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Re: Tracing receive signal for low signal

 

Better thinking is that the carrier-balanced 1-KHz signal is heard
farther back toward the audio section, after the BFO has done
its work.

Bob ¡ª KK5R
--------------------------------------------

On Sat, 12/22/18, Bob Lunsford via Groups.Io <nocrud222@...> wrote:

Subject: Re: [BITX20] Tracing receive signal for low signal
To: [email protected]
Date: Saturday, December 22, 2018, 12:55 PM

I also thought that injecting an AM signal is
like listening to an
AM broadcasting signal where you have
to zero-beat the carrier
and listen to the modulation. A 'scope
would be better to see the
carrier. But "ear-balling" the 1-KHz
signal can give an idea where
the signal is amplified and where it is
falling off. This is good
theory, at least. I'm sure someone in
the group has a better
suggestion.

Bob ¡ª KK5R
--------------------------------------------
On Sat, 12/22/18, Evan Hand <elhandjr@...>
wrote:

Subject: Re: [BITX20] Tracing receive
signal for low signal
To: [email protected]
Date: Saturday, December 22, 2018,
12:48 PM

If I am interperting what
you are doing correctly, you have an
AM signal at 7.15 Mhz
with 1 k hz modulation.? You are
injecting it starting at
the antenna and progressing towards
the audio section.? Is
that correct?

I would
suggest the you read the HF Signals
circuit description:


The first thing to note is
that the 7.15 mhz signal is mixed with
the local oscillator
of 45-75 mhz to get a 45 mhz signal
that is then amplified
ant further mixed back down to 12 mhz
and then detected by
beating an 11996500 BFO to get the
audio back out.?

Note that injecting a signal
further and further away from the
first mixer will result in
lower detection, if you are keeping it
at 7.15 mhz.

Hope that helps explain what
is happening, though not in solving
your problem.



I will reread the thread ans
see if I can help.? In the meantime
someone with more
experience than me might chime in with
a suggestion.

73
Evan
AC9TU
Re: Tracing receive signal for low signal

 

Dave

There is gain distributed rather evenly so not sure you are seeing anything unusual. Unlike a commercial rig with gobs of AGC, this rig requires using the gain control. Please evaluate into a good, full sized antenna with some headphones. Strong huge signals will require minimum gain setting, signals just above noise may require nearly all the gain.? also try this test using a good 40m antenna. Set ubitx for at least mid volume. The noise should go up when you plug in the antenna. If you can hear band noise, I suspect all is okay. If you want more audio, find a inexpensive amplified speaker.

Curt
Re: Tracing receive signal for low signal

 

I also thought that injecting an AM signal is like listening to an
AM broadcasting signal where you have to zero-beat the carrier
and listen to the modulation. A 'scope would be better to see the
carrier. But "ear-balling" the 1-KHz signal can give an idea where
the signal is amplified and where it is falling off. This is good
theory, at least. I'm sure someone in the group has a better
suggestion.

Bob ¡ª KK5R
--------------------------------------------

On Sat, 12/22/18, Evan Hand <elhandjr@...> wrote:

Subject: Re: [BITX20] Tracing receive signal for low signal
To: [email protected]
Date: Saturday, December 22, 2018, 12:48 PM

If I am interperting what
you are doing correctly, you have an AM signal at 7.15 Mhz
with 1 k hz modulation.? You are injecting it starting at
the antenna and progressing towards the audio section.? Is
that correct?

I would
suggest the you read the HF Signals circuit description:


The first thing to note is
that the 7.15 mhz signal is mixed with the local oscillator
of 45-75 mhz to get a 45 mhz signal that is then amplified
ant further mixed back down to 12 mhz and then detected by
beating an 11996500 BFO to get the audio back out.?

Note that injecting a signal
further and further away from the first mixer will result in
lower detection, if you are keeping it at 7.15 mhz.

Hope that helps explain what
is happening, though not in solving your problem.



I will reread the thread ans
see if I can help.? In the meantime someone with more
experience than me might chime in with a suggestion.

73
Evan
AC9TU
Re: Tracing receive signal for low signal

 

My first thought is that it may be some kind of bandpass filter
that is not on-frequency. However, very often the obvious is
not the problem in such cases. Signal injection and tracing is
the way to go, though, in my opinion.

