In article ,
Gordon wrote:

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?

Not terribly well. "Short" antennas (significantly less than 1/2
wavelength) have a very reactive impedance, and don't couple
efficiently to the E/M wave.

It may work well enough for your area (depending on the VHF signal
strength) or maybe not.

2) I have not trimmed or dressed the twin lead from the bowties.
I understand that twin-lead can act as antennas.

Yup. Sometimes a problem, sometimes not.

Sensitivity of twinlead to external fields can be reduced by twisting
the twinlead (one rotation every six inches or every foot is a decent
starting point) and by keeping it a few inches away from anything
metal. Use insulating standoffs to run it down the antenna mast.

Or, convert from the twinlead to a 75-ohm coax (e.g. RG-8) using a
balun, and run coax down to your TV.

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.

Trim it back to a reasonable minimum length, don't loop it back along
itself or run it next to itself (or other twinlead, or anything
metal), and twist it periodically.

4) Any suggestions for alternitive DIY designs?

You may want to consider adding a "folded dipole" in parallel with the
bowtie arrangement, with the dipole being cut to the wavelength of the
lowest-frequency VHF channel you'll want to receive.

If you need more gain or directivity on VHF than a dipole will give
you, then using a log-periodic antenna (the classic rooftop VHF/UHF
type) may be your best bet. These *can* be home-brewed but they're
more complex than a simple bowtie-and-reflector.

--
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!

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

On Apr 24, 10:33*pm, 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

If you search for "diy hdtv antenna" or "diy dtv antenna" you will
come up with other ideas. Someone posted a question a while back here
about a design that apparently is pretty forgiving and not too hard to
construct and is claimed to give decent gain; see
http://www.digitalhome.ca/ota/superantenna/.

Dave P's comments are good, though RG-8 is 50 ohm, not 75 ohm. Good
RG-6 type cable should work well for at least short runs, and it is
nominally 75 ohms. I don't know about your TV (or converter box), but
pretty much all the ones I've seen that receive digital TV broadcasts
have 75 ohm F connector inputs anyway, so you may as well go straight
to RG-6 at the source (the antenna).

Cheers,
Tom

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

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

Hi Gordon,

This is a goal in conflict if we are to take it at face value. For
one, DTV has design demands that call for widebandedness. This, and
the combination for VHF coverage combine to drive the design to being
large. This is typically the domain of outdoor antennas, and for good
reason (large for DTV is going to be honestly large).

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?

This is a simple matter of scaling. If the frequency shift is by an
order of, say, 2:1; then the size will increase by an order of 1:2.
Frequency and size are in an inverse relationship. Try doubling the
size of your current design, and looking for a gallon size peanut
butter jar.

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.

This is an indoor antenna. It is going to suffer from any number of
things in proximity and your attempts to dress the leads probably were
not responsible for the signal quality change you observed. I will
bet that attempt to make a neat assembly had a lot of re-arranging
going on in addition to the lead dressing.

3) Any suggestions to improve this design?

4) Any suggestions for alternitive DIY designs?

Wait until you have a problem before you try solutions. As I said
above, your goal is in conflict with interior available dimensions.
The truth of the matter is that a simple rabbit ears antenna might do
just as well as the best of the DIY designs littering pages across the
WWW.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

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

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

Hi Gordon,

This is a goal in conflict if we are to take it at face value. For
one, DTV has design demands that call for widebandedness. This, and
the combination for VHF coverage combine to drive the design to being
large. This is typically the domain of outdoor antennas, and for good
reason (large for DTV is going to be honestly large).

I know. I'm trying to find a good compromise. But it may not
exist. Unfortunatly, I can't mount an outdoor antenna. I rent,
and the landlord won't alow it.

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?

This is a simple matter of scaling. If the frequency shift is by an
order of, say, 2:1; then the size will increase by an order of 1:2.
Frequency and size are in an inverse relationship. Try doubling the
size of your current design, and looking for a gallon size peanut
butter jar.

I've done the math. Channel 2 has a wavelength of about 18 feet and
channel 50 is about 1.4 feet. More than a 2:1 ratio. I do catch a
break since the VHF lo band is going to be vacated in this area. So
channel 8 is the lowest frequency I need to worry about (wavelength
of approx 5.5 feet).


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.

This is an indoor antenna. It is going to suffer from any number of
things in proximity and your attempts to dress the leads probably were
not responsible for the signal quality change you observed. I will
bet that attempt to make a neat assembly had a lot of re-arranging
going on in addition to the lead dressing.


