Hello

Hope someone out there can help!
I've just started a private investigator business.
Part of the equipment I use is a recorder/receiver unit (basically a
sony tape machine with a receiver built on to it). The aerial appears
to be a black plastic coated, bendy single wire 16cm long with a small
3mm (approx) screw thread on the end which screws into the receiver.
It appears to be single core, in that, the screw thread is a solid
piece (not like a two piece jack plug for example).

I want to be able to connect an external car ariel to the receiver as
at present the receiver with the aerial screwed in is hidden inside
the car and the reception is very poor.

Some questions:
Is the aerial single core? I naively thought all aerials had a core
and screen.

Could I take a connection from the centre core of an existing wing
mounted car aerial and run a single wire to the receiver inside the
car?

If I used this method would the external car aerial have to be 16cm,
same as the plastic aerial?

Can these small 3mm screw threads on the end of the existing aerial be
bought from somewhere so I could connect my external aerial to the
receiver?

I hope this all makes sense and I would be very grateful for any
advice.

Thank you

Gidday

I would suspect that the recorder unit you have is not really intended
to take a remote antenna.

Generally speaking an aerial will be a single core. The core and screen
thing you are thinking of is likely to be coaxial cable, what you could
join a aerial to a receiver with. It isnt normally suppose to pickup or
radiate signal.

Connecting the existing wing mounted aerial *might* work but you may
receive a lot of noise from car accessories/ignition etc. If your
receiver had a coaxial connector on it things would be a lot easier!

The length of the aerial is nominally a function of the operating
frequency but I doubt the unit you have would be critical in that
regard. It wont hurt to extend the aerial anyway you like. Try it!
"Real" aerials connected to transmitters tend to require tuning to work
efficiently, but since you dont know the parameters of the device you
are connecting to it there isnt much point trying to work it out..

Your biggest enemy of receiving a good signal will be if the aerial is
inside the car metalwork.. If you cant stick it out the window then at
least have it at glass level. You may find that mounting it on the sun
visor would be a good position.

Also note that mounting the transmitter and its aerial is also
important. Try and not bury it in a metalwork and if possible put it
next to a window.

Apologies for not being much help.

Cheers Bob VK2YQA (Sydney Australia)

zentace wrote:
Hello

Hope someone out there can help!
I've just started a private investigator business.
Part of the equipment I use is a recorder/receiver unit (basically a
sony tape machine with a receiver built on to it). The aerial appears
to be a black plastic coated, bendy single wire 16cm long with a small
3mm (approx) screw thread on the end which screws into the receiver.
It appears to be single core, in that, the screw thread is a solid
piece (not like a two piece jack plug for example).

I want to be able to connect an external car ariel to the receiver as
at present the receiver with the aerial screwed in is hidden inside
the car and the reception is very poor.

Some questions:
Is the aerial single core? I naively thought all aerials had a core
and screen.

Could I take a connection from the centre core of an existing wing
mounted car aerial and run a single wire to the receiver inside the
car?

If I used this method would the external car aerial have to be 16cm,
same as the plastic aerial?

Can these small 3mm screw threads on the end of the existing aerial be
bought from somewhere so I could connect my external aerial to the
receiver?

I hope this all makes sense and I would be very grateful for any
advice.

Thank you

Gidday Bob

Thanks very much for replying to my questions.
I take it then, that if you connect a screened cable between the
aerial and the receiver, the length of the cable itself does not act
as an aerial because the screening prevents this?
So if the aerial is only one "core" where do I connect the screen? I
know I could connect it at the aerial end to the car body (earth) but
what about at the receiver end? Does it have to connect at all at that
end as long as the screen is connected to the car body?
By the way, the car itself will be stationary and switched off so
hopefully I won't have the problem of interference from the car
electrics.
Also the transmitter is apparently fixed frequency 100-125MHz and the
receiver switched to this.
I'll experiment and see!
Let me know if you have any thoughts about the screen.

Thanks again

Iain (Scotland)

Bob Bob wrote in message ...
Gidday

I would suspect that the recorder unit you have is not really intended
to take a remote antenna.

