|
I have a Kay Model 520 (Kay #80138) 0 - 10 scale rotary attenuator that I would like to use to allow me to test 100 Milliwatt to 5 Watt QRP transmitters using my TinySA, but I have not been able to find a spec sheet on the attenuator, so I don't know how many watts input it can handle and how much attenuation it will provide.
I, of course, do not want to overload the attenuator and/or the TinySA if I try to test my 5 watt QRP rig.? Anyone have any ideas?
EuGene, KA5NLY
|
I have a similar rotary attenuator that's
rated for 2 watts.? I'd use that as an upper limit.? The Kay model
is zero to ten dB.
73 charlie, k1xx
On 2/11/2021 5:17 PM, bigusmith via
groups.io wrote:
toggle quoted message
Show quoted text
I have a Kay Model 520 (Kay #80138) 0 - 10 scale rotary attenuator
that I would like to use to allow me to test 100 Milliwatt to 5
Watt QRP transmitters using my TinySA, but I have not been able to
find a spec sheet on the attenuator, so I don't know how many
watts input it can handle and how much attenuation it will
provide.
I, of course, do not want to overload the attenuator and/or the
TinySA if I try to test my 5 watt QRP rig.? Anyone have any ideas?
EuGene, KA5NLY
|
Dang!? That doesn't bode well for the utility of the Kay attenuator.? I am not used to dealing with RF output power in Decibels instead of watts, but from what little I have gleaned from discussions on-line, 10 Db attenuation wouldn't be enough to bring 1 watt of RF down to the level that would be comfortable for the TinySA.
I need to find a table which shows RF output in say, 1/2 watt steps from 1/2 watt to 5 watts, and at each step, how many Db of attenuation is needed to bring to RF down to the proper input level to feed into the TinySA.? I would pay $5 0r $10 in a heartbeat for such a chart, as I don't want to fry my TinySA and have to drop another fifty bucks for a replacement.
It would also be nice to know the proper input power to the TinySA...in watts, volts (DC, RMS, & PtoP), and Db's since I have run into attenuators which all use different units of measurements and I don't know how to compare them...it's the old apples and oranges gambit!
Somewhere, I read that the Kay 520 had 1- 60 Db attenuation (i guess that would be? 0,1, 2, 3, 6, 10, 20, 30, 40, 50, 60 DB or something of that ilk) but they didn't say what the max watts would be.
FleaBag (eBay) has a number of in-line 10 pole switched attenuators for sale at reasonable prices, but they all seem to be for very low power use with max input power of 0.25 0r 0.50 watts which wouldn't be useful for my 1 to 5 watt transmitters.? They say they are for Ham Radio use, but I don't know where they will find a big enough market among the QRPp milliwatters to have dozens of vendors selling 0.25 Watt attenuators.
I'm just rambling on now out of pure frustration.
EuGene, KA5NLY
|
?TRY? ? ? ? ? ? ??
|
Amazon.com: step attenuator rf
www.amazon.com
|
?Walt Cates,
WD0GOF
?
A
majority of acceptance is not proof of correctness.
toggle quoted message
Show quoted text
Dang!? That doesn't bode well for the utility of the Kay attenuator.? I am not used to dealing with RF output power in Decibels instead of watts, but from what little I have gleaned from discussions on-line, 10 Db attenuation wouldn't be enough to bring
1 watt of RF down to the level that would be comfortable for the TinySA.
I need to find a table which shows RF output in say, 1/2 watt steps from 1/2 watt to 5 watts, and at each step, how many Db of attenuation is needed to bring to RF down to the proper input level to feed into the TinySA.? I would pay $5 0r $10 in a heartbeat
for such a chart, as I don't want to fry my TinySA and have to drop another fifty bucks for a replacement.
It would also be nice to know the proper input power to the TinySA...in watts, volts (DC, RMS, & PtoP), and Db's since I have run into attenuators which all use different units of measurements and I don't know how to compare them...it's the old apples and oranges
gambit!
Somewhere, I read that the Kay 520 had 1- 60 Db attenuation (i guess that would be? 0,1, 2, 3, 6, 10, 20, 30, 40, 50, 60 DB or something of that ilk) but they didn't say what the max watts would be.
FleaBag (eBay) has a number of in-line 10 pole switched attenuators for sale at reasonable prices, but they all seem to be for very low power use with max input power of 0.25 0r 0.50 watts which wouldn't be useful for my 1 to 5 watt transmitters.? They say
they are for Ham Radio use, but I don't know where they will find a big enough market among the QRPp milliwatters to have dozens of vendors selling 0.25 Watt attenuators.
