Shure Mike Model #444 ??? / Freq scheme SSB

[Space Varmint]

Hi, I cannot find the pin out for a Shure mike model # 444. All the pdf's are other stuff about them but can't get pin out.

I used my scope to check it and it looks like if I run pin 7 to the center pin then pin 5 will be ground and pin 6 is mike output using PTT button. Just want to make sure. If anybody knows of a spec. sheet, it would be greatly appreciated.

Also, I would like to use a VFO for a receiver to create an SSB output signal to be amplified. If anyone has experience using SSB, then you know that you can be bitched at for being off frequency. I do not want to use one of my IFs for various reasons. Does anyone have a suggestion on using the VFO (1st LO) to produce the output frequency?

I will use some examples:

Let's say I am using 10Mhz as the 1st IF and IF Xtal filter. So on the receiver I would be running the VFO at 17MHz to receive 7MHz.

So I need a carrier frequency to run into my ballanced modulator along with the audio to produce a double sideband output. At that point I think I will mix it with something, then filter it. So I need another mixer to mix with the VFO freq. I need a good scheme so I will transmit right on my receive freq.

Any suggestions?

 

[Nigel Goodwin]

It's a commonplace occurance - but your receiver is 'designed' to make such a transceiver difficult.

But basically one VFO, one IF frequency (9 MHz was commonly used, and filters and crystals were easily available), you use the crystals for selecting upper or lower sideband, and the filter for both the receiver bandwidth and for removing the unwanted carrier on transmit (the carrier is removed by a double balanced mixer).

 

[Space Varmint]

Well you may be right but in most cases they use the IF to mix with & not the VFO. But not always. See that requires that you have an IF that produces a signal all the time. I would call that feedback. My receiver has no signal at either of the IFs unless it is tuned to a transmitting station. Even the noise won't generate a signal. So I want to use my VFO some way so that I will be tuned exactly to my receive frequency. If you are high or low by say 500 Hz then the beat note will be way off and it anoys allot of hams who have high dollar equipment to keep them right on freq. I'm just looking for suggestions. After I get some parts ordered I am gonna scheme something up. If anybody has a good one, I'm all ears.

 

[Nigel Goodwin]

Why would that require the IF to produce a signal all the time?, of course it doesn't, the double-balanced mixer used cancels the carrier out - and produces two sidebands. By selecting the correct BFO crystal (which is yet another reason why you use crystals) the crystal filter following the mixer outputs only the upper or lower sideband.

As you're using the same VFO, the same filter, and the same crystal, you will be transmitting on the exact same frequency as your receiver is tuned to.

This isn't some 'made up scheme', it's how it's been done for years and years, for all good reasons.

You mentioned before you have an ARRL Handbook - this should give a number of such examples.

EDIT:

If you've got the same 1974 version I have?

Check pages 409 and 414.

 

[Space Varmint]

I don't know. I forgot. Got to think. But you don't need upper & lower sideband crystals. There's another way to do it without. It's been a while.

 

[Nigel Goodwin]

I don't know. I forgot. Got to think. But you don't need upper & lower sideband crystals. There's another way to do it without. It's been a while.

You don't 'need' them - but it's simple, it's exact, and it works beautifully - and it keeps your tuning accurate on both transmit and receive.

 

[Space Varmint]

Yeah that's true. Well, I am working within my means. Unfortunately that's not allot...lol. But if you use crystal for upper and lower sideband, they have to match your filter. See, I will be building the crystal filter from crystals. So I know I will have to leave that part variable but is the BFO is not a nifty drifty I can get away with it being very close and should be able to adjust it right in. My main concern is the center frequency. I want that to be right on so that the BFO is all I will be concerned with.

If I use the same crystal frequency filter as the 1st IF in the receiver, that should work right? I'm concerned about the picking up the carrier frequency in the ballanced modulator, because I could build a crystal oscillator and I would be locked right on other than stray capacitances and temperature effects on the crystal. What scares me is the filter picking up the crystal oscillator and drowning out the modulated signal. What do you think? Should I be concerned with that? Maybe I need allot of shielding. I would like to put the modulator in one small, well you know, cat food can...lol.

 

[Space Varmint]

Also, does anyone know the impedance of these Shure mikes? If it is low Z then I need to take advantage of that. I need to avoid rf pick-up.

