Thats is why new is not always the best, I keep my ft 736r for 6 meters and
my knwd ts 950sdx, loaded with all the options for Hf.. and I hope the K3
will out preform them all. as I expected with the FT 2000 which was a flop
for me..
Keeping my fingers crossed, on the K3 , I am on the third wave....Bill
thanks for your input..really appreciated...
de
Wp4o, Ed
----- Original Message -----
From: "Bill Tippett" <[EMAIL PROTECTED]>
To: <elecraft@mailman.qth.net>
Sent: Sunday, September 30, 2007 7:08 PM
Subject: [Elecraft] Sherwood on ARRL Testing Methodology (LONG!)
Rob Sherwood gave his permission to post this on the
FT-2000 list. Since that is public information I am posting
it here also. BTW I agree with his comments on the "new"
methodology.
73, Bill W4ZV
What has gone wrong with the ARRL's new Product Reviews in QST?
For several years I participated as part of a group of hams who were
trying to improve the testing of radios reviewed in QST. Several reviews
in the past had included questionable data on receiver performance. A
sincere effort was initiated to correct testing problems within the lab,
and hopefully to also improve the "hands on" portion of the report.
As time went on, however, it appeared to me that the group had become
fixated on minutia, and at the same time the League was unwilling to look
at real problems in new radios being offered to the amateur radio
operator. I have not contributed lately in the steering committee, as I
felt I was banging my head against the wall.
Some of the nonsense coming out of the League has been around for a long
time, like the following quote from the 2004 review of the Icom IC-7800.
"I was able to hear calling US stations on back scatter that I don't
believe I would have heard on the '930." Did the reviewer bother to turn
on his TS-930? No, he just assumed he was hearing something unusual on
the receiver being reviewed (or hyped) in QST.
Has anything improved in 2007? The latest October review of the FT-2000D
(200 watt version of the FT-2000 that was earlier reviewed in February)
states the following: "Why would I need a 200 W transceiver? After using
it for a while, I was quite impressed with the extra punch the '2000D
offered during routine CW and SSB contacts compared to the 100 W version."
How could anyone tell a difference of 3 dB, especially compared to
operation of the FT-2000 eight months ago? This kind of reporting is
drivel.
What has changed in the ARRL reports?
Some of the changes are of minor interest, like measuring the noise figure
of an HF radio. Noise figure is generally used by VHF and UHF
enthusiasts, but adding these data points certain hurts nothing. Is noise
figure, or noise floor, or sensitivity a significant issue in today's
receivers? The 75A-4 has an excellent noise floor, as reported in the
January 2006 QST Annual Vintage Issue. Few of us have such a quiet
location that atmospheric and galactic noise don't overshadow the noise
floor of a modern receiver.
What we did get was additional confusion in the ethereal world of
third-order intercept (IP3), in place of real dynamic-range data. The
League used to measure it one way, then a second way, and now three ways.
Is this supposed to be helpful? The old way (measured at the noise floor)
was acceptable. The second way referenced an imprecise S5, now defined
as -97 dBm, and a third new way at 0 dBm. Zero dBm is really strong,
something we don't likely ever see, unless we are working Field Day or
Multi-Multi contests from near-by transmitters. (I am assuming we are not
living in Europe with their 5 megawatt AM broadcast transmitters.)
0 dBm is S9 + 73 dB, assuming any S meter reads that level accurately.
(The Flex 5000A would actually do that.) On my IC-781, 0 dBm reads S9 +
50 with 30 dB of internal attenuation, or something like S9 + 80 dB with
the attenuators off, if the S meter would read that high, which is does
not. What happens when you put two 0 dBm signals into an IC-781 at 20 kHz
spacing? The IMD reads S9 + 18 dB. At 2 kHz spacing the IMD reads S9 +
60 dB! The 781 is not a radio with performance problems, so what do these
new and improved measurements really mean?
If you look at the FT-2000 chart for IP3 at 2 kHz with the preamp off, you
see the IP3, measured at the noise floor, is -19 dBm. This is not a good
number, particularly since a Yaesu radio with "IPO" enabled (no preamp) is
similar to most other radios with the 10 dB attenuator enabled. Yet if
you measure the FT-2000 at 0 dBm, the IP3 calculates out to +15 dBm, which
sounds good. This new information is meaningless at best, or misleading
at its worst. Why is the IP3 so high at 0 dBM? Because the
inter-modulation is so strong (S9 + 60 dB) the AGC has basically turned
the gain of the radio off.
