure if desired.

When I've tried this I notice a considerable improvement with broadcast coverage compared to bottom loading. Has something to do with current distribution in the antenna but haven't had my coffee yet.
As Charlie_Dont_Surf recommended though your standard shortened T antenna (or capacity hat) just "works" and is even used down in the longwave band where shortened antennas are a must.

Of course getting as many radials down is the other functional section of the antenna and is equally important. Bare minimal tie to any large metal items earthed and experiment with that if you don't have the space or wire to put down over the ground.

It still amazes me how much people can pinch out of those pea shooter part 15 setups too. You'd think at some point there would be diminishing results but I guess sometimes every little thing in the overall antenna system does add up  8)
« Last Edit: February 13, 2024, 2030 UTC by Kage »
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Offline Brian

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Re: Distance with 10W on A.M. (M.W.)
« Reply #3 on: February 16, 2024, 1856 UTC »
I prefer top loading with a coil or even a combo of that and a T top hat or inverted L configuration, inductor at the 90 degree bend. Only drawback is the added top weight and the coil being much higher inductance compared to having it near the bottom tuning section when using a shortened antenna. Also getting the inductor turns right can be a pain since you have to take down and put up the contraption until it's tuned. This can be used as a single vertical antenna this way without needing to tie off wires at the top to a structure if desired.

When I've tried this I notice a considerable improvement with broadcast coverage compared to bottom loading. Has something to do with current distribution in the antenna but haven't had my coffee yet.
As Charlie_Dont_Surf recommended though your standard shortened T antenna (or capacity hat) just "works" and is even used down in the longwave band where shortened antennas are a must.

Of course getting as many radials down is the other functional section of the antenna and is equally important. Bare minimal tie to any large metal items earthed and experiment with that if you don't have the space or wire to put down over the ground.

It still amazes me how much people can pinch out of those pea shooter part 15 setups too. You'd think at some point there would be diminishing results but I guess sometimes every little thing in the overall antenna system does add up  8)
I designed and built a MW aerial many years ago that was 2 vertical wires, about 20 inches apart, held up by 3 sets of 2 top wires, also 20 ins apart, which went to 2 trees and the house chimney. It was only about 35 or 40 feet high. It worked quite well on 846 kHz (I'm in Europe). I moved the coil to the top and a friend a couple of miles away noticed an increase in signal strength.

Using 2 wires on the vertical increased the bandwidth of the aerial considerably which made tuning much easier and also was important as I was running wide audio bandwidth. Optimod 9100 with filters defeated.

Dropping the aerial to fine tune it was a PITA so I decided to add a little extra coil at the base and fine tune it there.
I have no idea what the base impedance was, or even what impedance the TX was seeing, but as it was a home built valve TX (about 400 watts) I just tuned the TX to match the aerial.

I wish i had pics of it now but it before the days of cheap cameras and phones  :-[

I moved house 18 years ago and brought the top coil with me. It was wound on a catering mayonnaise tub  :) I still have it. The guy who bought my old house developed the site and built 2 new houses on it. I wonder what he thought of all the buried wires were for?


Offline Charlie_Dont_Surf

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Re: Distance with 10W on A.M. (M.W.)
« Reply #4 on: March 21, 2024, 0702 UTC »
ON4UN's book on low-band DXing is a good reference for this since 160 meters is reasonably close to the top of the MW band.

Chapter 9 on vertical antennas shows the effect of bottom loading (with a coil), center-loading (again with a coil) and top-loading, along with the effects of a capacity hat. Bottom line: a vertical with a capacity hat is incrementally more efficient than a top or center-loaded vertical, both of which are incrementally more efficient than a bottom-loaded vertical.

Of course, if you aren't using a vertical (or near vertical) wire, a cap hat may not be possible and there may be other practical reasons for using some of the less efficient coil loading described. The horizontal portion of an inverted L is perhaps a little bit like a cap hat but that's not really why the inverted L works reasonably well, assuming it's long enough.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."