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A word of warning for those that want to measure the spectral purity of their transmitter.

As the tinySA is specced to accept +10dBm without attenuation and +30dBm for some seconds with maximum attenuation you may be tempted to connect the output of the transmitter to the tinySA, set the tinySA to max hold and transmit for a short time, long enough for one sweep.
Even when your transmitter stays below +30dBm you risk making a wrong measurement, or even worse, if you have attenuation on automatic, destroy the tinySA as the tinySA will only adjust (e.g. increase) the attenuation for the next sweep.

The spur free dynamic range of the tinySA is a bit above 70dB with an RBW of 300kHz. This means that any signal that is more than 70dB above the noise floor will cause internally generated harmonics.
Let's take an example:
Without attenuation and with an RBW of 300kHz the noise floor is at -95dBm. With an input signal of 0dBm you are 25dB above the spur free dynamic range so there will be internally generated harmonics.
For a good measurement you should apply 25dB of attenuation?

Make sure to update the FW of you first batch tinySA as the newer FW contains an overload warning (the marker info turns red) to help you make a good measurement.

I cannot imagine anyone being so absent- minded as to connect any test gear (other than dummy load or a power meter/inline swr meter etc) to ANY transmitter or generator of rf. Even leaving the extended telescopic attached to the Tinysa could damage it in the viscinity of a powerful PA especially if mismatched/poor grounding/leaky dummy load. ?You might be quite surprised how much RF you are exposing yourself to when transmitting - another use for the Tinysa.

I have used small 1,2 or 3 turn loops (insulated) about 1” diameter attached to a length of 316 coax very useful, also for sniffing around equipment and chaising sources of interference. The insulation is necessary in case components are touched by the loop. You can see what needs screening then (also useful as input to a scope sometimes).

Steve, G7PSZ

? ? ? I use a directional coupler when measuring the output of a transmitter.? The coupled port is -40dB down from the transmit level and the signal to the tinySA is well above its spur free range.?

? ? For protection when directly connected to other input sources, I purchased an RF Explorer power limiter which has a built-in power limiter, dc block and 6dB attenuator for input protection up to 30dBm.? Above 30dBm the power limiter becomes a sacrificial component rather than the tinySA.

? ? Both the directional coupler and power limiter were purchased to protect my higher priced spectrum analyzers.? They work just as well for the tinySA but each have the disadvantage of being priced at or above the cost of the tinySA.? The power limiter is spec'd to 3GHz which is over kill for the tinySA.? An interesting DIY project would be a power limiter or transient suppressor that only worked to the limits of the tinySA LOW or HIGH inputs.?

- Herb

I have always used a simple 40 dB. tap to measure transmitter output.? Works with SA or a simple power meter to check output power, or a scope to check modulation.They are very easy and inexpensive to build.

DuWayne kv4qb

I too use a tap to reduce the output of the device under test to acceptable levels for the test instrument.? I found a reference with all of the parts listed to make the tap, including the metal case for it.


One point I would make on the tap, be sure to run a characterization test (I used a NanoVNA for that test) to ensure a flat response over the frequency range in question.? I found that I needed to increase the capacitor specified to get a flat response (within 1 dB).? Ultimately I used a combination of capacitors that I had on hand to get the best match.

Just my 2 cents?
73
Evan
AC9TU

On Fri, Aug 21, 2020 at 03:45 AM, Stephen Laurence wrote:

I cannot imagine anyone being so absent- minded as to connect any test gear (other than dummy load or a power meter/inline swr meter etc) to ANY transmitter or generator of rf.

Then you have an unrealistic view of human nature. Humans, at times, make mistakes.
?
--
John AE5X

If you have extra attenuators (big if), a simple test is to measure the harmonic with and without one.? If the harmonic changes level by a value much different than the attenuator value, you're overloading the SA.

Brent, AB1LF

On Fri, Aug 21, 2020 at 10:20 AM, Brent DeWitt wrote:

If you have extra attenuators (big if), a simple test is to measure the harmonic with and without one

You better use the built in attenuator for testing the source of the harmonics

I mever nake mistteacks...

73,

Bill KU8H

bark less - wag more

I usually use a 30dB high power attenuator for a watt to milliwatt conversion, with an additional 10 or 20 dB low power attenuator for power levels of 10 or 100 watts respectively.
Gary
W9TD

On Fri, Aug 21, 2020 at 01:45 AM, Stephen Laurence wrote:

I cannot imagine anyone being so absent- minded as to connect any test gear (other than dummy load or a power meter/inline swr meter etc) to ANY transmitter or generator of rf.

You've apparently never used a signal generator from HP or Rohde & Schwarz and likely others.? Many of them have reverse power protection up to 50 watts, some up to 100 watts.? And you've apparently never used a communications service monitor, such as those from IFR, HP, Cushman, Motorola, and others.? Those are generally used for two-way radio service, and it is common to connect a transceiver to one.? Many of those will accept input power up to 100 watts, some as high as 150 watts.? If you had spent your career servicing mobile radios with a service monitor, you wouldn't think anything of keying up into a piece of test equipment.

Of course, you'd learn a? quick lesson the first time (and hopefully last time) you keyed a 100 watt transmitter into your tinySA!

Er, yes. ?I was not the person in danger of connecting a delicate piece of equipment to a transmitter, just offering some alternative strategies.

I did not spend my working life with peofessional/ commercial gear, but had radio/ electronics as a hobby from the age of 10. I added vintage computers along the way. My hobby actually kept me sane during the sometimes brutal years of my medical training.

My working life was spent anaesthetising many of my patients and waking some of them up again.

Steve L. G7PSZ

Having used expensive test equipment throughout my professional career, I learnt that it was always a good idea to keep a low power 20dB attenuator connected to the input of a spectrum analyser or output of an RF generator, unless on the odd occasion when you need higher sensitivity or more output power.

The attenuator would tend to act as an RF fuse if you ever accidentally stuffed too much RF up the cable, and would protect the more expensive equipment from major damage on the odd occasion when you did something silly in the haste of the moment.

However as the tiny SA costs almost as much as a decent attenuator at new prices, it would maybe seem that it is a cheaper option throw away the test equipment rather than risk an attenuator :-)

How times have changed.

Regards,

Martin

On Sat, Aug 22, 2020 at 06:59 AM, Martin wrote:

Having used expensive test equipment throughout my professional career, I learnt that it was always a good idea to keep a low power 20dB attenuator connected to the input of a spectrum analyser or output of an RF generator, unless on the odd occasion when you need higher sensitivity or more output power.

The attenuator would tend to act as an RF fuse if you ever accidentally stuffed too much RF up the cable, and would protect the more expensive equipment from major damage on the odd occasion when you did something silly in the haste of the moment.

However as the tiny SA costs almost as much as a decent attenuator at new prices, it would maybe seem that it is a cheaper option throw away the test equipment rather than risk an attenuator :-)

How times have changed.

Martin,
? ?My manager called me into his office one time inquiring about why we needed to order 20watt attenuators periodically.? After I explained the cost difference between the attenuators versus repairing the front end of a receiver or spectrum analyzer his only comment was, "Carry on".

? As you said its cheaper to purchase a spare tinySA than what we paid for lab quality attenuators. You can justify a second tinySA to yourself not only as a spare spectrum analyzer, but also as a separate RF source if you don't already own a suitable generator.

- Herb