Bob ¡ª KK5R

--------------------------------------------

On Sat, 12/22/18, Dave Space <davesspacebar@...> wrote:

Subject: [BITX20] Tracing receive signal for low signal
To: [email protected]
Date: Saturday, December 22, 2018, 12:22 PM

Let me start with I'm a noob at
diagnostics.

Since my signal is really low I started to do some tracing.

One thing I noticed is odd if I inject a signal further away
from the antenna source it gets softer listening to a 1khz
tone. (Isn't that the opposite of what you would expect)
(Injected 7.150mhz am signal with 1khz tone)

So for example injecting a signal at c200, 201, 202,203,204
gets progressively softer to? non existent at c204 with
a 100uv signal injected.? If I touch the L4 to inject
the signal I can hear the signal a little? but c204 I
hear nothing injecting there.? If I touch the base of
Q10 I hear nothing.? If I ramp up the signal generator
significantly 30x higher I can then hear a signal injecting
at the base of Q10.

What could cause this?

Usually I thought you would expect the signal to get
stronger the further in the receive path you get but it
actually got weaker and required 30x the signal at base of
Q10 to even hear it.??

Any ideas what I should check?? Or is this expected?

Thanks
Re: Tracing receive signal for low signal

 

If I am interperting what you are doing correctly, you have an AM signal at 7.15 Mhz with 1 k hz modulation.? You are injecting it starting at the antenna and progressing towards the audio section.? Is that correct?

I would suggest the you read the HF Signals circuit description:


The first thing to note is that the 7.15 mhz signal is mixed with the local oscillator of 45-75 mhz to get a 45 mhz signal that is then amplified ant further mixed back down to 12 mhz and then detected by beating an 11996500 BFO to get the audio back out.?

Note that injecting a signal further and further away from the first mixer will result in lower detection, if you are keeping it at 7.15 mhz.

Hope that helps explain what is happening, though not in solving your problem.

I will reread the thread ans see if I can help.? In the meantime someone with more experience than me might chime in with a suggestion.

73
Evan
AC9TU
Re: Tracing receive signal for low signal

 

This is for a ubitx board v4.
Tracing receive signal for low signal

 

Let me start with I'm a noob at diagnostics.

Since my signal is really low I started to do some tracing.

One thing I noticed is odd if I inject a signal further away from the antenna source it gets softer listening to a 1khz tone. (Isn't that the opposite of what you would expect) (Injected 7.150mhz am signal with 1khz tone)

So for example injecting a signal at c200, 201, 202,203,204 gets progressively softer to? non existent at c204 with a 100uv signal injected.? If I touch the L4 to inject the signal I can hear the signal a little? but c204 I hear nothing injecting there.? If I touch the base of Q10 I hear nothing.? If I ramp up the signal generator significantly 30x higher I can then hear a signal injecting at the base of Q10.

What could cause this?

Usually I thought you would expect the signal to get stronger the further in the receive path you get but it actually got weaker and required 30x the signal at base of Q10 to even hear it.??

Any ideas what I should check?? Or is this expected?

Thanks
Re: Ubitx - carbon mic

 

The earpiece in the telephone makes a good dynamic element
in a microphone but because the Bitx is designed for an electret
microphone and the electret elements are so common, I also
consider it a waste of time to go outside the design of the radio
as far as microph9nes are concerned.

You have me beat in regard to years of telecom service. {;->

Bob ¡ª KK5R
--------------------------------------------

On Sat, 12/22/18, MVS Sarma <mvssarma@...> wrote:

Subject: Re: [BITX20] Ubitx - carbon mic
To: [email protected]
Date: Saturday, December 22, 2018, 9:37 AM

Don'y bother. I had 40yeasrs of
experience in Indian Telecom.?I get your point ,
sir.?regardssarmavu3zmv

On Sat, Dec
22, 2018 at 8:00 PM Bob Lunsford via Groups.Io
<nocrud222@...>
wrote:
The telephone I referred
to for using the earpiece is here

and note that the device across the earpiece was
"shunted

to keep from hearing the dialing impulses."







