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Does anyone know where I can find the recommended Motorola 12 dB SINAD testing procedure?
I have a radio that has been to El Paso, TX (Mexico) 4 times. The last time I sent it back because it did not meet RX spec of 12 dB SINAD of .35 µV. I was measuring .50 µV SINAD (from the depot).
The tech at Motorola called me up saying that they were not able to duplicate the problem. After a somewhat heated discussion (through an English-Spanish translator), I found that they have no clue what SINAD is. I had them send the radio back to me for more testing.
Upon receiving the radio, I found that the technician who serviced my radio left the longest message in the notes field that I have ever seen! 13 lines of how good their testing equipment was, and that they use low loss cables (etc…) but then I found the problem…
The depot uses squelch opening/closing for the RX Spec!!!
I would love to show them what Motorola says is the correct procedure.
FYI, I am testing an MCS2000 UHF analog radio with an R2600 service monitor (isolation transformer in the audio line).
Thanks for any and all input,
WEC
[edit: Changed subject line to reflect that a photo was added]
Last edited by Wile E. Coyote on Sat Jul 28, 2007 8:39 am, edited 2 times in total.
"The bitterness of poor quality lingers longer than the sweetness of low cost"
Does anyone know where I can find the recommended Motorola 12 dB SINAD testing procedure?
If you really want to know, it's in the Motorola Service Monitor manuals, with a full-blown SINAD procedure. Very drawn out, and never use it. I have been spoiled by having a Sinadder when necessary. Too easy.
Doesn't the R2600 have a SINAD meter built in? (I am not familiar with that monitor model.)
If not, your simplest bet is to buy a Helper or GAW or Motorola Sinadder. I've been patient and bought the bare bones models on eBay for less than $ 25 (but be prepared to change the half dozen electrolytics in them, they dry out with age.) You put a 1 KHz tone on the signal into the radio, and starting from zero output, bring the signal up until the meter reads the db Sinad you want. Or, reduce the signal until you don't get the Sinad you want, then bring it up just to where you do, and read the sensitivity. But maybe you already knew that.
0.5 microvolt on UHF, even for 20db quieting, is not great for a 21st century radio. For a U44BBT T-Power 1961 vintage tube mobile, it's pretty good. As you know, the squelch should open long before quieting is reached, either by the 20db or Sinad method. A sensitivity discrepancy of this nature is almost always a problem with the RF stage only, such as the antenna switch, Mixer/RF amplifier section or antenna line interconnections. I have never heard of any service facility using the squelch opening to judge sensitivity.
In metrology, the first trick is knowing what to measure, then measuring it in as repeatable a fashion as possible.
So, what are you trying to determine? You are trying to determine the lowest signal level which will allow communications to be received.
Ignore squelch for the moment - assume the squelch can be forced open (e.g. a monitor button). Given that, what would be the best measurements of ability to communicate?
First, would be to send a large amount of speech through the radio and determine how understandable it is - that would be directly measuring what you are interested in. Unfortunately, there is no good, fast, automatic, and highly repeatable way to do this.
The next method is SINAD - measure how much the signal is degraded by noise, and relate that to intelligibility by some procedure. SINAD can be measured very quickly and repeatably.
(OT: for a digital system, the corresponding measurement is bit error rate. I have seen folks who think using SINAD to measure the performance of a digital radio is a good idea. The problem is that this measurement has a poor repeatability due to the forward error correction in the system: at one RF level you may have a solid signal, but drop it 0.1dB and suddenly you cross the threshold where forward error correction can no longer fix the signal and it turns to mush. However, that can also happen because bit errors are random, and if you get a string of them in the wrong place you can have the signal go away for no reason. The measurement has poor repeatability.)
Measuring where the radio squelches doesn't even fall into the list: I've seen radios where the squelch would close at 20dB SINAD, because either a) the last monkey who set the radio didn't like hearing noisy audio and would rather hear nothing or b) the monkey was simply clueless. In fact, we had to put special code into the automatic SINAD search function on the COM-120B for that very case: if we detected that the radio was squelching before we hit the desired SINAD we stopped the measurement and flagged it as "squelch limited".
