|
I've been reading the responses to my own thread on here and watching several YouTube videos and still feel like I do not have a good handle on the attenuation required.??
In the videos, I have seen multiple hams use a 40db 10w attenuator with no internal attenuation to test?a 5w HT with apparently no ill effects.? ?I've also seen some use more attenuation for lower power outputs.? ?To my understanding from reading what has been written here and these videos:
1. I would need around 60-80db of attenuation to safely input a 1w signal into the Ultra.? 2. I should not use the internal attenuator - or, alternatively, I should.? 3. I should use a variable attenuator in conjunction with the 40db attenuator, or I should just use 2 40db attenuators, or I should use the 40db attenuator plus the internal on "auto".? 4. I should use a CleanRF.com RF-S2K & dummy load with a 40W attenuator or by itself (but the CleanRF is only specced?for 3-30Mhz, so I don't understand how it would work anyway...)
I could really use some authoritative answers on how to safely test VHF/UHF/HF rigs without letting the smoke out of the Ultra.? ?I have the 40db attenuator (10w, covers the spectrum) already. I'm not sure what else I need to obtain.
Thanks,?
Joe AB2M
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OK, I'll try:
Your confusion may come from not understanding the dB and logarithms related to actual power.
1)? The advantage in reasoning/thinking in dB space is that the dB, like logarithms, add and subtract directly.?
2)? So converting to dB in power, usually dBm (dBmilliwatts or 1E-3 watts), allows one to directly deal with powers in adding and subtracting attenuation directly.?
3)? Also realize that every 10 dB, be it power or attenuation, is a power of 10 greater or lesser.? So if you start with 1-watt and insert a 10 dB attenuator, you end up with 100 mW.? If you start out with 10-watts and insert a 20 dB attenuator, you end up with 100 milliwatts.? Remember this as it makes things easier without converting to dBm or dBw (dBwatts).
4)? How to convert from RF power to dBm, again, remember dBm is in dBmilliwatts or 1E-3 watts which is 0.001 watts.
5)? Convert power to dBW: ? dBW = 10 x log10 [power in watts].? That "10" after the log indicated log[base 10].? The Brits. use the Neper which is log[base e], the "natural logarithm".We're concerned only with log[base 10]. ?
Example:?? Assume you have 10-watts.? So:? dBW = 10 x log [10-watts] = 10 x [1] = +10 dBW
6)? Since we now know dBm is 0.001-watts or 30 dB BELOW 1-watt, we must add that 30 dB to our +10 dBW to express the power in dBm (remember, there are "more" dBm's in a watt than a single watt or dBw).? So, our 10 dBW beomces +40 dBm.?
Now you can add and/or subtract directly the value of any attenuator you install to get power in dBm.??
Dave - W?LEV? ? ? ?
I've been reading the responses to my own thread on here and watching several YouTube videos and still feel like I do not have a good handle on the attenuation required.??
In the videos, I have seen multiple hams use a 40db 10w attenuator with no internal attenuation to test?a 5w HT with apparently no ill effects.? ?I've also seen some use more attenuation for lower power outputs.? ?To my understanding from reading what has been written here and these videos:
1. I would need around 60-80db of attenuation to safely input a 1w signal into the Ultra.? 2. I should not use the internal attenuator - or, alternatively, I should.? 3. I should use a variable attenuator in conjunction with the 40db attenuator, or I should just use 2 40db attenuators, or I should use the 40db attenuator plus the internal on "auto".? 4. I should use a CleanRF.com RF-S2K & dummy load with a 40W attenuator or by itself (but the CleanRF is only specced?for 3-30Mhz, so I don't understand how it would work anyway...)
I could really use some authoritative answers on how to safely test VHF/UHF/HF rigs without letting the smoke out of the Ultra.? ?I have the 40db attenuator (10w, covers the spectrum) already. I'm not sure what else I need to obtain.
Thanks,?
Joe AB2M
|
This all makes sense.? ?So what I do not understand is how with a 5w transmitter - which (if my math is right) is 37dbm, a 40db attenuator gets you to the minimum -25dbm safety threshold for the Ultra.? It would seem to me that it is -10dbm and therefore (risking) causing damage, no?