--------------------------------------------

On Sat, 12/22/18, Bob Lunsford via Groups.Io
<nocrud222@...>
wrote:



?Subject: Re: [BITX20] Ubitx - carbon mic

?To: [email protected]

?Date: Saturday, December 22, 2018, 8:54 AM



?Careful reading will show that I was not

?talking about the Wiki "Mouthpiece"

?which is a carbon unit but about the

?EARPIECE which is an earphone that

?closely resembles a dynamic microphone

?element.



?I worked in the telephone industry.

?First with General Telephone i 1965 and

?later for DoD as a system installer in

?foreign countries. The telephone "earpiece"

?is from a phone of the late '60's era.

?I hold one in my hand as we speak.



?Bob ¡ª KK5R



?--------------------------------------------

?On Sat, 12/22/18, MVS Sarma <mvssarma@...>

?wrote:



? Subject: Re: [BITX20] Ubitx - carbon

?mic

? To: [email protected]

? Date: Saturday, December 22, 2018,

?2:02 AM



? Not earpiece but

?mouthpiece.



? On Sat, Dec

? 22, 2018 at 5:17 AM Bob Lunsford via

?Groups.Io

? <nocrud222@...>

? wrote:

? Try the earpiece from an

? old cradle type telephone.



? The carbon mic element is not

?advisable since it has an

? inherent hiss that may have to be

?filtered out.







? The earpiece has a diode-looking

?device across the

? terminals, probably two diodes

?back-to-back to keep the

? switching clicks from blasting the

?telephone user. Remove

? this to avoid introducing some

?unknown/unwanted result.







? The earpiece is about 600 Ohms from

?what others have told

? me. Therefore, you will probably need

?a one-transistor amp

? for impedance matching. The amp

?previously cited may do

? it.







? Bob ¡ª KK5R









?--------------------------------------------



? On Fri, 12/21/18, iz oos <and2oosiz2@...>

? wrote:







? ?Subject: [BITX20] Ubitx - carbon

?mic



? ?To: [email protected]



? ?Date: Friday, December 21, 2018,

?9:51 AM







? ?Has anyone tried a carbon mic



? ?with the ubitx? How to wire it? The

?Shure 104C manual

? seems



? ?an interesting starting point.
Re: Ubitx - carbon mic

 

Don'y bother. I had 40yeasrs of experience in Indian Telecom.
?I get your point , sir.
?regards
sarma
vu3zmv


On Sat, Dec 22, 2018 at 8:00 PM Bob Lunsford via Groups.Io <nocrud222=[email protected]> wrote:
The telephone I referred to for using the earpiece is here
and note that the device across the earpiece was "shunted
to keep from hearing the dialing impulses."



--------------------------------------------
On Sat, 12/22/18, Bob Lunsford via Groups.Io <nocrud222=[email protected]> wrote:

?Subject: Re: [BITX20] Ubitx - carbon mic
?To: [email protected]
?Date: Saturday, December 22, 2018, 8:54 AM

?Careful reading will show that I was not
?talking about the Wiki "Mouthpiece"
?which is a carbon unit but about the
?EARPIECE which is an earphone that
?closely resembles a dynamic microphone
?element.

?I worked in the telephone industry.
?First with General Telephone i 1965 and
?later for DoD as a system installer in
?foreign countries. The telephone "earpiece"
?is from a phone of the late '60's era.
?I hold one in my hand as we speak.

?Bob ¡ª KK5R

?--------------------------------------------
?On Sat, 12/22/18, MVS Sarma <mvssarma@...>
?wrote:

? Subject: Re: [BITX20] Ubitx - carbon
?mic
? To: [email protected]
? Date: Saturday, December 22, 2018,
?2:02 AM

? Not earpiece but
?mouthpiece.

? On Sat, Dec
? 22, 2018 at 5:17 AM Bob Lunsford via
?Groups.Io
? <nocrud222=[email protected]>
? wrote:
? Try the earpiece from an
? old cradle type telephone.

? The carbon mic element is not
?advisable since it has an
? inherent hiss that may have to be
?filtered out.



? The earpiece has a diode-looking
?device across the
? terminals, probably two diodes
?back-to-back to keep the
? switching clicks from blasting the
?telephone user. Remove
? this to avoid introducing some
?unknown/unwanted result.



? The earpiece is about 600 Ohms from
?what others have told
? me. Therefore, you will probably need
?a one-transistor amp
? for impedance matching. The amp
?previously cited may do
? it.



