Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
Yeah, it's got the RF probe. Google translated it for me. Seems that the adjustable resistor
for the filament current of the RF probe tube is blown.
"The only downside is the fact that the hydrogen ferrous material resistance 6-4 has unfortunately blown. However, since an electric tube is installed in the AC probe, I bypassed the problem by connecting the switch head directly to the 6.3 V transformer voltage."
I don't think that's a good fix. That little tube in the probe is *very* expensive.
I actually scored one of these at the local ham swap last year - for $20, complete with RF probe.
Unfortunately, the tube in the probe was bad. Ebay yielded up a new one.
It's a fine instrument. DC Input resistance is soaringly high at 120 megohms.
- Jerry, KF6VB
|
Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
I have spotted a 410 b at a very good price, but I cannot understand german , it seems that has the original probe.
?
https://www.kleinanzeigen.de/s-anzeige/hewlett-packard-hp-410b-vacuum-tube-voltmeter/3059228060-168-1202
?
|
Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
You might mean the HP-410B?
Both that and the later 410C are still excellent very high input impedance meters with 100+ megohms inputs.
For valid and believable readings in and around oscillators and some AGC lines a quality and well working legacy meter with a see-and-not-be-seen input impedance is still the ticket. Their quick and easy better/worse, more/less meter movement is great for many alignment steps, too.
Dan WB4GRA
toggle quoted message
Show quoted text
On May 30, 2025, at 5:29?PM, Richard Knoppow via groups.io <1oldlens1@...> wrote:
? There are a great many good electronic meters out there.? My favorite is still the -hp- 420B. If you can find one with all the probes intact.? The 420B has an input load of 120 megohms DC.? There are very few circuits it will load.? I believe Drake used Heathkit VTVMs, which are rated at 11 megohms. 1 Meg of that is an isolating resistor in the probe.? The 420B also has a very high value isolator in the probe.? There will probably be no different in readings between the two but the 420B is often available cheap and is a favorite.?? ? Note that many electronic meters have a load of 10 or 11 megohms, but it's important to have an isolating resistor right at the probe.??
-------- Original message -------- From: "enriqueeeeee2001 via groups.io" <enriqueeeeee2001@...> Date: 5/30/25 1:55 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
[Edited Message Follows]
Yes, I have skipped the T15 T16 AND T17 alignment.. The following step , 6 , I have also tried it and I can clearly heard the signal generator note, as I said before , no movement in the meters but I could align the T11 to 14 for maximum beat note, but I think that it would better to have them aligned with an VTVM/S-meter.
?
Also is recommended that the T-11 to T14 the bottom and top cases should be on.
?
Would you recommend me to get and old VTVM or the result will be the same? Your opinion please before doing nothing.
|
Re: Understanding Receiver Sensitivity
I have been very pleased with using a sinad meter for checking the sensitivity of HF radios. It’s extremely quick and simple to use and the meters can be found on eBay for reasonable prices if you look a while.?
|
Re: Understanding Receiver Sensitivity
The ability of human hearing to separate "noise"? from a desired "signal" is remarkable.? Allows you to pick out conversations in noisy locations as well as read CW that is right in the noise.?
toggle quoted message
Show quoted text
-------- Original message -------- From: "Rob Sherwood via groups.io" <rob@...> Date: 5/30/25 2:16 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity
Just add that a 3 dB S+N/N ratio is the noise floor or MDS for a given bandwidth. Of course the minimum discernible signal isn’t really the weakest signal you can hear. ?
Rob, NC0B?
On May 29, 2025, at 11:12 PM, Scott N7NB <n7nb@...> wrote:
?
Rich: Thanks for your email.
I carefully reviewed your comments and I also reviewed the simplified 10 dB S+N/N methodology which I prepared for Barry, and contrary to your assertion my test methodology is correct, although I can’t claim that it’s perfect
as I’ve noted below.
Just so we’re all on the same page, I’ve taken the text I wrote earlier and reformatted it, verbatim, as a numbered list of steps:
-
Assuming you have a calibrated signal generator, set the rig to whatever band you want to begin with and inject a weak (say, 10 microvolt) signal on your test frequency.
-
Set the receiver's frequency so that you hear a tone of about 1 kHz (this frequency isn't critical).
-
Make sure you peak the preselector and confirm that the audio from this tone can be read on your AC voltmeter.
-
Turn off the signal generator and increase the audio level until noise from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is based on relative noise measurement so any range of the AC voltmeter will do).
-
Turn on the signal generator at a very low level (e.g., less than 1 microvolt) and slowly increase the signal generator output level until the 1 kHz tone reads 0 dB on the AC voltmeter.
