A "single conversion" question
 

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?

A "single conversion" question
 

Maybe read what Elecraft sez -- URL:

http://www.elecraft.com/Apps/why_is_...ver_single.htm
--
CL -- I doubt, therefore I might be !






"Larry" wrote in message
...
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?

A "single conversion" question
 

"Larry" ) writes:
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?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You needed
to convert radio to a lower frequency to get any sort of amplification. So
all superhets in the early days went to a lower frequency.

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).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

A "single conversion" question
 

"Caveat Lector" ) writes:
Maybe read what Elecraft sez -- URL:

http://www.elecraft.com/Apps/why_is_...ver_single.htm


Or, get a book and do it the old fashioned way.

Michael

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?


Look up ''preselector''.

A "single conversion" question
 

"David" 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?


Look up ''preselector''.


Oh Gee -- A tuned RF Amplifier
What a novel approach (;-)

My Hallicrafters S-40B circa 1948 had one of these
--
CL -- I doubt, therefore I might be !

A "single conversion" question
 

"Michael Black" wrote in message
...

"Larry" ) writes:
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?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You
needed
to convert radio to a lower frequency to get any sort of amplification.
So
all superhets in the early days went to a lower frequency.

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).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end
selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a
fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection
problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

Nice post. Quite informative.

--
rb

A "single conversion" question
 

"Ron Baker, Pluralitas!" wrote in message
...

"Michael Black" wrote in message
...

"Larry" ) writes:
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?


The number of conversions in a receiver means nothing. It's the detail
behind it that counts.

When Howard Armstrong came up with the superheterodyne receiver during or
right after WWI, tubes were pretty non-existent in terms of specs. You
needed
to convert radio to a lower frequency to get any sort of amplification.
So
all superhets in the early days went to a lower frequency.

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).

To get rid of that image frequency, you need the front end to be
selective enough to knock it out. At low frequencies, like the AM
broadcast band, it's easy, because the image is distant from the
desired signal by a fair amount. But as you move into the shortwave
frequencies, that 455KHz becomes a smaller and smaller percentage of the
signal frequency, and it becomes harder to get rid of the image. There
were all kinds of cheap receivers in the past (and maybe even today) that
had 455KHz IFs and you'd see reviews and they'd say "basically there is
no image rejection on the 20 to 30MHz band. The only way to stay with
455KHz and get good image rejection is to add more tuned circuits at
the front end, which some receivers like the HRO, did.

You can raise the IF frequency to improve image rejection. If you've
got a 9MHz IF, then you can get by with fairly little front end
selectivity,
because the image is 18MHz away from the signal you want to tune. It's
easy to reject a signal that far off.

But for quite some time, this wasn't possible because nobody could make
filters that high up. So the double-conversion receiver came into use.
Convert the signal down to a not too low frequency, to improve image
rejection, but then convert down to the usual 455KHz after that to get
good selectivity. If you have enough selectivity at the first IF so
it can reject a signal 910KHz away (and this is relatively easy for a
fixed
IF where you don't have to tune a bunch of tuned circuits at the same
time across the band), then you've mostly solved the image rejection
problem.

The double conversion in this case is just a workaround, to get good
image rejection, but also good selectivity with the second IF frequency.

When double conversion first hit, they'd often do a mix, where the
receiver would be single conversion to 455KHz on the lower bands, and
then a stage of selectivity at 2 or 3MHz would kick in on the higher
band(s) where it was needed, before another conversion to 455KHz.
These still used a tuneable local oscillator on the first mixer.

Of course, one whole layout of double conversion was to make the
first local oscillator crystal controlled. Then you'd have what
amounted to a tuneable receiver with a 455KHz IF, that tuned a fixed
range, often 500KHz. It would tune something like 3 to 3.5MHz, and
the first conversion would convert the desired signals to that range.
One disadvantage of this is that you needed a crystal for every 500KHz
or whatever the tuneable portion tuned. (Sometimes it got far worse,
with the receiver tuning 200KHz at a time.) On the other hand, the
advantage of this scheme was that by having the receiver tune a small
segment of the spectrum, and only tune that 3 to 3.5MHz band, you could
afford to make it linear tuning, and could afford to calibrate it well.
So these receivers brought in a level of tuning accuracy that often
hadn't been seen before.

