[ICOM] Sherwood Engineering test numbers
Glen Rosenthal
n0nr at hotmail.com
Mon Oct 16 15:52:34 EDT 2006
Here is some good reading from one of my correspondences with Rob I'd like
to share with the reflector:
10/16/2006: Rob Sherwood Wrote:
Discussion about the Icom 706MkIIG data on my web site prompted me to make
some
comments.
The first 706MkIIG I purchased new in 2001 had a 2 kHz dynamic range of 69
dB
using the standard SSB filter.
It was replaced in 2006 with an IC-7000 which was so unacceptable in noise
(QRN,
line noise and any transient noise) that it was replaced with a brand new
706MkIIG that included an Icom 500 Hz CW filter. This unit is the one on my
web
site, tested with the 500 Hz filter, and it measured better than I expected
at
2 kHz, namely 74 dB. By the way, the IC-7000 at 2 kHz measured 63 dB.
I encourage interested parties to read my paper "A Discussion of Measurement
Accuracy and Sample Variation" available on my web site on the front page
under
the button "Receiver Performance". (www.nc0b.com) If clicking on the button
doesn't open Adobe Reader, open the Acrobat Reader first, and then click on
the
button again, or simply right click and download the paper.
Some general comments:
Don't consider one number the only reason to purchase a radio, whether it be
dynamic range, sensitivity or whatever parameter you consider most important
for
your application. Let's use the 706MkIIG as an example of a radio with many
pluses and minuses. Since it is very small, I certainly prefer it over my
TR-4C
for mobile! Yet the noise blanker is awful, and the 30+ year old TR-4C's
noise
blanker puts it to shame. Also unlike the 34-PNB in the TR-4C, the NB in
the
706 overloads on SSB with any signal over S9 and is useless on AM. At least
the
IC-7000 corrected the NB problems. The front end of the 706 is minimal, and
on
HF mobile a narrow-band tuned antenna likely helps this limitation. The
706's
lack of a front end in a home QTH environment is especially disastrous on 2
meters if you have a good outdoor antenna. Out-of-band commercial signals
desense the radio as much as 20 dB. A 30 year old IC-211 will run circles
around an 706 on 2 meter simplex due to its superior front end. The
706MkIIG
has terrible splatter if you more than tickle the ALC, a problem certainly
noticed by adjacent QSOs if you are using it with a linear and a good
antenna.
Filter blow by is a real problem with the 706MkIIG on all three samples I
have
owned. Working an SSB WPX contest from the mobile made this more than
obvious,
with all the high-pitched monkey chatter leaking around the filter. I used
a
706MkIIG at one of my QTHs with an Alpha 99 and Hy-Gain 204BA and 402BA
yagis
for about a year. As long as I kept the noise blanker off, I felt the radio
performed quite well in the real world. I did not notice audio distortion
problems on receive on either SSB or CW. The 706 isn't a Pro III nor a 781,
but
for a backup base station rig, it was acceptable, particularly on SSB. I
think
sample variation is a bigger problem than most of us realize. I have used
three
different Pro IIs, and all three were different. One was virtually as good
as
my Pro III, one definitely had distortion problems in the audio section
unless
one used an amplified speaker, and the third one had intermod problems on 20
meters from the 19 meter broadcast band, and it "folded up" under QRN. My
706s
sounded so much cleaner on 2 meter SSB than my IC-970H, that I sold my 970
and
bought a IC-275H to replace it. The 275H has a front end, unlike the
706MkIIG,
so it worked much better during a 2 meter VHF contest.
Assuming you want a small DC-light rig for mobile, what do you choose for a
base
station? For me bigger is better. I prefer a 781 over a Pro III over a
706
simply due to size. Am I completely happy with any top-of-the-line rig on
the
market today? No, and that includes the IC-7800. Modern DSP rigs appear to
be
designed by computer geeks who don't operate radios. The Orion II, IC-7000,
IC-7800 and FTDX-9000 (and likely the FT-2000) all behave poorly with
transient
noise. The AGCs of these radios drastically overreact to ticks, clicks and
pops.
Listen to an IC-7000 in QRN, especially on CW, and tell me what is wrong.
Why
does one hear 5 kHz audio coming out the speaker during a static crash when
the
CW bandwidth is set to 500 Hz? There are lots of issues that don't get
covered
during lab testing and reported in a table. What we can discern in a table
is
general performance issues. What is the AGC threshold with the preamp off?
Do
I really want to be riding the volume control if the signal drops below 5
uV,
like with the 7800? Is the 2 kHz dynamic range over 80 or under 65 dB?
This
is a really big deal, and something I have been harping on since 1977! It
took
the League almost 30 years to start publishing close-in dynamic range. You
need
more close-in dynamic range on CW than on SSB since transmitted splatter is
an
important limit on SSB. Are you going to notice a 4 dB difference in 2 kHz
dynamic range between two radios? Likely not, but you will notice a 10 to
15
dB difference, especially on CW. Do you need a dynamic range better than 85
dB?
Probably not in the USA, but maybe in Europe on 40 meters due to broadcast
stations.
