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.

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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

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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

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 Fri, Feb 12, 2021 at 09:47 AM, Roger Need wrote:

On Wed, Feb 10, 2021 at 06:08 PM, John AE5X wrote:

Hello Eric,

I noticed an issue when using the tinySA in 'Low Output' mode:
The new "level steps" (-10dB -1dB set +1dB +10dB) in the latest firmware works great until a value is put into the 'External Amp' field. I was using 41 dB of external attenuation and had -41 dialed into this field.I then tried to change the output level by selecting the -10dB step and the SA ignored the external amp value and reverted to what would be displayed with no external value dialed in.

Has anyone else found this issue?

Roger,
? ? Yes, its an issue that I'm sure Erik has on his to do list.? Step? incrementing/decrementing also doesn't work with an external amplification value entered.? Best to add any external amplification or attenuation in mentally until Erik issues a FW fix.?

? ?A work around is to do any incrementing or decrementing before entering an external amplification/ attenuation value. The FW properly corrects the output level without error in that case.

Herb

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

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

On Wed, Feb 10, 2021 at 06:08 PM, John AE5X wrote:

Hello Eric,

I noticed an issue when using the tinySA in 'Low Output' mode:
The new "level steps" (-10dB -1dB set +1dB +10dB) in the latest firmware works great until a value is put into the 'External Amp' field. I was using 41 dB of external attenuation and had -41 dialed into this field.I then tried to change the output level by selecting the -10dB step and the SA ignored the external amp value and reverted to what would be displayed with no external value dialed in.

Has anyone else found this issue?

Roger

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



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73 de k1jbd
bammi

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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.

I've got a VNA and a SA, both as they came. I note that the SA has a bump in the case where the jog wheel is located, presumably to give a bit more protection to the jog wheel??? Has does that sit as regards the metal case... presumably the jog wheel is a bit more exposed?

It's difficult to work out from the web pictures but I am assuming the metal case firstly screws directly to the PCB on the rear-side and then the front half is attached to the whole via two end-screws, is that correct?

I've not yet opened the SA (if it ain't broke don't fix it) so I'm not clear how the plastic box assembles (I assumed the rear simply screws to the front and everything is held together inside hunky dory?).

On the VNA do you discard the back panel of the internal assembly when you fit the metal case or keep it attached?

Nigel G8AYM

?
There are two firmware upgrade software components: a driver and firmware upgrade software, DfuSe.?
The driver is included with the DfuSe software but it is not always properly installed.

Step by step instructions how to install the driver are in ''Absolute Beginner's Guide to NanoVNA''.?
This PDF guide could be downloaded from file section of nanovna-users group:

/g/nanovna-users/files/Absolute%20Beginner%20Guide%20to%20The%20NanoVNA

Martin 9A2JK

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

"If you are very brave you can try to lift the display and resolder the 18 wire flat cable."

Done! All good now, thanks. There was one very clearly not soldered, and a couple that 'might have been a little shy of solder. But the self test ran without issues and the waterfall is perfect!.
Thanks for all your help, it was awesome!
Kindest regards
David
PS, being able to use the second TinySA to calibrate the HIGH worked a treat. I've done it to both and that gives me everything I need. Thanks again.

Thats is consistent.
There seems to be an error in the interface to the display and unfortunately the display test (test 11) hangs instead of giving an error message.

Sorry, just to update as well, the waterfall also locks it up.
Thanks
David

No it doesn't work.
But its fine on the other one.

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

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

Can you check if the waterfall works?
DISPLAY/WATERFALL
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Hi,?
I have two Tinysa, one which arrived today and updated both to the latest firmware 1.1-85.
One completes the Self Test fine, whilst the new one (older on the serial number though) hangs at test 11. Its doesnt "fail", it just stops and needs a power reset.
Any ideas?
Cheers
David