Antenna's
 

What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?
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"www.activesignals.com" wrote in message
...
What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?

scantenna

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Keep the volume up

www.activesignals.com has a forum board.
www.activesignals.com for all listeners.
www.activesignals.com is a lot of fun.
www.activesignals.com is worth the look.

What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?

I myself love the Isotropic Antenna for scanning. The specs are amazing,
and no other antenna's specs can beat it.

Do you use the Isotropic feed line to your unit? Until I purchased the right
feed line it did not work properly, now it's perfect!


"Ketch Hupp" wrote in message
...
What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?

I myself love the Isotropic Antenna for scanning. The specs are
amazing,
and no other antenna's specs can beat it.

Scantenna on a 10ft TV mast from ratshasck.

"www.activesignals.com" wrote in message
...
What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?
--
Keep the volume up

www.activesignals.com has a forum board.
www.activesignals.com for all listeners.
www.activesignals.com is a lot of fun.
www.activesignals.com is worth the look.

Ketch Hupp wrote:

What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?

I myself love the Isotropic Antenna for scanning. The specs are amazing,
and no other antenna's specs can beat it.

It looks good on paper but with zero dbi gain it is a poor performer.
Add some loss in the feedline and you may not even hear any static.

On Tue, 30 Dec 2003 21:38:34 -0500, www.activesignals.com wrote:

What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?

I usually try to match bands, 800 Mhz antennas for the Trunking scanners
that stay on 800 Mhz. and a Discone for the General Purpose scanner that
has UHF & VHF channels in it.

Jim Douglas wrote:

Do you use the Isotropic feed line to your unit? Until I purchased the right
feed line it did not work properly, now it's perfect!

Well, it looked good on paper, but when I tried it with the antenna, it doesn't
seem to ever meet the specs in the real world conditions as it should when you
do the math.

Discone on 2m TV mast.

Cheep cheep cheep discontinued stock from Dickies, just a few grub screws
missing.

"www.activesignals.com" wrote in message
...
What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?
--
Keep the volume up

www.activesignals.com has a forum board.
www.activesignals.com for all listeners.
www.activesignals.com is a lot of fun.
www.activesignals.com is worth the look.

A Very Old Benelec 16 element Discone
the mast I had it on was 10 metres
the new "tower" should put it up....about the same height
but seeing as my new location is 5 metres higher and clear of most of
the houses
should be much better

I use Belden 9913 cable as well

Kev

"www.activesignals.com" wrote:

What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?
--
Keep the volume up

www.activesignals.com has a forum board.
www.activesignals.com for all listeners.
www.activesignals.com is a lot of fun.
www.activesignals.com is worth the look.

I just ordered a AX-31B, active UHF antenna, made by WiNRADiO, though Grove
Enterprises. It's a very small, indoor, directional log-periodic antenna,
with a 20dB amplifier. I intend to point it at Selfridge Air Base, about
fifteen miles from me. I can hear them now, on the telescoping antenna,
that came with the BC796D, but sometimes it's a little weak, with some
noise. This should provide full quieting on the signal.

[link] http://www.grove-ent.com/ANT4.html

I'm also considering the purchase of a PAR MON-3, omni-directional, outside
antenna, through Universal Radio. It's optimized for 144~174, 440~470, and
800~900MHz. They claim it has 1.7dBi. I like it for it's simplicity, and
ruggedness. Here in Michigan, we get some fairly high winds, and nasty
winters with ice storms that can really build up on an antenna.

[link] http://www.universal-radio.com/catal...ants/4464.html

I'll post my results when available.

Bill Crocker


"www.activesignals.com" wrote in message
...
What kind of antenna are you using with your scanner? Presently I have
a discone mounted about 25 feet high. What is your favorite?
--
Keep the volume up

www.activesignals.com has a forum board.
www.activesignals.com for all listeners.
www.activesignals.com is a lot of fun.
www.activesignals.com is worth the look.

Bill Crocker ...