 

[Nigel Goodwin]

Yeah that's true. Well, I am working within my means. Unfortunately that's not allot...lol. But if you use crystal for upper and lower sideband, they have to match your filter. See, I will be building the crystal filter from crystals. So I know I will have to leave that part variable but is the BFO is not a nifty drifty I can get away with it being very close and should be able to adjust it right in. My main concern is the center frequency. I want that to be right on so that the BFO is all I will be concerned with.

If you've got a BFO that you're adjusting to get the audio right, then you're not on tune - the point of using two crystals accurately positioned either side of the (missing) carrier is that it ensures you're spot on frequency, and that switching upper/lower doesn't affect the tuning at all.

One of the two designed I mentioned in ARRL actually used two 9MHz crystals, with trimmers to pull them either side of the 9MHz IF.

If I use the same crystal frequency filter as the 1st IF in the receiver, that should work right? I'm concerned about the picking up the carrier frequency in the ballanced modulator, because I could build a crystal oscillator and I would be locked right on other than stray capacitances and temperature effects on the crystal. What scares me is the filter picking up the crystal oscillator and drowning out the modulated signal. What do you think? Should I be concerned with that? Maybe I need allot of shielding. I would like to put the modulator in one small, well you know, cat food can...lol.

I'm completely confused by your concerns?, the two carrier frequencies (as used for your BFO) are both (whichever you're using) cancelled out in the double balanced mixer, and rejected by the very sharp and narrow crystal filter - all these parts are common to both transmit and receive.

Check the many examples in ARRL and RSGB books.

 

[Nigel Goodwin]

Also, does anyone know the impedance of these Shure mikes? If it is low Z then I need to take advantage of that. I need to avoid rf pick-up.

Again, I'm baffled by your concerns - presumably it's a comms mike?, it designed for that use - and your mike preamp should be well screened and suitably filtered, both to tailor the speech bandwidth, and to completely reject any RF.

 

[Space Varmint]

Again, I'm baffled by your concerns - presumably it's a comms mike?, it designed for that use - and your mike preamp should be well screened and suitably filtered, both to tailor the speech bandwidth, and to completely reject any RF.

To answer the first question, the filter will be after the ballanced modulator so I am concerned with pich up through the air.

On the second question, I can't find any amplifier designs you don't pay for, for the Shure mikes. If it is low Z then that will give additional rf rejection. I should probably assume it is but would like to know because if it is high Z then I want to efficiently get it into an OP Amp.

I'm gonna sling up a 40 meter "inverted V" antenna tonight and I got two amplifiers I built a while back. The final is an MRF454 80 watt amp. So just trying to get their quickly. As soon as I get the antenna up I could start using CW. I have a 40 meter PLL and the pre-amp is 0 t0 10 watts adjustable with wave shaping for key clicks. But want to get the SSB going ASAP.

 

[audioguru]

The datasheet for the Shure 444 mic is linked in Google.
It is unbalanced, "high impedance" and the recommended load is 100k ohms.
It cuts off frequencies below 300Hz and above 3kHz. It has a 10dB peak at 3kHz.

 

[Nigel Goodwin]

To answer the first question, the filter will be after the ballanced modulator so I am concerned with pich up through the air.

Of course the filter is after the modulator

Build it correctly, with proper decoupling and a little screening, there won't be any concerns. Bear in mind it's all at a fairly low level, low impedances, and short connections.

On the second question, I can't find any amplifier designs you don't pay for, for the Shure mikes. If it is low Z then that will give additional rf rejection. I should probably assume it is but would like to know because if it is high Z then I want to efficiently get it into an OP Amp.

Is there electronics in the mike?, if so it's low impedance - and it's most likely low impedance anyway - most mikes are. I've not been active as an amateur for a few years now, but I don't think I ever saw a mike that wasn't low impedance?.

I'm gonna sling up a 40 meter "inverted V" antenna tonight and I got two amplifiers I built a while back. The final is an MRF454 80 watt amp. So just trying to get their quickly. As soon as I get the antenna up I could start using CW. I have a 40 meter PLL and the pre-amp is 0 t0 10 watts adjustable with wave shaping for key clicks. But want to get the SSB going ASAP.

