RadioBanter - A DTV antenna

RadioBanter (https://www.radiobanter.com/)

- Antenna (https://www.radiobanter.com/antenna/)

- - A DTV antenna (https://www.radiobanter.com/antenna/142912-dtv-antenna.html)

Ian Jackson wrote:
In message , Richard Clark
writes

When the band shift comes, rabbit ears could work quite well. Don't
take the plunge into elaborate designs until you have some basis of
comparison is all I am suggesting.

I would start with sticking a screwdriver in the TV antenna socket.

While a properly designed and constructed DTV antenna, mounted in the
right place, will undoubtedly work well, some of the homebrew designs
you find on the internet are probably even less efficient than a
screwdriver.

I have seen some very clever antennas on the internet. More clever than
the BS this newsgroup is top-heavy with.

Dave Platt wrote:
The OTARD rule (to which you're referring) allows installation of an
over-the-air TV antenna, but it only applies if the antenna is
installed in an area which is exclusively for the tenant's use.

People who rent houses are usually able to take advantage of it.
Apartment dwellers often can't, because they aren't renting the whole
building and thus don't have "exclusive use" rights to the roof or
exterior.

However, they do have exclusive rights to their balcony
or patio so that's something to consider.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On 25 Apr 2009 06:33:45 +0100, Gordon wrote:

This seems to be the only news group devoted to the topic of antennas.
(and the origins of the universe). So maybe you guys can help me
with this.

Cosmology is often easier to understand than the antenna designs.

I have been experimenting with fabricating a decent
indoor DTV antenna.

Please define "decent". You know, the numbers.
How big? (max allowed length, width, height)
How much bandwidth (VHF, UHF, or both?)
Minimum (average) gain?
Mounting limitations?
Omni or directional? Rotator?

I'm also partial to NEC2 models of creative designs. They often show
problems that are not obvious until after the antenna is built. If
you're going to design your own, spend the time building a model.

I have tried several things.

You seem to have done your homework. Also see:
http://www.hdtvprimer.com/ANTENNAS/comparing.html
Some are indoor antennas, which should give you a clue as to what to
expect.

What I have
now is two bowties spaced about 7 inches apart on a wood dowel.
A peanut butter jar with rocks in it makes up the base.

2 element yagi like design?

It seems to give pretty good performance. It could be better.

But I am wondering about a few things.

1) Right now all the digital transmissions are in the UHF band.
but in 6 weeks, three stations will move back to their VHF
assignments in the VHF high band.
How well can I expect my antenna to work in that frequency band?

Dunno. I haven't seen any dimensions. Plug the current design into
an NEC model and see what comes out at VHF frequencies. My guess is
that it will be worse than hideous. You would do better with
adjustable rabbit ears.

2) I have not trimmed or dressed the twin lead from the bowties.
I understand that twin-lead can act as antennas. So what
is the best way to manage the twinlead? Cut it back? I noticed
that when i laid the leads together, in an attempt to make a
neat assembly, I got signal cancelation.

Lose the twin lead. The problem with balance line is that any
mechanical imbalance (i.e. proximity to walls, objects, people, etc)
will unbalance the line, causing some radiation. Such radiation shows
up as loss, something you can barely tolerate with such a minimal
antenna. If your design is setup for a 300 ohm match, install a balun
and run 75 ohm RG-6/u coax instead.

3) Any suggestions to improve this design?

Improve how? More gain? More bandwidth? Smaller? Numbers please.

4) Any suggestions for alternitive DIY designs?

Yes, but you may find them rather unconventional.

I once built a log periodic antenna on a sheet of plywood, using #14
AWG house wire and two parallel wires for the transmission line.
Elements were arranged on both sides of the plywood and secured with a
staple gun. This was for a ladyfriend, who was stuck with severe
limitations on outside antenna installations. I hung it from the
ceiling, which was the only place suitable for the monstrosity. 4-6dBi
gain from 60 to 800MHz (no channel 2). Where were a few ghosts, but
it worked much better than the rabbit ears and UHF loop it replaced.
However, it only lasted about a month. The landlord found out and
demanded its removal while muttering something about attracting flying
saucers and alien visitors. Oh well.

