Are "active" antennas good?

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joseph2020

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Has anyone tried the "active antennas" ? I have some basic schematics and a need for a good indoor antenna. I want something that will work 10 meters. Do they work? Thanks in advance.
 

LtDoc

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They won't work as well as a full sized, tuned antenna, but they do work. If they work well enough for your purposes, then good.
- 'Doc
 

joseph2020

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LtDoc, Thanks for your reply.

Anyone else ever try one? I appreciate all opinions. Thanks in advance
 

ka3jjz

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The only active antennas I know about are receive only - are there ones that allow for transmit too? How about some links and models?

Curious

73 Mike
 

prcguy

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I have a small active antenna next to a 102ft flat top dipole (G5RV) at about 35ft height and have compared them extensively.

The active antenna is a semi kit described here: http://www.arrl.org/files/file/Technology/tis/info/pdf/0109031.pdf

Much of my HF use is 40 and 80m NVIS within a few hundred miles where a low horizontal antenna is desirable and the G5RV outperforms the active antenna in signal to noise ratio and the active antenna has a higher noise floor. Signal levels vary but are not that much different between antennas much of the time. I would say the G5RV would pick out an extremely weak signal better than the active antenna in this mode.

On higher bands where distant signals are arriving at a lower angle and the vertical polarized active antenna is more appropriate it does a very good job and the differences between the antennas are less but the G5RV is still quieter and can generally pick out a very weak signal better than the active antenna.

On the AM broadcast band and below is where my particular active antenna really shines bringing in signals way stronger and in some cases better signal to noise than the G5RV. If a signal is copyable on these low frequencies on the G5RV its usually a bit more pleasant to listen due to the lack of noise but at some point the active antenna brings them way out of the noise even though the noise floor is also brought up but the signal to noise ratio can still be much better on the active antenna on VLF.

I don't use the active antenna much since the G5RV and other HF antennas here do 99%of what I need but if the AMRAD active antenna was the only HF receive antenna I could have due to space it would not be too bad.

The AMRAD is a semi kit that cost about $75 to build and it performs in the range of $300 to $500 assembled active antennas. An inexpensive active antenna would not give results anywhere close to what the AMRAD does due to overload and generation of Intermod and the results here would be greatly skewed toward the G5RV in that case.

So in a nutshell a really good active antenna will probably make most SW and HF users fairly happy in my opinion.
prcguy
 

joseph2020

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prcguy, thank you for your informative and educational reply. I learned a lot by reading it and the enclosed article from QST. It sounds like an active antenna may be a worthwhile project in the near future.. Thanks again.
 

gcgrotz

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Yes, the AMRAD is an excellent active antenna, but mainly for lower frequencies. I may be building one this winter for MW/LF dx-ing. Active antennas are mainly for space challenged applications like low frequencies where a full size antenna would be difficult to build.

If you want mainly 10 meters, could you fit a full size dipole (16 ft) in? Or even better try a full wave square loop which would be 8.5 ft on a side. That should work very well. Lot's of articles, just Google it.
 

joseph2020

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gcgrotz, Thanks for your reply and excellent suggestions on the 10 meter square loop, that may be possible.
 

gcgrotz

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You're welcome Joseph. I think I'm gonna put up a 40 meter loop. It shouldn't be too hard once the leaves are gone. Don't think I have room for 80 meters being 65 feet on a side.

I have an old dipole I'm thinking might do well on 10 meters hung vertically from a tree branch. There's a 10 meter contest in December that should be worth entering this year just for fun. There's a lot of Asia/Pacific countries I haven't worked!
 

zz0468

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I haven't built the AMRAD active antenna yet, but I have built one based on a JFET input to an MC1350P amplifier, it's on older design documented in several ARRL handbooks.

Mine worked quite well under some circumstances, although I found that the results could vary wildly, depending on the length of the probe. I've found that having an active antenna available is an excellent addition to a full size antenna, especially if there's a painless way to switch between antennas while operating.

I've found that they can be immune to certain noise sources that the full size antenna gets hammered with.
 
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