Topics

Microphone impedance?

Jamie Hanrahan
 

Does anyone know the input impedance and the D700A's microphone input?

And/or the microphone's output impedance?

Since the impedances of these things aren't "matched", they just need to be compatible (it's a bridging connection)... exact values aren't needed... just a ballpark.

Jamie Hanrahan
K6UHI

(Thanks to the group manager for approving my membership!)

Jamie Hanrahan
 

Er.. make the "the input impedance OF the D700A's microphone input"

(wishing Y!G let you edit posts)

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:

Does anyone know the input impedance and the D700A's microphone input?

And/or the microphone's output impedance?

Since the impedances of these things aren't "matched", they just need to be compatible (it's a bridging connection)... exact values aren't needed... just a ballpark.

Jamie Hanrahan
K6UHI

(Thanks to the group manager for approving my membership!)

noskosteve
 

--- "Jamie Hanrahan" wrote:
Does anyone know the input impedance of the D700A's microphone input?

And/or the microphone's output impedance?
... exact values aren't needed... just a ballpark.

Jamie Hanrahan K6UHI
The Mic circuit Zin is 18k, on the schematic there is an 18k to ground on the input of an OpAmp voltage follower.

The Mic Zout is hard to say. The test circuit in the manual uses 5.6k for either DTMF or audio. It is a two terminal electret mic and has a 820 ohm DC feed resistor, so it is something lower than that.

I'm curious what you want this for.
--
73, K9DCI

noskosteve
 

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:

Er.. make the "the input impedance OF the D700A's microphone input"

(wishing Y!G let you edit posts)
No, but you can delete and re-post. I have done this. I copy what I wrote, delete the post in the upper left, then paste into a word processor, make changes and repost.

The Word processor part isn't necessary, but Yahoo has been trashing things in mid post, so I do this as a safety.

--
73, Steve, K9DCI

Jamie Hanrahan
 

--- In TMD700A@..., "noskosteve" <noskosteve@...> wrote:
The Mic circuit Zin is 18k, on the schematic there is an 18k to ground on the input of an OpAmp voltage follower.
Thanks!


The Mic Zout is hard to say. The test circuit in the manual uses 5.6k for either DTMF or audio. It is a two terminal electret mic and has a 820 ohm DC feed resistor, so it is something lower than that.
I found in Kenwood's specs where they say 600 ohm. A very typical mic source impedance (it's pretty standard even in pro audio).

I'm curious what you want this for.
--
73, K9DCI
I am planning to put the control head at my desk and the main box in my attic. This will require about a 50 foot cable. I've already found that a simple extension will pick up too much noise. So I'm going to break out the mic connection and run it through a mic pre with balanced line-level output, and use shielded twisted pair. In the attic I will of course run it into a balanced line receiver (eliminating much of the noise through CMNR) and knock it back down to mic level (eliminating more noise).

This also lets me put a little level meter on the preamp output. (I am constantly getting reports that I'm talking too close to the mic and so overdeviating.)

The speaker output, the control pins in the mic cable, and the signals in the main control cable seem to do ok with a simple extension.

Thanks and 73,
K6UHI

noskosteve
 

OK, sounds cool. Yea. since the head is powered through that cable, you'd need some pretty heavy power and ground lines to limit drop.

Except...if the radio is truely overdeviating, that is a radio adjustment problem. They have deviation limiters (clipper).

If you are just "running into clip" alot and distorting ( I don't generally like to listen to that either), then that's another matter. I don't recall if there is a mic gain setting to change for that.

--
73, Steve, K9DCI

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:



--- In TMD700A@..., "noskosteve" <noskosteve@> wrote:
The Mic circuit Zin is 18k, on the schematic there is an 18k to ground on the input of an OpAmp voltage follower.
Thanks!


The Mic Zout is hard to say. The test circuit in the manual uses 5.6k for either DTMF or audio. It is a two terminal electret mic and has a 820 ohm DC feed resistor, so it is something lower than that.
I found in Kenwood's specs where they say 600 ohm. A very typical mic source impedance (it's pretty standard even in pro audio).

I'm curious what you want this for.
--
73, K9DCI
I am planning to put the control head at my desk and the main box in my attic. This will require about a 50 foot cable. I've already found that a simple extension will pick up too much noise. So I'm going to break out the mic connection and run it through a mic pre with balanced line-level output, and use shielded twisted pair. In the attic I will of course run it into a balanced line receiver (eliminating much of the noise through CMNR) and knock it back down to mic level (eliminating more noise).

