A "single conversion" question
 

I agree with the above posts...........they are right on the money. About
that advertisement.........I did see something like that with one of the
Eton radios (was it the S-350?). I think, unless they are using an I.F. much
higher than 455kHz, they are advertising the design deficiency as a merit,
instead of what it really is. You would need quite a bit of selectivity in
the stages ahead of the mixer in order to provide adequate image rejection.
An interesting point.....instead of going to a double conversion scheme in
the Zenith R-7000 (not to be confused with the American made Royal 7000) the
designer chose to continue with a single conversion scheme but changed the
I.F. to 10.7MHz for all tuning ranges. Not a bad radio.

Pete

"Korbin Dallas" wrote in message
...
On Sun, 13 Nov 2005 12:05:46 -0500, Larry wrote:

What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than
communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?

DSP -


--
Korbin Dallas
The name was changed to protect the guilty.

A "single conversion" question
 

On Sun, 13 Nov 2005 12:05:46 -0500, "Larry" wrote:

What am I missing here. Although my background is in electronics and
electrical engineering, I've specialized in power rather than communications
for thirty years. My scant and no doubt obsolete communications theory
always held that for great short-wave reception, double or even triple
conversion receivers were the norm. Now I see advertised, SW radios with
"... highly sensitive and selective latest state of the art single
conversion analog tuner circuitry....". What breakthrough has made single
conversion so state of the art?

Absolutle nothing, in fact single conversion sucks unless it is an up
conversion, and even then, mixer noise will wipe out reception above
about 10Mhz absent a good tuned RF amplifier in front. Of course
providing 3-5 Khz selectivity at 40Mhz tends to be a bit challenging.
Q on the order of 10,000......

Single Conversion with a 455khz IF strip doesn't have problems with
bandwidth, but image rejection in the SW bands sucks big time.

A "single conversion" question
 

On Sun, 13 Nov 2005 11:33:24 -0800, "Caveat Lector"
wrote:

Yep as MFJ sez its a Tuned RF Amplifier

"The MFJ-1045C RF Preselector let's you copy weak signals, while rejecting
out-of-band signals.
It's a high gain tuned RF amplifier that covers 1 to 54 MHz in four bands."
I had a bad ass S-40B about 15 years ago. I fully restored it to way
better than specs (I think. I tune old tube radios by ear with
atmospheric noise.) Made a calibration chart for it and thoroughly
enjoyed it. Gave it away.

A "single conversion" question
 

"matt weber" wrote in message
...
What breakthrough has made single
conversion so state of the art?


Absolutle nothing, in fact single conversion sucks unless it is an up
conversion, and even then, mixer noise will wipe out reception above
about 10Mhz absent a good tuned RF amplifier in front.

Why would up conversion mixer noise wipe out reception above 10 MHz? How
would the presumed mixer noise problem be fixed by a further conversion?

Of course
providing 3-5 Khz selectivity at 40Mhz tends to be a bit challenging.
Q on the order of 10,000......

Single Conversion with a 455khz IF strip doesn't have problems with
bandwidth, but image rejection in the SW bands sucks big time.

That's true enough with inexpensive receivers which relied on a single
(de)tuned circuit for RF selectivity. But the better receivers would
cascade two or more tuned stages, isolated with RF amplifiers.

Frank Dresser

A "single conversion" question
 

wrote in message
oups.com...
Not exactly twice, but I know what you mean. It would be at 20455Hz


Nope, either 10910 kHz or 9090 kHz, i.e. 10000 kHz plus or minus 2*455 kHz.
The LO is at 10000 kHz plus or minus the i.f. of 455 kHz. If it's at 10455
kHz, a signal at 10910 kHz will also mix to produce a 455 kHz i.f.; if 9545
kHz, a signal at 9090 kHz will also mix to 455 kHz.

[snip]
But then they realized a problem with that. Every time two frequencies
are heterodyned together, the sum and the difference result. This means
that there is an image frequency, ie one that is incidental to the
heterodyning but which you you don't want. If your IF frequency is
455KHz, and you want to receive WWV at 10MHz, there will also be an
image twice the IF frequency away (higher or lower depending on
whether the receiver's local oscillator is higher or lower than the
signal frequency).
[snip]

A "single conversion" question
 

I stand corrected. I was thinking of beating it down to baseband.

The low side mixer will reverse the spectrum.

Tom Holden wrote:
wrote in message
oups.com...
Not exactly twice, but I know what you mean. It would be at 20455Hz


Nope, either 10910 kHz or 9090 kHz, i.e. 10000 kHz plus or minus 2*455 kHz.
The LO is at 10000 kHz plus or minus the i.f. of 455 kHz. If it's at 10455
kHz, a signal at 10910 kHz will also mix to produce a 455 kHz i.f.; if 9545
kHz, a signal at 9090 kHz will also mix to 455 kHz.

[snip]
But then they realized a problem with that. Every time two frequencies
are heterodyned together, the sum and the difference result. This means
that there is an image frequency, ie one that is incidental to the
heterodyning but which you you don't want. If your IF frequency is
455KHz, and you want to receive WWV at 10MHz, there will also be an
image twice the IF frequency away (higher or lower depending on
whether the receiver's local oscillator is higher or lower than the
signal frequency).
[snip]

A "single conversion" question
 

I use a $16 speaker from radio shack with mine. Headphones for
serious dxing.

A "single conversion" question
 

m II wrote:
Michael Black wrote:
You needed
to convert radio to a lower frequency to get any sort of amplification.

Could you clarify this for me? I don't believe frequency generally has
an effect on the ability to amplify.

mike

This might have been true back in the audion days, but it would not
have been valid with octal or miniature tubes like a 6SK7 or a 6BA6.
These more modern tubes had plenty of gain at 455kcs.

After WW2, a lot of hams used a BC-453 ARC-5 receiver to make a double
conversion system out of their single-conversion shortwave radio. The
BC-453 was tuned to the 455kc IF, and its 85kc IF gave improved
selectivity.

A "single conversion" question
 

A "single conversion" question
 

m II wrote:
Perhaps he meant to say 'any sort of selectivity' ?

I re-read his posting, and I think he meant amplification. In context,
he was referring to the earliest vacuum tube days. The frequency
response of those tubes was limited. If I recall correctly, it was
limited by the physically large size and the spacing between the
filament, the grid, and the plate.