I'm just rambling on now out of pure frustration.
EuGene, KA5NLY
|
A 10db attenuation will reduce 1W to 100mW (or +20dBm or -10dBW), perhaps not enough to destroy the TSA but certainly enough to overload it and render useful measurements impossible.
You have to differentiate between damage levels and what is required for useful measurements!!!
73
Jeff
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of bigusmith via groups.io Sent: 12 February 2021 02:44 To: [email protected]Subject: Re: [tinysa] Step attenuator for QRP transmitter to TinySA Dang! That doesn't bode well for the utility of the Kay attenuator. I am not used to dealing with RF output power in Decibels instead of watts, but from what little I have gleaned from discussions on-line, 10 Db attenuation wouldn't be enough to bring 1 watt of RF down to the level that would be comfortable for the TinySA. I need to find a table which shows RF output in say, 1/2 watt steps from 1/2 watt to 5 watts, and at each step, how many Db of attenuation is needed to bring to RF down to the proper input level to feed into the TinySA. I would pay $5 0r $10 in a heartbeat for such a chart, as I don't want to fry my TinySA and have to drop another fifty bucks for a replacement. It would also be nice to know the proper input power to the TinySA...in watts, volts (DC, RMS, & PtoP), and Db's since I have run into attenuators which all use different units of measurements and I don't know how to compare them...it's the old apples and oranges gambit! Somewhere, I read that the Kay 520 had 1- 60 Db attenuation (i guess that would be 0,1, 2, 3, 6, 10, 20, 30, 40, 50, 60 DB or something of that ilk) but they didn't say what the max watts would be. FleaBag (eBay) has a number of in-line 10 pole switched attenuators for sale at reasonable prices, but they all seem to be for very low power use with max input power of 0.25 0r 0.50 watts which wouldn't be useful for my 1 to 5 watt transmitters. They say they are for Ham Radio use, but I don't know where they will find a big enough market among the QRPp milliwatters to have dozens of vendors selling 0.25 Watt attenuators. I'm just rambling on now out of pure frustration. EuGene, KA5NLY
|
Guys, Some simple rules; 100 Watt = +50dBm 10 Watt = +40dBm 1 Watt = +30dBm Target tinySA input level for best harmonics measurements - 20dBm So for 10 Watt transmitter you need 60dB attenuation For 1 Watt transmitter you need 50dB attenuation. Start with a 20dB 5 Watt attenuator? for a 1 Watt transmitter or a?30dB 25 Watt attenuator for a 10 Watt transmitter Do NOT use a 2 Watt eBay attenuator with a 1 Watt transmitter as these will get VERY hot and may self destroy? Add a 1 or 2 Watt 30 dB attenuator to protect the tinySA Use the internal attenuator only to check if harmonics are externally generated
------------------------------------------
For more info on the tinySA go to https://tinysa.org/wiki/
|
Also simple: Decibels add or subtract directly. 10 dB is a 10x or /10. 3 dB is 2x or /2. 0 dBm is 1 milliwatt. Most math can be easily done in your head. For example +13 dBm = (1mW x10) x 2 = 20 mW. 73 -Jim NU0C On Fri, 12 Feb 2021 02:56:40 -0800 "Erik Kaashoek" <erik@...> wrote: Guys,
Some simple rules;
100 Watt = +50dBm
10 Watt = +40dBm
1 Watt = +30dBm
Target tinySA input level for best harmonics measurements - 20dBm
So for 10 Watt transmitter you need 60dB attenuation
For 1 Watt transmitter you need 50dB attenuation.
Start with a 20dB 5 Watt attenuator? for a 1 Watt transmitter or a?30dB 25 Watt attenuator for a 10 Watt transmitter
Do NOT use a 2 Watt eBay attenuator with a 1 Watt transmitter as these will get VERY hot and may self destroy
Add a 1 or 2 Watt 30 dB attenuator to protect the tinySA
Use the internal attenuator only to check if harmonics are externally generated
------------------------------------------
For more info on the tinySA go to
|
I know what the original person was attempting to do but is
looking at the wrong way of doing it. You need to use a 40dB
resistive tap connected from the output of the transmitter via the
tap to a dummy load. This gives a fixed? attenuation of 40dB for a
measurement to be made. The tap dissipates very little power, most
goes to the dummy load. An attenuator can be used in the line from
the tap to the measuring device as well if needed but the signal
level here is much lower than the transmitter output.
