Radio Test Sets and related equipment

[MUTNAV]

It’s an oven stabilized rubidium reference or nothing!!! Actually, I don’t even have a service monitor, but I’ve been in plenty of big post production studios that use 10MHz rubidium master clocks to distribute word clock to every suite in the facility… big bucks for those!

-B

Something to keep in mind, is that if you actually end up with a profitable business, some equipment costs are tax deductible.

Thanks
Joel

 

[BMDaug]

I spent 18yrs in the broadcast industry where everything is locked to a precision 10MHz reference and the only reference I've come across in broadcast are GPS driven sources. This is for all the satellite, terrestrial TV, FM broadcast, etc, that I have worked on. When I first started in that business I purchased a rubidium standard to lock up my test equipment but it didn't get used much because of all because there was always the station GPS units I could lock to.

In my early retirement when I was doing consulting with a lot of travel I brought my cheap Chinese GPSDO with me on every job to lock up my test equipment and mostly a spectrum analyzer used for taking antenna pattern measurements. This requires very narrow RBW and long single sweep times where if the instrument drifts even 10Hz during the measurement it can ruin the test.

Nice! Ya it’s crazy how different industries find different solutions and in the case of audio, they covet certain things and this is one! I guess the niche that antelope unit fills is that it uses the rubidium to derive word clock at whatever the desired sample rate. So if the project is a 96kHz music project, it’ll take the 10MHz and derive 96kHz for the AD/DA converters and other digital gear to lock to… there’s an incredible ‘snake oil’ component to the audio industry. There are Grammy winning engineers that won’t let anyone calibrate gear that is known to be off… because that could have been the magic that won them all those Grammies!! It’s the same with clocking. There are people that swear by a certain brand of word clock, that they can hear a difference even if equipment cannot measure it. It’s the most subjective tech industry I’ve come across.

-B

P.S. @MUTNAV That’s a very good point! I can make a snake oil box, make millions and I won’t even need to write it off, but I would because that’s how millionaires become billionaires right?!

 

[MUTNAV]

Nice! Ya it’s crazy how different industries find different solutions and in the case of audio, they covet certain things and this is one! I guess the niche that antelope unit fills is that it uses the rubidium to derive word clock at whatever the desired sample rate. So if the project is a 96kHz music project, it’ll take the 10MHz and derive 96kHz for the AD/DA converters and other digital gear to lock to… there’s an incredible ‘snake oil’ component to the audio industry. There are Grammy winning engineers that won’t let anyone calibrate gear that is known to be off… because that could have been the magic that won them all those Grammies!! It’s the same with clocking. There are people that swear by a certain brand of word clock, that they can hear a difference even if equipment cannot measure it. It’s the most subjective tech industry I’ve come across.

-B

P.S. @MUTNAV That’s a very good point! I can make a snake oil box, make millions and I won’t even need to write it off, but I would because that’s how millionaires become billionaires right?!

I can't even imagine even a small lawn mowing service not depreciating equipment (like a truck) and taking advantage of tax breaks... It's there for them, the people getting tax breaks tend to be the ones taking risks, making stuff work, and innovating, and if someone wants to buy some test equipment and start a radio repair business, good for them, they'll need all the help they can get, but they need (generally) to be profitable first.

Thanks
Joel

 

[BMDaug]

I can't even imagine even a small lawn mowing service not depreciating equipment (like a truck) and taking advantage of tax breaks... It's there for them, the people getting tax breaks tend to be the ones taking risks, making stuff work, and innovating, and if someone wants to buy some test equipment and start a radio repair business, good for them, they'll need all the help they can get, but they need (generally) to be profitable first.

Thanks
Joel

I was making a joke about the audio industry being a bit whacker sometimes. Of course that’s what tax breaks are for… this wasn’t some communist rhetoric. My bad I guess!

-B

 

[btt]

Back in the day before GPSDO s, I would zero beat the test set oscillator against WWV using a shortwave radio to receive the signal. Having an S meter on the receiver was a good way to visualize the sub hertz beat.

