Built a 2m 1/2 wave rooftop (20 ft. up) and am confused about what I
should use to connect it to my Uniden BC 100. have lots of TV cable
but is there something better?

Thanx,

Reply to group please.

PM in Phoenix

On 10/22/2012 3:56 PM, Egg Salad wrote:
Built a 2m 1/2 wave rooftop (20 ft. up) and am confused about what I
should use to connect it to my Uniden BC 100. have lots of TV cable
but is there something better?

That is fine to use for your scanner feedline. The only time ohms are
important is when you are transmitting.

On Mon, 22 Oct 2012 17:16:11 -0700, Matt Warner -spam
wrote:

On 10/22/2012 3:56 PM, Egg Salad wrote:
Built a 2m 1/2 wave rooftop (20 ft. up) and am confused about what I
should use to connect it to my Uniden BC 100. have lots of TV cable
but is there something better?

That is fine to use for your scanner feedline. The only time ohms are
important is when you are transmitting.

Thank You Matt,

Been wondering about that since that since the old days of 300 ohm TV
twin lead (1965).

Thanx Again,

PML,

Pkoenix

Matt Warner wrote:

On 10/22/2012 3:56 PM, Egg Salad wrote:
Built a 2m 1/2 wave rooftop (20 ft. up) and am confused about what I
should use to connect it to my Uniden BC 100. have lots of TV cable
but is there something better?

That is fine to use for your scanner feedline. The only time ohms are
important is when you are transmitting.

I don't completely agree with that. Yes, once you get it working it's
not a big issue[*]. But if you have mismatches you have standing waves,
and if you have standing waves you have certain cable lengths that
give you weaker signal levels. So it's still helpful to use a matching
adapter (300 ohm to 75 ohm, for example) where appropriate, and reasonably
high quality coax. The difference between 50 and 75 ohms is probably not
a big deal here, though.

So are 2 meter signals the only things you'll be sending through this
path?
[*] You are probably not looking for long distance reception
(meteor scatter? earth-moon-earth?). For local reception, signal
levels don't matter so much. The receiver has a preamp and automatic
gain control, no doubt.

George

I don't understand the type of antenna he / she built.

A half wave what? J Pole?

A little secret - take a television antenna - UHF / VHF, turn it on it's side if you want. You can even use a antenna pre amp. USE a antenna rotor.

Connect the antenna to some good RG 6 Quad Shield and run it into your house, into the power injector, into some more good Quad Shield and adapter to BNC.

Turn the antenna in the direction you desire to receive in.

I used a Winegard 8200U antenna and a Channel Master CM 7777 pre amp and Channel Master rotor @ 24' in my backyard and was able to hear stations that I could not hear with my Yaesu 8900 and my Diamond V2000 antenna nor my Cushcraft 4 element 2 meter beam antenna.

If all you want to do is receive, it does not matter if the cable is 50 ohm or 75 ohm nominal impedance.. You are not going to get standing waves from reception - only transmission.

Even better cable is the hardline that the TV cable company uses from pole to pole. I think its nominal resistance is about 77 Ohm's, but its loss rate is . 07 or something or another in like 100 feet @ 500 Mhz.

Enjoy the scanner, do not expect to hear much with a home brew vertical dipole antenna.

Channel Jumper wrote:

If all you want to do is receive, it does not matter if the cable is 50
ohm or 75 ohm nominal impedance.. You are not going to get standing
waves from reception - only transmission.

Umm. Not true. Transmission and reception follow the same laws of
physics.

The reason you care for transmission has to do to some extent with
losses. If you have large standing waves you may actually be losing
power in the transmission line itself. Not to mention that with
a mismatched load you may not actually deliver much power to the
antenna, but that depends on the design of the transmitter, and of
the antenna tuner if one is present.

A receiver has a tremendous amount of gain and can compensate
for all sorts of mismatches - so you won't notice any difference
except on signals that are rather weak to begin with. It's at
that point you'll find that your transmission line has become
a notch filter that blocks certain signals without you knowing
it.

By building an antenna for a specific frequency band I am
assuming that that's what he wants to hear. For best reception
or transmission of any given frequency band and an antenna
designed for that band, go ahead and do the matching - why not?

Completely different thinking applies to random antennas typically
used for scanner listeners / SWLers. There, you accept what you
get for antenna performance and hope the gain in the first RF amp
compensates for a haphazard antenna / transmission line combination.

George Cornelius

Even better cable is the hardline that the TV cable company uses from
pole to pole. I think its nominal resistance is about 77 Ohm's, but its
loss rate is . 07 or something or another in like 100 feet @ 500 Mhz.

Enjoy the scanner, do not expect to hear much with a home brew vertical
dipole antenna.

"Channel Jumper" wrote in message
...

I don't understand the type of antenna he / she built.

A half wave what? J Pole?

A little secret - take a television antenna - UHF / VHF, turn it on it's
side if you want. You can even use a antenna pre amp. USE a antenna
rotor.

Connect the antenna to some good RG 6 Quad Shield and run it into your
house, into the power injector, into some more good Quad Shield and
adapter to BNC.

Turn the antenna in the direction you desire to receive in.

I used a Winegard 8200U antenna and a Channel Master CM 7777 pre amp and
Channel Master rotor @ 24' in my backyard and was able to hear stations
that I could not hear with my Yaesu 8900 and my Diamond V2000 antenna
nor my Cushcraft 4 element 2 meter beam antenna.

If all you want to do is receive, it does not matter if the cable is 50
ohm or 75 ohm nominal impedance.. You are not going to get standing
waves from reception - only transmission.

Even better cable is the hardline that the TV cable company uses from
pole to pole. I think its nominal resistance is about 77 Ohm's, but its
loss rate is . 07 or something or another in like 100 feet @ 500 Mhz.

Enjoy the scanner, do not expect to hear much with a home brew vertical
dipole antenna.


You'd be surprised. I built (actually, adapted) an offset-fed dipole from
an old rabbit ears (the kind that comes with the set) which is in my 2nd
floor 'shack'. Does a decent job across multiple frequencies.

HankG

It does a decent job compared to what?

Because you have no other antenna to compare it to - all you know is what you got locally with the rabbit ears...

Technicially it is not called SWR - sorry that is CB lingo - for the people who knows nothing and doesn't care to learn anything..

In communications we call it VSWR - since all we are concerned about is the VOLTAGE present.

power from a generator ( transceiver ) is measured in volts and amps which when multiplied together equals WATTS.

power from a antenna is measured in MICROWATTS....

How much of a standing wave are you going to generate with 10 microwatts?

Even still more - the SWR as you call it is not as important as the loss rate.

450 ohm ladder line could have a VSWR of 20:1 - yet have very little outcome on the performance of your antenna system - because the loss is very low in 100' @ 7 MHz.

Its only as we increase frequency that we concern ourselves more with loss.

140 something megacycles is not all that bad when it comes to line loss.
440 MHz on the other hand is a whole different story...

I would suggest that you do a little more internet research....