^ I'm also considering the purchase of a PAR MON-3, omni-
^ directional, outside antenna, through Universal Radio.
^ It's optimized for 144~174, 440~470, and 800~900MHz.
^ They claim it has 1.7dBi.

A di-pole has a gain of about 2.5 dBi. Before you spend money on an expensive
antenna, try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and 3.3".
One of each soldered to the center conductor and another of each soldered to
the shielding. This is not a transmitting antenna so no impedance matching
mechanism is necessary and the coax can run down alongside the lower half of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Frank

try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and 3.3".
One of each soldered to the center conductor and another of each soldered to
the shielding. This is not a transmitting antenna so no impedance matching
mechanism is necessary and the coax can run down alongside the lower half of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Hey Frank,
That is interesting and I know of the thinking behind it. Have you or someone
you know (maybe someone in this group) ever run an antenna like that and what
are/were the results. {?}

This might sound silly, but you wouldn't need a switch box would you to switch
to each 'antenna.'?? You mean you could use this 'one' antenna and just run it
straight to your scanner and as you searched different parts of the spectrum
the cut antenna would automatically work for the part/areas you were scanning?

Thanks for any reply by anyone. :-)

**I know in SWL you'd have to use a switchbox for a setup like that.

"Dxluver" wrote in message
...
try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the
weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and
3.3".
One of each soldered to the center conductor and another of each soldered
to
the shielding. This is not a transmitting antenna so no impedance
matching
mechanism is necessary and the coax can run down alongside the lower half
of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Hey Frank,
That is interesting and I know of the thinking behind it. Have you or
someone
you know (maybe someone in this group) ever run an antenna like that and
what
are/were the results. {?}

This might sound silly, but you wouldn't need a switch box would you to
switch
to each 'antenna.'?? You mean you could use this 'one' antenna and just
run it
straight to your scanner and as you searched different parts of the
spectrum
the cut antenna would automatically work for the part/areas you were
scanning?

Thanks for any reply by anyone. :-)

**I know in SWL you'd have to use a switchbox for a setup like that.

His idea is similar to the antennas that RS and maybe others sold. The ones
with "3" vertical radials one for VHF low, one for VHF Hi and one for UHF -
3 distinctly different length vertical elements - all mounted to a center
plate and connected to a SO239 with ground radials to boot. I made one like
it once out of a block of wood, 3 clothes hangers and 4 curtain rods - to
work in a pinch. I used 50 ohm coax. It worked quite well when made to
center of the bands they were to receive. No switch box needed. L.

His idea is similar to the antennas that RS and maybe others sold.

Thanks 'L'......I know of the thought process, for some reason it struck me
weird, guess it's late. ;-) But I like the idea of the PVC capped, that
shouldn't affect anything, should it?

Yeah boy, I can see this now, about 60ft. in the air....lol.

Does the factor 234 equal full wave or partial? 3.3" sounds a might small
for 850 mhz


"L." wrote in message
...

"Dxluver" wrote in message
...
try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the
weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and
3.3".
One of each soldered to the center conductor and another of each
soldered
to
the shielding. This is not a transmitting antenna so no impedance
matching
mechanism is necessary and the coax can run down alongside the lower
half
of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Hey Frank,
That is interesting and I know of the thinking behind it. Have you or
someone
you know (maybe someone in this group) ever run an antenna like that and
what
are/were the results. {?}

This might sound silly, but you wouldn't need a switch box would you to
switch
to each 'antenna.'?? You mean you could use this 'one' antenna and just
run it
straight to your scanner and as you searched different parts of the
spectrum
the cut antenna would automatically work for the part/areas you were
scanning?

Thanks for any reply by anyone. :-)

**I know in SWL you'd have to use a switchbox for a setup like that.

His idea is similar to the antennas that RS and maybe others sold. The
ones
with "3" vertical radials one for VHF low, one for VHF Hi and one for
UHF -
3 distinctly different length vertical elements - all mounted to a center
plate and connected to a SO239 with ground radials to boot. I made one
like
it once out of a block of wood, 3 clothes hangers and 4 curtain rods - to
work in a pinch. I used 50 ohm coax. It worked quite well when made to
center of the bands they were to receive. No switch box needed. L.