Another TV antenna I built took advantage of the chicken wire buried
under the stucco outside of the house. The chicken wire acted as the
antenna reflector, which was conveniently arranged in the right
direction. The driven elements were 4ea phased bow-tie dipoles,
hidden behind a decorative wood grating. It didn't work as well as I
predicted, but good enough to get decent OTA TV reception.

If you have a suitable window facing the right direction, you can do
something with aluminum foil tape. I use aluminum duct tape cut down
to size for this purpose. For electrical connections, copper stained
glass tape soldered to the coax cable. Any antenna with horizontal
polarization will work. You won't get much gain, but the outside
window location will somewhat compensate for the lack of gain by
offering a less cluttered line of sight to the TV xmitter.

Anyway, use your imagination, but also run the numbers and do a model.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Apr 26, 12:17*am, (Dave Platt) wrote:
Unfortunatly, I can't mount an outdoor antenna. *I rent,
and the landlord won't allow it.

Isn't there a federal law allowing TV antennas?
Or did you sign a personal contract agreeing
not to install a TV antenna?

The OTARD rule (to which you're referring) allows installation of an
over-the-air TV antenna, but it only applies if the antenna is
installed in an area which is exclusively for the tenant's use.

People who rent houses are usually able to take advantage of it.
Apartment dwellers often can't, because they aren't renting the whole
building and thus don't have "exclusive use" rights to the roof or
exterior.

--
Dave Platt * * * * * * * * * * * * * * * * * AE6EO
Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior
* I do _not_ wish to receive unsolicited commercial email, and I will
* * *boycott any company which has the gall to send me such ads!

Unless they have a balcony which is their "own space".

On Sun, 26 Apr 2009 16:54:12 -0700, Jeff Liebermann
wrote:

What I have
now is two bowties spaced about 7 inches apart on a wood dowel.
A peanut butter jar with rocks in it makes up the base.

Like this?
http://www.hdtvprimer.com/ANTENNAS/DoubleBow.html

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Dave Platt wrote:
Unfortunatly, I can't mount an outdoor antenna. I rent,
and the landlord won't allow it.
Isn't there a federal law allowing TV antennas?
Or did you sign a personal contract agreeing
not to install a TV antenna?

The OTARD rule (to which you're referring) allows installation of an
over-the-air TV antenna, but it only applies if the antenna is
installed in an area which is exclusively for the tenant's use.

People who rent houses are usually able to take advantage of it.
Apartment dwellers often can't, because they aren't renting the whole
building and thus don't have "exclusive use" rights to the roof or
exterior.

It's considerably more subtle than that, since there are large
commercial interests at play (unlike for ham antennas)..

Go to the FCC OTARD page and get the real scoop.
http://www.fcc.gov/mb/facts/otard.html

As a practical matter, the courts/adminstrative law judges have held
that the landlord's control does not cover, for instance, the air space
outside your window, so if you can mount the antenna within the window's
dimensions(either inside or outside), you're good to go. It is ok for
the landlord to prohibit, say, attaching to the wall outside, though.
Whether the window frame itself is "under your control" is another question.

Jeff Liebermann wrote in
:

On Sun, 26 Apr 2009 16:54:12 -0700, Jeff Liebermann
wrote:

What I have
now is two bowties spaced about 7 inches apart on a wood dowel.
A peanut butter jar with rocks in it makes up the base.

Like this?
http://www.hdtvprimer.com/ANTENNAS/DoubleBow.html

Sort of. At least that's the right configuration.
What I did was to go out and buy a pair of bowties
from Radio Shack. Then I got a dowel at Ace Hardware.
I clipped the bowties 7" apart (measured on center).
to the dowel. The bowties came with about 12" or so
of twin-lead attached. I ran these to a balun and
then through a short length of coax to the DTV converter.
I don't have a reflector, but one could be used to
improve directionality.

Jeff Liebermann wrote in
:

On 25 Apr 2009 06:33:45 +0100, Gordon wrote:

This seems to be the only news group devoted to the topic of antennas.
(and the origins of the universe). So maybe you guys can help me
with this.

Cosmology is often easier to understand than the antenna designs.

I have been experimenting with fabricating a decent
indoor DTV antenna.

Please define "decent". You know, the numbers.