-
The signal generator's power (in dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between the receiver's noise floor and the 1 kHz tone corresponds to the receiver's 10 dB S+N/N sensitivity in that band and on
that frequency.
If you compare the steps I’ve outlined above with an example online reference (e.g.,
), you’ll see that my methodology is correct, it’s just been adapted to what I perceived the need of the reader(s) to be. I could have prepared
a more precise methodology but that wouldn’t necessarily be helpful in the context of this thread.
That said, I believe my methodology would have been clearer if my reference to a “tone” in Step 2 read “beat note”. Likewise, I also admit that my subsequent references to a “tone” should have referenced a single frequency of
(approx.) 1 kHz beat note. In Step 3 I should have explicitly stated that the AC voltmeter is connected across the rig’s speaker, this was only implied and in Step 5 I should have stipulated that once the -10 dB audio reference is set, the audio gain must
not be changed. Finally, the reference to the receiver’s “noise floor” is intended to point back to the -10 dB reference level established in Step 4 a opposed to an absolute noise floor power measurement.
There are a few other changes that would have made it more precise (e.g., sensitivity in a given BW and other details) along with changes which would lower the measurement uncertainty (e.g., turning off the AGC, which is not possible
in some rigs such as the TR4, which is the rig which started this thread).
The methodology in my message was intended for individuals who don’t necessarily have an entire lab filled with test equipment and just want to understand, in a general sense, how to make a 10 dB S+N/N receiver sensitivity measurement.
As always, YMMV.
73.
Scott
N7NB
?
?
What you describe is not a valid measurement for CW.? The base measurement must take into account the presence of the carrier. The comparison is then made of this noise with the level from the BFO beat. Done in the same way as comparing
the presence and absence of modulation.? The output of the receiver needs some input to establish the gain.
? ?A more sophisticated method is to measure the equivalent input noise.? This is done with the use of a calibrated random noise source and a terminating resistance of known value.? It provides a measurement of input noise to the noise
of an ideal receiver (one that contributes no noise).? The theoretical "ideal" noise is calculated from the termination resistance and temperature.? Typical HF communication receivers have a "noise figure" on the order of 6 to 10db.??
Because this takes into account the bandwidth and shape factor of the receiver it is indecent of them allowing different designs to be compared.??
? The usual measurement of sensitivity is as I stated before, really only a way to tell if a receiver is working properly.?
There is a plethora of information on how to measure noise in receivers and amplifiers in the literature.??
? I certainly agree that measurement using the S-meter is not only invalid but stems from a sisunderstanding of the measurement and what is going on on the receiver.
-------- Original message --------
Date: 5/29/25 10:27 AM (GMT-08:00)
Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity
Barry: The TR-4's S-Meter (and almost all S-Meter implementations except for
some of the newest SDR products) are only intended to indicate relative
signal strength. There was no attempt made in the TR-4 to associate any
given S-Meter reading with the actual signal level.
CW S+N/N measurements are made with an AC voltmeter (with a dB scale)
connected across the receiver's audio output.
Assuming you have a calibrated signal generator, set the rig to whatever
band you want to begin with and inject a weak (say, 10 microvolt) signal on
your test frequency and set the receiver's frequency so that you hear a tone
of about 1 kHz (this frequency isn't critical). Make sure you peak the
preselector and confirm that the audio form this tone can be read on your AC
voltmeter.
Next, turn off the signal generator and increase the audio level until noise
from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is
based on relative noise measurement so any range of the AC voltmeter will
do). Because Drake tube equipment typically has a low internal noise level,
you'll probably find that you need to use a relatively low (i.e., sensitive)
range on the AC voltmeter to bring the needle up to -10 dB.
Next, turn on the signal generator at a very low level (e.g., less than 1
microvolt) and slowly increase the signal generator output level until the 1
kHz tone reads 0 dB on the AC voltmeter. The signal generator's power (in
dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between
the receiver's noise floor and the 1 kHz tone corresponds to the receiver's
10 dB S+N/N sensitivity in that band and on that frequency.
I believe you'll find that the methodology I've described above is very
similar to that which you used previously on the R-390A.
Personally, I greatly prefer the measurement of receiver sensitivity in
terms of 10 dB S+N/N CW method rather than using the 30% AM method because
the CW method is so widely used and it's easy to compare the numbers you
obtain to other rigs.