Sorry post was too short there!
Does the factor of 234 equal a full wave or partial wave like 1/4? 3.3"
sounds shorter than I'm used to seeing. Is there any reason, other than the
result being too tall of a device, to use an antenna that is not a full
wave?
Or to put it another way, if I build a di-pole ant. for 850 mhz what part of
a wave length will result in the best reception? Would there be any harm in
tuning for 2 wave lengths? See where that question is headed, if 2 is OK
then it will work on another freq as a 1(full) wave length antenna.
I seem to remember that 850 mhz was full wave at 13.8" so a half wave for
425 mhz is 13.8" too, is this right?


"Dxluver" wrote in message
...
try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the
weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and
3.3".
One of each soldered to the center conductor and another of each
soldered
to
the shielding. This is not a transmitting antenna so no impedance
matching
mechanism is necessary and the coax can run down alongside the lower
half
of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Hey Frank,
That is interesting and I know of the thinking behind it. Have you or
someone
you know (maybe someone in this group) ever run an antenna like that
and
what
are/were the results. {?}

This might sound silly, but you wouldn't need a switch box would you
to
switch
to each 'antenna.'?? You mean you could use this 'one' antenna and
just
run it
straight to your scanner and as you searched different parts of the
spectrum
the cut antenna would automatically work for the part/areas you were
scanning?

Thanks for any reply by anyone. :-)

**I know in SWL you'd have to use a switchbox for a setup like that.

His idea is similar to the antennas that RS and maybe others sold. The
ones
with "3" vertical radials one for VHF low, one for VHF Hi and one for
UHF -
3 distinctly different length vertical elements - all mounted to a
center
plate and connected to a SO239 with ground radials to boot. I made one
like
it once out of a block of wood, 3 clothes hangers and 4 curtain rods -
to
work in a pinch. I used 50 ohm coax. It worked quite well when made to
center of the bands they were to receive. No switch box needed. L.

To answer an earlier question: yes, I still use multi-element di-poles and
marconis.

Rich B. ...
^ Does the factor of 234 equal a full wave or partial wave
^ like 1/4? 3.3"

It's roughly a quarter wave.

^ sounds shorter than I'm used to seeing.

This is a receive antenna. A receive antenna will work over a much broader
spectrum than a transmit antenna will, so being precise is often wasted
effort.


^ Is there any reason, other than the result being too tall of a
^ device, to use an antenna that is not a full wave?

I tried a full-wave for 800 MHz and it didn't work as well as the
quarter-wave.


^ Would there be any harm in tuning for 2 wave lengths?

Probably not. I receive vertically polarized 800MHz signals very nicely with
a 10 foot horizontal di-pole.


^ I seem to remember that 850 mhz was full wave at 13.8" so
^ a half wave for 425 mhz is 13.8" too, is this right?

Again, you don't need to be that precise for a receive antenna, but the
formula for a quarter wave wire is:

feet=3.28*(meters=VF*75/MHz)

where VF is the velocity factor of the wire, a value usually between 0.6 and
0.95. But I doubt that you could find equipment sensitive enough to measure
the difference between receive antennas with and without the VF applied. For
a quarter-wave Marconi you use one of those wires, for a half-wave di-pole
you use two.

What you are referring to above is the use of harmonics in designing an
antenna. If one or more of the bands you are receiving are on a harmonic of
another band then you can eliminate those shorter wires in your multi-element
di-pole. A harmonic is an integer multiple of the frequency. For 106.25:

1 106.25
2 212.5
3 318.75
4 425
8 850

Theoretically you should receive best around each of those frequencies with
an antenna cut for about 106.25MHz. But I have not had to be that precise in
order to receive well. I suspect it would be like measuring sugar into a
cookie mix by counting the individual grains of sugar when you could probably
be off by a half-teaspoon and no one would notice the difference.