? Bob ¡ª KK5R




?--------------------------------------------

? On Fri, 12/21/18, iz oos <and2oosiz2@...>
? wrote:



? ?Subject: [BITX20] Ubitx - carbon
?mic

? ?To: [email protected]

? ?Date: Friday, December 21, 2018,
?9:51 AM



? ?Has anyone tried a carbon mic

? ?with the ubitx? How to wire it? The
?Shure 104C manual
? seems

? ?an interesting starting point.

























Re: Ubitx - carbon mic

 

The telephone I referred to for using the earpiece is here
and note that the device across the earpiece was "shunted
to keep from hearing the dialing impulses."



--------------------------------------------

On Sat, 12/22/18, Bob Lunsford via Groups.Io <nocrud222@...> wrote:

Subject: Re: [BITX20] Ubitx - carbon mic
To: [email protected]
Date: Saturday, December 22, 2018, 8:54 AM

Careful reading will show that I was not
talking about the Wiki "Mouthpiece"
which is a carbon unit but about the
EARPIECE which is an earphone that
closely resembles a dynamic microphone
element.

I worked in the telephone industry.
First with General Telephone i 1965 and
later for DoD as a system installer in
foreign countries. The telephone "earpiece"
is from a phone of the late '60's era.
I hold one in my hand as we speak.

Bob ¡ª KK5R

--------------------------------------------
On Sat, 12/22/18, MVS Sarma <mvssarma@...>
wrote:

Subject: Re: [BITX20] Ubitx - carbon
mic
To: [email protected]
Date: Saturday, December 22, 2018,
2:02 AM

Not earpiece but
mouthpiece.

On Sat, Dec
22, 2018 at 5:17 AM Bob Lunsford via
Groups.Io
<nocrud222@...>
wrote:
Try the earpiece from an
old cradle type telephone.

The carbon mic element is not
advisable since it has an
inherent hiss that may have to be
filtered out.



The earpiece has a diode-looking
device across the
terminals, probably two diodes
back-to-back to keep the
switching clicks from blasting the
telephone user. Remove
this to avoid introducing some
unknown/unwanted result.



The earpiece is about 600 Ohms from
what others have told
me. Therefore, you will probably need
a one-transistor amp
for impedance matching. The amp
previously cited may do
it.



Bob ¡ª KK5R




--------------------------------------------

On Fri, 12/21/18, iz oos <and2oosiz2@...>
wrote:



?Subject: [BITX20] Ubitx - carbon
mic

?To: [email protected]

?Date: Friday, December 21, 2018,
9:51 AM



?Has anyone tried a carbon mic

?with the ubitx? How to wire it? The
Shure 104C manual
seems

?an interesting starting point.
Re: Ubitx - carbon mic

 

Careful reading will show that I was not talking about the Wiki "Mouthpiece"
which is a carbon unit but about the EARPIECE which is an earphone that
closely resembles a dynamic microphone element.

I worked in the telephone industry. First with General Telephone i 1965 and
later for DoD as a system installer in foreign countries. The telephone "earpiece"
is from a phone of the late '60's era. I hold one in my hand as we speak.

Bob ¡ª KK5R

--------------------------------------------

On Sat, 12/22/18, MVS Sarma <mvssarma@...> wrote:

Subject: Re: [BITX20] Ubitx - carbon mic
To: [email protected]
Date: Saturday, December 22, 2018, 2:02 AM

Not earpiece but mouthpiece.

On Sat, Dec
22, 2018 at 5:17 AM Bob Lunsford via Groups.Io
<nocrud222@...>
wrote:
Try the earpiece from an
old cradle type telephone.

The carbon mic element is not advisable since it has an
inherent hiss that may have to be filtered out.



The earpiece has a diode-looking device across the
terminals, probably two diodes back-to-back to keep the
switching clicks from blasting the telephone user. Remove
this to avoid introducing some unknown/unwanted result.



The earpiece is about 600 Ohms from what others have told
me. Therefore, you will probably need a one-transistor amp
for impedance matching. The amp previously cited may do
it.