73,
Scott
N7NB
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of n4buq
Sent: Thursday, May 29, 2025 8:55 AM
To: DRAKE-RADIO <[email protected]>
Subject: [DRAKE-RADIO] Understanding Receiver Sensitivity
The TR-4 manual states the receive sensitivity should be "less than 1/2
microvolt for 10 db S+N/N."? The manual also states that each S unit on the
S-Meter corresponds to approximately 5 DB.
If I establish a reference point on the S-Meter for just noise, then feeding
a 0.5 uV voltage into the antenna jack should, at a minimum, increase the
S-Meter by two units.
Is that an oversimplification?? If so, what is a better way to measure
S+N/N.? I seem to recall that when I was doing that for the Collins R390As I
had, I was using an audio level meter (TS-585) and using AM detection to
measure the increase so maybe that's a better way (although, sadly, I no
longer have that TS-585).
Thanks,
Barry - N4BUQ
|
Re: Understanding Receiver Sensitivity
-------- Original message -------- From: "Rob Sherwood via groups.io" <rob@...> Date: 5/30/25 2:16 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity
Just add that a 3 dB S+N/N ratio is the noise floor or MDS for a given bandwidth. Of course the minimum discernible signal isn’t really the weakest signal you can hear. ?
Rob, NC0B?
On May 29, 2025, at 11:12 PM, Scott N7NB <n7nb@...> wrote:
?
Rich: Thanks for your email.
I carefully reviewed your comments and I also reviewed the simplified 10 dB S+N/N methodology which I prepared for Barry, and contrary to your assertion my test methodology is correct, although I can’t claim that it’s perfect
as I’ve noted below.
Just so we’re all on the same page, I’ve taken the text I wrote earlier and reformatted it, verbatim, as a numbered list of steps:
-
Assuming you have a calibrated signal generator, set the rig to whatever band you want to begin with and inject a weak (say, 10 microvolt) signal on your test frequency.
-
Set the receiver's frequency so that you hear a tone of about 1 kHz (this frequency isn't critical).
-
Make sure you peak the preselector and confirm that the audio from this tone can be read on your AC voltmeter.
-
Turn off the signal generator and increase the audio level until noise from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is based on relative noise measurement so any range of the AC voltmeter will do).
-
Turn on the signal generator at a very low level (e.g., less than 1 microvolt) and slowly increase the signal generator output level until the 1 kHz tone reads 0 dB on the AC voltmeter.
-
The signal generator's power (in dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between the receiver's noise floor and the 1 kHz tone corresponds to the receiver's 10 dB S+N/N sensitivity in that band and on
that frequency.
If you compare the steps I’ve outlined above with an example online reference (e.g.,
), you’ll see that my methodology is correct, it’s just been adapted to what I perceived the need of the reader(s) to be. I could have prepared
a more precise methodology but that wouldn’t necessarily be helpful in the context of this thread.
That said, I believe my methodology would have been clearer if my reference to a “tone” in Step 2 read “beat note”. Likewise, I also admit that my subsequent references to a “tone” should have referenced a single frequency of
(approx.) 1 kHz beat note. In Step 3 I should have explicitly stated that the AC voltmeter is connected across the rig’s speaker, this was only implied and in Step 5 I should have stipulated that once the -10 dB audio reference is set, the audio gain must
not be changed. Finally, the reference to the receiver’s “noise floor” is intended to point back to the -10 dB reference level established in Step 4 a opposed to an absolute noise floor power measurement.
There are a few other changes that would have made it more precise (e.g., sensitivity in a given BW and other details) along with changes which would lower the measurement uncertainty (e.g., turning off the AGC, which is not possible
in some rigs such as the TR4, which is the rig which started this thread).
The methodology in my message was intended for individuals who don’t necessarily have an entire lab filled with test equipment and just want to understand, in a general sense, how to make a 10 dB S+N/N receiver sensitivity measurement.
As always, YMMV.
73.
Scott
N7NB
?
?
What you describe is not a valid measurement for CW.? The base measurement must take into account the presence of the carrier. The comparison is then made of this noise with the level from the BFO beat. Done in the same way as comparing
the presence and absence of modulation.? The output of the receiver needs some input to establish the gain.
? ?A more sophisticated method is to measure the equivalent input noise.? This is done with the use of a calibrated random noise source and a terminating resistance of known value.? It provides a measurement of input noise to the noise
of an ideal receiver (one that contributes no noise).? The theoretical "ideal" noise is calculated from the termination resistance and temperature.? Typical HF communication receivers have a "noise figure" on the order of 6 to 10db.??
Because this takes into account the bandwidth and shape factor of the receiver it is indecent of them allowing different designs to be compared.??
? The usual measurement of sensitivity is as I stated before, really only a way to tell if a receiver is working properly.?
