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Cross modulation, by that I assume you mean Intermodulation distortion as I think they are similar.
I have been preaching Mini-Circuits for some time now to no avail (See this thread) https://www.electro-tech-online.com/threads/shure-mike-model-444-freq-scheme-ssb.85841/
but this is a great off the shelf solution for a Rx front end mixer.
Mini-Ckts has real good specs for intermod as well as Noise figure. I think you could almost build an entire RX unit from Mini-Ckt parts. They have amps, mixers, filters, and VCO's.
For the TX modulator, Mini-Circuits does not spec their parts below 500KHz so I am not sure how well the would work at audio modulation frequencies, but I suspect they would be fine. Maybe someone could test it and report the results.
What is your criterion for working great? What sort of test equipment have you used to verify your circuit?
This web site has a pretty good write up on mixer design. **broken link removed**
Note this excerpt from above cited website.
4 diodes are expensive -
well first off you could save yourself a lot of angst by buying a commercially manufactured mixer. Minicircuits SBL-1 would be an example. It comes in a can with a pin out the same as an 8 pin DIP and can be bought for only a few dollars. You could shop around for suitable diodes cheaply available e.g. Hewlett Packard's HP5082-2800 or similar. In North America Dan's Small Parts seem to have a variety and I think the mixer is also available. Links to all sites mentioned appear at the end of this tutorial.
5. diodes need to be well matched - don't even consider using 1N914 types if you want results. The HP 2800 types are pretty well matched but I'd still check a bunch for foward and back resistance.
What is your criterion for working great? What sort of test equipment have you used to verify your circuit?
This web site has a pretty good write up on mixer design. **broken link removed**
Note this excerpt from above cited website.
4 diodes are expensive -
well first off you could save yourself a lot of angst by buying a commercially manufactured mixer. Minicircuits SBL-1 would be an example. It comes in a can with a pin out the same as an 8 pin DIP and can be bought for only a few dollars. You could shop around for suitable diodes cheaply available e.g. Hewlett Packard's HP5082-2800 or similar. In North America Dan's Small Parts seem to have a variety and I think the mixer is also available. Links to all sites mentioned appear at the end of this tutorial.
5. diodes need to be well matched - don't even consider using 1N914 types if you want results. The HP 2800 types are pretty well matched but I'd still check a bunch for foward and back resistance.
My criteria is an attentive well trained ear and eyes. My equipment is cheap as they come. a 40MHz scope and a voltmeter and any signal generator is an oscillator built by muy and homebrew receiver.
Now, let me test the knowledge banks out there. It is my observation but I may be wrong, but it would appear.....two questions.
1. The offset of the crystal filter from the carrier will be the strongest audio output or least attenuated audio frequency????
2. The BFO in the receiver will be set to the same offset of the transmitter offset from carrier frequency???
#2: It all depends what you decide to do. There are few possibilities. You can use seperate IF frequencies (and filters) but always the offset will be determained by simple +/- maths (of two incoming frequencies, followed by +/- math, followed by the filter set to the "+" or to the "-").
- Some TRX use just one Xtal IF filter (one filter, one offset for Tx/Rx),
- Some use 2 Xtal Filters for the same IF (the classic is the 9MHz IF and XF9A filter for Tx and XF9B filter for Rx with the better quality filter being used for RX). IF freq is the same and the offset is the same i.e. only the filter changes but the rest of IF hardware is the same for Tx/Rx.
- Some TRX may have the signal chain totally seperated with different IF freq used for Tx and Rx. Therefore, for the same principal frequency the offset will be different due to the "math" as above..
My criteria is an attentive well trained ear and eyes. My equipment is cheap as they come. a 40MHz scope and a voltmeter and any signal generator is an oscillator built by muy and homebrew receiver.
Well, no one can fault you for having a lack of expensive equipment. I am sure most are in the same boat. Due to the lack of good test instruments makes it much more important to build by design. That is to say, use design blocks with confirmed specs, i.e. use a mixer with known spec of 6 dB loss for example. Select an RF amp in front with 16 dB gain and NF of 3 dB. You can then predict by design that your system will have a ~3dB NF and front end gain of 10dB. This takes the guesswork out, as you spec by design. You follow?
The SLB-1 minicircuit mixer (or at least it's equivalent) is offered on eBay right now @
**broken link removed**
The price is hmm.. quite acceptable (there are 2 of them in one lot from US)
Alternatively if you look for eBay user name "rfplus", he has them too (last auction for them finished yesterday or so) in the original SLB version and @ better price and down to earth postage. I bought from him before and I will buy again. I have him in my favourits and it is only the mattaer of watching. This nice fellow seem to be travelling a bit between Oz and the UK and, (for once) he is one of a very few who provide good description towards the items he is selling. I am sure he's doing very well on that..
In the links seen earlier (the example case); HP2800 (or 1N5711) are Shottky diodes and they do not come all that cheap. If you spend $20 on them you will end up with no more than 30 pieces (if someone was willing to sell them to you in that small quantity at that price). Even if you did buy a thousand of them at a consierable expense, you do need to spend considerable amount of time making the perfect match to choose the 4 that do.
How much is your time worth? Even not mentioning the two toroids you have to wire up in the quite perfect manner, you are on a lost cause. I am willing to sacrifice a couple of pizzas for the price of the couple of minicircuit SLBs that you can built too - but sacrificing at least a fortnight of commitment - time & moneywise. I‘ll go fishing instead.
Minicurcits do warranty the match of the diodes and the toroid transformers because their specs do warranty the whole mixer over the frequency range. It is the sole reason for my choice.
Respecting your view, I am not exactly sure what are you getting at..
I have not checked on the diode ring ICs although they probably do exist (I am pretty sure that I did see one before).
