A big, new transmitter hits 160 meters - ready for the winter season!

[steve_qix]

Bob K1KBW finished his long anticipated 24 MOSFET 160 meter RF deck this week!

This RF deck uses the same modulator/power supply as Bob's 24 FET 75 meter deck.

Bob has an amazing signal on 160, and the audio is absolutely silky-smooth.  And of course, Bob has the voice to go with it.

Here's a pic of the RF amplifier.  More pics can be found at http://www.k1kbw.com/160/160rig.htm

[Sam KS2AM]

Looks like you fixed the link:   http://www.k1kbw.com/160/160rig.htm

It looks great.

[W1AEX]

This might be Bob's best effort. The signal looks exceptionally clean on the band and it sounds beautiful. The recording was made on 160 meters as we chatted in the early evening for a few minutes. Bob was doing a little "performance testing" prior to the usual Thursday evening get-together. I think he has it dialed in perfectly for his voice. It's pretty easy on the ears!

Rob W1AEX

[KM1H]

Cant get it to play here

[W1AEX]

Really? It's a standard 128kbps 44.1khz mp3. Try to grab it again and see if it comes down ok. If not, I'll delete and then repost the attachment.

Rob

[Todd, KA1KAQ]

Works fine here, sounds like Bob. He puts a strong signal down this way on 75m.

[K5WLF]

Working fine here...

[K1JJ]

Nice looking rig.  

So you couldn't cornvice Bob to go with digital drive, I see... 

T

[steve_qix]

Nice looking rig.  

So you couldn't cornvice Bob to go with digital drive, I see... 

T

We did talk about it a lot, but since Bob's 75 meter transmitter is the older analog drive design, he was concerned about accidentally putting close to 100 watts into his digital drive board (which only needs a watt or 2) if he switched to 160, and forgot about the driver power level   Bob uses a big rice box as a driver.

I would have gone digital drive anyway, because it works better and is easier to implement.  Every rig in my shack is digital drive except my very old 16 FET 40 meter RF amp.

[flintstone mop]

So BOB,
What makes the nice sound??? I bet you'll say "it's very simple...a D-104 and 20megs on the grid".........RE-27?? Optimod???
It is big audio BOB!! Nice fully modulated stuff

Fred

[K1JJ]

Bob ain't here, man..

[Bill, KD0HG]

Set sumfin up and I'll be there!

[steve_qix]

So BOB,
What makes the nice sound??? I bet you'll say "it's very simple...a D-104 and 20megs on the grid".........RE-27?? Optimod???
It is big audio BOB!! Nice fully modulated stuff

Fred

There are several things that make Bob's signal (and N1GTU Blaine and W1IA Brent and W1VD Jay and WA1SSJ Wayne, and a lot of other guys with similar setups) sound so good:

1) The PWM and class H modulators used in these transmitters are really, really good.  Flat from DC (literally) to about 6 or so kHz.  No phase shift in the low end and no roll off.  It's hard to beat DC coupled and near perfect linearity.  And, those modulators will modulate the transmitters to just about 200% positive with no issues.  All of these rigs also have built-in negative peak limiters (dc coupled).

2) The microphone - most of, if not all of these guys (including me) are using large diaphragm condenser mics.  There just isn't anything quite as good.  I have an RE-20 - it's not as good as my B1 and the RE-20 is a fine mic, but the B1 sounds better.  The low end is superior and it is definitely flatter down there.

3) The EQ curve reduces the "mud" frequencies and brings up the presence rise.

4) In Bob's case, his voice is very good, so it brings out the transmitter's natural audio quality quite well, but even guys with not-so-good voices (like me  ) sound good on Bob's (or similar) setup.

Mostly, though, it's modulation capability combined with linearity and cleanliness, and nothing to mitigate the low end, right down to single cycles per second.  This is end-to-end; mic to RF.  Do this, and the signal can't help but sound great 

[w3jn]

We did talk about it a lot, but since Bob's 75 meter transmitter is the older analog drive design, he was concerned about accidentally putting close to 100 watts into his digital drive board (which only needs a watt or 2) if he switched to 160, and forgot about the driver power level   Bob uses a big rice box as a driver.

I would have gone digital drive anyway, because it works better and is easier to implement.  Every rig in my shack is digital drive except my very old 16 FET 40 meter RF amp.

   Bob consistently builds some of the best looking xmitters around, and his superb workmanship and care in layout is patently obvious in his projects.  With his attention to detail and experience as a machinist, as I recall, there's no reason he couldn't build a kickass VFO for that bad boy and be able to dispense with the ricebox driver for good.  No more reason for transorbs or worrying about fried FETs.

