Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Better sound from an SDR (such as a Flex) or other TX that uses a balanced modu




 
The AM Forum
June 29, 2017, 12:09:12 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1] 2 3   Go Down
  Print  
Author Topic: Better sound from an SDR (such as a Flex) or other TX that uses a balanced modu  (Read 3121 times)
0 Members and 1 Guest are viewing this topic.
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2271


Bap!


WWW
« on: February 21, 2017, 12:06:32 AM »

I picked up a Flex 5000 over the weekend at the Marlboro flea.  The price was right, so it followed me home....

Anyway, I put the thing on the air, hooked to my normal audio system that I use with the class E rigs.  The Flex has incredible frequency response, and is quite clean.  However, there was one problem - no negative peak limiter.  The result of this is the "folding back" AKA wavelets problem when one exceeds 100% modulation.  Such rigs don't really overmodulate - they fold back.   The resultant distortion is particularly annoying in standard AM detectors (fine in a sync detector)....

The flex has a particularly good low frequency response (down to single digits) so a negative peak limiter is very practical to use here, and there won't be any waveform "tilt".  So, I built a negative peak limiter followed by a 6 pole filter with the 3dB corner at 5.7kHz, and it works just great !!!

I can hit 200% positive modulation with 90% negative modulation no problem.  The audio when looking at the mod monitor looks identical to the class E rigs, and it sounds extremely similar as well.

The N.P.L. circuit is quite simple, and I will publish it here shortly (probably Tuesday - it's getting very late here).

I've heard a lot of Flexes and modified SSB rigs that have balanced modulators on the air - and they can sound really great except for that "folding back" problem when one hits 100% negative modulation.  The negative peak limiter takes care of all of this, allowing lots of audio on the carrier without the resultant "overmodulation" distortion.  The low pass filter prevents "splatter".  As I said earlier, this is the identical N.P.L. and filter as is used in the class E rigs, so the audio quality is not diminished at all.

Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
W2PFY
Contributing
Member
*
Offline Offline

Posts: 12922



« Reply #1 on: February 21, 2017, 01:02:52 AM »

Boy you work fast! Just got it home and now this! Great!
Logged

The secrecy of my job prevents me from knowing what I am doing.
WA2SQQ
Contributing
Member
*
Offline Offline

Posts: 387


« Reply #2 on: February 21, 2017, 08:22:20 AM »

I can't wait - is a PCB in the works?
Logged
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2271


Bap!


WWW
« Reply #3 on: February 21, 2017, 09:37:37 AM »

Here is the schematic:  Simple to build dead bug construction over a copper clad board (for RF immunity).  Maybe a board if there is enough interest.

Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
Carl WA1KPD
Contributing
Member
*
Offline Offline

Posts: 1419



WWW
« Reply #4 on: February 21, 2017, 10:53:10 AM »

Steve
I could be interested in a entire unit.
Carl
WA1KPD
Logged

"Okay, gang are you ready to play radio? Are you ready to shuffle off the mortal coil of mediocrity? I am if you are." Shepherd
KD6VXI
Contributing
Member
*
Online Online

Posts: 1543

Making Amplitude Modulation GREAT Again!


« Reply #5 on: February 21, 2017, 12:40:29 PM »

Steve
I could be interested in a entire unit.
Carl
WA1KPD

Basically,  the input network the latest pwm board.....   Yeah?

I had broken pieces out of that for my pwm and processor.   Although I used my assymetry board,  I use an npl on baseband audio as a stop gap.

--Shane
KD6VXI
Logged
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1167


more inpoot often yields more outpoot


« Reply #6 on: February 21, 2017, 01:26:45 PM »

pwb yes
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
W2PFY
Contributing
Member
*
Offline Offline

Posts: 12922



« Reply #7 on: February 21, 2017, 01:44:06 PM »

I would buy a completed QIX made unit with SLR connectors on both ends. I would also be interested in a board. Seems to me there would be a rather large demand among us hams and the CB market for base stations would eat them up. Maybe AM broadcast stations would like them as well unless they already have a very high price equivalent?

I think it would be a must have item for Flex owners..
Logged

The secrecy of my job prevents me from knowing what I am doing.
K1JJ
Contributing
Member
*
Offline Offline

Posts: 7490


"Let's go sailing, Tommy!" - Yaz


« Reply #8 on: February 21, 2017, 03:09:01 PM »

Steve,

Well, it looks like you may now be in the market to build a linear amplifier, unless it's just a hi hi FB 100 watt effort used as an exciter for the big rigs. This now opens up the whirl to hi-fi SSB and even CW.

Your perfect linear Segway would be developing a digital linear that runs 90% efficiency. Years ago there was a lot of talk about them being mainstream ham radio by now, but no ham manufacturers have stepped up to the plate.  We all still suffer with class B blow torches.

Be sure to make use of their version of "Pure Signal" software. This will make any ratty linear perform like a class A dreamboat.

T

Logged

“Remember, remember, this is now, and now, and now. Live it, feel it, cling to it. I want to become acutely aware of all I’ve taken for granted.”  -  Sylvia Plath

A Night in Tunisia:  https://www.youtube.com/watch?v=baMsQeQpUvw
WA2SQQ
Contributing
Member
*
Offline Offline

Posts: 387


« Reply #9 on: February 21, 2017, 03:11:22 PM »

I'd be interested in PCB or kit
Logged
W2PFY
Contributing
Member
*
Offline Offline

Posts: 12922



« Reply #10 on: February 21, 2017, 04:16:10 PM »

.
Logged

The secrecy of my job prevents me from knowing what I am doing.
W9BHI
Member

Offline Offline

Posts: 328


« Reply #11 on: February 21, 2017, 05:40:21 PM »

I already use a CRL PMC300A neg peak limiter into my Flex 3000 but I would certaily be interested in a PC board for this project.
Don W9BHI
Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 7671


CQ CQ CONTEST


WWW
« Reply #12 on: February 21, 2017, 07:11:29 PM »

Does the circuit need to be removed when operating SSB or FM?
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2271


Bap!