Actually, I tried to keep the situation as controlled as possible.
I initially had the leads just drapped down the "mast" (dowel) to
a balun. It was my wife that tried to improve the asthetics by
neatening up the twinleads. Then she complained that reception
was bad. That's when I was experimenting with the dressing of
the leads. Right now I have it "dressed ugly", but it works.

3) Any suggestions to improve this design?

4) Any suggestions for alternitive DIY designs?

Wait until you have a problem before you try solutions. As I said
above, your goal is in conflict with interior available dimensions.
The truth of the matter is that a simple rabbit ears antenna might do
just as well as the best of the DIY designs littering pages across the
WWW.

No, the rabbit ears didn't work very well at all. That's why I have been
experimenting. I have seen a lot of the DIY designs littering the
WWW. This dual bowtie design is mine, tho.


73's
Richard Clark, KB7QHC

On 26 Apr 2009 00:56:11 +0100, Gordon wrote:

I've done the math. Channel 2 has a wavelength of about 18 feet and
channel 50 is about 1.4 feet. More than a 2:1 ratio. I do catch a
break since the VHF lo band is going to be vacated in this area. So
channel 8 is the lowest frequency I need to worry about (wavelength
of approx 5.5 feet).

Hi Gordon,

Yes, you've got the minimum specifications there. The widest part of
your antenna, at an optimum, would be something under 3 feet (half the
channel 8 wavelength) - still pretty big for indoors, especially if
the stations are in an awkward angle.

And speaking of stationS (accent on the plural), your design
requirements are going to be complex if they are not all on the same
axis/direction. And speaking further of stationS, you will need to
cover a broad range of frequencies.

The usual, optimal design is called a Log Periodic Dipole Array (or
variants of Log _______ ). It would qualify for being both
widebanded enough for one, or many, adjacent channels (growing in
length and element count for additional channels). This is why I
described the optimal antenna as being "honestly" big.

Smaller antennas are not going to deliver performance - but, again,
you may not need optimum, nor performance when the time comes. The
bow tie you've described elsewhere seems a suitable compromise.

Actually, I tried to keep the situation as controlled as possible.
I initially had the leads just drapped down the "mast" (dowel) to
a balun. It was my wife that tried to improve the asthetics by
neatening up the twinleads. Then she complained that reception
was bad. That's when I was experimenting with the dressing of
the leads. Right now I have it "dressed ugly", but it works.

Twinlead is fairly robust "except" when it is in close (three widths)
to metal or an RF absorber. As marginal as your situation sounds, my
bets are still with clutter near the antenna which is MORE prone to
disturbance than the line is.

No, the rabbit ears didn't work very well at all. That's why I have been
experimenting. I have seen a lot of the DIY designs littering the
WWW. This dual bowtie design is mine, tho.

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.

73's
Richard Clark, KB7QHC

K7ITM wrote in news:9134ad02-e551-4c5c-becf-05717feb8546
@y6g2000prf.googlegroups.com:

If you search for "diy hdtv antenna" or "diy dtv antenna" you will
come up with other ideas. Someone posted a question a while back here
about a design that apparently is pretty forgiving and not too hard to
construct and is claimed to give decent gain; see
http://www.digitalhome.ca/ota/superantenna/.

I have done that. In fact I have seen plenty of designs: Yagis,
The Coathanger antenna, etc. I have printed up the design of the
Grey-Hoverman. I could even build up a copy of the pVC design
and place it against the house, outside.
We actually had the Radio Shack model that is mentioned
on that site. my dad had it in the pre-CATV days. When I began to
set up the DTV reciever, I asked my dad about the old antenna, but
he didn't know what became of it.


Dave P's comments are good, though RG-8 is 50 ohm, not 75 ohm. Good
RG-6 type cable should work well for at least short runs, and it is
nominally 75 ohms. I don't know about your TV (or converter box), but
pretty much all the ones I've seen that receive digital TV broadcasts
have 75 ohm F connector inputs anyway, so you may as well go straight
to RG-6 at the source (the antenna).

I'm not sure what type of RG I am using. I should point out that I
have the twinleads running down the dowel to a balun. From there,
about 3 to 4 feet of coax runs to the converter box. I could just
put the converter closer to the antenna and slip the balun right
onto the converter.

Gordon 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?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

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!

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.
--
Ian