THIS IS A LONG EMAIL. DELETE NOW IF YOU ARE NOT INTERESTED IN THE TRUTH...
Of course "noisy transmitters" is one of my hottest hot buttons.
Every time I bring up the topic, it usually morphs into blaming it on the
Lids.
So this time I will put some meat behind my claim and invite all of you to
read what one of the industry's top experts, Wayne Burdick, N6KR, co-found
and chief technical architect for Elecraft, has to say about noise and other
radios:
-------------------------------------------------------------------
Regarding K3 close-in phase noise vs. the Kenwood TS-590 and Flex radios
By Wayne Burdick, N6KR
Phase noise was recently discussed on the K3 Yahoo group, and I
thought I'd add my two cents. Or maybe three :)
The K3's phase noise at 1 kHz is pretty much state-of-the-art for a
DDS (direct digital synthesis) reference driving a wide-frequency-
range, low-noise PLL (phase locked loop). We took things a step
further by using a very narrow crystal filter after the DDS (about 2.5
kHz), dramatically cleaning up the DDS even before application to the
PLL. This forced us to use some pretty hairy math in calculating the
PLL divider values, but it was worth the effort.
The TS590 (and all currently shipping Flex radios) use a synth
subsystem that is quite different from the K3's. They use an
unfiltered DDS as their local oscillator, with no following PLL.
There are some advantages to this design choice. First, and maybe the
most relevant: it's cheaper than a DDS-driven-PLL overall, requiring
very few analog parts, essentially no alignment, and far less PCB
space. Second, such radios might have slightly lower phase noise at
some very close offset--although at such spacings, other factors such
as keying bandwidth or IMD typically dominate. Finally, use of a raw
DDS allows the VFO to switch frequencies rapidly. Such agility might
be useful for some digital modulation schemes.
However, that raw DDS VFO comes with a price: its output has many
discrete spurs that can, at specific VFO frequencies, cause "ghost"
signals to appear. This is due to mixing between the DDS spurs and
strong signals appearing anywhere inside the receiver's band-pass
filter (many MHz in most receivers, but not the K3--more on that
later). This is true even with the 14-bit DDS word size described in
the TS590's sales brochure.
The usual way to eliminate these wide-band spurs is to use a PLL to
clean up the DDS's output. Ironically, that sales brochure I mentioned
implies that eliminating the PLL was an advantage. Maybe they were
thinking about reduced manufacturing cost, though this wasn't stated
explicitly.
(BTW, a typical lab receive mixing test done at just one test
frequency will not necessarily show this characteristic. To reveal the
DDS spurs, you'd need to do such a test at many frequencies, moving
the VFO in very small increments. This is because the spurs are the
product of multiple digital sampling phenomena; they vary rapidly in
frequency and amplitude as the DDS's control word is changed. The lack
of such testing and transparency in the industry could explain why
mixing spurs are *not* a hot topic of conversation among those
considering a radio using a raw DDS VFO. Yet, like real ghosts, the
resulting signals could, nonetheless, sneak up on you :)
It is certainly a lot more expensive to add a high-performance PLL
into the system--just ask my engineering and manufacturing staff. But
I guess it depends on what you're trying to optimize. We wanted the K3
to perform extremely well in crowded band conditions, so we went to
the trouble to use a DDS-driven-PLL synth. (Or TWO of these synths if
you have the KRX3 sub receiver installed.) Flex may have elected to go
with raw DDS because of the need for a very agile VFO for SDR
applications. Kenwood may have been trying to keep costs low. Both are
certainly worthy goals.
Actually, we made it even harder on ourselves with the K3. We provide
narrow band-pass filters on every ham band, painstakingly aligned at
the factory, ensuring that as little out-of-band energy as possible is
presented to the mixer in the first place. This makes the synth's job
a little easier. Yet nearly all other transceivers these days use
"half-octave" band-pass filters that are many times the width of the
ham-band segment. They require no alignment, but they open the radio
up to more interfering signals. (You can add general-coverage band-
pass filters to the K3's main and/or sub receivers, of course, by
adding KBPF3 module. This has no effect on the ham-band performance.)
Note that like the K3, the KX3 uses a DDS-driven PLL synth. The K3 has
an advantage in temperature stability since it uses a separate
reference oscillator, but the KX3's phase noise is in the same very
low range, as evidenced by Sherwood's numbers.
Many other factors besides synth phase noise--including transmit
signal purity and receiver AGC behavior--also contribute to
performance in crowded conditions. This is why, some time ago, we
undertook a major redesign of the K3's AGC subsystem. This resulted in
excellent field reports from DXpeditions, etc., regarding the dynamics
of within-filter signals.
I won't go deeply into the SSB transmit purity issue, which has been
adequately described by others. But I will mention that the K3's TX
IMD at max power output is as good as or better than that of any other
12-volt-capable transmitter. And if you run at lower power when
driving an amp (typically 20-70 W), the IMD numbers are outstanding by
any measure.