Do the best you can with what is available for the time period. That is what I try to do myself. At some point in my career I realized that the best thing to do for production calibration was to measure the reference frequency of the DUT (device under test), at room temperature, after it has settled, and use that for the calibration.The firmware uses this measured reference frequency to calculate the divider values for the frequency synthesizer such that the output frequency matches the reference frequency into the PFD (phase frequency detector). For the newer systems, you really want to get this as close as you can. Some may not realize, but if you buy a TCXO with a spec of 0.1ppm, that does not mean that the frequency of your reference will be within 0.1ppm. It means that your TCXO will maintain a frequency within +/- 0.1ppm for the specified temperature range. The initial frequency accuracy is a different matter. The TCXO might be off by several hundered Hz, or maybe not. Keep in mind that this error in the reference will be multiplied the higher the synth output frequency is. I always specify that the reference is measured accurately (within a few Hz) and part of the device calibration. This way, the firmware can always calculate the best possible dividers for any given desired operating frequency of the synthesizer. I can't imagine not taking advantage of the GPS sources these days. Warning: Just because a device claims to be a GPSDO, does not make it a "good reference". I recommended the BG7TBL devices because this guy has designed a bunch of devices with various oven-controlled oscilators combined with firmware that have met the approval of many engineers that have compared it to various standards. He knows what he is doing with regards to GPSDO. The main point I'm trying to make here is that you should be very confident in the reference for your test equipment before you start adjusting anything. Think of the radioactive sources as the ultimate screw-driver turners adjusting your test equipment reference frequencies in order to ensure that your measurements are always right.

 

[Project25_MASTR]

I actually have one of the Leo Bodnar (mini GPSDO) that I bought specifically so I could align MTR3000's and SLRs.

That all being said, bare minimum I would go with a Motorola/General Dynamics R2600 series as you can still get support contracts on them from the manufacturer (the division that split from General Dynamics now goes by Freedom CTE). Ideally, you want to be using a test set capable of testing whatever radios/systems you want to work on. For example, my side gig is working with analog repeaters and P25 conventional with a mix of P25 Phase 1 trunking, tone remotes, tuning duplexers and cavity combiners. My R2670A (which is actually fully loaded for an R2670A with the trunking card, SecureNET card, IMBE vocoder, ASTRO and C4FM) can function test everything I work on.

 

[BMDaug]

I actually have one of the Leo Bodnar (mini GPSDO) that I bought specifically so I could align MTR3000's and SLRs.

That all being said, bare minimum I would go with a Motorola/General Dynamics R2600 series as you can still get support contracts on them from the manufacturer (the division that split from General Dynamics now goes by Freedom CTE). Ideally, you want to be using a test set capable of testing whatever radios/systems you want to work on. For example, my side gig is working with analog repeaters and P25 conventional with a mix of P25 Phase 1 trunking, tone remotes, tuning duplexers and cavity combiners. My R2670A (which is actually fully loaded for an R2670A with the trunking card, SecureNET card, IMBE vocoder, ASTRO and C4FM) can function test everything I work on.

Man, this is a great response! Thanks! Sounds like this would suit me quite nicely and it’s actually relatively affordable. Key word is relatively…

-B

 

[speedway_navigator]

Test methods for high precision GNSS receivers - Spirent

This ebook explains how to overcome multiple and obscuration effects on GNSS receivers. Spirent’s Sim3D solution creates a realistic environment for PNT testing to ensure precise positioning performance of your GNSS dependent product.

www.spirent.com

Great ebook about GPS/GNSS RFI and some interesting stats on timing requirements for 4G.
From the book:
----------------
the ITU’s G.8272 standard for 4G and LTE networks specifies that all
clocks in the network must be synchronised to within 100 nanoseconds of UTC, and this figure is expected
to be far more stringent for 5G.
-----------------
A friend of mine use to say 'that's like picking fly s*** out of pepper.'

 

[prcguy]

A trained human ear can hear things that test equipment cannot measure. I've seen (heard) this many times.

Nice! Ya it’s crazy how different industries find different solutions and in the case of audio, they covet certain things and this is one! I guess the niche that antelope unit fills is that it uses the rubidium to derive word clock at whatever the desired sample rate. So if the project is a 96kHz music project, it’ll take the 10MHz and derive 96kHz for the AD/DA converters and other digital gear to lock to… there’s an incredible ‘snake oil’ component to the audio industry. There are Grammy winning engineers that won’t let anyone calibrate gear that is known to be off… because that could have been the magic that won them all those Grammies!! It’s the same with clocking. There are people that swear by a certain brand of word clock, that they can hear a difference even if equipment cannot measure it. It’s the most subjective tech industry I’ve come across.

-B

P.S. @MUTNAV That’s a very good point! I can make a snake oil box, make millions and I won’t even need to write it off, but I would because that’s how millionaires become billionaires right?!

 

[BMDaug]

A trained human ear can hear things that test equipment cannot measure. I've seen (heard) this many times.

Oh I totally agree! This can happen for a variety of reasons, and whether it can be explained or not, it still sounds subjectively better (when it’s technically worse). Overdrive and distortion are obvious examples of this. People love tape saturation, transformer saturation, tube saturation/overdrive, even transistor distortion!