There is a plethora of information on how to measure noise in receivers and amplifiers in the literature.??
? I certainly agree that measurement using the S-meter is not only invalid but stems from a sisunderstanding of the measurement and what is going on on the receiver.
-------- Original message --------
Date: 5/29/25 10:27 AM (GMT-08:00)
Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity
Barry: The TR-4's S-Meter (and almost all S-Meter implementations except for
some of the newest SDR products) are only intended to indicate relative
signal strength. There was no attempt made in the TR-4 to associate any
given S-Meter reading with the actual signal level.
CW S+N/N measurements are made with an AC voltmeter (with a dB scale)
connected across the receiver's audio output.
Assuming you have a calibrated signal generator, set the rig to whatever
band you want to begin with and inject a weak (say, 10 microvolt) signal on
your test frequency and set the receiver's frequency so that you hear a tone
of about 1 kHz (this frequency isn't critical). Make sure you peak the
preselector and confirm that the audio form this tone can be read on your AC
voltmeter.
Next, turn off the signal generator and increase the audio level until noise
from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is
based on relative noise measurement so any range of the AC voltmeter will
do). Because Drake tube equipment typically has a low internal noise level,
you'll probably find that you need to use a relatively low (i.e., sensitive)
range on the AC voltmeter to bring the needle up to -10 dB.
Next, turn on the signal generator at a very low level (e.g., less than 1
microvolt) and slowly increase the signal generator output level until the 1
kHz tone reads 0 dB on the AC voltmeter. The signal generator's power (in
dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between
the receiver's noise floor and the 1 kHz tone corresponds to the receiver's
10 dB S+N/N sensitivity in that band and on that frequency.
I believe you'll find that the methodology I've described above is very
similar to that which you used previously on the R-390A.
Personally, I greatly prefer the measurement of receiver sensitivity in
terms of 10 dB S+N/N CW method rather than using the 30% AM method because
the CW method is so widely used and it's easy to compare the numbers you
obtain to other rigs.
73,
Scott
N7NB
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of n4buq
Sent: Thursday, May 29, 2025 8:55 AM
To: DRAKE-RADIO <[email protected]>
Subject: [DRAKE-RADIO] Understanding Receiver Sensitivity
The TR-4 manual states the receive sensitivity should be "less than 1/2
microvolt for 10 db S+N/N."? The manual also states that each S unit on the
S-Meter corresponds to approximately 5 DB.
If I establish a reference point on the S-Meter for just noise, then feeding
a 0.5 uV voltage into the antenna jack should, at a minimum, increase the
S-Meter by two units.
Is that an oversimplification?? If so, what is a better way to measure
S+N/N.? I seem to recall that when I was doing that for the Collins R390As I
had, I was using an audio level meter (TS-585) and using AM detection to
measure the increase so maybe that's a better way (although, sadly, I no
longer have that TS-585).
Thanks,
Barry - N4BUQ
|
Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
There are a great many good electronic meters out there.? My favorite is still the -hp- 420B. If you can find one with all the probes intact.? The 420B has an input load of 120 megohms DC.? There are very few circuits it will load.? I believe Drake used Heathkit VTVMs, which are rated at 11 megohms. 1 Meg of that is an isolating resistor in the probe.? The 420B also has a very high value isolator in the probe.? There will probably be no different in readings between the two but the 420B is often available cheap and is a favorite.?? ? Note that many electronic meters have a load of 10 or 11 megohms, but it's important to have an isolating resistor right at the probe.??
toggle quoted message
Show quoted text
-------- Original message -------- From: "enriqueeeeee2001 via groups.io" <enriqueeeeee2001@...> Date: 5/30/25 1:55 PM (GMT-08:00) Subject: Re: [DRAKE-RADIO] Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
[Edited Message Follows]
Yes, I have skipped the T15 T16 AND T17 alignment.. The following step , 6 , I have also tried it and I can clearly heard the signal generator note, as I said before , no movement in the meters but I could align the T11 to 14 for maximum beat note, but I think that it would better to have them aligned with an VTVM/S-meter.
?
Also is recommended that the T-11 to T14 the bottom and top cases should be on.
?
Would you recommend me to get and old VTVM or the result will be the same? Your opinion please before doing nothing.
|
Re: Understanding Receiver Sensitivity
Just add that a 3 dB S+N/N ratio is the noise floor or MDS for a given bandwidth. Of course the minimum discernible signal isn’t really the weakest signal you can hear. ?
toggle quoted message
Show quoted text
On May 29, 2025, at 11:12 PM, Scott N7NB <n7nb@...> wrote:
?