This also lets me put a little level meter on the preamp output. (I am constantly getting reports that I'm talking too close to the mic and so overdeviating.)

The speaker output, the control pins in the mic cable, and the signals in the main control cable seem to do ok with a simple extension.

Thanks and 73,
K6UHI

Jamie Hanrahan
 

Good point on the voltage drop in the head cable. What I can do is adapt it to 8P8C, using CAT6 for that extension with 24 gauge wires, and triple up on power and ground. That drops the loop R to about 0.8 ohms (it would be 2.5 ohms with just a single #24 each way). Good practice is that your feed R should be no more than 5% of the effective load R, so assuming the head runs on 12 volts, that puts the max head load at 300 mA.

It's tough to believe the head will pull more than that... I'll measure it. If it does I can always provide its own supply at the desk.

Control in and control out can each be paired with a ground line.

Ah...since the radio is deviation limited then it must be clipping, thanks for that. Further complication: Some repeaters seem to want lower audio levels than others.

This whole thing is of course a gross overcomplication, but that's part of the fun :)

--- In TMD700A@..., "noskosteve" <noskosteve@...> wrote:

OK, sounds cool. Yea. since the head is powered through that cable, you'd need some pretty heavy power and ground lines to limit drop.

Except...if the radio is truely overdeviating, that is a radio adjustment problem. They have deviation limiters (clipper).

If you are just "running into clip" alot and distorting ( I don't generally like to listen to that either), then that's another matter. I don't recall if there is a mic gain setting to change for that.

--
73, Steve, K9DCI
Thanks again and 73,
K6UHI

agcme2002
 

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:
so assuming the head runs on 12 volts, that puts the max head load at 300 mA.


The D700 head is supplied by an 8 volts regulator (unloaded voltage would be about 9.66 V according to the schematic).

noskosteve
 

Gee. Haven't read in a while. Surprised this isn't done yet. (;-)

But yes. It can't be differential data since there are only 2 lines, one for each direction.

It is not only the total supply voltage thing, but the ground is also for the digital signals and the drop will reduce noise margin so it could cause data errors.

It's a good thing you don't have Mic ground in there too.

--
73, Steve, K9DCI

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:

Good point on the voltage drop in the head cable. What I can do is adapt it to 8P8C, using CAT6 for that extension with 24 gauge wires, and triple up on power and ground. That drops the loop R to about 0.8 ohms (it would be 2.5 ohms with just a single #24 each way). Good practice is that your feed R should be no more than 5% of the effective load R, so assuming the head runs on 12 volts, that puts the max head load at 300 mA.

It's tough to believe the head will pull more than that... I'll measure it. If it does I can always provide its own supply at the desk.

Control in and control out can each be paired with a ground line.

Ah...since the radio is deviation limited then it must be clipping, thanks for that. Further complication: Some repeaters seem to want lower audio levels than others.

This whole thing is of course a gross overcomplication, but that's part of the fun :)

--- In TMD700A@..., "noskosteve" <noskosteve@> wrote:

OK, sounds cool. Yea. since the head is powered through that cable, you'd need some pretty heavy power and ground lines to limit drop.

Except...if the radio is truely overdeviating, that is a radio adjustment problem. They have deviation limiters (clipper).

If you are just "running into clip" alot and distorting ( I don't generally like to listen to that either), then that's another matter. I don't recall if there is a mic gain setting to change for that.

--
73, Steve, K9DCI
Thanks again and 73,
K6UHI

Jamie Hanrahan
 

Surprised this isn't done yet. (;-)
Overkill takes time :) Seriously I want to make darn sure this will work reliably before I snake cables through the walls. I don't want to find out later that I should have used a different kind of cable...

I'm running the mic audio through a completely separate STP cable.

If extending the speaker audio turns out to be a problem I should just give up electronics tinkering :) But I really wish KW had not used 3.5mm phone jacks for the speaker outs. Easily the least reliable audio connector in common use.

--- In TMD700A@..., "noskosteve" <noskosteve@...> wrote:


Gee. Haven't read in a while. Surprised this isn't done yet. (;-)

But yes. It can't be differential data since there are only 2 lines, one for each direction.

