SSB Carrier Supression

[Nigel Goodwin]

I think we're getting some cross-threading here - but those high frequencies are really important to speech quality. I don't know why people always focus on vowels and sonorants to the exclusion of everything else when this issue comes up. Stops and especially fricatives have significant spectral energy way up into the 10khz range.

And is all completely pointless in the context of this thread, where we're talking about SSB - the lowest quality voice transmission known to man.

There's no need for high frequencies, or high bandwidth - if you want that then meet in person and talk. But even with the low quality of USB perfectly acceptable speech is the result (at least on a properly designed system).

Attempting to do high bandwidth audio would not only be illegal (breaking the licence conditions), it would also limit your range to down the street, rather than across the Atlantic ocean.

 

[Mikebits]

Got to hand it to SV, he has created the never ending thread...

 

[flat5]

My upper hearing drops out above 12k and I can understand English speech just fine.

This chart suggests 7k is more than enough.
From **broken link removed**

 

[Space Varmint]

That sounds like a hairy subject. He really is an audio guru. believe me. Anyway I played around with the bandwidth and the modulated carrier offset and found that they definately effect the intelligibility of the signal.

Since I set the driver up as the antenna output,temporarily, I'm finally getting true readings from this push-pull pre-driver. finally got that sucker balanced and so far it's pushing the driver to produce a quarter to one half watt of true 7MHz power! Should be able to pump that into the final today and see what this MRF477 can really do.

 

[Space Varmint]

Got a stupid question. I think I already fixed it but here is my scheme. I am using 4 MHz crystals for my filter. Then I mix my carrier with 11MHz to get the 7MHz output frequency. So here's the deal. I've been running my carrier frequency at 1.5KHz below the crystal frequency thinking it would be the lower sideband. Well I was talking to a guy yesterday, K9LZJ Hank in Indiana and he has a really nice rig. It's a Flex NCR-5000 and it has a built in spectrum analyzer. He told me some interesting things about my signal. He said, and i heard this once before, that I was being heard upper and lower sideband. The bandwidth was about 5.3Khz. He said I sounded much better on the upper sideband when I want to be on lower sideband. He said i has a slight whistle on the lower side and I explained that my signal was too narrow and would make that sound, you know, tinny like in a tin can. But actually i should be about 2.5KHz wide. this explained why i had to widen my bandwidth to get my clarity on lower sideband. I went back and recalculated and believe i set my carrier on the wrong side od the crystal filter. Take a look and correct me if I am wrong.....stupid me....lol

What I had.......4MHz crystal and carrier running at 3.9985MHz. So when I converted with 11mhz beat note, I got 7.0015 which is upper sideband....right?

I just changed the carrier to 4.0015MHz. Now I narrowed the filter bandpass. Waiting to try it.

 

[Space Varmint]

I just checked in to the Communications Ontario net there Guru. It's about 10:30 am. My 8 watts is doing the business.

 

[srinivaas ganesan]

hi.. can anyone reccomend me a good book for communication systems...
is simon haykin good... i d like to learn a lot about communications and networks... wat are the good self study books..

 

[Space Varmint]

Shrader is a really good one. Someone stole mine.

Get any old ARRL handbooks you can get.

 

[flat5]

Hi SV! I've collected a lot of parts to build a SSB receiver.
What I don't have is blank pcb, a nibbler or drill to make islands (manhatten), toroids (t37-2 & t50-2 I guess), coil wire (#28 ?), and a good magnifier lamp

I also have not decided on band(s) or circuits. I think lower 40 to start. I'd like to use a igmosfet for first mixer and mc1496 for detector. I've built the audio amp (lm380n) already. Have 10 8mhz xtals so will use them for filter and bfo. Should be ok for lower 40 and 80 or 20 in the future, I hope. Even have an 8mhz osc. in a xtal package to play with. It might be the bfo, I'l see.

 

[Space Varmint]

Hi SV! I've collected a lot of parts to build a SSB receiver.
What I don't have is blank pcb, a nibbler or drill to make islands (manhatten), toroids (t37-2 & t50-2 I guess), coil wire (#28 ?), and a good magnifier lamp

I also have not decided on band(s) or circuits. I think lower 40 to start. I'd like to use a igmosfet for first mixer and mc1496 for detector. I've built the audio amp (lm380n) already. Have 10 8mhz xtals so will use them for filter and bfo. Should be ok for lower 40 and 80 or 20 in the future, I hope. Even have an 8mhz osc. in a xtal package to play with. It might be the bfo, I'l see.

Awesome! Just get a magnifying glass. That's what I used. Yes, you are using Amidon? T37-2s are great and you need a few FT-37-43s for your inductors and broad band transformers. Go with what you feel comfortable with but don't limit yourself on the receiver. Make it broadband 3 to 30MHz. For my BFO I used Amidon T80-6...very stable.

One more thing. Buffering is paramount to good rf design. I like Darlingtons because of the high current drive. When you get to the audio, talk to audioguru. Let him insult you a few times....lol....he helped me allot.