Rich: Thanks for your email.
I carefully reviewed your comments and I also reviewed the simplified 10 dB S+N/N methodology which I prepared for Barry, and contrary to your assertion my test methodology is correct, although I can’t claim that it’s perfect
as I’ve noted below.
Just so we’re all on the same page, I’ve taken the text I wrote earlier and reformatted it, verbatim, as a numbered list of steps:
-
Assuming you have a calibrated signal generator, set the rig to whatever band you want to begin with and inject a weak (say, 10 microvolt) signal on your test frequency.
-
Set the receiver's frequency so that you hear a tone of about 1 kHz (this frequency isn't critical).
-
Make sure you peak the preselector and confirm that the audio from this tone can be read on your AC voltmeter.
-
Turn off the signal generator and increase the audio level until noise from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is based on relative noise measurement so any range of the AC voltmeter will do).
-
Turn on the signal generator at a very low level (e.g., less than 1 microvolt) and slowly increase the signal generator output level until the 1 kHz tone reads 0 dB on the AC voltmeter.
-
The signal generator's power (in dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between the receiver's noise floor and the 1 kHz tone corresponds to the receiver's 10 dB S+N/N sensitivity in that band and on
that frequency.
If you compare the steps I’ve outlined above with an example online reference (e.g.,
), you’ll see that my methodology is correct, it’s just been adapted to what I perceived the need of the reader(s) to be. I could have prepared
a more precise methodology but that wouldn’t necessarily be helpful in the context of this thread.
That said, I believe my methodology would have been clearer if my reference to a “tone” in Step 2 read “beat note”. Likewise, I also admit that my subsequent references to a “tone” should have referenced a single frequency of
(approx.) 1 kHz beat note. In Step 3 I should have explicitly stated that the AC voltmeter is connected across the rig’s speaker, this was only implied and in Step 5 I should have stipulated that once the -10 dB audio reference is set, the audio gain must
not be changed. Finally, the reference to the receiver’s “noise floor” is intended to point back to the -10 dB reference level established in Step 4 a opposed to an absolute noise floor power measurement.
There are a few other changes that would have made it more precise (e.g., sensitivity in a given BW and other details) along with changes which would lower the measurement uncertainty (e.g., turning off the AGC, which is not possible
in some rigs such as the TR4, which is the rig which started this thread).
The methodology in my message was intended for individuals who don’t necessarily have an entire lab filled with test equipment and just want to understand, in a general sense, how to make a 10 dB S+N/N receiver sensitivity measurement.
As always, YMMV.
73.
Scott
N7NB
?
?
What you describe is not a valid measurement for CW.? The base measurement must take into account the presence of the carrier. The comparison is then made of this noise with the level from the BFO beat. Done in the same way as comparing
the presence and absence of modulation.? The output of the receiver needs some input to establish the gain.
? ?A more sophisticated method is to measure the equivalent input noise.? This is done with the use of a calibrated random noise source and a terminating resistance of known value.? It provides a measurement of input noise to the noise
of an ideal receiver (one that contributes no noise).? The theoretical "ideal" noise is calculated from the termination resistance and temperature.? Typical HF communication receivers have a "noise figure" on the order of 6 to 10db.??
Because this takes into account the bandwidth and shape factor of the receiver it is indecent of them allowing different designs to be compared.??
? The usual measurement of sensitivity is as I stated before, really only a way to tell if a receiver is working properly.?
There is a plethora of information on how to measure noise in receivers and amplifiers in the literature.??
? I certainly agree that measurement using the S-meter is not only invalid but stems from a sisunderstanding of the measurement and what is going on on the receiver.
-------- Original message --------
Date: 5/29/25 10:27 AM (GMT-08:00)
Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity
Barry: The TR-4's S-Meter (and almost all S-Meter implementations except for
some of the newest SDR products) are only intended to indicate relative
signal strength. There was no attempt made in the TR-4 to associate any
given S-Meter reading with the actual signal level.
CW S+N/N measurements are made with an AC voltmeter (with a dB scale)
connected across the receiver's audio output.
Assuming you have a calibrated signal generator, set the rig to whatever
band you want to begin with and inject a weak (say, 10 microvolt) signal on
your test frequency and set the receiver's frequency so that you hear a tone
of about 1 kHz (this frequency isn't critical). Make sure you peak the
preselector and confirm that the audio form this tone can be read on your AC
voltmeter.
