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K7DYY AM TRANSMITTER REVIEW SOLICITED




 
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W1KSZ
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« on: August 09, 2017, 10:26:11 PM »

In thinking about running QRO on AM, I just got the September issue of QST.
The article on the K7DYY Super Senior AM Transmitter has me intrigued.

Looking for comments, Pro and Con from present and former users.

Anyone ?

Tnx es 73, Dick, W1KSZ
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w1vtp
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« Reply #1 on: August 10, 2017, 01:07:53 PM »

I have several friends who own the "DYY" transmitter (as we call it here).  Some have absolutely no troubles while others have had to send their transmitter back for repair.

I understand that service is excellent.

Now. There are some points that need to be observed.  At no time should the peak power exceed 1,500 watts.  The myth of a 375 watt carrier should be discarded.  Know your peak power and adjust the carrier power downward accordingly.  High VSWR makes operating the "DYY" transmitter unpredictable depending where the transmitter is electrically positioned on the feed line.

So, keep your VSWR under control. If necessary use a tuner.  Start your carrier setting off at 200 watts and adjust the power upward until your voice peaks are just shy of 1,500 watts PEP.

Finally, consider the use of a phase rotator that should keep the positive peaks closer to 100%.

I heartily recommend Steve, WA1QIX's modulation monitor along with a good power meter - even a good scope and if necessary learn how to use them.  You should have a rewarding QRO experience.

GL es 73. Al W1VTP
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W1KSZ
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« Reply #2 on: August 10, 2017, 03:15:32 PM »

Phase Rotator ??

New one to me.

Thanks for the reply,

73, Dick, W1KSZ
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N1BCG
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« Reply #3 on: August 10, 2017, 04:11:52 PM »

The 1500W PEP number is important for any amateur AM transmitter. You can reach that legal limit in a number of ways as a function of power *and* modulation:

375W @ +100% = 1500W PEP

296W @ +125% = 1500W PEP

240W @ +150% = 1500W PEP

167W @ +200% = 1500W PEP

A phase rotator, aka all-pass filter, adds a gradually increasing positive phase shift to your audio starting at 0 degrees and increasing through 45, 90, 135, 180, etc as the frequency rises.

There are two key benefits for using such a circuit to reduce asymmetry in voice:

1) Increased loudness by reducing peak to average ratio thus reducing compression recovery time.

2) Lower distortion through reduced clipping in the processor and receiver detectors.

Peaks are fun to watch on a meter, but because they are of short duration (they're peaks, after all) they contribute little to perceived loudness. Also, mod iron is expensive to replace when insulation gets damaged by voltage spikes.

All broadcast processors built in the last 40 years use the technology. Here's some info about an early phase rotator for AM stations:

http://www.theonlineengineer.org/TheOLEBLOG/symmetra-peak/
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W1KSZ
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« Reply #4 on: August 10, 2017, 04:43:55 PM »

OK, so where does one find such a thing and where does it go in the XMTR chain ?

Google comes up with a lot of talk but little substance.

Tnx, Dick, W1KSZ

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N1BCG
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« Reply #5 on: August 10, 2017, 04:54:01 PM »

In order to be most effective, phase rotators need to preceed any dynamic processing (compressors, limiters). I picked up a complete board a couple of years ago for under $20, including shipping, but unfortunately I haven't seen similar deals recently.

The good news is that they can be made fairly easily using common components, but having one ready made is fantastic.


* PhaseRotator.JPG (38.53 KB, 400x300 - viewed 45 times.)
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VE3ELQ
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« Reply #6 on: August 10, 2017, 06:03:35 PM »

There is some more good info on phase rotators here:   http://www.w3am.com/8poleapf.html

73s  Nigel
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W1KSZ
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« Reply #7 on: August 10, 2017, 06:58:50 PM »

While doing some Searching and Re-Searching, I found that K7DYY offers a Pre-Amp for the D-104
that includes a Phase Rotator.

That seems like the path to take.

Thanks for the replies,

73, Dick, W1KSZ
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K6IC
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« Reply #8 on: August 10, 2017, 09:26:41 PM »

Hello Dick,

Have run the K7DYY Super Senior for just over five years.

Have been happy with it.
Have discovered several things about this transmitter ...   mine,  at least;

Am not able to modulate at 100% negative with the Carrier level set at 375 watts,  regardless of the wiring of the microphone (minimizing asymmetry effects).   Generally have needed to set the carrier level lower,  to approach 100 % negative.   This is generally at about 300 W carrier.

