Digital TV antennas

[FlyWright]

I can physically see the broadcast tower for most of the Sacramento stations in Walnut Grove, but sometimes the stations black out. I think it's because they are broadcasting over me?

This reminds me of when digital TV had just come out but was not yet the sole source as analog was still being broadcast. I added an analog-digital converter box to my existing analog TV onboard. With the box connected, I could see the same channels normally received in digital format.

It was time for the Summer Olympics. I was looking forward to watching the highlights onboard each evening. We went with friends to anchor out on Lost Slough for a week...near the base of the Walnut Grove antennae. When I turned on the digital box and TV, I got no signal! I was too close to the antennae and underneath the broadcast signal. With digital, it was either on or off....nothing like the snowy, static-littered images we'd see on the analog TV when the signal was weak.

When I disconnected the converter box and reverted to analog, I was able to watch the Olympics albeit with some snowy images at times. Digital is 1 or 0, on or off. At least the old analog allowed the weak signals to be watched.

 

[Heron]

I am surprised nobody mentioned raising the antenna on a temporary mast.

That helped a lot.....Used to be mounted in the bridge enclosure and I found some channels blank out when I turned on my LED lighting... Getting the antenna away from the lights solved that and improved reception...15-20 stations normally available here in Eastern NC..

 

[Lepke]

If you want distance, a directional one is best, 2nd best is outside non- directional. In an open flat area I could get stations more than 100 miles with a directional antenna. Probably 25 stations or more. But not worth it. Most stations are playing the same thing.
Best place to buy, Amazon or Ebay.

 

[AlaskaProf]

It's not size per se, but rather size relative to wavelength. I've forgotten all the formulae, but it was common to see antenna sizes like quarter wave, half wave, etc. -- length relative to frequency bandwidth -- and I'd guess (without doing any math) that those sizes are useful fractions of wavelength. IIRC, a "loop" is just a "whip" bent into a circle, with a bunch of tech stuff to get the functional length right...

-Chris

Actually, the formula is C=lambda f, and I understand it at the level you are explaining, but the question remains: if we use the formula above, we can establish that the optimal antenna for FM broadcast is about 60" (im to lazy to work the actual value), and a half-wave antenna works...well, because it does. A quarter-wave antenna of 15" is probably
impractical because it would need a counterpoise surface to create the other quarter.

I also understand that you can wrap a long antenna into a small space (best example: my Zenith Transoceanic had a big web of copper wire inside). SO...why does the 15" (external measure)antenna have better range than the 4" when it seems almost certain that inside there is a wire of similar length?

I know that a little knowledge is a dangerous thing, and confess that there's something here I still need to learn; what is that?

 

[AlaskaProf]

Okay, Hamrow did the math and I was off by half, but I'm not sure it answers...if I put up multiple antennae of the optimal length do I get better range? Is that what's going on inside the Shakespeare 19" disc?

 

[Hamrow]

Shakespeare (like many suppliers) does not easily share whats going on in the guts of their product, but I suspect that yes they have either long coil or multi-elements within that disc. They do "claim" a massive 30 dB of gain which means there is a low noise amplifier, which is intended to make up for the lack of physical size and of course you have to provide electric power to the antenna (as opposed to a "passive" antenna like most cars have).
I have not personally tried one of these shakespeare disc antennas but with 30dB, they certainly ought to pick up good range given enough height, like the way Heron mounted theirs.

 

[AlaskaProf]

Hamrow...

Thanks. I guess I get it.

I need to drop my mast to install a new+improved running light. Hmm time to break out my nomograph calculator. Maybe get one of the 19" model at "boat show price"

 

[Pura Vida]

I have the Shakespeare disc antenna on my boat and it works as good or beret than others I have rafted up with. It seems that Digital is on or off. We have a lot of ridges that will block the signal. On my old boat I had a cheap antenna that looked like a closed laptop $15 at Wal mart and it worked ok for the $$.

 

[catalinajack]

Shakespeare (like many suppliers) does not easily share whats going on in the guts of their product, but I suspect that yes they have either long coil or multi-elements within that disc. They do "claim" a massive 30 dB of gain which means there is a low noise amplifier, which is intended to make up for the lack of physical size and of course you have to provide electric power to the antenna (as opposed to a "passive" antenna like most cars have).
I have not personally tried one of these shakespeare disc antennas but with 30dB, they certainly ought to pick up good range given enough height, like the way Heron mounted theirs.

They do. I get Baltimore stations 40 miles away.

 

[aboatman]

The amplifier helps quite a bit but you can't amplify what's not there. If no signal from the station you want to watch is at the antenna, an amplifier will not help.

We hooked up to a marina's cable system not long ago and my scan got nothing. I asked the dockmaster and he said "Oh, we cancelled that last week. Everybody is streaming these days." Well, he was wrong. We are not streaming. Perhaps it's the wave of the future, perhaps not.