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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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12th Apr 2021, 1:37 am | #1 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,063
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BF998 based miniwhip active antenna
This post is linked to my post about the successful repair of this antenna under Hints, tips and solutions. I bought this antenna primarily for AM DXing with a modern Sangean digital portable receiver, but it also works well with vintage receivers equipped with an external aerial socket e.g. car aerial type.
My listening environment has grown increasingly noisier in recent times, even when using homebrew loop antennas, so I thought of giving this relatively inexpensive antenna a try. Performance is very good, but as with any active antenna in an electrically noisy environment, it amplifies noise as well as radio signals. However, in many situations, it makes the radio signals intelligible. I have tried it on MW, LW and SW with much improved reception. However, the problems with RF noise do not allow me to pick up weak SW signals below 5 MHz anymore, either with or without this antenna. Performance on MW is generally better late at night, when RF noise is reduced a little. The antenna is rated or 12V DC, but works well on 9V DC, either on battery or a non switchmode adaptor. I bought the barebones version and have assembled it as shown in the pictures. The antenna board has been fitted in an empty Smarties tube with another plastic stopper used to fit a PL259 socket. I found that it works best the higher it's mounted, so it is in the loft and downlinked to the power unit using TV cable. |
12th Apr 2021, 9:09 am | #2 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,038
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Re: BF998 based miniwhip active antenna
I like the smarties tube! I've always found these 'probe' antennas to be very good unless you have a high local noise level. Compared to loop antennas (I use a Wellbrook 1530) they pick up lots of noise.
I have read that 'choking off' the coax can work wonders, but whenever I've tried it it has made little difference. Speaking of noise, I have a new one. It goes from LF to about 250 MHz and sounds like yer basic 100 Hz 'grizzling noise'. It's bad enough on the loop (and seems to come from all directions), so I shudder to think what a mini-whip would make of it!
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Andy G1HBE. Last edited by Andrew2; 12th Apr 2021 at 9:16 am. |