10khz - 50mhz/55mhz antenna

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luckcolors
Posts: 3
Joined: Sat Jun 25, 2016 3:45 pm

10khz - 50mhz/55mhz antenna

Post by luckcolors » Wed Aug 10, 2016 11:43 am

Hello!

I'm back again with another question for you guys.
So i'm searching an active antenna who can reiceve preferably from 50-55mhz as down as possible to dc.
I already found the miniwhip chirio antenna who can receive from 30mhz -10 khz but the problem is with this one that i wouldn't receveive this "hole" (from 30mhz to 50) of frequencies.

Are there better designs of active atennas / miniwhip who can have this range?
Thanks in advance.
:)

joe36
Posts: 36
Joined: Wed Jul 20, 2016 11:09 pm
Location: Cass co. in. 46994

Re: 10khz - 50mhz/55mhz antenna

Post by joe36 » Sat Aug 20, 2016 6:33 pm

An active antenna is one that uses an active component such as a LNA. The usable frequency of this type antenna is the pass ban of the amplifier.
Now the question and I hope some help with the answers.
1 how much room do you have and how much effort do you want to expend.
The most efficient antenna will be a ¼ or a multiple of ¼ wave fed against a counterpoise. This can be by a ground or a conductor cut to ¼ wave multiples.
For 50 MHZ without doing the math is around 4 – 5 foot for DC it is infinite.
2 Do you want it to be portable?
If so use as long a collapsible antenna as possible fed against a ground. At 50 MHZ and down a LNA might or might not help.
Put a low pass filter on any antenna for low frequency’s that cuts off just over the highest frequency you want to use the antenna for.
3 non portable antennas. A large discone will work for rather low frequencies. Think 20 MHZ to 50 MHZ. 4-6 foot tall
A large discone is actually not near as good as a smaller one on higher frequency’s Above 50 a smaller say 2 foot tall for 50 to 250 and even smaller above that. Search discone design calculator.
Below 20 MHZ a wire outside is the best. You probably don’t need An LNA
Below 2 MHZ a small whip might as well be a bent coat hanger in the closet. If you want results. Best think no less than 100 foot fed against ground. You almost certainly don’t need a LNA.
.2 And down. This is getting into specialty receiving applications. Put as much wire in the air as possible. 1000 to several thousands of feet would not be uncommon. This is not to say 100 foot would not give some results . AT this frequency it is more a matter of what is practical. Use a low pass filter. A LNA is best not considered without special consideration. Filters and gain are a serious consideration
.02 All rules change. It gets to in-depth for a single answer. Google is your friend.
I hope this helps.
Joe KA9UCN

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