Bob ¡ª KK5R



--------------------------------------------

On Fri, 12/21/18, iz oos <and2oosiz2@...>
wrote:



?Subject: [BITX20] Ubitx - carbon mic

?To: [email protected]

?Date: Friday, December 21, 2018, 9:51 AM



?Has anyone tried a carbon mic

?with the ubitx? How to wire it? The Shure 104C manual
seems

?an interesting starting point.
Re: Low output on CW UBITX

 

Just check C81 and R83 if they are OK.

Also L1,2,3 & 4.

At 22/12/2018, you wrote:
Did some more tests, built an RF probe for my DMM, did the maths to come up with the following outputs in watts at about 13volts.


3.5 7 10 14 18 21 24 28
CW 0.9 0.6 2.8 2.2 1.3 2.6 1.0 0.6
SSB 3.6 3.9 2.6 2.4 3.5 1.8 1.1 1.0

As you can see, on some bands output is lower on CW than SSB and other bands it is the other way around.? I checked the inductors in the PA output LPFs and the windings looked about right (I didn't pull out the caps to check values).

So I remains with the problem why the radically different outputs between SSB and CW, that's aside from all the outputs being low.

Any further input valued - thanks team.

Cheers,

Rod
VK1ACE
Re: DAVE [BITX20] RF Preamp - Attenuator

Brian Arnott
 

Having sorted through my spares box I have found some SL621C chips (Metal can), after my own build I might have some to spare,whats the going rate for these?
Re: Low output on CW UBITX

 

Thanks for that insight I¡¯ll check those areas out and let u know how I go.

On Sat, 22 Dec 2018 at 8:51 pm, iz oos <and2oosiz2@...> wrote:

Hi as other have said the output is routed differently up to the first IF, then is the same. When I first did add a 45mhz parallel LC filter just after the first mixer, I got lower output on CW only. Jerry explained that, adding that filter for SSB would interact with the CW LO. Indeed it was the case. So a slight difference is fine in an unmodified unit. The problem in your unit is low output with both SSB and CW, so the problem should reside either in the local oscillator levels, the first mixer, the driver up to the antenna output. If you can at least measure the level outputs (with the probe) others should help you in detecting the problematic stage.


Il 22/dic/2018 05:25, "Rod Russell-Brown" <rodrussellbrown@...> ha scritto:
Did some more tests, built an RF probe for my DMM, did the maths to come up with the following outputs in watts at about 13volts.


 3.5 7 10 14 18 21 24 28
CW 0.9 0.6 2.8 2.2 1.3 2.6 1.0 0.6
SSB 3.6 3.9 2.6 2.4 3.5 1.8 1.1 1.0

As you can see, on some bands output is lower on CW than SSB and other bands it is the other way around.? I checked the inductors in the PA output LPFs and the windings looked about right (I didn't pull out the caps to check values).

So I remains with the problem why the radically different outputs between SSB and CW, that's aside from all the outputs being low.

Any further input valued - thanks team.

Cheers,

Rod
VK1ACE


On Thu, 20 Dec 2018 at 08:21, ajparent1/KB1GMX <kb1gmx@...> wrote:
From the last mixer to the antenna CW and SSB are same.

I've seen at least two with a wrong 40M LPF, though it was TX power amp but 80 and 20
had higher power than 40.
Seems the coils had about half the number of turns, they were likely 10M coils and the
caps were also questionable for correct value.? Rewound and recaped it then produced
normal power.

So it can be simple but not obvious.

Allison

--
Cheers,

Rod

__________________
Rod Russell-Brown
Southgate Christian Community
Re: Low output on CW UBITX

 

I mean the output levels at each stage between the PA and the first mixer and the levels at each LO (CLK).


Il 22/dic/2018 10:51, "iz oos" <and2oosiz2@...> ha scritto:

Hi as other have said the output is routed differently up to the first IF, then is the same. When I first did add a 45mhz parallel LC filter just after the first mixer, I got lower output on CW only. Jerry explained that, adding that filter for SSB would interact with the CW LO. Indeed it was the case. So a slight difference is fine in an unmodified unit. The problem in your unit is low output with both SSB and CW, so the problem should reside either in the local oscillator levels, the first mixer, the driver up to the antenna output. If you can at least measure the level outputs (with the probe) others should help you in detecting the problematic stage.


Il 22/dic/2018 05:25, "Rod Russell-Brown" <rodrussellbrown@...> ha scritto:
Did some more tests, built an RF probe for my DMM, did the maths to come up with the following outputs in watts at about 13volts.