In use, add the value of attenuation (40dB ) to the value read on
the tester. This is where the beauty of working in decibels comes
into its own.
toggle quoted message
Show quoted text
A 10db attenuation will reduce 1W to 100mW (or +20dBm or -10dBW), perhaps not enough to destroy the TSA but certainly enough to overload it and render useful measurements impossible.
You have to differentiate between damage levels and what is required for useful measurements!!!
73
Jeff
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of bigusmith via groups.io
Sent: 12 February 2021 02:44
To: [email protected]
Subject: Re: [tinysa] Step attenuator for QRP transmitter to TinySA
Dang! That doesn't bode well for the utility of the Kay attenuator. I am not used to dealing with RF output power in Decibels instead of watts, but from what little I have gleaned from discussions on-line, 10 Db attenuation wouldn't be enough to bring 1 watt of RF down to the level that would be comfortable for the TinySA.
I need to find a table which shows RF output in say, 1/2 watt steps from 1/2 watt to 5 watts, and at each step, how many Db of attenuation is needed to bring to RF down to the proper input level to feed into the TinySA. I would pay $5 0r $10 in a heartbeat for such a chart, as I don't want to fry my TinySA and have to drop another fifty bucks for a replacement.
It would also be nice to know the proper input power to the TinySA...in watts, volts (DC, RMS, & PtoP), and Db's since I have run into attenuators which all use different units of measurements and I don't know how to compare them...it's the old apples and oranges gambit!
Somewhere, I read that the Kay 520 had 1- 60 Db attenuation (i guess that would be 0,1, 2, 3, 6, 10, 20, 30, 40, 50, 60 DB or something of that ilk) but they didn't say what the max watts would be.
FleaBag (eBay) has a number of in-line 10 pole switched attenuators for sale at reasonable prices, but they all seem to be for very low power use with max input power of 0.25 0r 0.50 watts which wouldn't be useful for my 1 to 5 watt transmitters. They say they are for Ham Radio use, but I don't know where they will find a big enough market among the QRPp milliwatters to have dozens of vendors selling 0.25 Watt attenuators.
I'm just rambling on now out of pure frustration.
EuGene, KA5NLY
|
Eugene,
I can empathize with your frustration, went through similar decision making myself. My approach: I bought a high wattage 20 dB fixed attenuator to knock down the big signal, that i feed into low wattage but precise HP step attenuators and that goes into the tinySA. I characterized the big attenuator using a nanoVNA (i am assuming anyone who has a tinySA at least has a nanoVNA or better VNA), that way i know the total attenuation of the chain.
On ebay, If you are patient you can get good deals on HP 355c/HP 355D. I got mine from vendor Fastscrap both for $21.50, and i bought ?a Narda 766-20 high power attenuator from vendor planet-surplus for $22.
For a dBm to watts calculator i use this one on everythingRF
--
73 de k1jbd
bammi
|
Here's a link to a useful RF Power (both dBm and Watts) to voltage chart on Repeater Builders:??
It's easy to see the relationship between dBm and Watts using this chart.
There is a ton of information on the Repeater Builders website.? Look in the RF-Related Information on their website here:?http://www.repeater-builder.com/tech-info/techindex.html
Steve_WB8GRS
|
One thing to be wary of with these inexpensive step attenuators is they may not provide a 50 ohm input impedance. I bought a similar one (different brand) on eBay and it worked fine, except that the input impedance changed a LOT with the attenuation amount. I finally decided that was too dangerous for use with any rig and bought a really nice Bird 100W 30dB attenuator (only $60 on eBay) instead, which has a perfect 50 ohm impedance and a perfect 30 dB attenuation. That brings even a 100W (50 dBm) signal down to 0.1 W (20 dBm), at which point you can use inexpensive fixed attenuators. You can buy 10, 20, and 30 dB fixed attenuators that handle < 2W for only a few bucks on Amazon. They have true 50 ohm input impedance and seem to be calibrated pretty well. So combine a big fixed 30 dBm attenuator with a small 30 dBm attenuator and a 100W signal is down 60 dB to -10 dBm (0.01W), which is safe for the TinySA.