Next, turn off the signal generator and increase the audio level until noise
from the receiver shows -10 dB on any scale of the AC voltmeter (S+N/N is
based on relative noise measurement so any range of the AC voltmeter will
do). Because Drake tube equipment typically has a low internal noise level,
you'll probably find that you need to use a relatively low (i.e., sensitive)
range on the AC voltmeter to bring the needle up to -10 dB.
Next, turn on the signal generator at a very low level (e.g., less than 1
microvolt) and slowly increase the signal generator output level until the 1
kHz tone reads 0 dB on the AC voltmeter. The signal generator's power (in
dBm) or voltage (in microvolts) necessary to achieve a 10 dB ratio between
the receiver's noise floor and the 1 kHz tone corresponds to the receiver's
10 dB S+N/N sensitivity in that band and on that frequency.
I believe you'll find that the methodology I've described above is very
similar to that which you used previously on the R-390A.
Personally, I greatly prefer the measurement of receiver sensitivity in
terms of 10 dB S+N/N CW method rather than using the 30% AM method because
the CW method is so widely used and it's easy to compare the numbers you
obtain to other rigs.
73,
Scott
N7NB
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of n4buq
Sent: Thursday, May 29, 2025 8:55 AM
To: DRAKE-RADIO <[email protected]>
Subject: [DRAKE-RADIO] Understanding Receiver Sensitivity
The TR-4 manual states the receive sensitivity should be "less than 1/2
microvolt for 10 db S+N/N."? The manual also states that each S unit on the
S-Meter corresponds to approximately 5 DB.
If I establish a reference point on the S-Meter for just noise, then feeding
a 0.5 uV voltage into the antenna jack should, at a minimum, increase the
S-Meter by two units.
Is that an oversimplification?? If so, what is a better way to measure
S+N/N.? I seem to recall that when I was doing that for the Collins R390As I
had, I was using an audio level meter (TS-585) and using AM detection to
measure the increase so maybe that's a better way (although, sadly, I no
longer have that TS-585).
Thanks,
Barry - N4BUQ
|
Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
Yes, I have skipped the T15 T16 AND T17 alignment.. The following step , 6 , I have also tried it and I can clearly heard the signal generator note, as I said before , no movement in the meters but I could align the T11 to 14 for maximum beat note, but I think that it would better to have them aligned with an VTVM/S-meter.
?
Also is recommended that the T-11 to T14 the bottom and top cases should be on.
?
Would you recommend me to get and old VTVM or the result will be the same? Your opinion please before doing nothing.
|
Steve: Will take the MS4, david
You just saw it in a previous post. This one came in with a mid-late C Line, with a cut cord. Since I had to replace the cord and test it, I tried my “new” (to me) use of a gland strain relief.?
All voltages good, tested with a TR-4 after verifying voltages. Supply hums a little (the supply itself — not the audio). This is an original supply that has not been rebuilt. I can rebuild for an extra $150, including parts.?
$120 plus shipping from central NC (27253).?
Also have an MS-4 that is decent for $50 plus shipping. Shipped separately from AC-4, of course.?
The rest of the C Line will be available but not for awhile. The transmitter needs to be revived and receiver is pretty grotty. Receiver is mid-Late with a full deck of CW filters, Sherwood mixer and power supply upgrades.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
|
Okay, this one is strange. I may have bodged something and may need “second sight”.
I had to replace V1 socket because I ruined one pin whilst removing resistors. Rebuilt using a socket from a parts rig and reconnected everything, as far as I know.?
Xtal oscillator adjustment went fine. Peaked 40, 15 and 10. Receive is great on all bands. 10 doesn’t elicit S meter response but receive is strong. For an early set, receive is fine.?
Transmit is the opposite of what most people see: 15 and 10 are pretty good. 20 and lower are almost nothing. It was providing plenty of power before the repair. Now — it’s QRP. ?Counter sees correct frequency but power out is nearly nil.?
Reading the rotary switch diagrams is torture.?
Anything jump out at any of you?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Drake SPR-4 50 Khz IF and 50 Khz Filter alignment
When I aligned my SPR-4 I had a similar experience, where injecting a 50.0 kHz carrier per Section 5.3.1 (to adjust T17 for zero beat) or injecting a 50.8 kHz carrier (to align T11-T14 for maximum beat note audio in the CW mode) did not move the S-Meter, nor could I measure any DC voltage on the AVC line using a >10 M DC voltmeter. This is why I skipped alignment of the 50 kHz IF as described in 5.3.1, but I did adjust T17 for zero beat. If you inject a 5645 kHz carrier into the junction of R27 and C90 per Section 5.3.2, you should see the S-Meter reading vary slightly as the 5645 kHz carrier level is increased or decreased (i.e., using the S-Meter as an indicator of AVC voltage). If so, can you align the 5645 kHz IF when you follow the steps in Section 5.3.2? 73, Scott N7NB ?