There is another problem with conversion besides images. Every
conversion
decreases the immunity to overload, adds complication, and adds another
oscillator that if not carefully shielded and layed out, will cause
spurious responses.

So starting in the late fifties and early sixties, a new wave of
single conversion receivers hit. Crystal filters came along, that
offered good selectivity in the HF range, 9MHz being a common frequency.
That gave good selectivity and allowed for good image rejection with
only one IF frequency. Instead of having the ultimate selectivity way
down the signal chain, you could place it right after the first mixer,
leaving a stage or two before that good crystal filter. (Since the stages
after the crystal filter only had to see what was within the bandwidth
of that filter, it took a really strong signal to overload anything after
that filter, while in some of the previous examples many stages would
be seeing a lot of signal.)

Of course there were problems with that scheme. If the IF is in the
spectrum you want to receive, it can't be used around that frequency.
So there'd be a small gap around the IF frequency that you couldn't
really use the receiver. Also, crystal filters tend to be expensive,
so if you wanted a lot of different bandwidths, it may not have
been the best choice.

So you'd still see double conversion, with a good filter at the first
IF in the HF range, but as wide as the widest bandwidth you want,
and then a conversion to 455KHz or whatever where you could get more
of a range of filters. Or convert down to 50KHz, as Drake did, where
you could design good filters with relatively cheap LC circuits.

But then we also saw branch of receiver design where the first
IF would be above the signal frequency. IN the case of the shortwave
receiver, that puts it above 30MHz. That makes the image so far away
that front end tuning could really be cut down, with the real factor
being that the first mixer would see plenty of signals the receiver
isn't interested in, and could be prone to overload. Some designs
even went to a low pass filter at the front end, cutting off at
30MHz so the front end needed no tuning but saw nothing above 30MHz
where the image would be.

But once you place the IF in the 40Mhz or higher range, you've lost
the ability to build good filters. Either design limitations or cost
mean that you don't see narrow filters up there. More like 15KHz wide
or more, not really useful for shortwave listening. So there
was a move back to double conversion, with the second IF providing
the ultimate selectivity. Back to some of the tradeoffs of double
conversion, but at least image rejection was generally gone. This
wave of receivers caused other design decisions. Since the local
oscillator now had to be higher than 30MHz, stability really became
an issue, and that meant synthesized tuning took over. (Another
way of looking at it might be that you couldn't easily go to such
a high first IF unless you used synthesizer.)

And of course, conversions have also been used to add features
to a receiver, such as passband tuning.

So talking about double or triple conversion means nothing. You need
to talk about the actual IF frequency or frequencies, and the front
end selectivity, and whether the conversion is added for extra feature
or to get a basic thing.

Michael

Nice post. Quite informative.

--
rb


DITTO--
CL -- I doubt, therefore I might be !

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?

DSP -


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

A "single conversion" question
 

Michael Black - Thank Your Very Much ! :o)
It Was Worth Re-Posting ~ RHF

ABOUT - Radios : The Number of Conversions in a Receiver means
nothing...
http://groups.yahoo.com/group/Shortw...a/message/6514

" The Number of Conversions in a Receiver Means Nothing.
.. . . It's the Detail Behind It that Counts. "
- by Michael Black

