Wide Band Antenna

Is there such a things as an antenna that will get me everything from HF to VHF with reasonable strength?

I have a BNC telescope antenna that seems to get FM broadcast and higher but very little once you start going below 100 MHz.

Reply to
M. Hamed
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** Yep.

** Connected to what exactly ??

.... Phil

Reply to
Phil Allison

No.

w.

Reply to
Helmut Wabnig

** The OP's question is badly worded, mainly cos his thinking is so wobbly.

Does he want a single antenna covering from 3 to 300MHz or from 30 to 100MHz ??

The latter certainly exists.

If the congenital fool expects a plug in whip or something similar to work well with a shirt pocket size scanner receiver on the 80 metre band - he has another thing coming.

... Phil

Reply to
Phil Allison

not really. you didn't mention noise so maybe an 'active' antenna.

Think about what you are doing. The signal strength of what ws sent is a function of wavelength [inverse freqeuncy]. The signal strength what is received is kind of a function of how much area of that energy radiating outward getting less and less you can intercept. You intercept ALL you get almost all. Intercept a teeny, tiny bit; well not much there. Also, the energy you are intercepting comes from a source that has a characteristic impedance of 377 ohms. One way to intensify the signal is to make the antenna resonant, well that just means a high Q and a high Q means narrow band and you're right back to where you were with NO bandwidth range. Numbers apply to all this but speaking the overall effect enables understanding of all those numbers.

If this is a DIY project there are tons of projects with great descriptions.

Reply to
RobertMacy

Ok so the short answer is no. I have an RTL-SDR stick and I can get signals from the FM broadcast band well to 950MHz or even higher with one Antenna.

Now if I want to receive HF, do I have any other options besides these huge monster antennas?

Reply to
M. Hamed

Again, it ALL depends on your noise floor and the signal strength. A 1 inch wire is an adequate antenna *if* the signal is 'decent'.

A litle ferrite rod works very nicely down around 1MHz [AM Radio]

Reply to
RobertMacy

Are there limitations on that gizmo?

I don't know, but some people are playing with things intended for UK TV, a little USB gizmo. And since they are intended for tv, they suffer at lower frequencies because they weren't designed for low frequencies. So one issue perhaps is that performance rolls off below a certain frequency.

At VHF and UHF, as someone pointed out, short antennas are full length antennas. Of course, just because an antenna at a given frequency receives signals doesn't mean it's very good. If you want gain from the antenna, you have to have a bigger antenna.

At low frequencies, you may not have much gain, even if the antenna is large. It depends where in the HF spectrum, 10MHz a dipole is reasonably short, at 3MHz it would be quite a big larger. And in both cases, you only get a bit of gain, you'd have to double them to double antenna gain, and so on.

People have given suggestions. Forty years ago, I don't remember have much trouble receiving shortwave with an SP-600 and a random length of wire connected to the antenna. That was a long time ago, I'm not sure if it was the receiver or maybe just that there were so many signals, it didn't take much to still receive quite a few. I notice now, I have to take my shortwave receivers (with whip antennas) to the window in order to get much signal strength on signals, the house has become too well shielded, and likely also, there are all kinds of devices plugged in that generate noise, so the incoming signals have to be stronger than forty years go to be noticed.

Michael

Reply to
Michael Black

Of course, there's quite a bit of wire in there.

Car radios did the same thing in the old days, attach the antenna to the very high impedance point of a tuned circuit. That's why they needed that special cable between the antenna and the radio, and that trimmer that lessened the loading of the cable on the tuned circuit (or was it to compensate for the extra capacitance in that tuned circuit caused by the cable and antenna?).

It got rid of the direcionality of the loop, and the whip antenna acted like a "probe" to get the signal into the radio.

In effect, an early "active antenna", though by the time those came into being about the seventies, they used high impedance devices to transform the high impedance very low voltage signal from the whip into something the rest of the radio could handle. Eliminates the tuning, which makes it broad, though probably extra front end tuning could help some radios.

A lot or maybe most of the shortwave portables on the market have that stage of high impedance buffer so things work better with the built in antenna.

Michael

Reply to
Michael Black

I built one of those probes in the mid eighties, from precious little knowledge (no Internet yet, then).

It was little more than a yard-long whip antenna with a whisp of resistor to ground, going into the gate of an MPF-102 set up as a source follower. That was in the box with the antenna -- from that point on it was just RJ-58 to the radio several yards away.

It worked great on the roof of the university electronics building, although from my house all it picked up was the nearest electric fence.

--
Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

When I first read about them, in 1973 or 74, it was called a "voltag probe", which seemed descriptive. Get some of that voltage into the radio. Oddly, that circuit didn't look that different from previous JFET or MOSFET preamps, except that resistor from the gate to ground was quite large.

A lot of the "active antenna" circuits are very much like that, including the ones in portable shortwave radios.

Michael

Reply to
Michael Black

Good FETs such as the BF862 are astonishingly quiet, so if you don't overdrive them, they ought to do a very good job even from a crappy high-Z mess of an antenna.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Below 1MHz, atmospheric noise is so pronounced that it doesn't even have to be a good FET.

That probably extends up to 3 or even 10MHz, but I wouldn't bet my first born on that -- it'd be a tragedy if I had to keep him.

--
www.wescottdesign.com
Reply to
tim

All cows, all the time! ;-)

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Reply to
Michael A. Terrell

There are upconverters for them to use on SDR for HF.

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Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

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