Bottom line, look at the numbers, and then consider the other issues. Is
the
audio clean? Most of the FT-1000X radios I have used sound too harsh on
SSB,
and give me a headache. Can you easily operate the knobs, or are they too
small? Do you want a sensitive band scope to find weak signals on the high
bands when conditions are poor? How about reliability? Some new models
have
had a failure rate that are totally unacceptable. Can you flash the
firmware,
and is the firmware getting better or just changing in a never-ending cycle
of
experimentation with computer code? What does the radio sound like in QRN?
The
bottom line is you should really enjoy operating the radio, or get rid of
it!
73,
Rob Sherwood
NC0B
>From: John Geiger <johngeig at yahoo.com>
>Reply-To: ICOM Reflector <icom at mailman.qth.net>
>To: ICOM Reflector <icom at mailman.qth.net>
>Subject: Re: [ICOM] Sherwood Engineering test numbers
>Date: Mon, 16 Oct 2006 08:27:00 -0700 (PDT)
>
>Hi Tim,
>
>Given that this is true, how can one tell whether
>something has a good receiver or not, other than by
>using it? It seems that the numbers are very limited,
>then. And many of us can't afford to be the guinea
>pig for new radios that come out.
>
>73s John W5TD
>
>--- Tim Duffy K3LR <k3lr at k3lr.com> wrote:
>
> > Hi John:
> >
> > That is why I said "lots of strong signals on the
> > band".
> >
> > I have worked with Rob Sherwood for over 30 years.
> > His tests are the best.
> >
> > The way all of the receiver tests are performed,
> > does not give you a
> > look into "real world" situations. Using two tones
> > gives you a standard and
> > some guidance on which to compare, but you have to
> > look further in to see the
> > real world story.
> >
> > On the air means LOTS of strong signals. That is
> > MUCH different than the lab.
> >
> > 73!
> > Tim K3LR
> >
> > John Geiger wrote:
> >
> > > Hi Tim,
> > >
> > > Yes, I have heard others say that also. But that
> > > still doesn't get down to my original question-how
> > did
> > > it score so well on the IMD DR Sherwood test??
> > Better
> > > than many radios considered contest radios.
> > >
> > > 73s John W5TD
> > >
> > > --- Tim Duffy K3LR <k3lr at k3lr.com> wrote:
> > >
> > > > John:
> > > >
> > > > My 706 is a much better radio when using
> > antennas
> > > > that are somewhat inefficient
> > > > such as mobile and portable antennas.
> > > > If I hook my 706 up to a beam or a full-size
> > dipole,
> > > > the attenuators do a
> > > > wonderful job of protecting the front end and
> > making
> > > > the radio usable.
> > > >
> > > > Remember that the IC706 series receiver was
> > never
> > > > intended to compete along side
> > > > radios that cost far more and perform much
> > better
> > > > with lots of strong signals on
> > > > the band.
> > > >
> > > > 73!
> > > > Tim K3LR
> > > >
> > > > John Luthy wrote:
> > > >
> > > > > John,
> > > > >
> > > > > First I am NOT any kind of expert,
> > > > >
> > > > > But I have noticed that my 706MkIIg is almost
> > hard
> > > > to listen to,
> > > > > mostly because it hears everything, so I
> > wonder if
> > > > it is fed a small
> > > > > signal in a lab it might look like a very good
> > > > reciver,
> > > > > So I wonder if I would be happier with my 706
> > if
> > > > I had a differnt
> > > > > filters in it.
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "John Geiger" <johngeig at yahoo.com>
> > > > > To: <cq-contest at contesting.com>;
> > > > <yaesu at mailman.qth.net>;
> > > > > <icom at mailman.qth.net>;
> > <yaesu at contesting.com>;
> > > > > <dx-list at yahoogroups.com>
> > > > > Sent: Sunday, October 15, 2006 1:58 PM
> > > > > Subject: [ICOM] Sherwood Engineering test
> > numbers
> > > > >
> > > > > > How much stock does everyone place in the
> > > > Sherwood
> > > > > > Engineering receiver test numbers
> > > > (www.sherweng.com)?
> > > > > > While I admit that the 2khz spacing is a
> > much
> > > > more
> > > > > > useful measurement than the 20khz the ARRL
> > has
> > > > used
> > > > > > for a long time, and I believe that Rob
> > Sherwood
> > > > knows
> > > > > > what he is talking about when he tests
> > > > receivers, I
> > > > > > have a hard time believing some of his
> > numbers.
> > > > > >
> > > > > > For example, he measures the 2khz IMD DR for
> > the
> > > > Icom
> > > > > > 706MKIIG at 74db. This places it right in
> > line
> > > > with
> > > > > > the PROII and PROIII at 75db, and better
> > than
> > > > the
> > > > > > 756PRO (71db), FT1000D (69db), FT1000mp MK V
> > > > (69db),
> > > > > > and the Icom 746 (70db). Now I have owned
> > many
> > > > of
> > > > > > these radios, and I did not find the
> > 706MKIIG to
> > > > have
> > > > > > that good of a receiver, definitely not
> > better
> > > > than
> > > > > > the 756PRO or the Yaesu FT1000 series. It
> > > > overloaded
> > > > > > pretty bad under contest conditions. What
> > am I
> > > > > > missing in his measurements, that makes the
> > > > 706MKIIG
> > > > > > look so much better than these other radios?
> > > > > >
> > > > > > 73s John W5TD
> > > > > >
> > > > > >
> > > >
> > __________________________________________________
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