It is not only the total supply voltage thing, but the ground is also for the digital signals and the drop will reduce noise margin so it could cause data errors.

It's a good thing you don't have Mic ground in there too.

--
73, Steve, K9DCI

--- In TMD700A@..., "Jamie Hanrahan" <jeh@> wrote:

Good point on the voltage drop in the head cable. What I can do is adapt it to 8P8C, using CAT6 for that extension with 24 gauge wires, and triple up on power and ground. That drops the loop R to about 0.8 ohms (it would be 2.5 ohms with just a single #24 each way). Good practice is that your feed R should be no more than 5% of the effective load R, so assuming the head runs on 12 volts, that puts the max head load at 300 mA.

It's tough to believe the head will pull more than that... I'll measure it. If it does I can always provide its own supply at the desk.

Control in and control out can each be paired with a ground line.

Ah...since the radio is deviation limited then it must be clipping, thanks for that. Further complication: Some repeaters seem to want lower audio levels than others.

This whole thing is of course a gross overcomplication, but that's part of the fun :)

--- In TMD700A@..., "noskosteve" <noskosteve@> wrote:

OK, sounds cool. Yea. since the head is powered through that cable, you'd need some pretty heavy power and ground lines to limit drop.

Except...if the radio is truely overdeviating, that is a radio adjustment problem. They have deviation limiters (clipper).

If you are just "running into clip" alot and distorting ( I don't generally like to listen to that either), then that's another matter. I don't recall if there is a mic gain setting to change for that.

--
73, Steve, K9DCI
Thanks again and 73,
K6UHI

noskosteve
 

If you plan to cycle the connectors quite a bit, perhaps by moving the radio between house and car, do what i do. Make a short sacrificial cable. I did this on the control head cable since I never leave the control head in the car unattended.
Make a short cable that plugs into the radio and the speaker plugs into this cable, then leave the cable plugged into the radio and only use the other end of the short cable all the time. When it fails, you only replace the short cable and the radio jack hardly gets cycled.
I keep a spare sacrificial cable around here somewhere. (;-)

--
73, Steve, K9DCI

--- In TMD700A@..., "Jamie Hanrahan" <jeh@...> wrote:

Surprised this isn't done yet. (;-)
Overkill takes time :) Seriously I want to make darn sure this will work reliably before I snake cables through the walls. I don't want to find out later that I should have used a different kind of cable...

I'm running the mic audio through a completely separate STP cable.

If extending the speaker audio turns out to be a problem I should just give up electronics tinkering :) But I really wish KW had not used 3.5mm phone jacks for the speaker outs. Easily the least reliable audio connector in common use.

--- In TMD700A@..., "noskosteve" <noskosteve@> wrote:


Gee. Haven't read in a while. Surprised this isn't done yet. (;-)

But yes. It can't be differential data since there are only 2 lines, one for each direction.

It is not only the total supply voltage thing, but the ground is also for the digital signals and the drop will reduce noise margin so it could cause data errors.

It's a good thing you don't have Mic ground in there too.

--
73, Steve, K9DCI

--- In TMD700A@..., "Jamie Hanrahan" <jeh@> wrote:

Good point on the voltage drop in the head cable. What I can do is adapt it to 8P8C, using CAT6 for that extension with 24 gauge wires, and triple up on power and ground. That drops the loop R to about 0.8 ohms (it would be 2.5 ohms with just a single #24 each way). Good practice is that your feed R should be no more than 5% of the effective load R, so assuming the head runs on 12 volts, that puts the max head load at 300 mA.

It's tough to believe the head will pull more than that... I'll measure it. If it does I can always provide its own supply at the desk.

Control in and control out can each be paired with a ground line.

Ah...since the radio is deviation limited then it must be clipping, thanks for that. Further complication: Some repeaters seem to want lower audio levels than others.

This whole thing is of course a gross overcomplication, but that's part of the fun :)

--- In TMD700A@..., "noskosteve" <noskosteve@> wrote:

OK, sounds cool. Yea. since the head is powered through that cable, you'd need some pretty heavy power and ground lines to limit drop.

Except...if the radio is truely overdeviating, that is a radio adjustment problem. They have deviation limiters (clipper).

If you are just "running into clip" alot and distorting ( I don't generally like to listen to that either), then that's another matter. I don't recall if there is a mic gain setting to change for that.

--
73, Steve, K9DCI
Thanks again and 73,
K6UHI