73,
Wayne
N6KR
--------------------------------------------------------------
DON'T THINK THE PROBLEM IS LIMITED TO FLEX AND KENWOOD.
Icom and Yaesu are generally just as bad, unless you purchase their high end
radios!
Next time you recommend someone buy a JA radio, first make sure the he lives
far enough away from you that he won't pollute your airwaves.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Bob McGraw
- K4TAX
Sent: Sunday, July 06, 2014 2:30 PM
To: Discussion of Ten-Tec Equipment
Subject: [TenTec] On Noisy Transmitters
Rick brings up a very good point on transmitter noise. It is something most
users won't likely realize is something that does truly exist.
I find, with several I've measured, do produce wide band noise that is
transmitted across the spectrum. Basically it is polluting our bands with
noise, somewhat like one throwing trash out along the highway or leaving it
in the city park.
I for one am glad to see RSGB does measure and report this. I wish ARRL
would do the same. Of course it might affect their advertising revenue to
report a certain brand and model radio is a broadband noise generator.
I've just finished a weekend operation at Field Day. Using the Eagle I
found there was no noise generated when it went into transmit. {I already
knew this as I had measured it on the bench, which is one reason I elected
to use the radio.} To that end, I know, I had my spectrum analyzer sitting
on the table. As to other radios operating at the Field Day sight, well I
could see the noise floor rise when they transmitted. Some worse than
others.
Many of the radio companies are "self certifying" thus indicated their
product meets FCC specifications regarding purity of transmission. The
question is "do they really meet the specification or just say they do?".
I strongly suspect if many of these brands and models were evaluated by an
independent testing lab, they would not meet the requirements an thus would
not be legal to be sold or used in the US or other countries for that
matter.
Be a good citizen, "Give a hoot and don't pollute".
73
Bob, K4TAX
----- Original Message -----
From: "Rick - DJ0IP / NJ0IP" <Rick@DJ0IP.de>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Sunday, July 06, 2014 6:37 AM
Subject: Re: [TenTec] TT Mega Sale
> Actually the FTdx3000 has a noisy transmitter.
> You wouldn't know it by reading the ARRL review, but RSGB's Radcom
> reported
> that for it and the FTdx1200.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Richard
> Tschur
> Sent: Sunday, July 06, 2014 12:39 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] TT Mega Sale
>
>
> Bry,
> I just bought a second hand Eagle for pretty much the same price as they
> sell a new one now, well it is a little annoying, but I got the best radio
> I
> have ever had and have! So I don't worry too much about that fact. I have
> now 16 Ten Tec's and I love them all and they all stay here, means they
> are
> all keeper's! What I don't understand is, why do you wish you would have
> bought an FTDX 3000??? For me, any Jap radio is Chicken Soup, a Ten Tec is
> Eye Fillet! I would not want one for free.
> I'm just listening to my Eagle in the background and it sounds sooo sweet
> and quiet, RF gain down a fair bit, very much like FM with squelch. Just
> beautiful. I will never buy another Jap radio whatsoever.
> And in regards to the mega sale, I'm sure TT knows what they are doing and
> I'm also very sure, that this is not the end for TT! Guy's, be happy, we
> get
> a nice discount on the best radio's on the market! I just wish they would
> be
> a lot more popular here in VK. They love their "Chicken Soup" ;-))!
> 73's
> Richard VK3KVK
>
>
>
> On 04/07/14 11:31, Brian Carling wrote:
>> Annoying!! I just bought a used Omni VII for the same price they suddenly
> changed to for the new ones. Now I wish I had bought an FTDX3000.
>>
>> Best regards - Bry Carling
>>
>>
>>
>>> On Jul 3, 2014, at 6:53 PM, Toby Pennington <w4cakk@centurylink.net>
> wrote:
>>>
>>>
>>> These rigs are way overpriced anyway and it is good to see some
>>> realistic
> pricing especially of the Omni 7 and the Eagle.
>>>
>>> I do feel for the guys who may be trying to sell these rigs on the used
> market, or those who bought something before the sale began. This kind of
> sale is a FIRST for Ten Tec, and obviously may signify more than just a
> sale, perhaps something new is about to appear, or will come our way by
> the end of this year.
>>>
>>> Toby K4NH
>>>
>>>
>>>
>>>> On 7/3/2014 5:44 PM, Jim Vohland wrote:
>>>> Wow, that sure is a sale. Maybe some of the Ten Tec guru's can explain
> but this sure doesnt make sense from a business perspective to me.
> Knocking
> a grand off the Omni VII. 800 off the eagle and 300 off a Agro. I wish I
> was
> in the market for a new rig. Kinda scary though and makes me wonder about
> the future. Seems like a 'fire' sale. Just sayin.......Shoots the heck out
> of the used market for those trying to sell eagles and omni's.
>>>>
>>>> _______________________________________________
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>>>> TenTec@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/tentec
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>
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