 3.5 7 10 14 18 21 24 28
CW 0.9 0.6 2.8 2.2 1.3 2.6 1.0 0.6
SSB 3.6 3.9 2.6 2.4 3.5 1.8 1.1 1.0

As you can see, on some bands output is lower on CW than SSB and other bands it is the other way around.? I checked the inductors in the PA output LPFs and the windings looked about right (I didn't pull out the caps to check values).

So I remains with the problem why the radically different outputs between SSB and CW, that's aside from all the outputs being low.

Any further input valued - thanks team.

Cheers,

Rod
VK1ACE


On Thu, 20 Dec 2018 at 08:21, ajparent1/KB1GMX <kb1gmx@...> wrote:
From the last mixer to the antenna CW and SSB are same.

I've seen at least two with a wrong 40M LPF, though it was TX power amp but 80 and 20
had higher power than 40.
Seems the coils had about half the number of turns, they were likely 10M coils and the
caps were also questionable for correct value.? Rewound and recaped it then produced
normal power.

So it can be simple but not obvious.

Allison


Re: Low output on CW UBITX

 

Hi as other have said the output is routed differently up to the first IF, then is the same. When I first did add a 45mhz parallel LC filter just after the first mixer, I got lower output on CW only. Jerry explained that, adding that filter for SSB would interact with the CW LO. Indeed it was the case. So a slight difference is fine in an unmodified unit. The problem in your unit is low output with both SSB and CW, so the problem should reside either in the local oscillator levels, the first mixer, the driver up to the antenna output. If you can at least measure the level outputs (with the probe) others should help you in detecting the problematic stage.


Il 22/dic/2018 05:25, "Rod Russell-Brown" <rodrussellbrown@...> ha scritto:
Did some more tests, built an RF probe for my DMM, did the maths to come up with the following outputs in watts at about 13volts.


 3.5 7 10 14 18 21 24 28
CW 0.9 0.6 2.8 2.2 1.3 2.6 1.0 0.6
SSB 3.6 3.9 2.6 2.4 3.5 1.8 1.1 1.0

As you can see, on some bands output is lower on CW than SSB and other bands it is the other way around.? I checked the inductors in the PA output LPFs and the windings looked about right (I didn't pull out the caps to check values).

So I remains with the problem why the radically different outputs between SSB and CW, that's aside from all the outputs being low.

Any further input valued - thanks team.

Cheers,

Rod
VK1ACE


On Thu, 20 Dec 2018 at 08:21, ajparent1/KB1GMX <kb1gmx@...> wrote:
From the last mixer to the antenna CW and SSB are same.

I've seen at least two with a wrong 40M LPF, though it was TX power amp but 80 and 20
had higher power than 40.
Seems the coils had about half the number of turns, they were likely 10M coils and the
caps were also questionable for correct value.? Rewound and recaped it then produced
normal power.

So it can be simple but not obvious.

Allison

Re: Ubitx - carbon mic

 

Neither HF amateur is expected to transmit Hi-Fi. I suppose, if managed, it should suite well. Only issue is biassing needed for the mic. You need to flow 10mA into the mic.ll the best for a trial.

?A


On Sat, Dec 22, 2018 at 3:06 PM iz oos <and2oosiz2@...> wrote:

Thanks for the comments. I know (wikipedia hihi) the limitations of carbon types, but I remember old telephones were not hifi but very effective in speech. The carbon type needs dc and maybe the one of the ubitx mic input might be used. Also it should deliver quite a high level of output so no preamp should be used. And I am surprised that Shure still produces a carbon mic. About the Piezo elements I have some ceramic high impedance elements. I would think a buffer based on a 2N3904 might be used to have proper modulation with the ubitx. I wish to know your opinions on this as well.


Il 22/dic/2018 08:02, "MVS Sarma" <mvssarma@...> ha scritto:
Not earpiece but mouthpiece.


On Sat, Dec 22, 2018 at 5:17 AM Bob Lunsford via Groups.Io <nocrud222=[email protected]> wrote:
Try the earpiece from an old cradle type telephone.
The carbon mic element is not advisable since it has an inherent hiss that may have to be filtered out.

The earpiece has a diode-looking device across the terminals, probably two diodes back-to-back to keep the switching clicks from blasting the telephone user. Remove this to avoid introducing some unknown/unwanted result.

