SSB Carrier Supression

[Space Varmint]

Only if it's designed right!

Nigel Nigel, why do you bash me so much. The fact still remains, my receiver will pull QRP stations out of the mud and it sounds great.

If I had time I build more and reduce it down little by little. Maybe I might throw in some MC1351's to replace a few amp stages.

All I got to do now is straighten up this transmitter and I will have a ball. I see now that I am getting 20 watts out of the MRF477 but I got some feedback creeping in on me. I can straighten it out. I'm stuck with what I have available. I bought very few parts for all of this. The Xmitter and Rcvr are both 95% junk box parts. I literally took old boards apart to get some of the parts I needed.

 

[xanadunow]

Filter

is a filter and you decide where to cut it left, right or center. For the SSB purpose - 300 to 2700Hz is a pretty good standard, however there have been notions of much narrower SSB. I do not exactly remember the technique employed but it did not have much taking. I think it was designed around the 1700Hz as the upper limit but I am no longer sure on that.

xanadunow

 

[Space Varmint]

When you transmit the audio signal, you are concerned with maintaining the power to "pass the message" in the most efficient manner.

There are only two ways to do it.

You need to employ, both the pass band filter to limit the range of audio frequencies and the compressor to effectively control the level of modulation. Distortions do come in with the compressor - but "pass the message" is the bottom line, hence you do have to live with it and make somwhere the "cut" balancing these two requirements within the compressor.

As it is a serial arrangement, i.e. flter/compressor - do follow each other; would you get caught at - which one of these two would be first in line following the input from the mic?

Regards,
xanadunow

I don't believe that. All you have to do is back off from the mic. The part about the audio filter is probably a good idea, but I am trying to get around it for now. I want it to be simplistic in design. I have many constraints.

I have seen where audio filters are used but I know that sending limited bandwidth also chops off the extra audio freq. Anyway I am way past that point. Right now I need this linear amp to work right. I will probable work with the output filter first.

 

[xanadunow]

Well SV, I do hope you have a valid licence and.. sure, your sideband is full of these frequencies you do not need. But - join audioguru and go FM for the quality you want..

xanadunow

 

[xanadunow]

Constraints

are not limited to a great expense but the lack of some common approach and the simplest one I did see - was to use a redundand "throw away" radio-casette (from the tip) and after ripping some boards out of it, to utilize the auto-gain audio recording control circuit as the means of a "compressor".

If it is good enough for "audio" recording, it would also be usefull for "audio" transmitting and there is some room to play, to tune it (at little expense)

You have your compression and it may even come with a mic and you can add your banpass filter to it too (it'be in the right order).

xanadunow

 

[Space Varmint]

please look how it is done today; Icom 7700

I got a better way. Put it out there and let 'em hear. I need more fire in the wire. Problem is, when I hook up to my 80 watt linear it stomps my receive so bad I'm not sure what's going on. Since it is hooked to same power supply it could be loading the receiver.

 

[audioguru]

Ham radio is half-duplex. You transmit when your receiver is turned off and you receive when your transmitter is turned off.

Or you transmit on one frequency and receive on a completely different frequency.

 

[Space Varmint]

Ham radio is half-duplex. You transmit when your receiver is turned off and you receive when your transmitter is turned off.

Or you transmit on one frequency and receive on a completely different frequency.

Ever hear of VOX?

 

[Mikebits]

Is your RX and TX sharing the same antenna? If so you should wire your PTT line to disable the RX path or you may blow your RF front end with 80W. Or maybe I am not following what you have setup.

Also I would recommend that for your RX and TX that you run seperate regulators for all your stages. For example; Audio stage 1 regulator, Lo stage 1 regulator, IF stage 1 regulator. That is how we did it at Cubic and our radio's were Mil std.

This would give all your stages good DC isolation.

 

[audioguru]

A problem with VOX is when the mic picks up the sound from the speaker when it is receiving and it switches to transmit when it shouldn't.