#2: It all depends what you decide to do. There are few possibilities. You can use seperate IF frequencies (and filters) but always the offset will be determained by simple +/- maths (of two incoming frequencies, followed by +/- math, followed by the filter set to the "+" or to the "-").
- Some TRX use just one Xtal IF filter (one filter, one offset for Tx/Rx),
- Some use 2 Xtal Filters for the same IF (the classic is the 9MHz IF and XF9A filter for Tx and XF9B filter for Rx with the better quality filter being used for RX). IF freq is the same and the offset is the same i.e. only the filter changes but the rest of IF hardware is the same for Tx/Rx.
- Some TRX may have the signal chain totally seperated with different IF freq used for Tx and Rx. Therefore, for the same principal frequency the offset will be different due to the "math" as above..
Alright alright...I'm not talking about in a transceiver. I'm talking in actual practice. What I am saying, is to have the actual proper beat note, if the transmitter's carrier is set 1.5KHz below the carrier, as in the carrier of the balanced modulator, then a receiving station would have to tune the BFO oscillator to the same 1.5KHz offset in order to make it appear as a normal AM signal. Is this correct? I believe I'm finding it to be so. Where before I had read that you would zero beat the signal with what would be the carrier. This works in AM but the audio intelligence is not offset as in SSB. You see, these are things taht are neglected to be cover in most all of the material I come across.
Alright alright...I'm not talking about in a transceiver. I'm talking in actual practice. What I am saying, is to have the actual proper beat note, if the transmitter's carrier is set 1.5KHz below the carrier, as in the carrier of the balanced modulator, then a receiving station would have to tune the BFO oscillator to the same 1.5KHz offset in order to make it appear as a normal AM signal. Is this correct? I believe I'm finding it to be so. Where before I had read that you would zero beat the signal with what would be the carrier. This works in AM but the audio intelligence is not offset as in SSB. You see, these are things taht are neglected to be cover in most all of the material I come across.
If you are using a crystal or mechanical filter in the generation or demodulating of SSB then the center frequency and bandwidth of the filter bandpass is the key variable that determines what the frequency the carrier or bfo frequency is. If one wishes to be able to be able to generate and demodulate both USB and LSB then the carrier frequencies needs to be able to switch to two different frequencies one above the filter bandpass and one below the bandpass. One can have a constant carrier frequency but then needs to switch between two different filters with center frequencies offset from the carrier frequency by the proper amount, and this of course is a more expensive route to take as the filters tend to be more expensive then carrier crystals or an adjustable carrier oscillator. A typical SSB design might have three different carrier offset frequencies require for USB, LSB and CW.
One problem to be aware of is what kind of crystal filter you are going to use. There are the more expensive types that have a perfectly symmetrical pass-band where the shape of the sides are the same, where as a lower cost crystal ladder design using identical frequency crystal tend to asymmetrical sides where one is nice and vertical and the opposite side tends to roll off by a long amount. The offset carrier should be next to the sharper side of the filter for best carrier suppression.
The ARRL handbook years ago use to have very clear explanation and examples circuits about the different methods and implementation of SSB as far as carrier offset Vs filter center frequencies.
The, so called - "zero beat" is used to make your receiver to "match" the carrier frequency of the transmitted signal (he will hear you on CW when you match and respond in kind). On SSB the principal is to find the best clarity of the signal and it means - you did find the carrier too. It is the same thing - you are determined to find the carrier.
You could be finding the "zero beat" with your VFO, but outside of your IF.. figure that one out
Yeah, that is a good explanation. I remember the old books too. Your right. Anyway, I don't know what to say, but I tell ya, I'm using the 914s and I am getting excellent carrier suppression. If I listen to the signal on the outside antenna, I cannot even pick up the carrier. I think it's about ready. I need a little more drive to excite the amps. I will do some more filtering there. Right now I've got it mixed up to 7MHz from 4MHz. The signal still a little raspy looking through a 3 pole LC filter. So will catch that on the back end. But, no audio....no sound.
I found a recording of real ducks quacking and it sounds just like your radio except its sound is clear. But I can't attach it here. And I am a poet and don't even know it.
The answer, in simple terms - is in the indication of the "S meter" of your receiver. There is only one combination of VFO/BFO (tunable) positions to give the best strenght of the signal (CW), and for SSB it is easier - the BFO is already "pre-set" by a Xtal to USB or LSB.
Did you ever wonder what happens when the TX designer and RX designer have choosen a different offset? Well, it does not really matter all that much because you do tune to the best "clarity and/or strenght" (on SSB it is within no more than 200Hz) and this is what (does or not) makes it - in communication.
I think the offset of the carrier is key. If I touch the can that the up converter is in, I can hear the carrier a little and it's pitch is about the same offset audio frequency as the offset of the crystal filter. Now in double sideband I know you look for zero beat.
I found a recording of real ducks quacking and it sounds just like your radio except its sound is clear. But I can't attach it here. And I am a poet and don't even know it.
I'm listening to some English dude in Honolulu right now with perfect audio clarity on my home brew. But you wouldn't know an SSB signal if it snuck up and bit you in the ass.
Man! Can hardly wait until the wife go off to her grandmother's funeral. I got this thing ready! I got to compare it to the signal level of my CW PLL which I believe the output buffers/amps are on 12 volts. I forgot. I got this thing blaring at 6 volts and the SSB is unidentifiable from any other out there. It sounds great!
I cut the BFO off on the receiver and I can barely pick up a little crackling. Totally unintelligible until I turn the BFO back on. I mean the carrier is nothing. I did change the filter to a ladder type after the modulator. What's cool is I got a couple of variable PC mount caps and put them in a 3 crystal network. I can adjust it to where even the SSB sounds tinny from not enough bandwidth.
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