Rob
|
On Thu, Feb 11, 2021 at 08:43 PM, bigusmith wrote:
I would pay $5 0r $10 in a heartbeat for such a chart
Print one out, their are plenty of sites that have good charts. You can also save the page of a "webcalc" to your machine and use it without having internet if you want. when I first started to use "DB's" I thought I would never feel comfortable with it but with a little practice the light went off.? the more you use it the easier it will become. Also, I had very good luck with some 30db 10W DC-3G SMA attenuators from China. At $19.99 with free shipping I took a chance and found them very flat? (+- .2db) up to 3.5G.?
|
On 2/12/2021 1:32 PM, Rob French wrote:
One thing to be wary of with these inexpensive step attenuators is
they may not provide a 50 ohm input impedance. I bought a similar
one (different brand) on eBay and it worked fine, except that the
input impedance changed a LOT with the attenuation amount. I
finally decided that was too dangerous for use with any rig and
bought a really nice Bird 100W 30dB attenuator (only $60 on eBay)
instead, which has a perfect 50 ohm impedance and a perfect 30 dB
attenuation. That brings even a 100W (50 dBm) signal down to 0.1 W
(20 dBm), at which point you can use inexpensive fixed
attenuators. You can buy 10, 20, and 30 dB fixed attenuators that
handle < 2W for only a few bucks on Amazon. They have true 50
ohm input impedance and seem to be calibrated pretty well. So
combine a big fixed 30 dBm attenuator with a small 30 dBm
attenuator and a 100W signal is down 60 dB to -10 dBm (0.01W),
which is safe for the TinySA.
Rob
_._,_._,_
I bought a cheap step attenuator with toggle switches.? It has
a max attenuation of 92 Db.? I guess this is true--at audio.?
Supposed to be good to 30 Mhz.? On checking it with a sig gen and
SDR rx it only has max of 50 Db above about an MHz.? I took it
apart.? No isolation between sections, RF connectors not even
grounded to chassis due to thick powder coating.? Pretty
hopeless.? I got one of the many pushbutton ones on Amazon, they
are rated to 3GHz and check good to 1 GHz, the most my generator
will do.? Don't know power ratings, wouldn't want to put more than
20Db into it though.
Eric WA3UYI
|
|
This email has been checked for viruses by Avast antivirus software.
|
|
On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:
I am not used to dealing with RF output power in Decibels instead of watts
Get used to it, you'll find dB very useful.? There are lots of things in radio - and pretty much any kind of electronics - that aren't convenient to measure in watts.? If your transmitter puts out 100 watts, and you run it into a linear amplifier that puts out 1000 watts, I suppose you could say the gain of the amplifier is 900 watts, but then what if you only ran 50 watts into the amplifier?? You can't say the gain is 900 watts, therefor the output will be 950 watts, it just ain't so.? But if we say the gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we have something we can work with. 10 dB is a power gain of 10 times, so our amplifier will put out 500 watts with 50 watts in. And what is the sensitivity of your receiver in watts?? Well, if you ran any amount of watts into your receiver, all you'd get out of it is smoke.? Watts doesn't work here.? So we measure receiver sensitivity in dBm -? that is, dB relative to one milliwatt.? A typical receiver might have a sensitivity of -120dBm.? If we put a 30 dB attenuator in line, the combination now has a sensitivity of -90 dBm.? Suppose you have a receiver with a sensitivity of -120 dBm at your house, and there's a transmitter up on a nearby hill, what is the path loss in watts?? Doesn't make sense. However, you could say that the path loss is 100 dB, that's a number that would make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up on the hill, you could calculate that the power at your receiver is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would hear that just fine. So, there are lots of things that aren't measured or expressed well in watts, but if we use dB (or dBm) can easily be measured or expressed.? And that's why so many things in electronics are expressed in dB, or in dB relative to some value. If you're wondering why the B in dB is capitalized, it's because the "Bel" was named after Alexander Graham Bell, and Bell being a proper name, we capitalize it.? We should also capitalize Volts, Watts, Ohms - all come from somebody's name -? and a bunch of others, but we get sloppy and often don't bother.
|
Thanks Jim, a lot of good points in your reply.
On 12/02/2021 22:17, Jim Allyn - N7JA
wrote:
toggle quoted message
Show quoted text
On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:
I am not used to dealing with RF output power in
Decibels instead of watts
Get used to it, you'll find dB very useful.? There are lots of
things in radio - and pretty much any kind of electronics - that
aren't convenient to measure in watts.? If your transmitter puts
out 100 watts, and you run it into a linear amplifier that puts
out 1000 watts, I suppose you could say the gain of the amplifier
is 900 watts, but then what if you only ran 50 watts into the
amplifier?? You can't say the gain is 900 watts, therefor the
output will be 950 watts, it just ain't so.? But if we say the
gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we
have something we can work with. 10 dB is a power gain of 10
times, so our amplifier will put out 500 watts with 50 watts in.
