Analog UHF TV signal reception improvement idea

[HSter]

Like I said rabbit ears won't pick up those far away stations. A bowtie can be built with little more than scrap coat hangers, tinfoil & wood (plus a balun)

Can I have the link/instructions, s’il vous plaît?

 

[blueroomelectronics]

Here's one, looks pretty rough. There are better in the HDTV forums.
DIY HDTV Antenna
**broken link removed**

 

[stevez]

HSter - a dipole is a very simple antenna - usually a half wavelength long at the frequency of interest. You could make a simple dipole out of the telescoping portion of rabbit ears though at UHF they'd be relatively short.

If you take a look at the design of a yagi antenna you will see multiple elements - the driven element is about half wavelength and is connected to the antenna. The other elements are a little longer (reflector) or a little shorter (directors) and are spaced based on antenna requirements. You could make the reflector and directors from telescoping elements. The feedpoint impedance is affected by the other elements - the balun helps to deal with that. The challenge with this design is the limitation on bandwidth.

If faced with a similar problem I'd take a close look at the bowtie. The gain, front to back ratio and impedance are different for each design. Ultimately a good choice is one you can construct that does the job.

 

[Sceadwian]

What's the directionality and gain of those bowties? A 10 second google didn't net me any info. A biquad will give you 12db of gain. It's net impedance is listed at 50ohms but I'm not sure what the actual impedance at resonance is. As long as it's not a long run it's going to give you higher gain than an equivlant omnidirectional antenna, and likley better than less directional antennas. Dipoles I think are at best 1-3 DB gain depending on the distance from the transmitter as they have a null zone near the antenna. I've had good luck with coax dipoles from 20+ miles away though. For simplicity of construction you can't beat a dipole, you just cut off the outer insulator of a piece of coax at 1/4 wavelength and throw it out, peel the shielding down and around the outter insulator and clamp it. You then have a half wave dipole.

 

[blueroomelectronics]

A four-way bow tie , 7-10 dB gain is recomended for metropolitan areas with strong signal. Eight-way bow tie (similar), 10-13db gain for suburban areas with medium signal. A four way bow tie antenna tends to be multidirectional, pick up signal from the front and back and are a bad choice for multipath. The 8 bay Cm4228 is more directional than the 4 bay cm4221 and works better for multipath.

Yagi vs BowTie [Archive] - RochesterHDTV - Western New York High Definition Television. We discuss HDTV, DTV, Home Theater discussion, reviews, deals and more!

 

[Sceadwian]

Sounds like a Biquad would do even better.

 

[blueroomelectronics]

I've been looking at a Yagi as I do want directional and my bowtie is just a little spotty (it's in the attic)

 

[Sceadwian]

Biquads have better directionality, and higher gain, they have side lobes but that doesn't matter unless you're building a tracking transmitter. Their bandwidth is better and I think the impedance matching is better as well, though I'm a little sketchy about the whole truth of the impedance matching.

 

[Tesla23]

HSter, your ideas are basically right, you could use multiple versions of any antenna if you could arrange to add all the signals in phase.

My favourite indoor antenna for UHF TV dx'ing is a TEM mode horn.

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This is broadband and really easy to make in a quick and dirty fashion, and almost no-one knows about them. I used to use a large cardboard box (e.g. from a household appliance) and just keep two sides. Using kitchen aluminum foil make the triangles, if you need to join it simply overlap a few inches and use sticky tape. You can adjust the angle between the triangles by opening/closing the cardboard sides. Use a 300ohm to 75 ohm balun to connect your coax to the apex. At 500MHz, making the sides of the triangle 1.2m gives you about 15dB of gain - nothing else to do (except bear the brunt of your family's jokes as you play with your large cardboard box!) I used to be able to knock one up within about 20min of finding that what I wanted to watch was on a distant channel.

 

[HSter]

HSter, your ideas are basically right, you could use multiple versions of any antenna if you could arrange to add all the signals in phase.

How do i do that, pls?

This is broadband and really easy to make in a quick and dirty fashion, and almost no-one knows about them. I used to use a large cardboard box (e.g. from a household appliance) and just keep two sides. Using kitchen aluminum foil make the triangles, if you need to join it simply overlap a few inches and use sticky tape. You can adjust the angle between the triangles by opening/closing the cardboard sides. Use a 300ohm to 75 ohm balun to connect your coax to the apex. At 500MHz, making the sides of the triangle 1.2m gives you about 15dB of gain - nothing else to do (except bear the brunt of your family's jokes as you play with your large cardboard box!) I used to be able to knock one up within about 20min of finding that what I wanted to watch was on a distant channel.

Pls, could you describe the construction details a bit more,
1. Is the entire inside of the horn/only the triangles lined with aluminium foil?
2. must the triangle be made with wires?
3. 450 ohm TV cable?
4. must A-A be as close to each other as possible, so as to get 60 degrees?
5. Broadband?, Does that mean i don't need to design the ant to the desired frequency of 582MHz? making the D= 103.2m ( 40'')?


Thanks!

 

[HSter]

HSter - a dipole is a very simple antenna - usually a half wavelength long at the frequency of interest. You could make a simple dipole out of the telescoping portion of rabbit ears though at UHF they'd be relatively short.

If you take a look at the design of a yagi antenna you will see multiple elements - the driven element is about half wavelength and is connected to the antenna. The other elements are a little longer (reflector) or a little shorter (directors) and are spaced based on antenna requirements. You could make the reflector and directors from telescoping elements. The feedpoint impedance is affected by the other elements - the balun helps to deal with that. The challenge with this design is the limitation on bandwidth.