I would seriously suggest you get the receiver redesigned properly first - there's nothing in that design that's going to help in a transmitter, and a lot that's going to make it badly wrong.

There's load's of books available - try looking how things are done - don't just 'make it up' and bodge bits until it works.

 

[Nigel Goodwin]

The datasheet for the Shure 444 mic is linked in Google.
It is unbalanced, "high impedance" and the recommended load is 100k ohms.
It cuts off frequencies below 300Hz and above 3kHz. It has a 10dB peak at 3kHz.

Whoa! - that's a shock!.

 

[Space Varmint]

Alright, it's low Z. Just found this: **broken link removed**

 

[audioguru]

The newer Shure 522 mic is completely different from the old Shure 444 that you are talking about. **broken link removed**

 

[Space Varmint]

The newer Shure 522 mic is completely different from the old Shure 444 that you are talking about. **broken link removed**

You said a 100K? Dern, no wonder I can't get any output from the OP AMP.

I got this dern 750KHz broadcast station right near my house and of course that's all I got so far.

 

[Space Varmint]

quote from Nigel:

I would seriously suggest you get the receiver redesigned properly first - there's nothing in that design that's going to help in a transmitter, and a lot that's going to make it badly wrong.

Thank you for such a sweet compliment

Dude, the receiver is working great. I love it. But just out of curiosity, what is it that you find so terribly wrong? I mean, I have told you that the schematic was a first iteration of the final design which still may not be final, like take for instance, I added a coax cable to the antenna input thereby changing the input impedance to 50 ohms and unfortunately it radically changed the pre-selector.

But I want to know what in particular you find just totally unacceptable? Let's talk turkey. It appears you got something to say.

 

[Nigel Goodwin]

But I want to know what in particular you find just totally unacceptable? Let's talk turkey. It appears you got something to say.

Does it bear any resemblance to the parts you've posted?.

If so, it has far too many audio stages, almost none of which are required, and almost none of which have supply decoupling - these are adding instability, noise, and distortion - and nothing of any use. The stages appear to be thrown together, with no concept of design or calculating values - and with random darlington pairs appearing for no good reason. There also appears to be no sensible audio filtering, just odd capacitors here and there.

Likewise the rest of the stages are poorly, or not at all, decoupled (and mostly badly designed).

All you need for the audio stages is:

Detector.
One amplifier stage (optional).
Bandpass filter (simple opamp would be handy).
Power amplifier.

Just checked the two ARRL designs I mentioned earlier, one use a passive low-pass filter followed by a 741, driving headphones. The second uses a passive low-pass filter directly driving a power amp IC to a speaker.

Perhaps you would care to go through the design of one of the stages?, it's reasons for been there, and how (and why) you calculated the values.

Sorry, but it's truely the worst radio design I've ever seen, even beating the super-regen fisaco's of a year or two ago.

 

[Space Varmint]

Does it bear any resemblance to the parts you've posted?.

If so, it has far too many audio stages, almost none of which are required, and almost none of which have supply decoupling - these are adding instability, noise, and distortion - and nothing of any use. The stages appear to be thrown together, with no concept of design or calculating values - and with random darlington pairs appearing for no good reason. There also appears to be no sensible audio filtering, just odd capacitors here and there.

Likewise the rest of the stages are poorly, or not at all, decoupled (and mostly badly designed).

All you need for the audio stages is:

Detector.
One amplifier stage (optional).
Bandpass filter (simple opamp would be handy).
Power amplifier.

Just checked the two ARRL designs I mentioned earlier, one use a passive low-pass filter followed by a 741, driving headphones. The second uses a passive low-pass filter directly driving a power amp IC to a speaker.

Perhaps you would care to go through the design of one of the stages?, it's reasons for been there, and how (and why) you calculated the values.

Sorry, but it's truely the worst radio design I've ever seen, even beating the super-regen fisaco's of a year or two ago.

Your talking head phones. There's a big difference between head phones and using a speaker especially in SSB. You can use head phones in a direct conversion receiver. In fact it is nearly impossible to use a speaker in a DC receiver. Thanks to audioguru I got just the audio I was looking for at the output.

I keep trying to explain to you that you have to use the extra stages because you do not any single stage to do too much amplification. This is due to the dynamic range of the receiver. Anyway, let me post what I have now and it is final. It's a keeper and it works great!