Superheterodyne LO question
 

I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?
As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

TIA

Liam

A local oscillator is local, that is -- it is an oscillator in the receiver
that generates a signal to heterodyne (beat) with the incoming signal to
produce plus and minus difference signals, the minus usually being the
Intermediate freq (IF). See URL:
http://www.see.ed.ac.uk/~gjrp/EE3/Co...re6/sld005.htm

" As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

Yes many a superhet has a fixed LO particularily VHF and up older designs --
used xtal or xtals -- with a crystal oscillator circuit for stability, but a
tuneable LO or now a days a synthesixed LO is more common.

Have fun


"Liam Ness" wrote in message
...
I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?
As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

TIA

Liam

A local oscillator is local, that is -- it is an oscillator in the receiver
that generates a signal to heterodyne (beat) with the incoming signal to
produce plus and minus difference signals, the minus usually being the
Intermediate freq (IF). See URL:
http://www.see.ed.ac.uk/~gjrp/EE3/Co...re6/sld005.htm

" As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

Yes many a superhet has a fixed LO particularily VHF and up older designs --
used xtal or xtals -- with a crystal oscillator circuit for stability, but a
tuneable LO or now a days a synthesixed LO is more common.

Have fun


"Liam Ness" wrote in message
...
I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?
As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

TIA

Liam

In article , Liam Ness
says...

I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?

As its name implies, the local oscillator is exactly that: Local
to the radio itself. In other words, your first statement is correct.

As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

Sure, you could, but why bother? The only place I've seen external
LO's used is in specialized test equipment, like tracking generators.


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
"Quando Omni Flunkus Moritati" (Red Green)

In article , Liam Ness
says...

I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?

As its name implies, the local oscillator is exactly that: Local
to the radio itself. In other words, your first statement is correct.

As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

Sure, you could, but why bother? The only place I've seen external
LO's used is in specialized test equipment, like tracking generators.


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
"Quando Omni Flunkus Moritati" (Red Green)