"Noel" wrote in message
...
On Thu, 08 Jul 2004 11:25:32 GMT, "Frank Dresser"
wrote:


With a single IF, what you say is true. But with a dual conversion
surely part of the design is that the image is almost inevitably out
of the coverage range of the receiver?



Many dual conversion radios used a first IF between something like 1.6 to 10
Mc. They could still get images from other SW frequencies.

The later ones, with the IFs above 30 Mhz would only get images at VHF
frequenies, which are very simple to supress.

Frank Dresser

In article ,
Frank Dresser wrote:

My first wild guess is 10855 wasn't the actual frequency of the
transmission, but it was the image of 11765. 11765 is in a standard
shortwave broadcast band. My older copy of Passport says that the BBC used
that frequency, but I don't know if they're still using it.

BBC African track from 5:00-6:00 UTC. Same program as 6005 kHz.
On most days, it's 1/2 hour of world news and Daybreak Africa
for 1/2 hour.

Mark Zenier Washington State resident

Michael Black schrieb:

Early double conversion receivers would have their IF in the 2MHz or so
range.

As for an example, all the Grundig Satellits from the 208 up to the 3400
(the last drum tuner model) used a combo of 1.85 MHz 1st IF and 460 kHz
2nd IF; this combo supposedly only generates a very small number of
birdies on SW. BTW the lowest SW range (2...3 MHz or somesuch) usually
was single conversion there.

And there was a whole other design of double conversion receivers that were
common at one time. These were in effect a single conversion receiver
that covered a fixed range of 500KHz or so. The exact turning range varied
with receiver, but it was usually in the low MHz range. In order to
get other bands, a crystal controlled converter was placed ahead of this
receiver, and you'd need another crystal for each band you wanted to tune.

A number of Drake receivers come to mind here, but also several (usually
pocket-sized) dual conversion receivers with crystals for the broadcast
bands built-in (particularly Sony models with a 1st IF of 10.7 MHz -
ICF-7600A, ICF-7601, ICF-SW20/22).

It's only in the past twenty to thirty or so years that upconversion to a
frequency above 30MHz became common, especially for hobby receivers.

That's about right, the first comsumer-level 55.845 MHz designs are from
the early 80s (Grundig Satellit 600, Sony ICF-7600D/ICF-2002). IFs that
high weren't practical before mass-production PLL circuitry came along,
a simple matter of frequency stability. (Given the same stability in
ppm, an oscillator on 1.85 MHz +/- 460 kHz or 10.7 MHz +/- 455 kHz will
be much less drifty than the same part on 55.845 MHz +/- 455 kHz. With a
PLL, this pretty much becomes a non-issue, but you get no small amount
of phase noise in return, which can frequently be observed with PLL rigs
from the '80s or with inexpensive PLL receivers even today.)

Stephan
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PS:

High 1st IFs like 55.845 MHz aren't quite uncritical, particularly with
very compact receivers - you easily get leakage around the 1st IF
crystal filter. You can observe this very nicely with Sony's ICF-SW7600
(-910 kHz rejection ~20 dB) or ICF-SW7600G/GR (~30-40 dB rejection). It
would be interesting to know the performance of the little ICF-SW07 in
this regard.

Stephan
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I was disappointed in the strong images in my FP200. Then I realized that
should there be interference on the desired frequency, the image just might be
in the clear for solid listening. G

Bill, K5BY

Concerning the poor (2X 2nd I.F.) rejection, 2nd LO leakage back into
the 1st mixer can also cause this problem. I remember this problem with
the first dual conversion receiver that I built, and it wasn't until I
shielded the 2nd LO that things cleared up. Using radio chips with
micropowered oscillators solved that problem, along with my going to SMD
components.

Pete

"Frank Dresser" wrote in message
...

My first wild guess is 10855 wasn't the actual frequency of the
transmission, but it was the image of 11765. 11765 is in a standard
shortwave broadcast band. My older copy of Passport says that the BBC
used
that frequency, but I don't know if they're still using it.

Ha! I think you've figured it out, Frank. I should have caught that one
myself! Thanks again for your help.

"Honus" wrote in message
...


Ha! I think you've figured it out, Frank. I should have caught that one
myself! Thanks again for your help.



Yeah, it seems likely you were hearing an image if you were hearing a
broadcast station way out of band. It's not so clear if you were hearing
some utility station, but there's less utility traffic on the bands than
there was thirty years ago.

Bill McFadden posts his Handy Shortwave Chart on this group on a regular
basis. If you haven't seen it, here's a link:

http://www.rdrop.com/users/billmc/handy_chart

Although it's worth remembering that many stations broadcast just past the
edges of the officially recognized bands.

Frank Dresser

ut there's less utility traffic on the bands than
there was thirty years ago.

Is it still worth it to get a CW/RTTY decoder which are still advertised in
magazines such as "Popular Communications" and "Monitoring Times"?

Concerning the poor (2X 2nd I.F.) rejection, 2nd LO leakage back into
the 1st mixer can also cause this problem. I remember this problem with

My radio has 3 or 4 local oscillators. It's a triple-conversion reciever on
lower frequencies and a quadruple-conversion receiver on higher frequencies.

There are three IF frequencies listed for it in the manual.

It doesn't list a fourth IF frequency, but since it's quadruple-conversion on
higher frequencies, I'm assuming that it also has a fourth local oscillator.

Or am I way off-base here?