Joe
OK, I'll try:
Your confusion may come from not understanding the dB and logarithms related to actual power.
1)? The advantage in reasoning/thinking in dB space is that the dB, like logarithms, add and subtract directly.?
2)? So converting to dB in power, usually dBm (dBmilliwatts or 1E-3 watts), allows one to directly deal with powers in adding and subtracting attenuation directly.?
3)? Also realize that every 10 dB, be it power or attenuation, is a power of 10 greater or lesser.? So if you start with 1-watt and insert a 10 dB attenuator, you end up with 100 mW.? If you start out with 10-watts and insert a 20 dB attenuator, you end up with 100 milliwatts.? Remember this as it makes things easier without converting to dBm or dBw (dBwatts).
4)? How to convert from RF power to dBm, again, remember dBm is in dBmilliwatts or 1E-3 watts which is 0.001 watts.
5)? Convert power to dBW: ? dBW = 10 x log10 [power in watts].? That "10" after the log indicated log[base 10].? The Brits. use the Neper which is log[base e], the "natural logarithm".We're concerned only with log[base 10]. ?
Example:?? Assume you have 10-watts.? So:? dBW = 10 x log [10-watts] = 10 x [1] = +10 dBW
6)? Since we now know dBm is 0.001-watts or 30 dB BELOW 1-watt, we must add that 30 dB to our +10 dBW to express the power in dBm (remember, there are "more" dBm's in a watt than a single watt or dBw).? So, our 10 dBW beomces +40 dBm.?
Now you can add and/or subtract directly the value of any attenuator you install to get power in dBm.??
Dave - W?LEV? ? ? ?
I've been reading the responses to my own thread on here and watching several YouTube videos and still feel like I do not have a good handle on the attenuation required.??
In the videos, I have seen multiple hams use a 40db 10w attenuator with no internal attenuation to test?a 5w HT with apparently no ill effects.? ?I've also seen some use more attenuation for lower power outputs.? ?To my understanding from reading what has been written here and these videos:
1. I would need around 60-80db of attenuation to safely input a 1w signal into the Ultra.? 2. I should not use the internal attenuator - or, alternatively, I should.? 3. I should use a variable attenuator in conjunction with the 40db attenuator, or I should just use 2 40db attenuators, or I should use the 40db attenuator plus the internal on "auto".? 4. I should use a CleanRF.com RF-S2K & dummy load with a 40W attenuator or by itself (but the CleanRF is only specced?for 3-30Mhz, so I don't understand how it would work anyway...)
I could really use some authoritative answers on how to safely test VHF/UHF/HF rigs without letting the smoke out of the Ultra.? ?I have the 40db attenuator (10w, covers the spectrum) already. I'm not sure what else I need to obtain.
Thanks,?
Joe AB2M
--
|
OK, really quick...
Your math is correct.
+37dBm - 40dB= -3dBm
To get to -25dBm --> you need +37 dBm - 62dB = -25 dBm
73,?
Geoff --> AB6BT
On 1/23/2025 1:03 PM, Joe Tomasone
wrote:
toggle quoted message
Show quoted text
This all makes sense.? ?So what I do not understand
is how with a 5w transmitter - which (if my math is right) is
37dbm, a 40db attenuator gets you to the minimum -25dbm safety
threshold for the Ultra.? It would seem to me that it is -10dbm
and therefore (risking) causing damage, no?
Joe
OK, I'll try:
Your confusion may come from not
understanding the dB and logarithms related to actual
power.
1)? The advantage in
reasoning/thinking in dB space is that the dB, like
logarithms, add and subtract directly.?
2)? So converting to dB in power,
usually dBm (dBmilliwatts or 1E-3 watts), allows one to
directly deal with powers in adding and subtracting
attenuation directly.?
3)? Also realize that every 10
dB, be it power or attenuation, is a power of 10 greater
or lesser.? So if you start with 1-watt and insert a 10 dB
attenuator, you end up with 100 mW.? If you start out with
10-watts and insert a 20 dB attenuator, you end up with
100 milliwatts.? Remember this as it makes things easier
without converting to dBm or dBw (dBwatts).