* * * EXTRACTED from NewsGroups : Rec.Radio.Shortwave
= = = From: * (Michael Black)
= = = Date: 13 Nov 2005 17:50:05 GMT
= = = Local: Sun, Nov 13 2005 9:50 am
= = = Subject: A "Single Conversion" Question


iane ~ RHF
.
.
Tous Sont Bienvenus ! - - - Groupe par Radio
d'auditeur d'onde courte pour des Antennes de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Alle Sind Willkommen ! - - - Shortwave Radiozuhörer
Gruppe für SWL Antennen
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Tutti Sono Benvenuti ! - - - Gruppo Radiofonico
dell'ascoltatore di onda corta per le Antenne di SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Todos São Bem-vindos ! - - - Grupo de Rádio
do ouvinte do Shortwave para Antenas de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
Ð’Ñ�е Ð*адушны ! - - - Группа оператора
на приеме коротковолнового диапазона
Radio дл� Aнтенн SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
¡Todos Son Agradables! - - - Grupo de Radio del oyente
de la onda corta para las Antenas de SWL
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
= = = = = Translation = = = = =
All are Welcome - - - To Join the Shortwave Listeners
(SWL) Antenna Group on YAHOO !
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/
.
.
.. .

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.

A "single conversion" question
 

On Mon, 14 Nov 2005 04:07:57 GMT, "Frank Dresser"
wrote:


"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?
The bind is in many low end receiver designs, the mixer is also the
local oscillator, so most SW receivers that are variants of the All
America 5 design (and there were many) had very poor performance above
10Mhz or so.

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.
Actually most interesting design in a single conversion receiver I
think I ever was was in the mid 1960's Squires-Saunders built one with
a tuned RF stage with a Q muliplier on it, so they had a Q of a couple
thousand on the front end and made a killing on the gain as a result
of gain-bandwidth product. Suffices to say that with that sort of
front end selectivity, image rejection wasn't a problem. Obviously
impedance matching with the antenna was crucial to performance, but it
was undoubtedly the best single conversion HF receiver every
commercially built (and had a price tag to match).

Frank Dresser

A "single conversion" question
 

matt weber ) writes:

Actually most interesting design in a single conversion receiver I
think I ever was was in the mid 1960's Squires-Saunders built one with
a tuned RF stage with a Q muliplier on it, so they had a Q of a couple
thousand on the front end and made a killing on the gain as a result
of gain-bandwidth product. Suffices to say that with that sort of
front end selectivity, image rejection wasn't a problem. Obviously
impedance matching with the antenna was crucial to performance, but it
was undoubtedly the best single conversion HF receiver every
commercially built (and had a price tag to match).

But the Squires-Saunders had a high IF. According to one quick check,
it was a first IF tuneable from 5 to 5.5MHz, and then 1MHz. That
was part of the wave of receivers with crystal controlled first mixers, in
order to get a nice tuning range and stability. If they'd gone to
a fixed IF, then either the local oscillator would have to be switched
from band to band, or premixed with a crystal oscillator before the signal
went into the signal mixer.

Note it's an example of how down conversion can still work. For so
long, people always thought in terms of the early superhet with the
IF being down in the hundreds of KHz range, but the issue isn't that
it was converted down but that the IF was so low.

That Squires-Saunders arrive as crystal filters were still a new
thing. There's a famous 1963 article in QST by Squires or Saunders (I
forget which), discussing the philosophy and design of the receiver.
Some of the issues were keep rf amplification before the mixer to
a minimun, and use the 7360 beam deflection tube for the mixer for
a well balanced mixer. Few or no receivers used a balanced mixer
before the SS-1R, at least not affordable receivers. So the front
end Q-multiplier was brought in to deal with the simple front end.
For the rest of the decade, the basic concept, a 7360 mixer and a front
end q-multiplier, bounced around in various construction articles. But
in some ways it was just because it had been done, because there
were no front end Q-multipliers after the late sixties or early seventies.
And of course, solid state components came along, making it easier to
build a balanced mixer, be it with schottky diodes or active components,
without a bunch of bulky tubes.

All the receivers I saw that used a front end Q-multiplier used a high
IF, ie at least 2MHz and most often 9MHz.

Michael

A "single conversion" question
 

) writes:
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.


Howard Armstrong received the patent for the superhet, US patent number
1,342,885 in 1920. He wanted to receive what were astoundingly high
frequencies at the time, like in the 2 or 3MHz range.