Rupert Neve, who is considered the creator of the large format mixing console, and who delivered consoles used to make Beatles albums and countless others, was a huge proponent of audio perception… not just hearing. For instance, the human ear is pretty band limited. One of his clients identified a channel on their mixing console that they just didn’t like and on further investigation, an out of band oscillation was identified at something like 50kHz. So even though the ear couldn’t “hear” it, the human mind perceived something.

Audio engineering deals with psychology and emotion and adding the human element creates incredible subjectivity! It’s an amazing industry. I have some power cables that, based on many MANY blind tests performed by myself and others, make powered studio monitors sound more dynamic. There are those that go much further for what most believe to be diminishing returns… like elevating wiring on blocks so that it is suspended above the ground using the air as a dielectric. Most things audiophiles do are theoretically helpful, but the cost of some of these endeavors is excessive.

I’m not trying to discredit those people, but for most listeners, the final output format is through a streaming device to a pair of Bluetooth headphones. Much of this playback method is lossy and Grammies are won by people recording albums in their bedrooms! This just emphasizes that the music itself is 90% of it and the recording methods employed can vary wildly… as long as they sound “right”.

-Brian

 

[speedway_navigator]

John Royer was a sound engineer who worked on the PA system at the Indy motor speedway. He did some consulting for the Mormon tabernacle in Salt Lake city after they had complaints about their new speaker system. He said he had a CD with music that would use most of the audio spectrum, he had them play it and after a minute he told them some of the speakers were out of phase.

They insisted it could not be because they paid for the high end pro series. He said "you paid my plane ticket and fee, I'm telling you this is my professional opinion."
They rented a lift and pulled the speakers down, almost half were wired in reverse.

 

[BMDaug]

John Royer was a sound engineer who worked on the PA system at the Indy motor speedway. He did some consulting for the Mormon tabernacle in Salt Lake city after they had complaints about their new speaker system. He said he had a CD with music that would use most of the audio spectrum, he had them play it and after a minute he told them some of the speakers were out of phase.

They insisted it could not be because they paid for the high end pro series. He said "you paid my plane ticket and fee, I'm telling you this is my professional opinion."
They rented a lift and pulled the speakers down, almost half were wired in reverse.

Ya, that’s a noob mistake… probably two different install techs working simultaneously on the project. It’s really easy to tell when one speaker in a pair is out of phase, but if you are dealing with line arrays or many point source speakers in a large space, it can be less obvious.

When a pair of speakers and the content being reproduced are all phase coherent, and a listener sits between them, a phantom center speaker is created since the sound waves from both speakers are reaching the listener at the exact same time. When the content is phase coherent and one of the speakers is phase reversed, the reproduced content will sound like it’s coming from everywhere EXCEPT from between the speakers. It’s a strange sensation and plays with the human brain’s ability to locate the origination of sounds based on the amount of time it takes for a sound to reach one ear versus the other.

We use a lot of test and analysis equipment when designing audio equipment. No single piece is as expensive as a service monitor, but it’s still thousands of dollars. The difference is that when you use a service monitor, you get everything aligned perfectly and in spec and the radio performs best… you can design audio equipment using test equipment to come upon the cleanest, purest design and then set it up and listen to it and prefer what is technically a poorer and less pure design. Tube amps and the harmonics they impart are a great example of this. Listening tests are paramount.

With radio equipment, you are designing the “speaker” (transmitter) and the “ear” (receiver) so matching one to the other using test equipment works much better!

-B

 

[WPXS472]

Coming from the acoustic guitar world where some really insane things are almost universally considered to be fact, I say that if it can't be measured, but you perceive it anyway, you have an over active imagination. Like once when someone asked me what I would think if I saw a ghost. I replied that I would know I had been hallucinating. I have seen things that I knew weren't real, and heard sounds that I knew originated in my own brain.
With regard to the topic at hand. If you aren't in a hurry, you can find bargains in radio test equipment. Read first, shop carefully. There are certain used HP instruments designed for cellular testing that have pretty low resale value, but can work very well for normal, FM radio work. About rubidiums, I have a few. They are pretty stable, but aren't necessarily accurate. They have to be calibrated to a known accurate source. My choice is almost any GPSDO that has been on continuously for a couple of weeks. Just because it says it is a GPSDO, doesn't always make it a good source. The word "Disciplined" can have many meanings.

 

[prcguy]

I've personally been in blind, double blind audio tests with others hearing things that cannot be measured. Its real. Not only can differences between AC power cables be heard but any and all changes in low level cables and speaker cables. Problem is few of us own a stereo system that can resolve these small differences.