4)? How to convert from RF power
to dBm, again, remember dBm is in dBmilliwatts or 1E-3
watts which is 0.001 watts.
5)? Convert power to dBW: ? dBW =
10 x log10 [power in watts].? That "10" after the log
indicated log[base 10].? The Brits. use the Neper which is
log[base e], the "natural logarithm".We're concerned only
with log[base 10]. ?
Example:?? Assume you have
10-watts.? So:? dBW = 10 x log [10-watts] = 10 x [1] = +10
dBW
6)? Since we now know dBm is
0.001-watts or 30 dB BELOW 1-watt, we must add that 30 dB
to our +10 dBW to express the power in dBm (remember,
there are "more" dBm's in a watt than a single watt or
dBw).? So, our 10 dBW beomces +40 dBm.?
Now you can add and/or subtract
directly the value of any attenuator you install to get
power in dBm.??
Dave - W?LEV? ? ? ?
I've been reading the responses to my own
thread on here and watching several YouTube videos and
still feel like I do not have a good handle on the
attenuation required.??
In the videos, I have seen multiple hams use a 40db
10w attenuator with no internal attenuation to test?a
5w HT with apparently no ill effects.? ?I've also seen
some use more attenuation for lower power outputs.?
?To my understanding from reading what has been
written here and these videos:
1. I would need around 60-80db of attenuation to
safely input a 1w signal into the Ultra.?
2. I should not use the internal attenuator - or,
alternatively, I should.?
3. I should use a variable attenuator in
conjunction with the 40db attenuator, or I should just
use 2 40db attenuators, or I should use the 40db
attenuator plus the internal on "auto".?
4. I should use a CleanRF.com RF-S2K & dummy
load with a 40W attenuator or by itself (but the
CleanRF is only specced?for 3-30Mhz, so I don't
understand how it would work anyway...)
I could really use some authoritative answers on how
to safely test VHF/UHF/HF rigs without letting the
smoke out of the Ultra.? ?I have the 40db attenuator
(10w, covers the spectrum) already. I'm not sure what
else I need to obtain.
Thanks,?
Joe AB2M
--
|
Yes, installation of a 40 dB attenuator and starting with 5-watts or +37 dBm (yes, your math is correct), will yield +37 dBm minus 40 dB = -3 dBm or 0.0005 watts.?
The "safe" input level Eric states into the TinySAs is +10 dBm, so our are "safe" as -3 dBm is well below that level.?
However, the specifications also state that for faithful rendation of the input signal - harmonics and spurs, an input level of -25 dBm should be maintained.? For that you would require an additional 22 dB of attenuation.? That additional attenuator need not be a power unit as now you're starting from -3 dBm, so even a 0.5 or 0.25 or 0.10-watt attenuator will be sufficient.
Dave - W?LEV
This all makes sense.? ?So what I do not understand is how with a 5w transmitter - which (if my math is right) is 37dbm, a 40db attenuator gets you to the minimum -25dbm safety threshold for the Ultra.? It would seem to me that it is -10dbm and therefore (risking) causing damage, no?
Joe
OK, I'll try:
Your confusion may come from not understanding the dB and logarithms related to actual power.
1)? The advantage in reasoning/thinking in dB space is that the dB, like logarithms, add and subtract directly.?
2)? So converting to dB in power, usually dBm (dBmilliwatts or 1E-3 watts), allows one to directly deal with powers in adding and subtracting attenuation directly.?
3)? Also realize that every 10 dB, be it power or attenuation, is a power of 10 greater or lesser.? So if you start with 1-watt and insert a 10 dB attenuator, you end up with 100 mW.? If you start out with 10-watts and insert a 20 dB attenuator, you end up with 100 milliwatts.? Remember this as it makes things easier without converting to dBm or dBw (dBwatts).
4)? How to convert from RF power to dBm, again, remember dBm is in dBmilliwatts or 1E-3 watts which is 0.001 watts.