The earpiece is about 600 Ohms from what others have told me. Therefore, you will probably need a one-transistor amp for impedance matching. The amp previously cited may do it.

Bob ¡ª KK5R

--------------------------------------------
On Fri, 12/21/18, iz oos <and2oosiz2@...> wrote:

?Subject: [BITX20] Ubitx - carbon mic
?To: [email protected]
?Date: Friday, December 21, 2018, 9:51 AM

?Has anyone tried a carbon mic
?with the ubitx? How to wire it? The Shure 104C manual seems
?an interesting starting point.







Re: Ubitx - carbon mic

 

Thanks for the comments. I know (wikipedia hihi) the limitations of carbon types, but I remember old telephones were not hifi but very effective in speech. The carbon type needs dc and maybe the one of the ubitx mic input might be used. Also it should deliver quite a high level of output so no preamp should be used. And I am surprised that Shure still produces a carbon mic. About the Piezo elements I have some ceramic high impedance elements. I would think a buffer based on a 2N3904 might be used to have proper modulation with the ubitx. I wish to know your opinions on this as well.


Il 22/dic/2018 08:02, "MVS Sarma" <mvssarma@...> ha scritto:
Not earpiece but mouthpiece.


On Sat, Dec 22, 2018 at 5:17 AM Bob Lunsford via Groups.Io <nocrud222=[email protected]> wrote:
Try the earpiece from an old cradle type telephone.
The carbon mic element is not advisable since it has an inherent hiss that may have to be filtered out.

The earpiece has a diode-looking device across the terminals, probably two diodes back-to-back to keep the switching clicks from blasting the telephone user. Remove this to avoid introducing some unknown/unwanted result.

The earpiece is about 600 Ohms from what others have told me. Therefore, you will probably need a one-transistor amp for impedance matching. The amp previously cited may do it.

Bob ¡ª KK5R

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On Fri, 12/21/18, iz oos <and2oosiz2@...> wrote:

?Subject: [BITX20] Ubitx - carbon mic
?To: [email protected]
?Date: Friday, December 21, 2018, 9:51 AM

?Has anyone tried a carbon mic
?with the ubitx? How to wire it? The Shure 104C manual seems
?an interesting starting point.







Re: Ubitx - carbon mic

 

Not earpiece but mouthpiece.


On Sat, Dec 22, 2018 at 5:17 AM Bob Lunsford via Groups.Io <nocrud222=[email protected]> wrote:
Try the earpiece from an old cradle type telephone.
The carbon mic element is not advisable since it has an inherent hiss that may have to be filtered out.

The earpiece has a diode-looking device across the terminals, probably two diodes back-to-back to keep the switching clicks from blasting the telephone user. Remove this to avoid introducing some unknown/unwanted result.

The earpiece is about 600 Ohms from what others have told me. Therefore, you will probably need a one-transistor amp for impedance matching. The amp previously cited may do it.

Bob ¡ª KK5R

--------------------------------------------
On Fri, 12/21/18, iz oos <and2oosiz2@...> wrote:

?Subject: [BITX20] Ubitx - carbon mic
?To: [email protected]
?Date: Friday, December 21, 2018, 9:51 AM

?Has anyone tried a carbon mic
?with the ubitx? How to wire it? The Shure 104C manual seems
?an interesting starting point.







Re: Ubitx - carbon mic

 

Another quirky alternative: Piezo!
Trying to 'mic up' a guitar for stage performance (an Epiphone "Texan', professional-quailty!), I tried a 'Shadow' contact transducer. It failed on fitting, giving a mere whisper, so I investigated - its little piezo disc had cracked, near the lead attachment. I had a piezo disc - the 20mm dia.'prrrp-prrrp' ringer of a (once-fashinable) "Pert-'Phone". Careful not to distort it in fitting, with a thin layer of 'Blu-Tack' (like used chewing-gum) and O, the glory! I haven't used it as a mic, but did note some signal in free air. In the words of a mouse to his friend in a "Cheezels" ad, "Gotta be worth a crack, Nigel.... Nigel?"
p.s. I did the same for a 'Gibson'-style mandolin, too - too fiddly to fit inside, but worked well outside and not really too indecorative ... :)
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