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 91 
 on: February 18, 2018, 06:22:07 PM 
Started by WD4DMZ - Last post by KB2WIG


I replace my C69 with a 1600 V , .0022uF Orange drop. 'Cause that's all I had.


klc

 92 
 on: February 18, 2018, 05:39:54 PM 
Started by WD4DMZ - Last post by MikeKE0ZUinkcmo
I'd guess the R2 only has one, across the modulator transformer.   Some of the early R1s had two.  Wouldn't hurt while you're in there.

 93 
 on: February 18, 2018, 05:21:34 PM 
Started by ka1tdq - Last post by ka1tdq
The transmitter is functional again.  The arcing is gone with the gate driver power supply sequenced and the audio is clean in the headphones.  In the picture is the gate waveforms for a little over 300 watts carrier.  This was transmitting into a dummy load, and it's not tuned exactly as it should be, but it's close.

Next is to try the dipole again.  I need to do some work on my tuner before I do that test, but at least it's generating RF again (rather than smoke and fire).

Jon


 94 
 on: February 18, 2018, 04:30:43 PM 
Started by KB1VWC - Last post by W2PFY
Yes sad news indeed! I spoke to him a number of times on 75 & 40 meters and he was alway pleasant and enthusiastic. I like to think that he may be gone from us but that energy that we all have lives on in that other wavelength!

RIP Sid.........

 95 
 on: February 18, 2018, 04:21:29 PM 
Started by KZ4P - Last post by KZ4P
I've found myself operating on AM Phone a lot lately and so starting to look for a vintage set, Apache TX-1, Mohawk RX-1 and an HA-10 Warrior. Can be a set or a set or piece by piece I'm looking to assemble a station. Will pick up within a reasonable distance of Lovettsville,VA. Need to be able to drive there and back in a single day.

Thanks,

Brian. --KZ4P

 96 
 on: February 18, 2018, 03:36:51 PM 
Started by KB1VWC - Last post by KB1VWC
  Some sad news to post. We lost Sid W1TNA on Thursday the 15th after a short bought with cancer. I had no clue he was even sick. Sid had contacted me a couple of weeks ago for a possible ride to the Marlboro Fest on the 17th. I had been taxi service from Cape Cod on a couple of occasions for Sid to Nearfest and other festers.  I basically said that as long as I was going, he was more than welcome to come along. I hadn't heard from Sid by Friday (which was unusual) so I shot him a quick Email. This reply came back from his daughter almost immediately.

"Dear Steve,
I am so sorry to be writing this in an email, this is Jody (Sidís daughter).  My father passed away yesterday. He learned he had metastatic cancer about a month ago. He really wanted to fight it but unfortunately did not tolerate the chemotherapy. We are all heartbroken and will miss him terribly.

Take care,
Jody"

  I'll miss the drives with him. If I ever got a word in edgewise, it was unusual. He told me on more than one occasion, that getting back into AM re-vitalized his Ham radio passion. Can't be a lot of the original W1 calls left. We should all treasure the QSO's.

  Steve Harris



 97 
 on: February 18, 2018, 03:27:37 PM 
Started by Opcom - Last post by WA4WAX
High pass is not a deal breaker, but I do not like "hot rotors".

Are you running into a balanced or unbalanced load?

Matt

 98 
 on: February 18, 2018, 02:02:29 PM 
Started by Opcom - Last post by W1ITT
The first job of an antenna tuner is to match impedances, and sometimes to provide a transition between balanced and unbalanced ports.  Once you have that accomplished, harmonic suppression can be a nice bonus, and that's done with a low pass configuration, obviously. 
I suspect that many tuner designs are driven by the availability of variable capacitors which are common and relatively inexpensive.  But if you have good rotary inductors, or at least fixed coils with a lot of switch taps available, you can go that route.  It just costs more.  There are numerous configurations (or "topologies" as smart people like to call them) that will match two impedances.  For we who don't operate on a generous project budget, we make do with what we can procure.  Most modern commercially available transmitters meet the harmonic requirements all by themselves, so a high-pass "topology" wouldn't be a deal breaker.  Go with what you have or can get for components.  There's more than one way to skin this cat. 

 99 
 on: February 18, 2018, 01:37:41 PM 
Started by ka1tdq - Last post by ka1tdq
I'm using a Heising modulator for this transmitter.  The audio amp is a commercial unit which provides 8 (or 4, I forget) ohms to the Heising circuit. 

Everything is sequenced using a mechanical sequencer.  Timing is dependent upon hand motion.  Ha, ha. It goes IXDD 12 VDC and antenna relay, drain voltage, then modulator cut-in.  It goes in reverse order from TX to RX.

Sequencing is there, but during my testing phase this time, I forgot that I kept the drive on all the time.  That gives the drain power supply ample incentive to draw an arc and keep it going.  I've now put the IXDD power supply in the sequence. 

I'll test everything again later on today when I won't propagate (if I get back from going out in time).  If not, I'll just blast over a QSO.  Just kidding, I won't.

Jon

 100 
 on: February 18, 2018, 12:58:36 PM 
Started by ka1tdq - Last post by steve_qix
*DON'T* cut off the drain drive until AFTER the DC input to the RF amplifier has fallen to zero.

This is a sequencing problem, and it is absolutely necessary to solve it or there will be failures.

So, when going from transmit to receive, the modulator needs to be put into a state where it generates no output first.  The drive stays on.  Then some number of milliseconds after that (maybe 200ms or so - give the modulator plenty of time for the output to fall to 0), stop the drive to the gates of the RF amplifier.

I don't remember (or maybe I didn't ever know) what you are using for a modulator.  If you're using a PWM type of modulator, stop the pulse train.  That will reduce the modulator output to 0V real fast.

If you're using something else such as an analog modulator, you could use a couple of IRFP260Ns in parallel as an electronic switch.  The devices are put into saturation when you're operating, so the loss is negligible, and put into cutoff when you're in receive.

There are different ways to handle it, but the bottom line is - the drive STAYS ON until the DC fed to the RF amplifier is at 0V.

Regards,  Steve

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