If faced with a similar problem I'd take a close look at the bowtie. The gain, front to back ratio and impedance are different for each design. Ultimately a good choice is one you can construct that does the job.

Thanks Stevez for your reply & explaining the other ant. types.

Actually, i've constructed a 5 element Yagi-Uda array using the 8mm aluminium elements of a scrap yagi array - i connected the ant to the TV without a balun - the performace output was not great (the signal with rabbit ear was even stronger - better reception).

Does the effect of the balun count that much?

The channel 32 = 582MHz, so lambda = 51.6 cm (20.31'') thus, lambda/2 ? 25.8. This is very short, so the array is rather small.

 

[Tesla23]

How do i do that, pls?

Unless you are building an established design (e.g. bow tie array etc) I'd skip it until you gain a good understanding of impedance matching, transmission lines and baluns. There are lots of good TV antenna 'recipes' that have been worked out that actually work quite well.

Pls, could you describe the construction details a bit more,
1. Is the entire inside of the horn/only the triangles lined with aluminium foil?
2. must the triangle be made with wires?
3. 450 ohm TV cable?
4. must A-A be as close to each other as possible, so as to get 60 degrees?
5. Broadband?, Does that mean i don't need to design the ant to the desired frequency of 582MHz? making the D= 103.2m ( 40'')?

Thanks!

1. Essentially you make two triangles, they come close together at one vertex and then they flare out at about 60 degrees.
2. no, I used Al foil, any metal could be used. Mesh would be OK at lower frequencies (or fine mesh for higher freq). If you use a mesh, I'd suggest using solid plate/foil for say the first 20cm or so.
3. the feed impedance is about 400 ohms, close enough to 300 ohm feeder, or use a 300ohm to 75 ohm balun. This is important, don't just connect it to 75 ohm coax.
4. say 1cm apart, not super critical. I used a standard balun with about 150mm of bare stranded copper wire on each terminal, I simply laid these on the Al foil and laid a strip of sticky tape on top of each one.
5. yes, this is one of the major benefits, it is very broadband so dimensions are not critical. The bigger the better (more gain).

 

[Sceadwian]

The horn antenna has 4db less gain than a biquad and would require impedance matching. The biquad will output right to a TV.

 

[Tesla23]

The horn antenna has 4db less gain than a biquad and would require impedance matching. The biquad will output right to a TV.

Both antennas would work great, the horn is easy to lash up for indoor use, but harder to weatherproof and mount in wind. If you want more gain from the horn make it bigger, I would suggest it is much easier for a beginner to get lots of gain from a big horn than any sort of array.

The biquad is a great antenna, and you will get 15-17dBi of gain from an array of 4, and it is easy to make it rugged and weatherproof. The point I was making is that you can't lash it up in 20 mins (or I can't at least), and there are quite a few points that could trap a beginner.

I would disagree with your points though, a horn with D=2.5 wavelengths is much more likely to give you 17dBi than a home made 4 element biquad, and the biquad has 50 ohm impedance which is a worse mismatch to your 75 ohm TV than the horn fed through a normal balun. (Neither mismatch is really worth worrying about though).

 

[Gregory]

I can give you basic measurements for singel element aerial with a photo that I use and I also have a Kingray masthead amplifyer 22Volts ac and a digital set top box which gives me a very good reception.
Lt me know If you whant this Informtion.
The other way is If there is a hill close to you, you can use a passive aerial method.
I hope I can help you out
Greg

 

[unclejed613]

you can make a yagi out of loops of wire. your driven element will be a loop of wire equal to 1 wavelength at the desired frequency (for 600Mhz, this would be 1/2 meter of wire, formed into a loop). then 1/10 wavelength behind this loop is a loop that's 10 percent larger (only the driven element is broken for the coax connection, all the others are closed loops), and in front of the driven element are loops spaced 1/10 wavelength apart, but they're 10 percent smaller than the driven element. all of these loops are on the same axis. that's a simple yagi using loop antennas. dimensions don't have to be exact for it to work. you can also do it with 1/4 wavelength loops but the dimensions must be more exact

 

[blueroomelectronics]

I'm just that close to buying a Yagi for the attic.

 

[audioguru]

About 41 years ago I bought the biggest and best TV antenna that was made. It had plenty of gain from channel 2 to channel 83.
I could receive 3 stations on one channel from 3 different directions (I used a rotor).
I could pick a reflection from a building for the fewest ghosts on local stations.

Now I have digital cable TV that is a lot better.

 

[blueroomelectronics]

OTA HDTV is not as compressed as digital cable. I have a digital HDTV cable box and an Apple TV so I find I only need the basics (locals & networks)
The bowtie is nearly perfect. CITY tv uses a very low power signal from the CN tower and it can come and go. I was hoping the Yagi would give me a more reliable signal.
Then I'll drop the cable subscription.

 

[Sceadwian]

I'm starting to dislike my cable provider. The services are fantastic and there is a lot of really cool stuff on the horizon (I live in one of Time Warner Cables primary test cities so we get a lot of stuff before everyone else) but the rates are going up every 6 months or so and there are no options to not use certain parts of the service to keep costs down. And now in a few months they're going to be putting a bandwidth cap on cable modem usage which is just plain abusive to users, as it standard currently they're going to charge 4 dollars per gig over your cutoff without enough tiers for middlemen users like me. It's one of the few situations where I think the government seriously needs to start regulating things a little bit more, there just aren't any options anymore, cable wants you to pay big bucks for the whole package so they can float their smaller channels off the profits from the larger ones. But it screws someone trying to keep their costs down that don't use all the services provided.