Have noticed,   that the maximum amount of carrier output really depends upon the ambient temperature of the shack.  When the shack was COLD,  could only make about 200 W of carrier.   COLD was about 38 degrees F ...   yea,  HEAT the shack.

DYY Bruce is very responsive in making revs to earlier transmitters,   to incorporate design changes that he has developed,   over time, for earlier transmitters.

Believe Bruce has improved these transmitters since introduction.

Bruce seems to be a very good Engineer,   and makes a good product,  that he stands behind.

I have not yet asked him to make any revs to the transmitter here.

If the choice was weather to buy a new Super Senior today,   I would do so again.

FWIW,   73,  Good Luck,   Vic
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w1vtp
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« Reply #9 on: August 11, 2017, 08:16:36 AM »

While doing some Searching and Re-Searching, I found that K7DYY offers a Pre-Amp for the D-104
that includes a Phase Rotator.

That seems like the path to take.

Thanks for the replies,

73, Dick, W1KSZ

Last time I knew, the K7DYY board which goes under the G stand of a D104 has issues with the gate design where there is an artificial sound that occurs when the audio level (the speaker) overcomes the fan noise of the DYY rig which the downward expander switches from the downward expanded mode to the "normal" mode.  There are better ways but if you're stuck on using a D104 - which is an excellent mic when it is operating properly.  Then maybe that K7DYY board is the solution for you. One more thing. Janis AB2RA has some insightful info on mics that work well with the K7DYY processor board.

I'd consider a line level approach with appropriate equipment including compressor limiters, EQ's and of course phase limiters.  The K7DYY approach is simple and perhaps effective - check with Janis AB2RA who has done some work with this board on her own ( see this link:  http://wireless-girl.com/Projects/AMTransmitters/K7DYYaudioboard.html )

GL, Al
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W1KSZ
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« Reply #10 on: August 11, 2017, 10:15:22 AM »

The newer (Mark II) boards have a jumper that can be installed to disable the Noise Gate function.

I am not stuck on the D-104 mike, it's just that I have three of them. One on the Collins S-Line, a
second on a G-50 and a spare.
But, I am open to recommendations concerning other microphones.

What do other folks use on their Super Seniors ?

73, Dick, W1KSZ
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W6TOM
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« Reply #11 on: August 11, 2017, 11:03:42 AM »

  I bought the 80/40 Super Senior last year from a guy in TX who had only used it a few times and with the uninstalled audio board. My transmitter was originally purchased in 2015.

  The audio board was installed in a D-104 I had on hand, clearance is very tight between the audio board and the bottom cover of the D-104, I made a small bracket to off set the audio board lower in the D-104 base.

   I had lots of issues with the transmitter tripping due to over modulation, it took me quite a awhile to get the audio gain set where that doesn't occur and I still need to be careful not to shout into the mic. I've had one over modulation trip since I got the audio board adjusted.

   It is VERY sensitive to the antenna match, I need to use an antenna tuner or you will get a SWR trip off.

   The modulation level and carrier power level interact with temperature, I had the carrier set to 300 watts but my shack is in the garage. So with the carrier level set at 300 watts but my garage can vary from the high 40's in Winter to 90 in the Summer. The carrier level drifts up with temperature, it can change 50 watts. Now I have it set at 250 watts of carrier and the trip issue seems to be OK if I make sure I have a good match and am careful not to shout into the mic. The over modulation trip and SWR trip issues seem to interact as the carrier increases with temperature.

   I get good audio reports, I am not a high fidelity audio guy, my background was Utility Radio Systems, good communications audio, so the audio chain is the D-104 and K7DYY audio board.

   I'm happy with the Super Senior and my only suggestion would be to improve the carrier level settings so they aren't as temperature sensitive. For you guys who have a shack that has a more constant temperature these issues may not be as noticeable.


* Clearance.JPG (278.73 KB, 1024x768 - viewed 27 times.)

* Audio Board Wiring.JPG (119.08 KB, 964x768 - viewed 30 times.)
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N1BCG
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« Reply #12 on: August 11, 2017, 11:03:52 AM »

Most commercially made amateur transmitters have very limited frequency response and that greatly limits the benefits of using a microphone with a broad and flat frequency response.

Conversely, the Super Senior falls solidly into the "high fidelity" category of transmitters, so the selection of microphone will make an enormous difference in how the operator will sound. Fortunately, microphones that compliment that sound don't need to be high end studio models, although many AMers have found deals on those mics and put them to use.