The single trickiest thing is to make sure you have everything set up correctly when you make your measurement: usually radio manufacturers specify that a C-weighting filter be used when making the measurement rather than a flat filter. This will make the SINAD look a lot better than using no filter, as it will remove the high frequency noise. You also need to insure that no CTCSS tone, DCS data,or power line hum is making its way through to the meter (or that the meter can filter the tone out). If you are picking the signal up from a port which is controlled by the volume knob, you need to make sure it is turned UP enough to have enough signal over any residual noise from the audio amplifier, but not up so far as to start distorting the signal in the audio path, which will reduce the SINAD.
I've seen problems where a tech was trying to reproduce somebody else's measurement, and didn't get all of the above correct, and was bitching about how the other guy was wrong. When I showed him the spec and that he was not configured per spec, and that once configured correctly he did indeed get the same reading.... well, he blamed me for making the instrument too complicated.
This is my opinion, not Aeroflex's.
I WILL NOT give you proprietary information. I make too much money to jeopardize my job.
I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.
WB6NVH wrote:Doesn't the R2600 have a SINAD meter built in? (I am not familiar with that monitor model.)
Yeah, I think the entire R2600 line has SINAD as a standard option. When I was speaking with the tech at the depot, he insisted that their monitor was not capable of it. Later when I asked them what external sinader they were using, they said it was in the monitor. I'm thinking there is probably a literal loss of translation between me and the tech (since I do not believe he could speak english). Either way, the tech notes I received verified what I was thinking in black & white.
When I get the chance, I will attach a copy of the notes field. You will see exactly what I mean! If you are really curious, PM me with your email and I can send you a JPG of it. The tech was so torqued, that he made a copy of it and taped it (heavily) on to the top of the radio!
~WEC
"The bitterness of poor quality lingers longer than the sweetness of low cost"
sinad is a performance level whereas squelch is really only a preference.
Lots of radios still have a squelch knob just like a volume knob.
Is all this getting confused with 20dB quietning?
tvsjr wrote:You expect MexiMoto techs to understand that? What's next... gonna try to explain the difference in accuracy and precision?
Don't you mean Mexi-CTDI techs? They're the ones "fixing" your radios, not Motorola.
Well, yeah... I tend to lump that entire giant circlejerk under the MexiMoto umbrella.
Personally, if I were the OP, the next time the radio went back, it would be *real* deaf. I would, of course, not advocate him doing anything illegal or immoral in the process.
We'll the problem is obvious now, no one at the MEXO-ROLAs in-service center has any sensibility.
I'd cut and paste that into an e-mail and forward it to Elgin or Schaumburgh just to embarrass them for having idots who cannot even speak English in their service facility.
Tell them your dept. refuses to deal with people who can't speak English.
Before someone suggest buying Kenwood, does anyone know if the Kenwood service techs speak English ?
I've never had an issue with the Kenwood service techs' ability to speak english. Also, I've never had a fix require more than one trip in... then again, out of nearly 100 x180 mobiles/portables in service, I've only sent a few in.
Just a little update - I talked to a few people in Elgin, and sent them a copy of the same photo I posted here. Eventually it got handed to Mexi-Moto again, and this was their resolution:
MEXI-MOTO wrote:...As i stated then, the unit will be replaced with the same serial number and it will be returned with default (factory) settings, if possible please reprogram the unit manually (do not use archive information) to ensure the problem (Rx sensitivity) is not related to any corruption in the codeplug or programming. The matter was already escalated to manager level and the quality deparment was made aware of the issue...
Sounds like the typical mother M blow-off way of saying "here is a new radio. Go away"! So it looks like this is the end of the road. I have no idea if the techs will be advised of the proper use of the SINAD option.
WEC
PS - I wonder if this found it's way to the complaint deparment. Those guys have GOT to get some spell check going.
"The bitterness of poor quality lingers longer than the sweetness of low cost"