And what is the sensitivity of your receiver in watts?? Well, if
you ran any amount of watts into your receiver, all you'd get out
of it is smoke.? Watts doesn't work here.? So we measure receiver
sensitivity in dBm -? that is, dB relative to one milliwatt.? A
typical receiver might have a sensitivity of -120dBm.? If we put a
30 dB attenuator in line, the combination now has a sensitivity of
-90 dBm.? Suppose you have a receiver with a sensitivity of -120
dBm at your house, and there's a transmitter up on a nearby hill,
what is the path loss in watts?? Doesn't make sense. However, you
could say that the path loss is 100 dB, that's a number that would
make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up
on the hill, you could calculate that the power at your receiver
is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would
hear that just fine.
So, there are lots of things that aren't measured or expressed
well in watts, but if we use dB (or dBm) can easily be measured or
expressed.? And that's why so many things in electronics are
expressed in dB, or in dB relative to some value.
If you're wondering why the B in dB is capitalized, it's because
the "Bel" was named after Alexander Graham Bell, and Bell being a
proper name, we capitalize it.? We should also capitalize Volts,
Watts, Ohms - all come from somebody's name -? and a bunch of
others, but we get sloppy and often don't bother.
|
Excellent explanation Jim.
In my early military career in electronics, we were given a hand out that clearly explained the dB in all of its forms, it was a great tool, but we were supposed to hand it back in at the end of the course... they ended up one short, that was over 40 years ago.... I still have it.
John VE7KKQ
On Fri, Feb 12, 2021 at 2:33 PM Jim Allyn - N7JA < jim@...> wrote: On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:
I am not used to dealing with RF output power in Decibels instead of watts
Get used to it, you'll find dB very useful.? There are lots of things in radio - and pretty much any kind of electronics - that aren't convenient to measure in watts.? If your transmitter puts out 100 watts, and you run it into a linear amplifier that puts out 1000 watts, I suppose you could say the gain of the amplifier is 900 watts, but then what if you only ran 50 watts into the amplifier?? You can't say the gain is 900 watts, therefor the output will be 950 watts, it just ain't so.? But if we say the gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we have something we can work with. 10 dB is a power gain of 10 times, so our amplifier will put out 500 watts with 50 watts in.
And what is the sensitivity of your receiver in watts?? Well, if you ran any amount of watts into your receiver, all you'd get out of it is smoke.? Watts doesn't work here.? So we measure receiver sensitivity in dBm -? that is, dB relative to one milliwatt.? A typical receiver might have a sensitivity of -120dBm.? If we put a 30 dB attenuator in line, the combination now has a sensitivity of -90 dBm.? Suppose you have a receiver with a sensitivity of -120 dBm at your house, and there's a transmitter up on a nearby hill, what is the path loss in watts?? Doesn't make sense. However, you could say that the path loss is 100 dB, that's a number that would make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up on the hill, you could calculate that the power at your receiver is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would hear that just fine.
So, there are lots of things that aren't measured or expressed well in watts, but if we use dB (or dBm) can easily be measured or expressed.? And that's why so many things in electronics are expressed in dB, or in dB relative to some value.
If you're wondering why the B in dB is capitalized, it's because the "Bel" was named after Alexander Graham Bell, and Bell being a proper name, we capitalize it.? We should also capitalize Volts, Watts, Ohms - all come from somebody's name -? and a bunch of others, but we get sloppy and often don't bother.
|
This is a great thread, thanks for sharing. I have a cheap 70w amp kit, and before using it I wanted to test the spurious transmissions etc. It looks like I'll need a 50db tap and then a lower power 20 or 30db inline attenuator to the tinySA. I already have a 300w dummy load. The math short cuts also help as well :)
Heath
On Fri, Feb 12, 2021 at 2:33 PM Jim Allyn - N7JA < jim@...> wrote: On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:
I am not used to dealing with RF output power in Decibels instead of watts
Get used to it, you'll find dB very useful.? There are lots of things in radio - and pretty much any kind of electronics - that aren't convenient to measure in watts.? If your transmitter puts out 100 watts, and you run it into a linear amplifier that puts out 1000 watts, I suppose you could say the gain of the amplifier is 900 watts, but then what if you only ran 50 watts into the amplifier?? You can't say the gain is 900 watts, therefor the output will be 950 watts, it just ain't so.? But if we say the gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we have something we can work with. 10 dB is a power gain of 10 times, so our amplifier will put out 500 watts with 50 watts in.
