Joe,
Here is a resend of an old thread.. Maybe this helps explain better
than I can about the effects and reasons for roofing filters.
Dudley
-------- Original Message --------
Subject: Re: [Flexradio] Fw: [Elecraft] Comparison: K3 and SDR 5000A
Date: Sun, 07 Oct 2007 08:41:29 -0600
From: Rob Sherwood <r...@nc0b.com>
To: 'Richard Smith' <smit...@comcast.net>, FlexRadio@flex-radio.biz,
Gerald Youngblood <ger...@flex-radio.com>
References: <007201c80853$2d850820$680fa...@w1ezx2>
<176601c8087d$e0fbc630$720fa...@toshibasatellite>
Here is a slight correction to Gerald's statement.
I don't publish IP3 numbers on my web site.
When they appear in an expanded report, they are calculated from data taken at the noise floor.
It is a 3 dB peak in the RMS reading, not 1 dB that I use, like the ARRL did
for years.
As of the October FT-2000D review, the League dropped publishing dynamic range
numbers completely.
A footnote explains how to calculate dynamic range (DR3) from their data.
The League has muddled the water by now publishing data at the noise floor, S5
(now defined as -97 dBm) and at 0 (zero) dBm.
I consider the 0 dBm data meaningless. Most radios will be in such a state of
overload, the IMD will be in the S9 +20 to S9 + 60 dB range, depending on the
test spacing (for an up conversion radio).
An e-mail relayed to me from the K3 reflector implies the DR3 numbers may
return in the future. I am totally against publishing a 0 dBm measurement. In
the case of the FT-2000D, a -69 dB DR3 at 2 kHz becomes a +15 dBm intercept.
This is either confusing at best, or misleading. You decide.
73, Rob Sherwood, NC0B
"Gerald Youngblood" <ger...@flex-radio.com> 10/6/2007 7:03 pm >>>
There are both misconceptions and apples/oranges measurements here. The IMD
DR3 numbers quoted by Elecraft are almost certainly measured using the ARRL
lab methodology (IP3 Measured at S5). Using the ARRL S5 IP3 test methods,
we measure the FLEX-5000 at 100+ dB IMD DR3 at any spacing (including 100 Hz
or less). Those are top class numbers at any spacing.
Note that Sherwood uses a different measurement technique where IP3 is
measured at a 1 dB rise in the noise floor. Sherwood measured the FLEX-5000
at 96 dB at any spacing using his methods. Sherwood's website shows the
Elecraft K2 at 80 dB IMD DR3 at 2 kHz and 98 dB at 20 kHz. There is no
independent measurement info on the K3.
By the way, I have tremendous respect for Elecraft. This is only an effort
to clear up some misinformation.
73,
Gerald
Gerald Youngblood, K5SDR
FlexRadio Systems
Ph: 512-535-4713
Fax: 512-233-5143
Email: ger...@flex-radio.com
Web: www.flex-radio.com
-----Original Message-----
From: flexradio-boun...@flex-radio.biz
[mailto:flexradio-boun...@flex-radio.biz] On Behalf Of Richard Smith
Sent: Saturday, October 06, 2007 2:58 PM
To: FlexRadio@flex-radio.biz
Subject: [Flexradio] Fw: [Elecraft] Comparison: K3 and SDR 5000A
I believe there are significant misconceptions here that
should be addressed by someone closer to the Flex Radio
product than myself. As I understand it, there is no need
for a "roofing filter" in the SDR-5000 because of its direct
conversion architecture - the same thing that makes my K2 so
good without a roofing filter. Yet I have now seen shots
taken at the SDR-5000 in several places for its lack of a
roofing filter. Am I ignorant of the facts, or are they?
Also, making the decision to purchase one radio over another
based on a perceived shortfall in the 20 kHz dynamic range
when the close in 2 kHz dynamic range of the SDR-5000 is
superb, and possibly the best in the industry, seems wrong.
Am I missing something?
Rich W1EZ
----- Original Message -----
From: "John A. McCabe" <johnamcc...@verizon.net>
To: <elecr...@mailman.qth.net>
Sent: Saturday, October 06, 2007 2:24 PM
Subject: Re: [Elecraft] Comparison: K3 and SDR 5000A
> Hi John,
>
> Although I do not have a 5000, I do have a SDR-1000.
Elecraft and Flex are
> both Good companies that produce great radios. However, I
believe one
> major difference between the K3 and the Flex 5000 will be
in wider space
> dynamic range. The close-in 2Khz dynamic range for the 5000
I believe was
> measured by Rob Sherwood at 96db which is a good number.
But the 5000
> does not have roofing filters, so if I am not mistaken, the
96db IMD
> dynamic range will the same at 2Khz, 5Khz, 10Khz, 20Khz,
and beyond, as
> it is with most sound card based SDR's. To me a 96db
Dynamic range beyond
> 20Khz is not good. I believe that a 96DB dynamic range is
around 40-45db
> over S9, so if my calculations are correct, IMD could be a
problem from a
> 45db over S9 signal 20Khz or more away. That is one of the
reason's why I
> chose the K3 over the 5000. The K3's close in numbers will
be around the
> same is the 5000, but the wider spaced measurements I
expect to be much
> better then the Flex-5000.
>
>
> John, KD8K
> _______________________________________________
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> Post to: elecr...@mailman.qth.net
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> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
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--
73,
Dudley
WA5QPZ
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