You could visit a music store or browse the internet and find decent recording microphones in the <$50 range. As an experiment, I once tried a tiny electret element from a mobile phone headset and was surprised by the frequency response (although the lack of a proper enclosure was noticable).

The bottom line is that you will surely receive compliments on your clear, natural sound when using the DYY transmitter as long as it's fed with equally good audio.
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W1KSZ
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« Reply #13 on: August 11, 2017, 11:40:32 AM »

In rummaging through the Mike Box, I found a Kenwood M-60. I can use it and the D-104 and see which sounds better.

73, Dick, W1KSZ
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W1DAN
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« Reply #14 on: August 11, 2017, 05:56:13 PM »

Dick:

Here are my thoughts as I help Peter W1ZZZ with his Super Senior (I also own an older Senior).

Peter's early unit had some failures which Bruce resolved. Every repair has been done by Bruce for free and with a quick turn-around. You cannot get better service than that. I know Bruce is working very hard to keep his customers happy.

There are three very minor issues in my mind:

1. Fan noise. If your mic is within a couple of feet from the transmitter, fan noise will be picked up over the air. Not a big deal.

2. At W1ZZZ we set the carrier at about 240 Watts. This allows for about 125% positive modulation from broadcast processing, which the transmitter passes very faithfully. More carrier power just limits the available positive audio envelope.

3. SWR. The unit likes a good antenna match. If there is SWR (something like above 1.5:1-can't remember), the transmitter will safety-trip. Dialing in a tuner can be difficult as the amplifier output changes as you pass through a match.

In all, the transmitter does quite well and sounds very clean and natural. It is small and light. Since the last repair it has been very reliable with no issues at all, so I feel Bruce has found the bugs. He also backs his product up more than most anyone else.

73,
Dan
W1DAN
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W1KSZ
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« Reply #15 on: August 11, 2017, 07:27:44 PM »

Looks like I better do a scan on my Antenna and see what the VSWR looks like.

It's an OCF Dipole, apex at around 35' (for local Q's) and the ends slope down to
about 6' of the ground. Works well with the local crowd.

I tried an NVIS Antenna but it didn't work anywhere near as well as the OCF.

On the other side of the house is the DX setup.

73, Dick, W1KSZ
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ka1tdq
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« Reply #16 on: August 11, 2017, 07:45:44 PM »

Dick,

Your antenna is almost identical to mine; 35' apex with the ends sloping to just a few feet above ground.  I've worked the east coast numerous times on 75 meters from Arizona.  Just wanted to chime in...

Also, I've heard a couple QSO's out this way from guys running the Super Senior.  The audio sounds totally fine to me!  

Jon
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W1KSZ
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« Reply #17 on: August 12, 2017, 12:16:52 PM »

Are you using a Super Senior with the OCF Dipole ? What's your VSWR like on 80 & 40 ?

73, Dick, W1KSZ
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ka1tdq
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« Reply #18 on: August 12, 2017, 01:49:14 PM »

Actually, no. I'm using a home brew class E rig at 400 watts carrier.  My antenna is similar in arrangement (apex at the same height and slopes to the ground), but it's a resonant center fed dipole.  Not "completely" resonant... it's like 1.3:1, but who's counting?

Anyway, I've had QSO's with Tim in Maine and Steve in Massachusetts a couple times with the antenna.  Tim actually reported that I was louder than the other guy he was talking to in Idaho (or, one of those states... I forget which one).

Jon

PS> I'm in Vegas right now typing this out on my phone. I'm doing the old man thing. I'm sitting down waiting for my wife.


* IMG_1856.JPG (2934.11 KB, 4032x3024 - viewed 49 times.)
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K6JEK
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RF in the shack


« Reply #19 on: August 13, 2017, 12:41:37 PM »

In order to be most effective, phase rotators need to precede any dynamic processing (compressors, limiters).
...
Got my attention on this old thread. I use a Symetrix 528e ahead of my WA1QIX design Class E. I checked the block diagram just now. It has a "symmetry correction circuit" in the output section, that is after everything else, not before. I wonder why.

I haven't been using it. My voice is very asymmetric. I have the phase set for more positive.  I infer from this discussion and the links, I might be better off, louder, smarter, more clever, and funnier if I pushed that button and reduced the asymmetry. Correct?

PS: Here's what's wrong with Super Seniors. They end your AM radio experimentation. Seems like everyone I talk to who has one stopped building or buying anything new after that. They all sound great, of course, but the hobby, folks, the hobby.