Decent is subjective. When I first hooked up the
converter box I used the rabbit ears. They didn't
work worth a darn. Signal strength (according to
the OSD indicator) was 40 at best. THe picture
and sound were constantly breaking up. I then hooked
up a bowtie and got better reception, but only barely.
That's when i got the idea for the double bowtie. Now
my worst signal strength is 40 and my best is 75.
Still could use some improvement, but picture quality
is good.

How big? (max allowed length, width, height)

That's the thing. I don't have room for a ginormus
antenna.

How much bandwidth (VHF, UHF, or both?)

Right now, UHF 27 to 48.
After the change over, add VHF 8, 10, and 12.

Minimum (average) gain?
Mounting limitations?

Prefer indoor not outdoor. A high ceiling makes that
mounting arangement unusable. Although I could hang
a flat antenna on the wall around the corner from the
TV.

Omni or directional? Rotator?

All the stations are located within a 7 degree cluster, due
east from my location. Directional is good. No rotor needed.

I'm also partial to NEC2 models of creative designs. They often show
problems that are not obvious until after the antenna is built. If
you're going to design your own, spend the time building a model.

I have tried several things.

You seem to have done your homework. Also see:
http://www.hdtvprimer.com/ANTENNAS/comparing.html
Some are indoor antennas, which should give you a clue as to what to
expect.

What I have
now is two bowties spaced about 7 inches apart on a wood dowel.
A peanut butter jar with rocks in it makes up the base.

2 element yagi like design?

It seems to give pretty good performance. It could be better.

But I am wondering about a few things.

1) Right now all the digital transmissions are in the UHF band.
but in 6 weeks, three stations will move back to their VHF
assignments in the VHF high band.
How well can I expect my antenna to work in that frequency band?

Dunno. I haven't seen any dimensions. Plug the current design into
an NEC model and see what comes out at VHF frequencies. My guess is
that it will be worse than hideous. You would do better with
adjustable rabbit ears.

2) I have not trimmed or dressed the twin lead from the bowties.
I understand that twin-lead can act as antennas. So what
is the best way to manage the twinlead? Cut it back? I noticed
that when i laid the leads together, in an attempt to make a
neat assembly, I got signal cancelation.

Lose the twin lead. The problem with balance line is that any
mechanical imbalance (i.e. proximity to walls, objects, people, etc)
will unbalance the line, causing some radiation. Such radiation shows
up as loss, something you can barely tolerate with such a minimal
antenna. If your design is setup for a 300 ohm match, install a balun
and run 75 ohm RG-6/u coax instead.

3) Any suggestions to improve this design?

Improve how? More gain? More bandwidth? Smaller? Numbers please.

4) Any suggestions for alternitive DIY designs?

Yes, but you may find them rather unconventional.

I once built a log periodic antenna on a sheet of plywood, using #14
AWG house wire and two parallel wires for the transmission line.
Elements were arranged on both sides of the plywood and secured with a
staple gun. This was for a ladyfriend, who was stuck with severe
limitations on outside antenna installations. I hung it from the
ceiling, which was the only place suitable for the monstrosity. 4-6dBi
gain from 60 to 800MHz (no channel 2). Where were a few ghosts, but
it worked much better than the rabbit ears and UHF loop it replaced.
However, it only lasted about a month. The landlord found out and
demanded its removal while muttering something about attracting flying
saucers and alien visitors. Oh well.

Another TV antenna I built took advantage of the chicken wire buried
under the stucco outside of the house. The chicken wire acted as the
antenna reflector, which was conveniently arranged in the right
direction. The driven elements were 4ea phased bow-tie dipoles,
hidden behind a decorative wood grating. It didn't work as well as I
predicted, but good enough to get decent OTA TV reception.

If you have a suitable window facing the right direction, you can do
something with aluminum foil tape. I use aluminum duct tape cut down
to size for this purpose. For electrical connections, copper stained
glass tape soldered to the coax cable. Any antenna with horizontal
polarization will work. You won't get much gain, but the outside
window location will somewhat compensate for the lack of gain by
offering a less cluttered line of sight to the TV xmitter.

Anyway, use your imagination, but also run the numbers and do a model.

Ian Jackson wrote in
:

I would start with sticking a screwdriver in the TV antenna socket.

While a properly designed and constructed DTV antenna, mounted in the
right place, will undoubtedly work well, some of the homebrew designs
you find on the internet are probably even less efficient than a
screwdriver.

You mean, like the beer can antenna?? Sorry, I don't have
a link.