Forums

Wide Band Antenna

Started by M. Hamed September 27, 2014
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.
 M. Hamed wrote:

> Is there such a things as an antenna that will get me everything from HF to VHF with reasonable strength? >
** Yep.
> > I have a BNC telescope antenna ..
** Connected to what exactly ?? .... Phil
On Sat, 27 Sep 2014 19:12:14 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

> M. Hamed wrote: > >> Is there such a things as an antenna that will get me everything from HF to VHF with reasonable strength? >> > >** Yep. >
No. w.
>> >> I have a BNC telescope antenna .. > > >** Connected to what exactly ?? > > >.... Phil
Helmut Wabnig wrote:
> Phil Allison >> M. Hamed wrote: > > > >> Is there such a things as an antenna that will get me everything from HF to VHF with reasonable strength?
> > >** Yep.
> > No.
** 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
On Sat, 27 Sep 2014 10:23:31 -0700, M. Hamed <mhdpublic@gmail.com> wrote:

> 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.
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. <http://www.yagicad.com/>
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?
On Sun, 28 Sep 2014 10:55:57 -0700, M. Hamed <mhdpublic@gmail.com> wrote:

> 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?
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]
On Sun, 28 Sep 2014, M. Hamed wrote:

> 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? >
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
On Sun, 28 Sep 2014, RobertMacy wrote:

> On Sun, 28 Sep 2014 10:55:57 -0700, M. Hamed <mhdpublic@gmail.com> wrote: > >> 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? > > 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]
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
On Sun, 28 Sep 2014 20:31:30 -0400, Michael Black wrote:

> On Sun, 28 Sep 2014, RobertMacy wrote: > >> On Sun, 28 Sep 2014 10:55:57 -0700, M. Hamed <mhdpublic@gmail.com> >> wrote: >> >>> 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? >> >> 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] > > 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.
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 http://www.wescottdesign.com