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From: [email protected] <[email protected]> On Behalf Of enriqueeeeee2001 via groups.io
Sent: Thursday, May 29, 2025 11:18 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] Drake SPR-4 50 Khz IF and 50 Khz Filter alignment? Yes, it moves with the background noise. As a last attempt I have been thinking about purchasing a 'real' VTVM voltmeter with isolated probes, quite sure that I can find one of those old ones in a good shape.
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It's noticeable but not horrible.? Almost certainly due to transformer laminations: some of them are just louder.
No hum on audio that's greater than normal.? Resting AC with supply hooked to no load is about 420 mA, which is normal.? Supply has a fairly high serial number -- it was bought with the C Line that went with it.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, May 30th, 2025 at 12:40 PM, n4buq <n4buq@...> wrote:
I? don't need the AC-4 but I am curious as to how much hum it produces.? Mine hums a bit but setting it on a softer surface seems to help with that.? I presumed this was normal but maybe not?
Barry - N4BUQ
You just saw it in a previous post. This one came in with a mid-late C Line, with a cut cord. Since I had to replace the cord and test it, I tried my “new” (to me) use of a gland strain relief.?
All voltages good, tested with a TR-4 after verifying voltages. Supply hums a little (the supply itself — not the audio). This is an original supply that has not been rebuilt. I can rebuild for an extra $150, including parts.?
$120 plus shipping from central NC (27253).?
Also have an MS-4 that is decent for $50 plus shipping. Shipped separately from AC-4, of course.?
The rest of the C Line will be available but not for awhile. The transmitter needs to be revived and receiver is pretty grotty. Receiver is mid-Late with a full deck of CW filters, Sherwood mixer and power supply upgrades.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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I? don't need the AC-4 but I am curious as to how much hum it produces.? Mine hums a bit but setting it on a softer surface seems to help with that.? I presumed this was normal but maybe not?
Barry - N4BUQ
You just saw it in a previous post. This one came in with a mid-late C Line, with a cut cord. Since I had to replace the cord and test it, I tried my “new” (to me) use of a gland strain relief.?
All voltages good, tested with a TR-4 after verifying voltages. Supply hums a little (the supply itself — not the audio). This is an original supply that has not been rebuilt. I can rebuild for an extra $150, including parts.?
$120 plus shipping from central NC (27253).?
Also have an MS-4 that is decent for $50 plus shipping. Shipped separately from AC-4, of course.?
The rest of the C Line will be available but not for awhile. The transmitter needs to be revived and receiver is pretty grotty. Receiver is mid-Late with a full deck of CW filters, Sherwood mixer and power supply upgrades.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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You just saw it in a previous post. This one came in with a mid-late C Line, with a cut cord. Since I had to replace the cord and test it, I tried my “new” (to me) use of a gland strain relief.?
All voltages good, tested with a TR-4 after verifying voltages. Supply hums a little (the supply itself — not the audio). This is an original supply that has not been rebuilt. I can rebuild for an extra $150, including parts.?
$120 plus shipping from central NC (27253).?
Also have an MS-4 that is decent for $50 plus shipping. Shipped separately from AC-4, of course.?
The rest of the C Line will be available but not for awhile. The transmitter needs to be revived and receiver is pretty grotty. Receiver is mid-Late with a full deck of CW filters, Sherwood mixer and power supply upgrades.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Glands for power cords
Correction:
You will need to do a minor bit of metalwork. The gland nut interferes with the tab on the bottom cover where the cord comes in.?
Ten seconds on my stationary belt sander removed enough tab material to get everything to fit!
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Fri, May 30, 2025 at 11:14, Steve Wedge, W1ES/4 via groups.io < w1es@...> wrote:
Amazon.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Fri, May 30, 2025 at 11:11, Stan Gammons via groups.io <
buttercup11421@...> wrote:
Where did you get the gland and what part number is it?
73
Stan
KM4HQE
On 5/30/25 10:06, Steve Wedge, W1ES/4 via groups.io wrote:
Per the previous thread on ways to replace the oversized 2-wire AC cord in the AC-4, I’ve found the perfect part: no drilling, no special tools, just pass an 18 AWG 3-conductor cord through the gland, solder the wires to the appropriate terminals, pass the gland through the existing hole without enlarging tighter and Bob’s yer uncle.?
Yes, 18 AWG is sufficient, as it can safely be used up to 10A.?
It took me as long to snap the pic and post it here.?