Frank

What I read here no switch box will be needed.
The radio will pick the element that is most resident to the frequency your
scanner locks onto and will let you receive accordingly.


"Dxluver" wrote in message
...
try a homemade vertical di-pole with one element for each band you
want to receive soldered to some good coax. For protection from the
weather
you can seal it in a suitable length of PVC pipe with endcaps.

For the bands you mention above, your elements would be: 17", 6", and
3.3".
One of each soldered to the center conductor and another of each soldered
to
the shielding. This is not a transmitting antenna so no impedance
matching
mechanism is necessary and the coax can run down alongside the lower half
of
the di-pole.

To calculate other lengths: FEET=234/MHz (i.e. 17'=234/160.000).

Hey Frank,
That is interesting and I know of the thinking behind it. Have you or
someone
you know (maybe someone in this group) ever run an antenna like that and
what
are/were the results. {?}

This might sound silly, but you wouldn't need a switch box would you to
switch
to each 'antenna.'?? You mean you could use this 'one' antenna and just
run it
straight to your scanner and as you searched different parts of the
spectrum
the cut antenna would automatically work for the part/areas you were
scanning?

Thanks for any reply by anyone. :-)

**I know in SWL you'd have to use a switchbox for a setup like that.




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As you make the antenna longer in relation to a 1/4 wave, two things happen.
The 234/FMHz is the formula for a 1/4 wave antenna. This is not all that
accurate, nor does it need to be, for VHF and up. At 800 MHz the diameter of
the antenna has a large effect. For receiving purposes it really isn't all
that critical. The fatter the antenna, the better would be a reasonable rule
of thumb for VHF and up receiving. If your interested, I can give you the
formuli for determining the K-factor. (How much to shorten an antennas as it
becomes larger in diameter)

Line of sight transmissions are either there or there not, a better antenna
will decrease noise on a week station, but the greatest antenna ever built
will not pull in an out of range signal.

1. the impedance changes - this may require a matching system between the
antenna and the receiver for maximum efficiency.

2. The angle of elevation changes, for example a very long vertical in
relationship to frequency would work well only straight up! (assuming
vertical polarization.)

All antennas are compromises, for local line of site to the horizon (VHF
reception and higher multidirectional) it is tough to beat a 1/4 wave cut
for the particular band and sloping radials to increase the impedance.

"Rich B." wrote in message
...
Sorry post was too short there!
Does the factor of 234 equal a full wave or partial wave like 1/4? 3.3"
sounds shorter than I'm used to seeing. Is there any reason, other than
the
result being too tall of a device, to use an antenna that is not a full
wave?
Or to put it another way, if I build a di-pole ant. for 850 mhz what part
of
a wave length will result in the best reception? Would there be any harm
in
tuning for 2 wave lengths? See where that question is headed, if 2 is OK
then it will work on another freq as a 1(full) wave length antenna.
I seem to remember that 850 mhz was full wave at 13.8" so a half wave for
425 mhz is 13.8" too, is this right?

What I read here no switch box will be needed.
The radio will pick the element that is most resident to the frequency your
scanner locks onto and will let you receive accordingly.

That's what I thought.
Thanks for the reply :-)

Dxluver ...

^ The radio will pick the element that is most resident to
^ the frequency your scanner locks onto and will let you
^ receive accordingly.

No. All signals from all elements are sent to the receiver. With a
transmitter, the signal will be sent to all elements but most of the
radiation will occur from the most resonate element.

Frank

No. All signals from all elements are sent to the receiver

Well then. What is the sense in building that antenna? Is this worth the
time? Is it going to make the signal sound like crap because if it is, I can
do that all by myself. :-)

Would you not agree that the element that is closest to resonance is also
the best match? With that as a given more signal is derived from that
element.

The radiation reception angle would also be lower. For example 2 elements,
one cut for 50 MHz and the other at 800 MHz. The 50 MHz element would appear
as a long wire on 800 MHz and would receive only signals directly overhead.