Steve, you have nothing to apologize for voice-quality wise.  Your voice actually brings out the best in these xmitters, enough low-hanging BAness to it but a good amount of mid-range as well.  Bob's voice tends towards the bassy, and when I copy your guys out here in Europe he's harder to hear than you, despite the fact that your carrier levels are roughly equivalent in the high noise level here.

[WA1GFZ]

Nice Job with vertical fins to boot. I would add a little support at the vacuum variable end of the coil. There is a fair amount of weight on the cap seals setting up a lot of stress. Long term or a good bump could break the seal.
Steve, why not convince Bob to spend $100 on a good function generator like an HP3325A or B and go digital.
BUUUT, I am a fan of transformer coupled drive to prevent cascading failures.
many rigs, 1 FET goes leaky and KA-BOOM. High voltage up a gate drive back through the driver substrate diode and on to the driver DC bus.
My 160 meter  rig with transformer coupled square wave drive (with discrete FETs) I once blew a FET off the heat sink and kept on talking. 
All Bob would need to do is add a little board with a pair of IXDD414s driving a push pull pair or 4 11N90s creating a low impedance square wave driver. 

[steve_qix]

Yeah, the cascading failure thing used to be an issue with both analog drive and digital drive.  The way to stop it in the analog drive world is with transzorbs across the gate busses.  With digital drive, transzorbs across the power supply lines of the drivers.  Although, with digital drive I have never had a driver failure of any kind, even when experimenting, and that will sometimes cause a FET failure.  Those 18V transzorbs really do the job!

[WA1GFZ]

If you ever have a drain to gate leakage or short a transorb is just a firecracker.

[steve_qix]

If you ever have a drain to gate leakage or short a transorb is just a firecracker.

I had a few of them [drain to gate shorts] in the early development days, and the transzorbs saved the day every time!  But, the modulator / power supply was also properly designed, and immediately (within a fraction of a millisecond) shut down the output, so there really wasn't a lot of power available to dissipate.  The transzorbs themselves weren't even damaged.

Eventually, I simply migrated to digital drive which eliminated the root of the problem (parasitics caused by varying drive levels).

Without the modulator's overload shutdown circuitry, there could be big problems, because all that energy has to go somewhere, and would most likely blow the transzorb and probably cause damage within the modulator itself.  It's truly amazing the number of people who want to build class E or class D transmitters, and think they can "not include" the overload shutdown circuit!!!  I won't even sell boards or kits to anyone who has this in mind.  Solid state modulators and transmitters work extremely well, but since they can also deliver close to infinite power [for some very small amount of time], it is absolutely necessary to have something that will shut things down quickly in the event of an overload!

[WA1GFZ]

BTW Steve the electronics industry is having big problems with Transorb quality issues. Microsemi used to be the best until guess why.....outsourced off shore.
I once hit 3 15KP transorbs with a 3/4 Megwatt pulse at 85 degrees C and they took 20 shots without failure. Today's parts I don know. We use them by the thousands.

[wb4whj]

Bob K1KBW finished his long anticipated 24 MOSFET 160 meter RF deck this week!

This RF deck uses the same modulator/power supply as Bob's 24 FET 75 meter deck.

Bob has an amazing signal on 160, and the audio is absolutely silky-smooth.  And of course, Bob has the voice to go with it.

Here's a pic of the RF amplifier.  More pics can be found at http://www.k1kbw.com/160/160rig.htm

   Very good looking job!

[flintstone mop]

Hey BOB
Whilst listening to a QSO and watching the waveform on my 'scope, certain bass notes in your voice are triangular. Is this from the Pulse Width modulation characteristic?

[K1JJ]

Whilst listening to a QSO and watching the waveform on my 'scope, certain bass notes in your voice are triangular. Is this from the Pulse Width modulation characteristic?

That's the famous "shark fin" effect resulting from a near perfect low end response, minimal low-end  phase shift AND a voice with three BA's. Having a transmitter this clean gives you the capability of running the audio phase in this polarity. Most transformer-coupled rigs cannot produce this near pristine low-end response, thus run in the opposite phase for max audio at the higher audio freqs.  I see this same effect with my class E rig and 4X1 AM rigs.  They require different polarities for best performance.  But even with my voice I still see shark fins with the class E rig.


BTW, "Bob's not here, man."   He doesn't get on this BB and talks here only through mediums...

T

[W2PFY]

I'll second JJ comment about Bob, he doesn't believe in any BB's.

[flintstone mop]

I'll second JJ comment about Bob, he doesn't believe in any BB's.

My problem on the BB too much and not on the air.....!!!!!!!!!
Talking about Ham radio and not doing it!!!!

[steve_qix]

I'll second JJ comment about Bob, he doesn't believe in any BB's.

My problem on the BB too much and not on the air.....!!!!!!!!!
Talking about Ham radio and not doing it!!!!

YEAH!  So get on 160 so we can have another QSO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1