If you’re still concerned that the power cord isn’t “beefy” enough, look at the size of the conductors that follow inside the AC-4.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Glands for power cords
Amazon.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Fri, May 30, 2025 at 11:11, Stan Gammons via groups.io < buttercup11421@...> wrote: Where did you get the gland and what part number is it?
73
Stan
KM4HQE
On 5/30/25 10:06, Steve Wedge, W1ES/4 via groups.io wrote:
Per the previous thread on ways to replace the oversized 2-wire AC cord in the AC-4, I’ve found the perfect part: no drilling, no special tools, just pass an 18 AWG 3-conductor cord through the gland, solder the wires to the appropriate terminals, pass the gland through the existing hole without enlarging tighter and Bob’s yer uncle.?
Yes, 18 AWG is sufficient, as it can safely be used up to 10A.?
It took me as long to snap the pic and post it here.?
If you’re still concerned that the power cord isn’t “beefy” enough, look at the size of the conductors that follow inside the AC-4.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Glands for power cords
Where did you get the gland and what part number is it?
73
Stan
KM4HQE
On 5/30/25 10:06, Steve Wedge, W1ES/4
via groups.io wrote:
toggle quoted message
Show quoted text
Per the previous thread on ways to replace the
oversized 2-wire AC cord in the AC-4, I’ve found the perfect
part: no drilling, no special tools, just pass an 18 AWG
3-conductor cord through the gland, solder the wires to the
appropriate terminals, pass the gland through the existing hole
without enlarging tighter and Bob’s yer uncle.?
Yes, 18 AWG is sufficient, as it can safely be
used up to 10A.?
It took me as long to snap the pic and post it
here.?
If you’re still concerned that the power cord
isn’t “beefy” enough, look at the size of the conductors that
follow inside the AC-4.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
|
Per the previous thread on ways to replace the oversized 2-wire AC cord in the AC-4, I’ve found the perfect part: no drilling, no special tools, just pass an 18 AWG 3-conductor cord through the gland, solder the wires to the appropriate terminals, pass the gland through the existing hole without enlarging tighter and Bob’s yer uncle.? 
Yes, 18 AWG is sufficient, as it can safely be used up to 10A.?
It took me as long to snap the pic and post it here.?
If you’re still concerned that the power cord isn’t “beefy” enough, look at the size of the conductors that follow inside the AC-4.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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Re: Understanding Receiver Sensitivity
It’s important to note that measuring receiver sensitivity through use of the 20 dB quieting methodology is only valid for FM. Decades ago the 20 dB quieting method was replaced with 12 dB SINAD because an FM receiver could display excellent 20 dB quieting but sound terrible with actual signals at or near the measured sensitivity. SINAD is superior to 20 dB quieting because it takes receiver distortion into account. SINAD can be used to measure receiver sensitivity of modes other than FM, so it’s a very flexible test methodology (see ). 73, Scott N7NB ?
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From: [email protected] <[email protected]> On Behalf Of n4buq
Sent: Friday, May 30, 2025 6:52 AM
To: DRAKE-RADIO <[email protected]>
Subject: Re: [DRAKE-RADIO] Understanding Receiver Sensitivity? I had never heard of the "quieting" method.? I presume since it is discussed with respect to FM receivers, then this is done with a typical AM/CW receiver, then it is performed with the BFO off, correct? GEMINI AI - Comprehensive Analysis of Communications Receiver Sensitivity Measurement<snip>4.2.1 20 dB Quieting MethodThe 20 dB Quieting method is a traditional and relatively simple test for analog FM radios, measuring the RF input level required to reduce the receiver's audio output noise by 20 dB. ? The procedure typically involves: - Connecting an AC voltmeter across the receiver's speaker leads. ?
- With no RF signal applied, opening the squelch and adjusting the volume control to establish a reference noise reading on the voltmeter (e.g., 1 to 2 volts, or 0 dB on a dB scale). ?
- Applying an unmodulated RF carrier from a signal generator to the receiver's input. ?
- Gradually increasing the RF signal level until the voltmeter reading drops to 1/10th of the initial noise reading, or 20 dB lower. ?
- The RF signal level at this point is recorded as the 20 dB quieting sensitivity. This can sometimes be estimated by a trained ear, listening for the point where noise and crackling sounds significantly decrease. ?
While straightforward and requiring minimal equipment, this method has a significant limitation: it primarily measures the reduction in noise and does not account for signal distortion. Consequently, it may not accurately reflect the receiver's ability to properly demodulate and produce intelligible audio or information, as a signal can be "quiet" but still distorted and unintelligible.
<snip>
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Rob Sherwood