 

[xanadunow]

VOX/break-in

Mike has nailed in again.. protect your RX SV. Put some diodes on your RX ant input and just shut it short to the ground (the RX input when you're transmitting). You do need to help your RX to recover from the shock. And - accept the audioguru statement. It is half-duplex very much as he stated.

Seperate aerials are of some benefit when tunning in on DX stations.

You can also seperate the TX from RX. What I mean here is the seperation expressed in the terms of a distance.

It would be close to some 30 years ago when I did have my friend's RX patched to my phone line - and, operating on CW - I could actually hear a single "dot" sent from my correspondent in the middle of me sending a single letter. He was astound and asked me what kind of break-in I am using. My friend was some 500kms+ away from me. My friend had to cooperate in this experiment because he was the one who manually operated the receiver.

Today, in the age of computers and internet it is even easier. There are several www sites that would allow you to "tune-in" (use their RX and control the RX frequency in the real time). I do not use it. It is cheating when communicating, but a good way to check your propagation to the region you target. There is nothing better than to hear yourself "talking"

Yes, I am talking another continent here ofcourse.

Well, this is some wrap-up for you on the VOX issue.

Regards,
xanadunow

 

[xanadunow]

A problem with VOX is when the mic picks up the sound from the speaker when it is receiving and it switches to transmit when it shouldn't.

No.. I am pretty sure we do reverse the phase to make sure it would not happen.

xanadunow

 

[Mikebits]

No.. I am pretty sure we do reverse the phase to make sure it would not happen.

xanadunow

I doubt most VOX designs are that sophisticated. If I understand your meaning, What your saying is that the RX audio output is compared against TX mic input and if same signal no modulation occurs. This would be difficult at best as distance from speaker to mic would have unknown phase delay. Hands free car phones use this technique through the use of a DSP based asic, and the performance is iffy.

IEC: On-Line Education: WPF: Echo Cancellation

 

[audioguru]

You cannot simply swap the wires to change the phase to cause sound cancellation. Because each frequency has its own phasing, delay and echoes.

 

[xanadunow]

I have to check before you trash me..

 

[xanadunow]

Phase

is not a part of the VOX implementation for the purpose of Tx/Rx operation as I did state earlier and I do have to retract this statement. It was a logical conclusion drawn from never having expirienced the problem of the speaker actually triggering my transmitter.

One of those things that are just there and one does not think about it twice, just use it.

For this purpose, I do go from being "pretty sure" to being "pretty wrong" and confused because my memory does tell me different to what I can find right now.

As I can not support my statement, I am retracting it forthwith.

We are all humans and I do reserve the right to be wrong - you know

Regards,
xanadunow

 

[Mikebits]

is not a part of the VOX implementation for the purpose of Tx/Rx operation as I did state earlier and I do have to retract this statement. It was a logical conclusion drawn from never having expirienced the problem of the speaker actually triggering my transmitter.

One of those things that are just there and one does not think about it twice, just use it.

For this purpose, I do go from being "pretty sure" to being "pretty wrong" and confused because my memory does tell me different to what I can find right now.

As I can not support my statement, I am retracting it forthwith.

We are all humans and I do reserve the right to be wrong - you know

Regards,
xanadunow

I think you are beating yourself up more than anyone else has. So I do certify herewith and hence thereafter that you may feel fine in giving yourself a break

Note: this certification in not transferable in any future post and any future post must fall under scrutiny of non aforementioned forum members... hehe that was fun

 

[xanadunow]

Smile

Being a newbie I do not want to be beaten to a "pulp"; I do have a lot of experience to share and I do certainly deserve the criticism if it is due and at all other times as expected.

One more thing Mike, that eye is scary - did I mention it before?

As for having a break.. Well, I am having the break

Regards,
xanadunow

 

[Mikebits]

What I am trying to say is... No worries mate

Don't like the eye huh? Maybe I should find a new avi.

 

[xanadunow]

I know

Don't change anything, you'll look different