Simple SSB modulator only with DDS? - Page 1
Forum section: electronics / rf-microwave

author: Scratch.HTF
author_rank: Regular Contributor
timestamp: May 18, 2022, 01:41:22 am
content: I've come across a DDS-based AM modulator which uses an external connection for programming full scale DAC current (e.g.Rsetin the AD9851) for RF modulation, but has anyone used only a DDS to generate SSB signals including at different RF frequencies?

author: antenna
author_rank: Frequent Contributor
timestamp: May 18, 2022, 02:52:57 am
content: The ARRL Handbook talks about using I/Q modulators to do it. I think you can do it with trigonometry.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 18, 2022, 03:29:20 am
content: Sure. You just multiply by an amplitude scale factor after the phase to sin/cos evaluation.

author: radiolistener
author_rank: Super Contributor
timestamp: May 18, 2022, 02:44:02 pm
content: Quote from: Scratch.HTF on May 18, 2022, 01:41:22 amYou're needs filters to cut-off the carrier and second side band in order to get SSB. You can do it with electromechanical or quartz filter. Another approach is to use digital signal processing (DSP) and DAC. It also needs to apply filters but with DSP it happens in digital domain.You can do it on intermediate frequency and shift frequency up/down with mixer and additional oscillator. In such way you can do it at different RF frequencies

author: UR5FFR
author_rank: Contributor
timestamp: May 18, 2022, 06:15:17 pm
content: Quote from: Scratch.HTF on May 18, 2022, 01:41:22 amYes, this is possible. PE1NNZ make this on ATTINY45 micro-controller and a AD9834 DDS.http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.html

author: iMo
author_rank: Super Contributor
timestamp: May 29, 2022, 08:49:10 am
content: Here is a "DDS only SSB modulator", for example:https://tj-lab.org/2020/12/04/fully-digital-ssb-generator2/

author: AussieBruce
author_rank: Regular Contributor
timestamp: May 29, 2022, 12:22:05 pm
content: Google Weaver Modulator, this is probably the most used basis for DDS SSB. You'll get a number of hits that will give you some idea on the principles involved. Unless you have strong capabilities with a dev platform that can handle the data rates you'll need you will want to stick to a fully proven and documented design, this is certainly not a beginner project. In particular, the filters involved require very high order as well as carefully profiled phase performance. The filter design is realistically only practical with the help of serious, and very expensive software tools such as Matlab Professional with DSP addons.The closest I've come to a 'followable' design is a website by a group of hams in Italy, they have links to Italtel which provide the toolkit power they need. They describe a complete 9 MHz SSB generator running on a fairly old Xilinx FPGA, even hobby level gate array protoboards these days would eat it up. There's enough detail there for someone with reasonable signal processing and HDL language capability to put something together, with the exception of the filters. Unfortunately (Sorry!) I can't find the website, maybe someone here knows where it is.

author: LaserSteve
author_rank: Super Contributor
timestamp: May 29, 2022, 07:50:42 pm
content: Hilbert Transform on the DSP?

author: fourfathom
author_rank: Super Contributor
timestamp: June 06, 2022, 12:51:37 am
content: Take a look at PiTX for direct generation of SSB, FM, AM with the Raspberry Pi. This uses the internal timer only, no external modulators or filters, and about 10 mW RF is generated on a Pi output pin. To be a good citizen you need to add a low-pass or bandpass filter to reduce the sampling spurs. I ran one of these as a WSPR beacon (MFSK) for a few years. The Pi can generate signals from 130 KHz up to 750 MHz (with very interesting spurs).https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-with-just-a-raspberry-pi/Here's a ham-club presentation I did for the RPi WSPR beacon. I's not SSB, but still pretty interesting:http://wb6cxc.com/wp-content/uploads/2016/03/Ham-Presentation1.pdf

author: mag_therm
author_rank: Frequent Contributor
timestamp: June 06, 2022, 07:51:30 pm
content: Hardware and vintage methods:There is the phasing method of using two gilbert cells each with L.O. and signal respectively phase shifted by 90 degrees.Interested in the history , I found a 1946 paper by R.B. Dome "Wideband phase shift networks" ( will come up on search)where he described audio filters that can give a +45 and -45 degree phase shift of suitable accuracy, directly on the baseband audio.His filters do not hold 45 degrees over the baseband, but he claimed the pair of them track with about 45 degrees difference over audio range.Assuming I understood his filters, the model in qucs was unable to achieve phase shift accuracy to sufficiently suppress the unwanted sideband.However using that idea to phase shift L.O and incoming signal for a 14 MHZ down converter works very accurately, just with two pairs of RC networks.(tracking with fraction of a degree difference over the 20 metre band.)I have artworked a circuit to try but not sure if I will build it as it is also easy to filter the wanted downconverter signal .Incidentally I am using a Nooelec AD9850 40MHz DDS Function Generator Module to injection lock a vintage tube receiver.Trying various methods, the best way so far is by using the 6BE6 converter tube and feeding the DDS into the control grid with the oscillator otherwise a conventional Hartley on the oscillator grid , which stays on level both when locked to DDS or with DDS off.It is working well from 7 MHz to 18 MHz, but does have spurs (usually out of the way) and I will try a better filter and shielded box.Attached is screenshot of GUI written in bash and gtkdialog to control the AD9850 in serial mode.https://app.box.com/s/v24an4ea1iiib9jvcpyeh49j9wx0518ihttps://app.box.com/s/w328smgvhyn0ya4eb3bb0yvbsvx06fuahttps://app.box.com/s/jjyuodfiqw90o39pabxoviwwn7gpdcn3https://app.box.com/s/tf7936ph90rf4vljgbo427sevbtn6i85