[TenTec] On Noisy Transmitters

[Rick - DJ0IP / NJ0IP]

Hi Dave,

First, keep in mind that there are several ways that a transmitter can be
dirty/noisy:

1. Intermodulation distortion, usually stated as dB down on the 3rd order
IMD signal - but that's not the full story.  Some transceivers meet spec on
the 3rd order but their higher order IMD are much stronger than most other
transmitters on the market. This causes in-band pollution due to a very
broad signal. The FT-450D is a good example of this kind of radio.  

2. Close in noise; this would be noise measured a few tens of kHz above or
below the transceiver.  You would notice this at a field day site with
several transmitters where you have two transmitters on the same band, for
instance one in CW and the other in SSB on 40m (a common occurrence).  If
you have a couple hundred feet separation between their antennas and
especially is one is horizontally polarized and the other is vertically
polarized, AND you get strong interference every time you key one, then you
have this problem.

3. Broadband noise; this is when the broadband noise level is so high that
it disturbs radios in the near vicinity receiving on other bands.  This is
the one that is most troublesome for multi-multi contest stations or field
day stations. 

4. Key clicks, caused by too fast of a rise time of the CW signal. These can
be very broad-banded and cause the AGC of other receivers all over the world
to trigger, thus desensitizing their receivers. The Yaesu FT-1000 had this
problem for many years, even though W8JI developed a $3 fix for the problem,
right after the rig came out.  Shows you how much Yaesu cared about fixing
problems.

So you would measure in different ways for each of these.

Of course one good way (which few of us can do) is to measure it with a
spectrum analyzer, as Bob does. You'll have to ask him about using it.  I
haven't used a spectrum analyzer since I worked in the lab for Rhode und
Schwarz, back in the 1970s.

For close-in noise, you will need two transceivers, or one transceiver (the
one being tested) and a second external receiver.  THE KEY HERE IS, the
second RX MUST BE connected to an outdoor antenna.  DANGER!  You can also
blow up its front end this way.  You need antennas that are separated by
about 200 ft. or so.  Then with the radios tuned about 50 kHz apart, TURN
THE MIC GAIN ALL THE WAY DOWN and key the transmitter to be tested in SSB
mode.  Do not speak into the mic.  If it has close in broadband noise, it
will impact the S-meter reading severally on the 2nd radio.

For broadband noise, you set up similar to above but have the radios on
different bands, MAKING SURE TO AVOID EXACT HARMONIC FREQUENCIES!  Then once
again you simply key the mic (SSB mode, with mic gain down).  If it causes
your 2nd RX's S-meter to rise, it has broadband noise.  Many of the cheap JA
rigs will cause a 57 to 59 signal on all other radios, even though they are
tuned to other bands.

Just for kicks, try this with an old analog radio.  It would be very rare
for it to have broadband noise because it has no synthesizer.  Actually it
can't have any, but maybe there is a way that I am unaware of, so I'll just
call it rare.  Once you have done this, you have a stake in the ground for
knowing how a clean radio should behave.

Every now and then we run these tests at one of our multi-multi contest
stations on all the transceivers we can find.  There we have lots of
antennas but generally pretty far apart.  If one of the radios causes noise
to all others, it gets banned from the site.  Most of the low cost Japanese
radios have been banned because they disturb the other 5 bands when they
transmit.

I am uncertain of what level of close-in noise is tolerable in praxis.
However the broadband noise is very easy to detect using the procedure
described above.

The real trouble begins when the poor unsuspecting owner of one of these
noise generators connects an amplifier to it and pollutes all the bands.
THIS IS WHAT HAPPENS WHEN THE "EXPERTS" TESTING RADIOS FAIL TO REPORT THE
WHOLE STORY!
Cheap is cheap in more ways than most people realize.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Dave
Edwards
Sent: Sunday, July 06, 2014 3:01 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] On Noisy Transmitters

Rick....Without a bench of equipment...or a spectrum analyzer....is there a
way I can "notice" phase noise of a noisy transmitter...or compare it to one
that is not noisy in my shack?
I would think there should be some way to see the difference in a very noisy
transmitter..perhaps my Yaesu FT890...vs. something that should not be
noisy...like an old Drake C line..or Kenwood TS520?
I'd just like to sniff around and see what I can see!
....Dave



On 7/6/14, 8:46 AM, Rick - DJ0IP / NJ0IP wrote:
> 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 at 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 at DJ0IP.de>
> To: "'Discussion of Ten-Tec Equipment'" <tentec at 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 at 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 at 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.
>>>>> _______________________________________________
>>>>> TenTec mailing list
>>>>> TenTec at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/tentec
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