Active antenna pros & cons

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Active antenna pros & cons

Postby dcheech » Thu Jan 02, 2014 10:03 pm

Hi, do active antennas always work on HF? Please excuse my lack of knowledge. I need discreet antennas at the moment, so longwire solutions are difficult at the minute. Regards, David
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Re: Active antenna pros & cons

Postby m0lsx » Thu Jan 02, 2014 11:28 pm

For SWL (Short Wave Listening,) I use around 10 meters of wire, that I simply hang around the room.. How discreet do you want??

I have never seen a alleged so called "Active Antenna" that is anything more than expensive rubbish.. Unless you are talking about a loop antenna & they are very hi Q, so have very very narrow tuning band. But a loop is good.
What sort of money are you looking to spend??
Do you have self build capability??
Antennas like the miracle whip, make truly excellent SWL antenna & they are easy to build especially if you don't want TX capability...
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Re: Active antenna pros & cons

Postby dcheech » Fri Jan 03, 2014 3:31 pm

Hi, thanks very much for your prompt advice.

I've rigged up a temporary 60 foot longwire to try tonight. 20 feet of it is indoors, the other 40 feet of it is outside looking like the washing line & about 8 feet up parallel to clear open ground. Antenna lineup is dead straight East /West, end of longwire is due East with Receiver 60 feet due West of it.

Thanks again for clearing my thoughts to try a few simple things before splashing cash on something uncertain to be helpful.

I will post an update tomorrow. If this works, my next question will be about appropriate surge protection on such a setup.

Regards, David
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Re: Active antenna pros & cons

Postby m0lsx » Fri Jan 03, 2014 4:04 pm

What is your Shortwave RX???? A wire that long on something like a portable radio could well overload it & make matters worse not better...I have a old Trio which tunes 0.11 to 30MHz rx & which handles 50 meters of wire with ease, plus few portables, my best RX is a Eton G3 globe traveller which tunes 0.15 to 30 mhz, plus VHF band 2 broadcast & air & with that anything over 10 meters gives me all sorts of problems..


If you can, there are some simple things you can do to improve a random wire...
Use a balun, this is a transformer, normally for SWL one coil has one wind the other 9 winds, so it is a 9:1. The reason for the random length is that you do not want to transform a tuned antenna into a untuned antenna..A balun will give you some electrical separation between the antenna & some also give the opportunity to provide a earth path, this also makes a difference. The next addition is a SWL ATU (Correctly called a Atnenna MATCHING Unit, not tuning unit, as it does not tune the antenna.) I use a Global AT-200 which I brought secondhand for about £30 (they are also branded as a Mizuho) This is about as good as SWL ATU's get, but my cheap £20 amateur radio QRP wire tuner, also does an excellent job.
A third addition is a tuning bridge, this produces a noise which allows you to tune the system more efficiently that just for the loudest static, which is the normal method...


Short wire...a wire that you or someone else says is a short length
Long Wire..a wire that you or someone else believes to be long.
Random wire..a wire of any random length..This is done so that it is not resonant at any used frequency..
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Re: Active antenna pros & cons

Postby dcheech » Mon Jan 06, 2014 9:38 pm

Hi,

Current SWL receiver is TECSUN PL660.

Stage 1 experiment, 60 foot long single wire connected directly to antenna socket. No balun, no grounding. Being careful about grounding antenna, receiver & me before connecting. SWL sensitivity = +1000%, noise = + 200% some of the time, sometimes very clear reception. Range received so far 2875Khz to 17840Khz.

Regards, David
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