On frequencies above about 25 MHz, the best transmitting antenna for a
purpose is also the best receiving antenna for that same purpose.

The largest current will flow in a resonant antenna. We are interested in
developing the signal in microvolts across the fixed input impedance of the
receiver.

E=I/R meaning voltage is equal to the amount of current divided by the fixed
resistance of the receiver input. Increasing current then results in
increasing voltage, the holy grail to hear somebody. Note that ALL receivers
are characterized in microvolts required for a specific S/N ratio.

The other off resonance elements do not develop the necessary current
levels. They don't hurt anything, but are no real help. Ergo an element for
each band, either cut for a band or electrically cut by traps is a good way
to go.

Didn't mean to get so long winded...


"Frank" wrote in message
news:01c3d48e$08201270$0125250a@pixpqlbeqgavtlhm.. .
Dxluver ...

^ The radio will pick the element that is most resident to
^ the frequency your scanner locks onto and will let you
^ receive accordingly.

No. All signals from all elements are sent to the receiver. With a
transmitter, the signal will be sent to all elements but most of the
radiation will occur from the most resonate element.

Frank

Dxluver ...
^ No. All signals from all elements are sent to the receiver
^
^ What is the sense in building that antenna? Is this worth the
^ time?

It is true with ALL antennas. An antenna translates RF energy to electrical
energy, regardless of frequency. Frequencies that are close to resonant with
the antenna are more easily translated so their presence in the resulting
electrical signal is stronger. It is the receivers job to isolate the desired
frequency from the electrical signal.

Frank

w4jle ...

^ Would you not agree that the element that is closest to
^ resonance is also the best match?

No. Your question is phrased as a negative so my negative answer is an
agreement with the context of the question. I do not, not agree.

^ With that as a given more signal is derived from that
^ element.

Agreed.


^ The radiation reception angle would also be lower. For
^ example 2 elements, one cut for 50 MHz and the other at
^ 800 MHz. The 50 MHz element would appear as a long wire
^ on 800 MHz and would receive only signals directly overhead.

It works well. I assume you modeled the antenna with a software package and
that you used a vertical orientation. I use insulated wires that are
separated from each other only by the insulation. The wires are soldered
together at the BNC connector.


^ On frequencies above about 25 MHz, the best transmitting
^ antenna for a purpose is also the best receiving antenna
^ for that same purpose.

Graphically, the difference is like the difference between a 200m flagpole
and a 200m building. They both reach the same height -- the height
representing the "best" reception -- but the building covers a much greater
area, with the area representing the usable signal. In this analogy, the
flagpole is representing a transmit antenna and the building represents a
receive antenna.

So yes, the best transmit antenna is also the best receive antenna but the
receive has a much range that it is "best" at.



^ The largest current will flow in a resonant antenna. We are
^ interested in developing the signal in microvolts across the
^ fixed input impedance of the receiver.

The ability of an antenna to receive is irrespective of any electrical or
electronic equipment attached to it. An antenna captures electromagnetic
radiation and, if there is somewhere for it to flow, converts it to
electrical energy.


^ E=I/R meaning voltage is equal to the amount of current
^ divided by the fixed resistance of the receiver input.

That's E=I*R.


^ Note that ALL receivers are characterized in microvolts
^ required for a specific S/N ratio.

The ratio of desired frequencies to undesired frequencies.


^ The other off resonance elements do not develop the
^ necessary current levels.

That applies only when transmitting. When transmitting you are applying a
single frequency (plus and minus the bandwidth of the transmitter) to the
antenna system. In this case, the element that is most resonant will
translate most of that signal.

In the case of a receive antenna, the antenna is receiving ALL frequencies
and those that are close in wavelength to an element are received at a
greater level.

Frank

Whoops, sorry for the typo...

"Frank" wrote in message
news:01c3d51d$7bafea00$0125250a@ttakgbbprqsnyewb.. .
w4jle ...


^ E=I/R meaning voltage is equal to the amount of current
^ divided by the fixed resistance of the receiver input.

That's E=I*R.