Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Class D 80 meter rig progressing




 
The AM Forum
August 09, 2020, 01:37:48 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 ... 3 [4]   Go Down
  Print  
Author Topic: Class D 80 meter rig progressing  (Read 13705 times)
0 Members and 1 Guest are viewing this topic.
vk3alk
Member

Offline Offline

Posts: 118


« Reply #75 on: March 05, 2020, 09:33:03 PM »

Hi Pat...

Sound like things are coming along....

Have you decided what materials / cores your going to use for the PWMs LPF ?
Also Cutoff frequency .... load .... etc:
What sampling frequency are you going to use ?



Wayne
Logged
N4LTA
Contributing
Member
*
Offline Offline

Posts: 989


« Reply #76 on: March 09, 2020, 10:17:50 PM »

Have tested the Modulator and completed the filter designed for 15 ohms. I have the power supplies, voltage regulator, metering and the modulator board mounted in a rack mount enclosure.

It has been tested with a PWM signal from a generator that is Nigel's design and seems to be working as designed. I have swept it from 100 Hz to 15 kHz and run for 48 hours.

Next I will run it with a load and see where I am with the filter and power supply. The modulator board is shown in the second image with the filter installed connected to the voltage regulator board.

Pat
N4LTA


* modulator.jpg (101.86 KB, 640x480 - viewed 127 times.)

* mod board.jpg (86.6 KB, 640x480 - viewed 120 times.)

* frontpanel.jpg (89.09 KB, 640x480 - viewed 108 times.)
Logged
vk3alk
Member

Offline Offline

Posts: 118


« Reply #77 on: March 10, 2020, 08:29:02 AM »

Hi Pat....

Yes its coming along.....looks good...
Was your transmitter load 28 ohms or have you changed it now....or did you use 15 ohms because of the amount of turns on the toroids etc:
Just wondering.....
Also what cutoff frequency have you used for the LPF ?
I think your sampling frequency was 150-160Khz......


Wayne
Logged
N4LTA
Contributing
Member
*
Offline Offline

Posts: 989


« Reply #78 on: March 10, 2020, 12:29:54 PM »

Hi Wayne,

I used Jim Tonnes paper to design the filter. Presently the cutoff for the filter is about 9 kHz. The cores are from CWS BYtemark as recommended by Steve and M0VRF and made for this type application. My sampling frequency is about 140kHz  but very easy to change.

I am building a new transmitter double sided board with an onboard 74F74 phase inverter and 3 amp regulated power supply for the drivers and a 5 volt regulator for the 74F74 .

I also have to play with the turns on the output transformer to get the PWM input impedance down and hopefully close to 15 ohms. 15 ohms is about as high as I could get with the cores I have.

I may have to use something else as a core material if I can't get it lower - or maybe better raise the cut toff frequency of the filter.

Pat
N4LTA
Logged
vk3alk
Member

Offline Offline

Posts: 118


« Reply #79 on: March 10, 2020, 05:32:16 PM »

Hi Pat...

Jim Tonnes filter calculator is good and use it often....

9Khz is FAR too low for the cutoff frequency for your PWM LPF....
Steve uses 15Khz and I use even higher at 25Khz...
In the real world there is a lot of ripple at the 3db point going back towards your audio frequencies so I would use 15Khz at the minimum  Smiley .....
I think Steve quoted somewhere that 2.5 times your highest audio frequency is the lowest frequency for the cutoff of your filter....
It saves all those turns on your Toroids as well...

OK on the new TX ...


Wayne
Logged
N4LTA
Contributing
Member
*
Offline Offline

Posts: 989


« Reply #80 on: March 11, 2020, 10:22:10 AM »

I used Jim Tonnes filter design white paper for Class D and E PWM filters. Have you read it?  I just normalized his 1 ohm design to 15 ohms. I just guessed at the cut off from the graph in his paper.


Pat
N4LTA
Logged
M0VRF
Member

Offline Offline

Posts: 103


« Reply #81 on: March 11, 2020, 02:04:01 PM »

You can use a much higher frequency and put a top cap across the last inductor to notch out the clock as that's all the filter is for.

I use a cut off of 45KHz with a -60dB notch at 150KHz.

J.
Logged
vk3alk
Member

Offline Offline

Posts: 118


« Reply #82 on: March 11, 2020, 11:04:29 PM »

Hi Pat...
This part of the Modulator is really interesting and is worthwhile spending time reading up on....etc:...
If you play around with the Tonnes Calculator you will discover how the number of poles / cutoff frequency / loading etc: can have on your transmitter overall....
But bad things can happen without you knowing or realizing etc:
I don't use Motor Controllers for any of my PWM Generators .... for 2 main reasons...
......Sawtooth waveform
......Free running oscillator
My Generators are all Crystal locked divided down and pickoff 250Khz .....there is a reason for that frequency but will leave that for now....
Just say you decided on using Jons LPF with a 45Khz cutoff....and notching out the PWM sideband....
Running 1500 watts PEP all good.....but just say at some temperature your Motor Controller went frequency wobbly..... Shocked won't hurt the motor..
Your only defence is your notch filter now ineffective and relying only on the 40db attentuation of your filter....
Although the chance of this happening is low .... the fact that it can happen is why you design your filters.....

Hope I have not rattled on too much and Jon not saying your filters are a poor design  Smiley

Thats all....


Wayne

Logged
N4LTA
Contributing
Member
*
Offline Offline

Posts: 989


« Reply #83 on: April 11, 2020, 01:00:16 PM »

My project took a turn for the worse. Had a serious fire in my garage and lost nearly everything. All is insured but it sill be a long recovery. Will be out of the house for 4-6 months. No one was hurt so all is OK.

Pat
N4LTA
Logged
K6IC
Contributing
Member
*
Offline Offline

Posts: 736


« Reply #84 on: April 11, 2020, 01:31:47 PM »

WOW,  Pat,   very sorry to hear of this.

Please take care.  Hope that you have a "safe" place to live in the interim.

73  GL,  Vic
Logged
vk3alk
Member

Offline Offline

Posts: 118


« Reply #85 on: April 11, 2020, 07:36:46 PM »

Ohhh I'm very sorry to hear that too Pat.....

We never know whats going to happen...


Wayne
Logged
YB1AHY
Member

Offline Offline

Posts: 27


me


WWW
« Reply #86 on: April 11, 2020, 09:53:49 PM »

I'm sorry to hear this incident, hopefully returning to normal soon

de agus
Logged
N4LTA
Contributing
Member
*
Offline Offline

Posts: 989


« Reply #87 on: April 12, 2020, 04:24:14 PM »

Thanks for all of your thoughts. I had a workroom with a large table and two metal lathes and all my power tools and a newly purchased R388 and DX 60. These were melted with everything destroyed. About 35 Akro Mills cabinets full of new and vintage stuff, a new 3cx1200 and socket, a new 4-1000 and socket and two new 4cx400C tubes as well as probably 500 or so vacuum tubes - all good ones not junk TV tubes as well as  thousands of active and passive components. My semiconductor bins had hundreds of older Mosfets and FETs that are no longer available. The more that I search the worse it seems. I think the parts and items will all be paid for but there is no way to replace.

Again - no one was injured and all will work out. I will get a new shop built as I want and a new electronic lab. I lost a $12000 telescope and $5000 more in other telescope equipment.
I have a roll off roof observatory where most of my telescope equipment was located and it was not damaged. I sold a $6500 TEC refractor a couple of week before and it would have been lost if not sold.

Pat
N4LTA
Logged
Pages: 1 ... 3 [4]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.038 seconds with 18 queries.