5)? Convert power to dBW: ? dBW = 10 x log10 [power in watts].? That "10" after the log indicated log[base 10].? The Brits. use the Neper which is log[base e], the "natural logarithm".We're concerned only with log[base 10]. ?
Example:?? Assume you have 10-watts.? So:? dBW = 10 x log [10-watts] = 10 x [1] = +10 dBW
6)? Since we now know dBm is 0.001-watts or 30 dB BELOW 1-watt, we must add that 30 dB to our +10 dBW to express the power in dBm (remember, there are "more" dBm's in a watt than a single watt or dBw).? So, our 10 dBW beomces +40 dBm.?
Now you can add and/or subtract directly the value of any attenuator you install to get power in dBm.??
Dave - W?LEV? ? ? ?
I've been reading the responses to my own thread on here and watching several YouTube videos and still feel like I do not have a good handle on the attenuation required.??
In the videos, I have seen multiple hams use a 40db 10w attenuator with no internal attenuation to test?a 5w HT with apparently no ill effects.? ?I've also seen some use more attenuation for lower power outputs.? ?To my understanding from reading what has been written here and these videos:
1. I would need around 60-80db of attenuation to safely input a 1w signal into the Ultra.? 2. I should not use the internal attenuator - or, alternatively, I should.? 3. I should use a variable attenuator in conjunction with the 40db attenuator, or I should just use 2 40db attenuators, or I should use the 40db attenuator plus the internal on "auto".? 4. I should use a CleanRF.com RF-S2K & dummy load with a 40W attenuator or by itself (but the CleanRF is only specced?for 3-30Mhz, so I don't understand how it would work anyway...)
I could really use some authoritative answers on how to safely test VHF/UHF/HF rigs without letting the smoke out of the Ultra.? ?I have the 40db attenuator (10w, covers the spectrum) already. I'm not sure what else I need to obtain.
Thanks,?
Joe AB2M
--
|
Good advice here:
?
John NU3E
|
On Thu, Jan 23, 2025 at 08:53 PM, W0LEV wrote:
The Brits. use the Neper which is log[base e], the "natural logarithm".We're concerned only with log[base 10]. ?
We don't use natural logarithms (base e) for RF Power dB, we use those for certain things in maths, like everyone else.
?
The easiest way to use dBm without the maths is to remember 10dB = 10x power and 3dB = 2x power, with some fixed points like
0dBm = 1mW and +30dBm = 1W and add or subtract from there.
?
I would recommend buying or building a 20dB or 30dB directional coupler for the frequencies of interest that can handle 10W power input, then attenuate the coupled output.? Using a lot of attenuators in series is asking for trouble.
?
Ian G4IXT
|
Actually, that Wiki had this to say about the Ultra:?
- Absolute maximum input level of +6dBm with 0dB internal attenuation
- Absolute maximum short term peak input power of +20dBm with 30dB internal attenuation
- Suggested maximum input power of +0dBm with internal attenuation in automatic mode
- For best measurements keep input power below -25dBm
So it would seem that -3dbm and zero internal attenuation won't harm anything, but also won't give the best measurement.? ?I might set it up that way just to compare the results when I have more than 40db of attenuation available.?
Good advice here:
?
John NU3E
|
Why don't you just experiment? If you start with a cheap 30db attenuator that dissipates 10 watts (about $25 Amazon) and input 5 watts you end up with 0.5 watts output. Now you can string on a bunch of cheap 10 or 20 db 2 watt attenuators (~$15 for 2 Amazon) until you get to say 60 or 80 db total attenuation. Then give it a try. Add or subtract attenuation until you have traces you like
?
Protecting the SA is NOT the only objective. You need more than that to get good clean signals. How much more is up to you. Personally I like 80 db on a 1 Watt input (I don't use the internal attenuator). That's one hundred millionth of a watt into the SA! I get great traces! This is a very sensitive instrument! YMMV
?
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Sorry, mistake... 30 db on 5 watts gives you a 0.005 watt output, not 0.5... But anyway, my point is buy a few inexpensive attenuators and experiment. Better to begin with too much and subtract..
|
Better, LEARN to use the dB and logarithms.? That was ninth or tenth grade for me.?