Generally speaking an aerial will be a single core. The core and screen
thing you are thinking of is likely to be coaxial cable, what you could
join a aerial to a receiver with. It isnt normally suppose to pickup or
radiate signal.

Connecting the existing wing mounted aerial *might* work but you may
receive a lot of noise from car accessories/ignition etc. If your
receiver had a coaxial connector on it things would be a lot easier!

The length of the aerial is nominally a function of the operating
frequency but I doubt the unit you have would be critical in that
regard. It wont hurt to extend the aerial anyway you like. Try it!
"Real" aerials connected to transmitters tend to require tuning to work
efficiently, but since you dont know the parameters of the device you
are connecting to it there isnt much point trying to work it out..

Your biggest enemy of receiving a good signal will be if the aerial is
inside the car metalwork.. If you cant stick it out the window then at
least have it at glass level. You may find that mounting it on the sun
visor would be a good position.

Also note that mounting the transmitter and its aerial is also
important. Try and not bury it in a metalwork and if possible put it
next to a window.

Apologies for not being much help.

Cheers Bob VK2YQA (Sydney Australia)

zentace wrote:
Hello

Hope someone out there can help!
I've just started a private investigator business.
Part of the equipment I use is a recorder/receiver unit (basically a
sony tape machine with a receiver built on to it). The aerial appears
to be a black plastic coated, bendy single wire 16cm long with a small
3mm (approx) screw thread on the end which screws into the receiver.
It appears to be single core, in that, the screw thread is a solid
piece (not like a two piece jack plug for example).

I want to be able to connect an external car ariel to the receiver as
at present the receiver with the aerial screwed in is hidden inside
the car and the reception is very poor.

Some questions:
Is the aerial single core? I naively thought all aerials had a core
and screen.

Could I take a connection from the centre core of an existing wing
mounted car aerial and run a single wire to the receiver inside the
car?

If I used this method would the external car aerial have to be 16cm,
same as the plastic aerial?

Can these small 3mm screw threads on the end of the existing aerial be
bought from somewhere so I could connect my external aerial to the
receiver?

I hope this all makes sense and I would be very grateful for any
advice.

Thank you

Hi Iain

Without going into a lot of transmission line theory.... grin

For the purposes of this post, coax is the same as "screened cable". I'd
suggest you use coax though (RG58 will do) as its impedance doesnt vary
along its length and it is a known value... unlike plain screened cable.

When you setup a radio in a car the antenna attachment on the radio end
is normally a coaxial connector. The centre conductor goes into the
"live" part of the box and the screen goes to the metal chassis of the
radio itself. At the antenna end the centre coax conductor connects to
the whip itself and the screen is connected to the car body at the point
where the whip starts. The whip is of course insulated from the car body.

In a correctly installed and tuned installation (usually the whip
length) the coax doesnt pickup any noise.

You dont need to connect the radio end screen to the car body. In your
case you might be able to use a nearby metal screw on the radio. The
last alternative maybe to use the negative power line where it enters
the radio. The idea is to get the screen connection as close to the
receiver input ground as possible. The more exposed centre conductor
there is at the radio end the less efficient the system is.

Given the frequency you have mentioned a "good" whip length will be
around 570mm. There are of course a number of unknowns in setting up
this system so dont try playing with the whip length too much.

Cheers Bob VK2YQA

zentace wrote:
Gidday Bob

Thanks very much for replying to my questions.
I take it then, that if you connect a screened cable between the
aerial and the receiver, the length of the cable itself does not act
as an aerial because the screening prevents this?
So if the aerial is only one "core" where do I connect the screen? I
know I could connect it at the aerial end to the car body (earth) but
what about at the receiver end? Does it have to connect at all at that
end as long as the screen is connected to the car body?
By the way, the car itself will be stationary and switched off so
hopefully I won't have the problem of interference from the car
electrics.
Also the transmitter is apparently fixed frequency 100-125MHz and the
receiver switched to this.
I'll experiment and see!
Let me know if you have any thoughts about the screen.

Thanks again

Iain (Scotland)