I've been fortunate to have heard a few systems that can and in one extreme case the owner had evaluated many cables between his preamp and power amp, all tube of course, and found the best most natural sound came from two strands of solid telephone wire out of the old 25 pair bundles. This is the roughly 22ga solid copper wires with various color striped insulation. So he had a ground and hot wire of this stuff spaced a few inches apart with RCA phono connectors on each end and it was suspended in air on blocks.

I can easily hear the difference between the two old solid conductor telephone wires and various expensive RCA type cables. To take this even further there is a noticeable difference between the blue insulated telephone wire and the red insulation. Turns out the red dye attacks the copper over many years and leaves a thin oxide where the blue insulated wire was still shiny copper after maybe 50yrs. This was old telephone wire pulled out of bindings years ago.

Coming from the acoustic guitar world where some really insane things are almost universally considered to be fact, I say that if it can't be measured, but you perceive it anyway, you have an over active imagination. Like once when someone asked me what I would think if I saw a ghost. I replied that I would know I had been hallucinating. I have seen things that I knew weren't real, and heard sounds that I knew originated in my own brain.
With regard to the topic at hand. If you aren't in a hurry, you can find bargains in radio test equipment. Read first, shop carefully. There are certain used HP instruments designed for cellular testing that have pretty low resale value, but can work very well for normal, FM radio work. About rubidiums, I have a few. They are pretty stable, but aren't necessarily accurate. They have to be calibrated to a known accurate source. My choice is almost any GPSDO that has been on continuously for a couple of weeks. Just because it says it is a GPSDO, doesn't always make it a good source. The word "Disciplined" can have many meanings.

[/QUOTE]

 

[RFI-EMI-GUY]

A trained human ear can hear things that test equipment cannot measure. I've seen (heard) this many times.

My first job at /\/\ was final test for Centracom. I could easily hear 1% distortion of a sinewave without looking at the meter. However I seriously doubt I could hear the difference in a decent speaker system with 14 gauge zip cord versus expensive "monster cables".

 

[BMDaug]

My first job at /\/\ was final test for Centracom. I could easily hear 1% distortion of a sinewave without looking at the meter.

Oh ya! 1% is huge for audio! When I worked with Rupert, the mastering gear I QC’d was out of spec if total harmonic distortion plus noise was above .0009%. Most units checked out at .0007% at any frequency between 4Hz and 120kHz all the way up the voltage rail limited amplitude of +28.5dBu.

Once I was told by my boss to “try and break the unit” (perform stress tests)… the final output stage contained a custom wound transformer. Transformers obviously don’t like DC, so I left the signal generator at a frequency of 4Hz and an amplitude of +28.5dBu. Upon returning the next day, the resistors preceding the transformer primary were burnt black, but the THD+N was still sitting at .0007%.

-B

P.S. I totally believe the telephone wire jacket color making a difference over time. Rupert Neve in his early days, used surplus military telephone wire for internal console wiring and was accosted by a customer who insisted that the wire was special and demanded to know where he could buy the same wire. It had a green jacket… The people I know find audiophile power cables to be more extreme than signal cables. After all, a signal cable actually carries the signal voltage between devices and signal voltage is rather low. The argument about power cables was always “you’re telling me this six foot power cable that costs $650, plugs into a 75 cent outlet and on to 100’ of romex is supposed to make a difference?” Then they listened…

 

[Project25_MASTR]

My first job at /\/\ was final test for Centracom. I could easily hear 1% distortion of a sinewave without looking at the meter. However I seriously doubt I could hear the difference in a decent speaker system with 14 gauge zip cord versus expensive "monster cables".

Frankly, most of us who work in the industry and have either field or bench experience hear 1 kHz @ 12 dB SINAD in our sleep. Even to the point we can approximate it within a dB or so without using a SINAD meter.

 

[ramal121]

Frankly, most of us who work in the industry and have either field or bench experience hear 1 kHz @ 12 dB SINAD in our sleep. Even to the point we can approximate it within a dB or so without using a SINAD meter.

Now that I can do. But the audiophile stuff is beyond me. My crappy little class D amp playing mp3's to some ho-hum bookshelf speakers via 24 ga speaker wire just rocks my world. Guess I'm just hard of good definition.

 

[BMDaug]

Frankly, most of us who work in the industry and have either field or bench experience hear 1 kHz @ 12 dB SINAD in our sleep…

I think that’s called tinnitus!

-B

 

[prcguy]

I find I can tune a radio by ear as good as using a SINAD meter.

Frankly, most of us who work in the industry and have either field or bench experience hear 1 kHz @ 12 dB SINAD in our sleep. Even to the point we can approximate it within a dB or so without using a SINAD meter.