PS2: (I should talk. I built that class E over a dozen years ago. I've built several transmitters since. On AM I only use the class E)
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N1BCG
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« Reply #20 on: August 13, 2017, 01:02:11 PM »

I use a Symetrix 528e ahead of my WA1QIX design Class E. I checked the block diagram just now. It has a "symmetry correction circuit" in the output section, that is after everything else, not before. I wonder why.

Using a 528E opens up a whole separate can of worms. It's designed as a studio processor where the EQ is after the compression stage compared to a transmission processor where the audio limiting circuitry is the last stage before the transmitter.

I believe you can reverse the order with external jumpers (or maybe you have). The problem using it as-is occurs when the EQ defeats the limiting action of the compressor as audio frequency changes. For example, using 1 kHz as a reference for 100% modulation, boosting highs for clarity will result in overmodulation since the EQ will take the levels from the compressor and add gain. Same for lows if they're boosted.

The only purpose for an EQ after limiting is for bandwidth limiting where it is used to attenuate frequencies.

The 528 series is an extremely popular processor yet this important caveat is not well publicized. Following it with a wideband limiter solves the issue though.
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K6JEK
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« Reply #21 on: August 13, 2017, 04:57:08 PM »

I use a Symetrix 528e ahead of my WA1QIX design Class E. I checked the block diagram just now. It has a "symmetry correction circuit" in the output section, that is after everything else, not before. I wonder why.

Using a 528E opens up a whole separate can of worms. It's designed as a studio processor where the EQ is after the compression stage compared to a transmission processor where the audio limiting circuitry is the last stage before the transmitter.

I believe you can reverse the order with external jumpers (or maybe you have).
...

You can and I have. Music stores sell these great little jumpers just perfect for the situation. I got mine at The Starving Musician.
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WD5JKO
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WD5JKO


« Reply #22 on: August 17, 2017, 09:25:16 PM »

I just got the Sept. issue of QST. Looking at k7dyy article, figure 3 says it is a 2 tone plot. Sure looks like a single 700 hz tone to me, with the 2nd harmonic down only about -24 db. That would be around 5% distortion at 100% modulation.

Jim
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W3RSW
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Rick & "Roosevelt"


« Reply #23 on: August 19, 2017, 01:17:41 PM »

Interestingly, if you take out the single 0 dB spike, fc,  in the middle, both side tones are 6dB down as expected and third IM is down about 33dB, 5 th is about 43 dB down, etc.

And the abscissa is marked off in IM subtractive and additive freq's from "fc" as is expected.

All except the 0dB center spike which is usually phantom is indicative of a two tone IMD plot.

And where did you get fc defined as 700 HZ for your purported single tone?   Is that the center freq. delta of upper and lower tones of ARRL's two tone generator?
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WD5JKO


« Reply #24 on: August 19, 2017, 02:19:59 PM »

All except the 0dB center spike which is usually phantom is indicative of a two tone IMD plot.

And where did you get fc defined as 700 HZ for your purported single tone?   Is that the center freq. delta of upper and lower tones of ARRL's two tone generator?


  That fc is the carrier. With AM, two tones, each tone if equal amplitude will be 12db down from fc (frequency domain) when the modulation envelope of the complex tone hits the baseline (time domain), and 2X the carrier level. Also with two tone test on AM, that means two equal amplitude blips either side of Fc.

   The figure 3 plot only shows one tone each side of the carrier (at 6db below Fc or 100% modulation), and then the even and odd harmonics declining in amplitude each side of Fc. Trying to measure the 7oohz when the scale is 2Kh/div is subjective, but then the third harmonic is just above (right side USB) the 2 Khz line, and just below (left side, LSB). Therefore I conclude they are using 700hz, single tone, at 100% modulation. The 2nd harmonic distortion is around 5-6%.

   I post a two tone test I did with AM here, at reply 14:

http://amfone.net/Amforum/index.php?topic=42220.msg306536#msg306536

   It appears to me that the lab guys at ARRL never did a two tone test with AM before, so they ended up dropping the higher tone, and then fudging it.  Tongue

    Added a image from the link I referenced above, and the DYY Fig 3 mentioned. Then added a scope plot during a 2 tone 700/1900hz test. It is difficult on many scopes to get a stable trigger.

Jim
Wd5JKO

 


* 20A_10W_AM_2_Tone_100_Percent_Mod.jpg (60.34 KB, 906x649 - viewed 15 times.)

* DYY.jpg (37.25 KB, 715x436 - viewed 17 times.)

* AM_2_Tone.JPG (1214.48 KB, 2048x1536 - viewed 9 times.)
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