WWW
« Reply #13 on: February 21, 2017, 09:53:47 PM »

Does the circuit need to be removed when operating SSB or FM?

Hey, that's a good feature that may be worth adding.  Never thought of that because, for me anyway, I never operate any other modes.  However, that is not true of most folks.  I guess a Negative Peak Limiter "Disable" feature would be worth adding.  Leave everything else in line so the levels don't change - just disable the negative peak limiting.   Or alternatively provide a bypass feature.

I'll take input on this - might as well get it right the first time  Smiley

Regards,  Steve
Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
K0ARA
Contributing
Member
*
Offline Offline

Posts: 104


The Bull


« Reply #14 on: February 21, 2017, 10:22:21 PM »

I would be interested in a PCB.
Logged

Mike KŘARA                99.9% AM
                 AMI  #1692
WBear2GCR
Member

Offline Offline

Posts: 3344


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #15 on: February 21, 2017, 10:44:47 PM »

Just for clarity.

This is an inboard modification?
or an outboard audio mic or line level device??

                      _-_-bear
Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2271


Bap!


WWW
« Reply #16 on: February 21, 2017, 11:36:03 PM »

Strictly outboard.
Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 7671


CQ CQ CONTEST


WWW
« Reply #17 on: February 22, 2017, 12:56:04 AM »

FYI:
For the Flex Series:
Flex 5000 has single(unbalanced) and balanced mike inputs.
Flex 3000 has single(unbalanced) mike input.
Flex 1500 has single(unbalanced) mike input.
Flex 6300 has single(unbalanced) mike input.
Flex 6500 and 6700 have single(unbalanced) and balanced mike inputs.

Just a thought; since many SDR-type rigs run off 12 volts DC, it would have been convenient to design your circuit to run off the same 12 volt line.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
KG6PQQ
Member

Offline Offline

Posts: 3


« Reply #18 on: February 22, 2017, 04:26:46 AM »

Count me in for a board
Logged
WA2SQQ
Contributing
Member
*
Offline Offline

Posts: 387


« Reply #19 on: February 22, 2017, 08:13:52 AM »

If you decide to move forward with this, it might be worth submitting it to QST for possible publication. That would certainly sell PCB's (and or kits) and would compliment the ARRL's recent interest in AM. For me , this would be the missing element in my audio chain.
Logged
W9BHI
Member

Offline Offline

Posts: 328


« Reply #20 on: February 22, 2017, 11:24:28 AM »

I like the idea of the negative peak limiter but why would you need a low pass filter after it?
The audio bandwidth can be set in the Flex software.
It uses a brick wall low pass filter.

Don W9BHI
Logged
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2271


Bap!


WWW
« Reply #21 on: February 22, 2017, 11:44:06 AM »

I like the idea of the negative peak limiter but why would you need a low pass filter after it?
The audio bandwidth can be set in the Flex software.
It uses a brick wall low pass filter.

Don W9BHI

That's a fine question!  Not all rigs have a low pass filter (this circuit is designed to be used with other good rigs other than just SDRs), and also the filter shown in the schematic is "gentler" (6 poles) than the brick wall filter in the SDR and sounds a bit nicer to the ear.  In my own Flex, I actually set the transmit filter to 7.5kHz (each side of center), but the filter in the negative peak limiter, which is the same one I use in the class E rigs, has the corner set to 5.7kHz. 

At night, or if I need more filtering because there is a nearby QSO, I kick in a steep filter (an additional 8 poles, giving a total of 14 poles) which is part of the audio chain for all rigs in the shack.

The filtering in the SDR is a nice thing to have for sure (if you're got an SDR)  Wink  !

I have to say I am quite pleased with the performance of the receiver (it is absolutely amazing) and the transmitter.  I think it's the first commercial piece of ham equipment I've ever encountered which needed no modifications whatsoever and works perfectly in all respects right out of the box.
Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
W9BHI
Member

Offline Offline

Posts: 328


« Reply #22 on: February 22, 2017, 01:46:50 PM »

Steve,
I'm glad you approve of the Flex 5000A.
I have had mine for about a year now and couldn't do without it's great receiver.
Don't get me wrong, I still love the boat anchor stuff like my BC-1G and R-390A.
Some people just don't even want to hear about SDR radio's.
Too bad, I think it's the future of ham radio.(but what do I know)
I will be listening for you sometime on 3873 to hear how you sound.
Thanks for all of the work you do on this stuff.
Don W9BHI

 
Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 7671


CQ CQ CONTEST


WWW
« Reply #23 on: February 22, 2017, 02:11:15 PM »

I guess the Flex 5000A is at a point in its life cycle where owners are curious and going into the diddle/enhancement mode with their rigs. I've received several requests for the printed service manual over the last several weeks. Maybe we'll see some user mods over the next several months.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
WA2SQQ
Contributing
Member
*
Offline Offline

Posts: 387


« Reply #24 on: February 22, 2017, 02:17:18 PM »

I think we will be seeing more Flex radios in general. While at the Orlando Hamcation I stopped by the Flex booth. They were demo'ing their new amp and I overheard Steve Hicks mention that they've got the adaptive pre-distorion working very nicely with the new amp. I suspect that it may be part of v2.0x

I also saw three Anan users put deposits on Flex radios.
Logged
Pages: [1] 2 3   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 0.062 seconds with 18 queries.