Most operators will run an FT-2000 with preamp 1 enabled, since it gives a
reasonable noise floor, sensitivity and AGC threshold. Yet no information
is available with this typical setting for the newly touted IP3 reporting
method, which at 2 kHz would be about -30 dBm for the League's sample.
(The FT-2000 I measured was considerably worse.) To get a meaningful
dynamic-range number, the reader now has to subtract two numbers. Why is
this important data now missing, or at least obfuscated? Could it be the
big advertisers in QST didn't like seeing 2 kHz dynamic-range numbers that
are typically around 70 dB? Only the League could take a measured 2 kHz
dynamic range of 69 dB at 2 kHz and calculate it into a +15 dBm intercept
at 0 dBm. Talk about smoke and mirrors!
The League is also going to differentiate between blocking (gain
compression) and phase noise limited (a typical problem with synthesized
radio). A narrow band audio spectrum analyzer is needed to measure
blocking this new way. (I used this method on my Flex 5000A report
because of the phase noise.) The ear is not going to hear what the
analyzer sees, but the League may have made an improvement here. At least
the two measurements now will be differentiated.
What is the League completely missing?
Most new DSP radios have serious problems in QRN, and with any kind of
transient impulse noise. Has QST reported on these problems? They have
not said a word. I gave a talk on this subject at the 2007 Dayton
Hamvention, to try to point out that all is not well in the current state
of radio design. The IC-7000 is a prime example of a radio that is nearly
useless in QRN, as is the FT-2000. Every DSP-chip based radio designed in
the last few years has an AGC problem to some extent. Fast rise-time
noises are improperly handled by the AGC, drastically exaggerating the
impulse noise.
I recently finalized an AGC test, using an HP fast-rise-time pulse
generator. It basically approximates an electric fence. The generator
was set for one pulse per second. The rise time was < 10 nanosecond, with
a duration of around 1 microsecond. The level was set to 1 volt peak, to
propagate a pulse well into the HF spectrum. The first radio tested with
this new method was the FT-2000, with preamp 1 enabled. This produces a
rather typical CW noise floor of -124 dBm, an SSB sensitivity reading of
0.3 uV, and an excellent AGC threshold of 1.3 uV. With a reference non-DSP
IC-781 that has similar specifications, the S meter on the pulse test read
less than S1, barely moving the S meter. On the FT-2000 the impulse noise
read S7, pulse after pulse after pulse.
While many hams seem oblivious to these AGC problems, at least some
operators are voicing their concern. I was pleased to hear from a new ham
at a recent Colorado hamfest describe his observations on his IC-7000.
Even though he had no past frame of reference from an analog radio, he
noted how strangely his Icom reacted to the slightest click or tick.
Merely turning on a light switch would kick his S meter up many S units.
I noticed the exact same problem two years ago on all the DSP radios
coming though my lab and ham shack.
When I queried the League on their review of the IC-7000, saying they
totally missed the AGC problems on transient noise and QRN, they simply
said they listened to it in December when there was no QRN. What is their
excuse this time on the FT-2000D? This radio had to have been evaluated
during the summer of 2007 when there was plenty of thunderstorm static.
What did the FT-2000D review happen to say about the dynamic range numbers
with the different roofing filters? After giving a full paragraph to
explaining why narrower roofing filters are usually helpful, the League
simply said, "We noticed little difference in performance between the 3
and 6 kHz roofing filers in any of the FT-2000s tested, though, at any
signal spacing."
On the FT-2000 data recently posted on my web site, the dynamic range
actually dropped from 90 dB at 20 kHz with the 6 kHz roofing filter to 81
dB with the 3 kHz roofing filter. At 2 kHz spacing there was minimal
difference, 63 dB (3 kHz filter) and 61 dB (6 kHz filter). Dynamic range
numbers in the low 60s are not acceptable for serious operators.
Finally, one more bizarre comment from the "hands-on" QST reviewer. The
u-Tune unit adds modest selectivity in the front end, and significant
insertion loss, as seen by the degraded noise floor. Yet the reviewer
found the u-Tune unit to be helpful "on 20 meters before the band closed
with the u-Tune unit switched on." One wonders why a little added RF
selectivity and 10 dB insertion loss would help when the band was fading
out. If this statement is accurate, which I question, there is something
seriously wrong with this radio beyond AGC and roofing-filter problems, a
subject totally ignored by the review.
When will the day come when the information in QST is more than a fluff
review, and a free multi-page advertisement for the manufacturer?
73,
Rob Sherwood
NC0B
Rev C1
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