And what is the sensitivity of your receiver in watts?? Well, if you ran any amount of watts into your receiver, all you'd get out of it is smoke.? Watts doesn't work here.? So we measure receiver sensitivity in dBm -? that is, dB relative to one milliwatt.? A typical receiver might have a sensitivity of -120dBm.? If we put a 30 dB attenuator in line, the combination now has a sensitivity of -90 dBm.? Suppose you have a receiver with a sensitivity of -120 dBm at your house, and there's a transmitter up on a nearby hill, what is the path loss in watts?? Doesn't make sense. However, you could say that the path loss is 100 dB, that's a number that would make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up on the hill, you could calculate that the power at your receiver is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would hear that just fine.
So, there are lots of things that aren't measured or expressed well in watts, but if we use dB (or dBm) can easily be measured or expressed.? And that's why so many things in electronics are expressed in dB, or in dB relative to some value.
If you're wondering why the B in dB is capitalized, it's because the "Bel" was named after Alexander Graham Bell, and Bell being a proper name, we capitalize it.? We should also capitalize Volts, Watts, Ohms - all come from somebody's name -? and a bunch of others, but we get sloppy and often don't bother.
|
can you share?
Tom Sides ?KI7FTK
skype: Thomas Sides 4243 e. st Charles ave Phx AZ 85042
Excellent explanation Jim.
In my early military career in electronics, we were given a hand out that clearly explained the dB in all of its forms, it was a great tool, but we were supposed to hand it back in at the end of the course... they ended up one short, that was over 40 years ago.... I still have it.
John VE7KKQ
On Fri, Feb 12, 2021 at 2:33 PM Jim Allyn - N7JA < jim@...> wrote: On Thu, Feb 11, 2021 at 06:43 PM, bigusmith wrote:
I am not used to dealing with RF output power in Decibels instead of watts
Get used to it, you'll find dB very useful.? There are lots of things in radio - and pretty much any kind of electronics - that aren't convenient to measure in watts.? If your transmitter puts out 100 watts, and you run it into a linear amplifier that puts out 1000 watts, I suppose you could say the gain of the amplifier is 900 watts, but then what if you only ran 50 watts into the amplifier?? You can't say the gain is 900 watts, therefor the output will be 950 watts, it just ain't so.? But if we say the gain of the amplifier is 10 log(1000 watts/100 watts) = 10 dB, we have something we can work with. 10 dB is a power gain of 10 times, so our amplifier will put out 500 watts with 50 watts in.
And what is the sensitivity of your receiver in watts?? Well, if you ran any amount of watts into your receiver, all you'd get out of it is smoke.? Watts doesn't work here.? So we measure receiver sensitivity in dBm -? that is, dB relative to one milliwatt.? A typical receiver might have a sensitivity of -120dBm.? If we put a 30 dB attenuator in line, the combination now has a sensitivity of -90 dBm.? Suppose you have a receiver with a sensitivity of -120 dBm at your house, and there's a transmitter up on a nearby hill, what is the path loss in watts?? Doesn't make sense. However, you could say that the path loss is 100 dB, that's a number that would make sense.?? Then if you had a 10 watt (+40 dBm) transmitter up on the hill, you could calculate that the power at your receiver is (40 dBm - 100 dB path loss) = -60 dBm, and your receiver would hear that just fine.
So, there are lots of things that aren't measured or expressed well in watts, but if we use dB (or dBm) can easily be measured or expressed.? And that's why so many things in electronics are expressed in dB, or in dB relative to some value.
If you're wondering why the B in dB is capitalized, it's because the "Bel" was named after Alexander Graham Bell, and Bell being a proper name, we capitalize it.? We should also capitalize Volts, Watts, Ohms - all come from somebody's name -? and a bunch of others, but we get sloppy and often don't bother.
|
Shameless plug:
Hope it is still possible to order PCBs from JLCPCB.
The power rating is probably about 1/4W for 1206 resistors, so you need a high power fixed attenuator in front of this one.
73, Mike AF7KR
|
You can also use switches and a PCB is not absolutely needed  and the inside  The copper/PCB ground planes combined with the 0805 resistors makes it flat within 1dB up to 500MHz and max practical attenuation is 55dB ( 5+10+20+20)? In the shown attenuator there is one additional 20dB stage totalling 75dB but that is too much in this construction. --
------------------------------------------
For more info on the tinySA go to https://tinysa.org/wiki/
|
bigusmith
waltcates
Jim Shorney
WS1M - bammi
Jim Allyn - N7JA
Tominaz