PTT Implementation

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PTT Implementation

Postby Bronek M0DAF » Mon Aug 15, 2011 1:36 am

I am building a PWM modulator (using Steve’s kits) and am in the process of designing the PTT circuitry. I have seen KD3CN’s electromechanical implementation, but am working on an electronic sequencer. Can anyone help me on two points?

In Steve’s design the mains to the HT supply is switched with PTT to prevent voltage spikes when the PWM pulse train is initiated. Has anyone tried keeping the HT on, but ramping up the carrier from zero to full in, say, 0.5 s. That would avoid a voltage spike and is easy to do electronically.

I notice that KD3CN switches the supply to the IXDD414s in the RF deck. Is that necessary?

Better still, has anyone built an electronic sequencer for this transmitter?

Thank you

Bronek M0DAF
Posts: 8
Joined: Sun Sep 04, 2005 3:08 am
Location: York, England

Re: PTT Implementation

Postby W3FJJ » Mon Aug 15, 2011 7:31 am

Hi Bronek, I'm also in process of getting PWM rig going, using QIX boards and am interested in the Keying sequence.
I'm not sure If I'm right, so some one please correct me.

I am planning on having power supply Caps charged full all the time and
and use a relay controlled by the Efficiency Board to switch it to the modulator. I plan on switching Antenna first, 20 ms later switch VFO drive to RF AMP
then 20ms later switch efficiency board, which should turn on drive to modulator and switch VCC to modulator/RF... Switch in the opposite order, when I un-key.
Again I like to hear from some one if this is not a good before I blow thing up :)

I built this sequencer circuit, which works FB, you can buy a kit from the site, but I already had all the parts in my junk box...

73 Chuck-W3FJJ
Posts: 9
Joined: Fri Aug 05, 2011 7:15 am

Re: PTT Implementation

Postby Gilly » Mon Aug 15, 2011 9:25 am

Hi Chuck & Bronek

Yes Chuck ... my sequence of PTT is about the same as yours but I do not use the protective circuit board.....
I know I should but .....well have only had one disaster so far and just hope thats it.....really... :mrgreen:
Your power levels are far greater than here in Australia....
I also Mute early in the order as well.....

The circuit I use Bruce KF1Z sent me...its similar to this and quite simple really.... ... r_orig.gif

Have built 4 and all works problems at all...

The main thing is the antenna first and very last the HV to the Modulator / TX ....
Maybe Bruce could resend his circuit again.....

This is a photo of mine etc:


You may have to right click on the image and go view...

Thats about it .... its late here ... will go over it again in the morning...


Class E Enthusiast
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Joined: Tue May 15, 2007 6:59 pm
Location: Mt.Eliza Victoria Australia

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