Last night I heard some Ozzies talking to a Brit G3MLU and KN2UU I think the Ozzies call was. He was using only 5 watts.

Your first mixer is the whole ball of wax. Get it right and if you keep up with good design practices your receiver will be top notch. On my AGC I had to control 2 or three different stages in the IFs. AGC is critical for communications work. Also in your pre-selector or atleast right across the rf front end amp, put a switch to add attenuation. I use about 22 ohms to ground. This is used to reject intermod.

 

[Space Varmint]

And.....shielding! No SHIELDING. Go with no more than 3 or four stages before you shield it all. Pick frequencies that go together but don't allow feedback. Toroids have natural shielding properties but only to a degree. All shields must be grounded.

 

[Mikebits]

Awesome! Just get a magnifying glass. That's what I used. Yes, you are using Amidon? T37-2s are great and you need a few FT-37-43s for your inductors and broad band transformers. Go with what you feel comfortable with but don't limit yourself on the receiver. Make it broadband 3 to 30MHz. For my BFO I used Amidon T80-6...very stable.

One more thing. Buffering is paramount to good rf design. I like Darlingtons because of the high current drive. When you get to the audio, talk to audioguru. Let him insult you a few times....lol....he helped me allot.

Last night I heard some Ozzies talking to a Brit G3MLU and KN2UU I think the Ozzies call was. He was using only 5 watts.

Your first mixer is the whole ball of wax. Get it right and if you keep up with good design practices your receiver will be top notch. On my AGC I had to control 2 or three different stages in the IFs. AGC is critical for communications work. Also in your pre-selector or atleast right across the rf front end amp, put a switch to add attenuation. I use about 22 ohms to ground. This is used to reject intermod.

Darlingtons do not work well at RF. The reason is the long switch delay.
SV is correct, A good RX mixer is real important. I would go with a prefab unit like one from Mini-ckts. Front end amp is also important. First stage Noise figure determines overall receiver performance. Set you goal on a front end amp with 3 dB or less NF. Check out mini circuits web site also.

Mini-Circuits RF/IF Designer's Guide

have fun...

 

[Space Varmint]

Darlingtons do not work well at RF. The reason is the long switch delay.
SV is correct, A good RX mixer is real important. I would go with a prefab unit like one from Mini-ckts. Front end amp is also important. First stage Noise figure determines overall receiver performance. Set you goal on a front end amp with 3 dB or less NF. Check out mini circuits web site also.

Mini-Circuits RF/IF Designer's Guide

have fun...

Uh Oh, here we go again. Darlingtons work very well in rf. A Darlington is actually an ECL device and they switch faster than CE amps. Thats why cray computers use ECL in the data & address busses. One of the most significant factors is the isolation of a Darlington. High Z in and low Z high current out is ideal for sourcing an important CE amp.

 

[Space Varmint]

Hi SV! I've collected a lot of parts to build a SSB receiver.
What I don't have is blank pcb, a nibbler or drill to make islands (manhatten), toroids (t37-2 & t50-2 I guess), coil wire (#28 ?), and a good magnifier lamp

I also have not decided on band(s) or circuits. I think lower 40 to start. I'd like to use a igmosfet for first mixer and mc1496 for detector. I've built the audio amp (lm380n) already. Have 10 8mhz xtals so will use them for filter and bfo. Should be ok for lower 40 and 80 or 20 in the future, I hope. Even have an 8mhz osc. in a xtal package to play with. It might be the bfo, I'l see.

Oh, I didn't answer all. Use a lighter gauge enameled wire like no. 36. Radio shack sells nice perf board you can cut. Other wise I use double side copper clad and hand rought the board with a drimmel tool and router bit.

 

[Mikebits]

Darlingtons are not good at RF, your a poo poo head...

 

[Space Varmint]

I've been listening to VK1GG...Chris Carrol from Australia for about an hour. He's running portable I believe he said 2 watts on 40 meters. I wanted to give him a holler bt wife has to get up early morning I just changed my crystal filter...again...in my transmitter. I think it's much better. I CQed today and got answered right back. Very hard to tune with out spectrum analyzer. Characteristics of a properly tuned Xtal filter are all vowels outputting approx same amplitude. Output signal very clean. Wish I had used a different final. I'm getting 8 to 9 watts out. MFJ has one with same transistor they claim is 10 watts.

 

[Space Varmint]

Darlingtons are not good at RF, your a poo poo head...

I have used Darlingtons for years as buffers at HF. One very good example is following an oscillator. They prevent loading and give a strong current drive for a CE amp which will convert the current to a very large voltage gain. Beautiful isolation as if the oscillator was free running with no load! Best choice. I've tried them all.

 

[Sceadwian]

Don't they produce a lot of distortion?

 

[Mikebits]

The large junction between base emitter to base emitter introduce many unstable conditions in a darlington. They are best suited for audio, and are crap for RF.

 

[Space Varmint]

Damn! I'm listening to 2I0FLO Irene from Ireland. She was just CQing for DX.