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.

"Gordon" wrote in message
...

snip


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

.... but since you've built a small antenna and it's working, you may have
options for _placement_ that will enhance your reception further. It may
work better at one east-facing window than another and it may work best at a
particular height off the floor at that "better window." (Outside TV
antennas are sometimes installed after one guy walks the roof with the
antenna on a stick, while somebody else monitors the signal; the antenna is
finally mounted when they pick the "sweet spot," like on a tennis racket.)

Adding coaxial cable usually reduces the signal, but if your "better window"
only requires a smidgeon more of coax, maybe you should try it.

"Sal M. Onella" wrote in
:


"Gordon" wrote in message
...

snip


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

... but since you've built a small antenna and it's working, you may
have options for _placement_ that will enhance your reception further.
It may work better at one east-facing window than another and it may
work best at a particular height off the floor at that "better
window." (Outside TV antennas are sometimes installed after one guy
walks the roof with the antenna on a stick, while somebody else
monitors the signal; the antenna is finally mounted when they pick
the "sweet spot," like on a tennis racket.)

Adding coaxial cable usually reduces the signal, but if your "better
window" only requires a smidgeon more of coax, maybe you should try
it.




I don't have any east facing windows. I did take the antenna outside
and put it up on a pole. Just as an experiment. I was not able to
get much better performance. But it was only 6 or 7 feet high.
I supose I could add another element. It would be a cheap enough
experiment. Eliminating the coax is a real possibility.

On Apr 25, 1:33*am, 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. *

I have been experimenting with fabricating a decent
indoor DTV antenna. *I have tried several things. *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.

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?

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.

3) Any suggestions to improve this design?

4) Any suggestions for alternitive DIY designs?

Thanks

Gordon, I installed a large radio shack "tagi" type TV receiving
antenna in my attic 10 years since the house came wired for it. I
pointed the antenna in the general direction of the transmitting
antennae in my area and received excellent analog reception even with
the 5-10dB attenuation that occurs with VHF and UHF from the wooden
roof with asphalt shingles. I even have a rotor but never had to
really use it.

Now, with DTV, the exact same antenna gives me excellent reception as
well, just as good as analog (but of course "better" due to the nature
of DTV broadcasts).

I think for DTV that uses both UHF and VHF, you should be able to use
the same antenna that you used with the analog system that used UHF
and VHF and (as you know) you will probably find that the digital
signal is better in any case. Whatever their technology, these are all
multiband receiving antennas and the spectra for DTV and analog TV are
much the same. There are no technical aspects that need to be covered
here because there really is no problem.

Regards,

73 de AI4QJ

wrote in
:

On Apr 25, 1:33*am, 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. *

I have been experimenting with fabricating a decent
indoor DTV antenna. *I have tried several things. *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.

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?

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.

3) Any suggestions to improve this design?

4) Any suggestions for alternitive DIY designs?

Thanks

Gordon, I installed a large radio shack "tagi" type TV receiving
antenna in my attic 10 years since the house came wired for it. I
pointed the antenna in the general direction of the transmitting
antennae in my area and received excellent analog reception even with
the 5-10dB attenuation that occurs with VHF and UHF from the wooden
roof with asphalt shingles. I even have a rotor but never had to
really use it.

Now, with DTV, the exact same antenna gives me excellent reception as
well, just as good as analog (but of course "better" due to the nature
of DTV broadcasts).

I think for DTV that uses both UHF and VHF, you should be able to use
the same antenna that you used with the analog system that used UHF
and VHF and (as you know) you will probably find that the digital
signal is better in any case. Whatever their technology, these are all
multiband receiving antennas and the spectra for DTV and analog TV are
much the same. There are no technical aspects that need to be covered
here because there really is no problem.

Regards,

73 de AI4QJ


I guess a bit of background info is in order.
Last March (2008), I decided that I didn't want to pay
$52.00 a month to Comcast for the privelidge of watching
TV or watching my family sit on their asses zoning out
in front of the Boob Tube. So I dropped Cable.
Well, some TV watching is OK. So I hooked up the Rabbit
Ears and Bowtie to watch analoge TV. Reception was poor
to lousy. The problem is that I live in a Triplex that
is oriented East-West. All the transmitters are to the
east of here (in a roughly 10 degree cluster, less than
10 miles away). I am in the western most unit of the
triplex. Which means that I am trying to receive through
the entire length of the unit. The atic space is kinda
tough to get to. The living room has no atic space,
It has a highly slopped ceiling that pretty much follows the
roof line up and over the 2nd floor.
So last June I hooked up a DTV converter box. At first I
used the rabbit ears and got the same poor reception. Then
I tried a set top loop/rabbit ears (a little bit better).
Then I pulled the loop out, and plugged in an old bow-tie
(that made things better). Then I tried the bowtie all
by itself and things got much better. That's when I
decided that a bit more directionality might help. So I
cobbled up the current setup. Two bowties, 7" apart on
a wooden dowel, set in a weighted base. And it actually
works 98% of the time. Today we had good conditions and
the SSI was in the 50s to 70s (yellow and low green)
over all the channels (except for HSN, which is off axis
and I don't care about). So far I have not been able to get
a SSI over 80.
One thing that has helped with the current setup: I am allowing
the twinleads to fall freely down the dowel. I have one
on each side and I am using bread bag clips to keep the
leads separated from each other. It has made reception
more consistent across the channels.
So today I figured I would try to build a better antenna.
I got two dowels and some 14ga wire and (using some plans off
the internet) I built a Hoverman antenna. It didn't work
one whit better than the dual bowtie I already have. At
this point, I may move the hoverman outside and see if I get
better reception there. Or, since the bowtie works so well,
just add more elements to that one.