No, I'm not bragging, but just attempting to motivate the new class of "students" to learn something highly useful in dealing with RF power.? The whole professional RF / uW industry uses dBm and dBW almost universally.? If you're going to stick with the hobby, please learn the basics.
Dave - W?LEV
On Fri, Jan 24, 2025 at 5:00?PM Matthew Rapaport via <quineatal= [email protected]> wrote: Sorry, mistake... 30 db on 5 watts gives you a 0.005 watt output, not 0.5... But anyway, my point is buy a few inexpensive attenuators and experiment. Better to begin with too much and subtract..
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Ian said: I would recommend buying or building a 20dB or 30dB directional coupler for the frequencies of interest that can handle 10W power input, then attenuate the coupled output. ?
?
Unless you have the equipment to characterize couplers at higher frequencies..i.e. harmonics if that is what a person wants to measure, couplers will not give you the right result. A coupler made for say 120-180Mhz and 40db coupling will NOT display signal levels of a 144Mhz harmonic? at 288 and above correctly. The only way to reliably measure harmonics is to either use restive attenuators or use couplers whose coupling factors are known for every harmonic you are interested in. In my line of work, couplers are used to measure signal ranging from a few watts to hundreds of KW. Not only are the coupling factors known for the fundamental, but also for every harmonic the FCC requires us to measure. And trust me when I say that directional couplers can easy give you 10 and more dB of erroneous level at harmonic frequencies. Possibly even more if the directivity is low and the load has a low return loss (bad VSWR) at the higher frequencies.
?
At home I have several high power attenuators I use, the largest is a 2.5kw 40dB attenuator to measure legal limit amplifiers but the one I use most is a 30db 500w Bird attenuator with a 100db (1db steps) variable attenuator after.
?
Resistive attenuators are the average persons way to do quality measurements. Get a good set of quality attenuators and start from there.
?
John
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Jim's advice is "right on" !!!? Read it and internalize it!!
However, WITH THE PROPER EQUIPMENT and knowledge, you can make your own couplers.? As a minimum a good spectrum analyzer with a tracking generator is necessary. In a pinch, a good signal generator can be substituted for the tracking generator.? But, good equipment and a GOOD KNOWLEDGE of RF CONSTRUCTION TECHNIQUES is also necessary to roll your own successfully.
Of recent, I've run across a number of relatively good online construction articles addressing home brew couplers.? BUT.....and that's a HUGE but, avoid UToob in that respect.?
Dave - W?LEV
Dave - W?LEV
On Fri, Jan 24, 2025 at 6:25?PM John Cunliffe W7ZQ via <w7zq= [email protected]> wrote: Ian said: I would recommend buying or building a 20dB or 30dB directional coupler for the frequencies of interest that can handle 10W power input, then attenuate the coupled output. ?
?
Unless you have the equipment to characterize couplers at higher frequencies..i.e. harmonics if that is what a person wants to measure, couplers will not give you the right result. A coupler made for say 120-180Mhz and 40db coupling will NOT display signal levels of a 144Mhz harmonic? at 288 and above correctly. The only way to reliably measure harmonics is to either use restive attenuators or use couplers whose coupling factors are known for every harmonic you are interested in. In my line of work, couplers are used to measure signal ranging from a few watts to hundreds of KW. Not only are the coupling factors known for the fundamental, but also for every harmonic the FCC requires us to measure. And trust me when I say that directional couplers can easy give you 10 and more dB of erroneous level at harmonic frequencies. Possibly even more if the directivity is low and the load has a low return loss (bad VSWR) at the higher frequencies.
?
At home I have several high power attenuators I use, the largest is a 2.5kw 40dB attenuator to measure legal limit amplifiers but the one I use most is a 30db 500w Bird attenuator with a 100db (1db steps) variable attenuator after.
?
Resistive attenuators are the average persons way to do quality measurements. Get a good set of quality attenuators and start from there.
?