At the time he cooked it up, even at the time the patent was issued,
there was no commercial radio broadcasting. The spectrum above
what is now the AM broadcast band was deemed useless (which is
why amateurs were relegated to "200 meters and down" after WWI.

I don't recall the schematic in Armstrong's patent, but if you look
in the history books, you find early schematics that use a chain
of RC coupled tubes for the IF strip, no selectivity.

Amplification has always lagged after frequency use. During WWII,
radar development was limited because they had problems getting
receiving tubes to work in the microwave frequencies, so they went
to diode mixers. It's pretty much always been easier to convert
to a lower frequency for amplification.

Michael

A "single conversion" question
 

"matt weber" wrote in message
...
On Mon, 14 Nov 2005 04:07:57 GMT, "Frank Dresser"
wrote:


"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?


The bind is in many low end receiver designs, the mixer is also the
local oscillator, so most SW receivers that are variants of the All
America 5 design (and there were many) had very poor performance above
10Mhz or so.

OK, but I thought we were talking about up conversion.

I don't think converter tubes lose much gain above 10 MHz, but they are
awfully noisy, and their noise really jumps out at higher frequencies.
Beyond that, many of those old radios had a high impedance antenna input,
and the typical coax run would shunt the high frequencies.

I don't think there was much upconversion above 10 MHz during the converter
tube era, however.



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.


Actually most interesting design in a single conversion receiver I
think I ever was was in the mid 1960's Squires-Saunders built one with
a tuned RF stage with a Q muliplier on it, so they had a Q of a couple
thousand on the front end and made a killing on the gain as a result
of gain-bandwidth product. Suffices to say that with that sort of
front end selectivity, image rejection wasn't a problem. Obviously
impedance matching with the antenna was crucial to performance, but it
was undoubtedly the best single conversion HF receiver every
commercially built (and had a price tag to match).


Dunno. I never worked with that radio, and I never even worked with a
regenerative preselector. There was a regen preselector projector in one of
my ARRL handbooks, but I've been too lazy and unmotivated to build it. I do
know that regens have a sharp peak in their response curve, but their skirts
have a gentle roll off, typical of a single tuned circuit. I sorta picture
a very strong adjacent signal on the slope breaking through and modulating a
weak signal at the peak Maybe not, but all the other high end single
conversion radios I can think of used multiple RF stages, biased in the
linear (enough) region.

Frank Dresser

A "single conversion" question
 

"Michael Black" wrote in message
...

) writes:
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.


Howard Armstrong received the patent for the superhet, US patent number
1,342,885 in 1920. He wanted to receive what were astoundingly high
frequencies at the time, like in the 2 or 3MHz range.

The story I remember is, during World War One, it was feared the Germans had
developed a way to communicate at 100 meters. Armstrong wanted to intercept
those communications, if they existed.


At the time he cooked it up, even at the time the patent was issued,
there was no commercial radio broadcasting. The spectrum above
what is now the AM broadcast band was deemed useless (which is
why amateurs were relegated to "200 meters and down" after WWI.

I don't recall the schematic in Armstrong's patent, but if you look
in the history books, you find early schematics that use a chain
of RC coupled tubes for the IF strip, no selectivity.

It's worth mentioning that there's a practical limit as to how much gain can
be obtained at any one frequency, and that practical limit was much lower
back in the earliest days. The superhet split it's gain at supersonic and
sonic frequencies, and could have much more gain without breaking out into
uncontrolled oscillation than a simple audio frequency amplifier. The tubes
of that era were just about useless as amplifiers at 3 MHz.

After Armstrong's invention, better triodes combined with better circuits
such as the Neutrodyne, as well as the screen grid tubes, put the TRF back
in the game into the early 30s, or so.





Amplification has always lagged after frequency use. During WWII,
radar development was limited because they had problems getting
receiving tubes to work in the microwave frequencies, so they went
to diode mixers. It's pretty much always been easier to convert
to a lower frequency for amplification.

Michael


Frank Dresser