Barbara, this is actually a trick question.
I assume you mean dual "IF" conversion vs. single "IF" conversion.
However now that FlexRadio is on the scene, their definition of single
conversion is RF straight to AF.
BTW, this is also the original definition!
For the past 40 years or so, when we said single conversion, we were
referring to a radio like the original Omni or Argonaut which had a
single 9
MHz IF. We called it single conversion, but actually by definition it is
dual conversion because the RF is converted to the IF frequency (which is
actually still RF) and then converted to audio.
Thus dual conversion (as referred to in the past 40 years) and as seen in
the Omni VI, with 9MHz and 5MHz IF frequencies, was actually triple
conversion, because the signal still gets converted to audio.
None of this would be worth discussing if Flex had not come out with a
new
version of an old design.
So when I read your email, I don't know if you are referring to single
conversion as used by Flex or single conversion as used by Ten-Tec in the
Corsair.
If you mean dual-IF-conversion (like Omni VI), there are a couple of
advantages:
- you need two IF frequencies with small filters (typically crystal) to
be
able to have passband tuning. For instance, the K2 with its single 9MHz
IF
has no passband tuning.
- good quality filters with maybe 80dB of ultimate attenuation, when
used
in a single conversion rig, will typically have only 60dB of ultimate
attenuation, due to signal leakage around the filter. If you add a
second,
similar filter with the same IF frequency in series, you get maybe 90 dB,
but if the second filter is on a different IF frequency, you can get as
much
as 120dB of ultimate attenuation. THESE ARE BALLPARK NUMBERS, but your
get
the idea.
- dual conversion using a higher "FIRST" IF (above 30 MHz) has the
advantage that you have fewer birdies which fall inside the ham bands
(usually none). Radios with single conversion or dual conversion with
their
first conversion on lower frequencies (5MHz or 9MHz) typically have
birdies
which fall within the ham bands... BUT...
- IF filters at higher frequencies are not nearly of as good of quality
as
those at lower frequencies (due to a thing called fractional bandwidth),
so
you don't have the ultimate attenuation that you have with IF's at lower
frequencies. This usually deteriorates the close-in DR3 significantly,
which kills us in contests.
You pays your money and you takes your choice.
Do you want a good general coverage radio with no birdies in the 0 to 30
MHz
range, but lesser performance on the ham bands, or do you want a radio
with
much better performance on the ham bands but maybe 2 or 3 birdies (albeit
usually only S5 or less) within some ham bands?
I WILL GO WITH THE BETTER PERFORMING RIG ANY TIME.
73
Rick, DJ0IP
On 08/20/2010 10:37 AM, Barbara wrote:
Please tell me some of the improvements dual conversi9on vx. single
conversion receiver? thanks jjdavis
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