John
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On Fri, Jan 24, 2025 at 11:10 AM, Joe Tomasone wrote:
For best measurements keep input power below -25dBm
This is the total power going into the front-end mixer, AFTER the internal and any external attenuators/couplers/amplifiers, not just the signal you are looking at.??
So, with 30dB attenuation +5dBm (total) into the input connector should be just fine.
There are different (lower!) but similar limits when the LNA is engaged.??
?
Many commercial analyzers default to 10dB attenuation to ensure a good front end impedance match, it also increases the input power tolerance.
73, Don N2VGU
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On Fri, Jan 24, 2025 at 11:53 AM, Matthew Rapaport wrote:
(I don't use the internal attenuator)
What is your rationale for not doing so?? The designer put it there for good reasons.??
73, Don N2VGU
|
1. I like the effect of the LNA in my signal and test environments.?
?
2. Even when I do not use the LNA putting little external attenuators on is trivially easy. They are not expensive, and their presence reminds me of what's hanging between the signal and the SA..
?
Just a personal preference in the end...
|
The internal attenuators are included in the calibration process?
?
External attenuators however small and cute are not included in that process and depending on which aisle of AliExcess you shop in can vary markedly from spec at higher frequencies .. ? ?
|
Ah, good points... But I have tested my attenuators with a VNA and they perform to spec within their rated range (the inexpensive ones usually claim DC to 1.3gHz). At the very top of that they might drop a tiny bit....?
?
But you need SOME external attenuation in any case because 30 dB is not enough for good measurements even with only 1 Watt input directly connected to the SA...?
?
Finally if you're to use the LNA you can't use the internal attenuator. Even if I'm not using the LNA I prefer to keep it available.?
?
?
?
?
|
Spot on (John W7ZQ).
?
- Andy -
|
Resent due to send error / no edit mode available.
?
--------------
?
This question often gets asked.
?
Here's my current test setup for measuring those ubiquitous 5w handheld rigs.
?
At the antenna connector of the HT / walkie talkie I use a 5w rated 40db attenuator.
This is followed by a 2 watt rated 30db attenuator.
Both are available quite cheaply from the usual online suppliers.
?
Note - good practice for newbies.
Remember that the highest power attenuator is the FIRST one to connect to a transmitter etc.
?
In order to keep the input level to the Tiny SA? at? safe level I practice the following:
?
1 - Turn off the Internal LNA.
2 - Connect the attenuators in the correct order. Highest power rated direct to the TX etc.
3 - For safe use of the Tiny SA products I like to use an input level of typically -25dbm or -30dbm.
?
This not only ensures a level that does not induce potential spurious responses, but also
gives another level of input protection should I accidentally have the internal LNA switched on.
?
In other words - if you got a 5w rig then you a safe way to use the Tiny SA is to use 70db
of attenuation without relying upon the internal attenuator. (Safer)
?
4 - Using a typical sweep from say 140-1500Mhz and a wide RBW will allow you to
quickly sweep the band in a sensible time (using max hold function) whilst giving you
enough dynamic range for a basic go / no go result. For most ham radio stuff we
mostly interested in knowing if something is crap or not. So if we can see typically
some 50-60db below the carrier then we've got an answer.
?
Good enough for ham radio purposes before the pedants crawl out like cockroaches.
?
I've attached some screengrabs of an old Baofeng UV5R and a Quansheng UV5R Plus
(the latter is a different rig, don't confuse it with the Baofeng just becuse of the model
number!!).
?
I'm NOT here to argue FCC crap, just reporting the results ok !
?
Oh and just for some fun I set up my Yaesu VX7R on RX for the 2nd
harmonic of the 2m band and left it on by the window with a clear path
for a walking route, and had an audio recording device placed next to it.
?
Then went for a walk with the Quansheng on 2m with it's stock rubber duck.
I made my first test transmission at 50 metres away, then approx 200m, then 500m.?
?
The 2m band harmonic was never heard on the home receiver even at 50 yds.
No it's not an ISO9000 quality test but it does give us a reference to start with.
?
[If you wanna debate this stuff then maybe another forum should be used]
?
73 de Andy
?
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John Cunliffe W7ZQ
Donald S Brant Jr
Bruce Akhurst
