Batboard

First off, I am a Technician working for a Motorola Channel Partner (aka authorized dealer). I have been given several DTR550 & 650 radios to "check" for a customer. These radios may or may not have issues/faults. Due to their spread spectrum nature they are difficult to test with a conventional service monitor. Also, since that customer is not even sure if the radios have issues or not I don't really want to send all of them to Motorola unless I have evidence suggesting a problem.

I tried hooking all of the 2nd gen DTR550/650's (removable antennas) to a couple different spectrum analyzers I noticed on both analyzers that the constantly moving spikes peak at -5dBm although the radios are rated at either 1 or 2 watts. I was expecting to see either 30 or 33dBm from these radios. I don't have a known good radio to compare against so what I would like to know is if this is normal or if it suggests that all of these units have low power output. I know that digital signals can have misleading power output and also because these are spread spectrum radios perhaps the frequency is changing before both analyzers had a chance to accurately represent the power level. I suppose there is also the possibility that during handshaking an RSSI measurement could be taken and these radios might dial the transmit power down opposed to transmitting at full power all the time.

Also if anyone has any ideas on how to better test DTR radios for proper operation it would be greatly appreciated.

Thanks,
~Andy~

Do you have a HP E6501A VXI Receiver ($ 15,000)

Aside from that, have you tried to get the service manual from /\/\. At one time, they had a FTP Server for directed sales (& MSS's?), to get technical data on-demand. I've only had one pair of Motorola DTR550/650 Radios come across my bench, in the last 5-10 years, they just needed new batteries.... I was lucky. Without a working unit, to compare with, you're shooting blind using conventional test equipment.

If they power-up, do they sync with each other? If not, it could be a 'simple' programming issue. Unfortunately, I have no technical data on them, what so ever.

Good Luck!

- trg,

The DTR series, as far as I know, are not CPS adjustable/programmable. There may be legal issues with spread spectrum capable radios being CPS programmed that may cause the actual carriers to hop into adjacent service spectrum and wreak havoc. Just going on assumed thoughts about this only, not based on legalities.

With spread spectrum you are going to see spikes across the band, this is normal, as the TX signal is actually going from 'X' to 'Y' at a given rate, and at a given RF level.
You have to set your display to maximum spread, and be able to cover at least 2 megs or more.
This is one carrier type that I would love to have in my service monitors. I am unsure of the latest versions, but the ability to decode and analyze SS signals is a great help with amateur and non radio related equipment.

You should be able to get a snap shot of peak levels, regardless of the entire spread of the carrier, you might be able to get several in fact and normalize the entire picture to see where and if, there are differences. baseband power should be under a watt for the DTR series IIRC.

Note, there is more than a single type of spread spectrum modulation/carrier schemes available. Simple spread spectrum, reduced carrier, frequency hopping- direct sequence Etc..
But I think the DTR series is simply spread spectrum, without the complex schemes listed above.
I do not recall how wide the SS signals of the DTR radios are, as to the actual spread, so it is best to start with a display set to 10 megs, or greated if possible, and narrow it if necessary.

The transceivers hop at 11 hops per second so the relatively short dwell time does not get sampled well when measuring power. The hopset does repeat after 50 hops so you can "accumulate" the vaue for one frequency by setting a marker for Peak Hold.

If all the units in a conducted test came close to the same value, then it is a good bet that the TX power is nominal.

User misunderstanding is much more likely to be the problem here.

Craig

I have an Aeroflex 3920 ($40,000+) it can do DMR and has all the bells & whistles but it can't keep up to the spread spectrum frequency hopping nature of the DTR radios. Plus I have IFR COM120's and a Motorola branded monitor too. Digital signals often give invalid power readings on service monitors and even the same radio gives different readings on each type of service monitor that I have. I have tried to get a service manual but there is none available from Motorola. All of them are able to "talk" to each other and all have the default factory programming in them. DTR's are programmable but there is only the ability to select 10 different hopping algorithms and then 100 different privacy codes similar to the TRBO color codes. I managed to get a hold of a brand new working radio but other than driving down the road and comparing range I have no good method to test them. The old DTR's with the fixed antenna get significantly less range then the newer units with removable antennas. I only have a new unit with the removable antennas so it’s hard to even compare the range to the older fixed antenna radios. Plus all that tells me is if the range is comparable to a new unit which could have degraded slightly over time. All the radios including the new one get similar -5dBm on the Aeroflex 3920. If one radio has poor range I still don't know if it would still show -5dBm or if it would be less. I have tested receive and transmit audio and the only issue I've found is intermittent PTT or sticking PTT on a couple radios. I repaired the PTT switches then sent all of them back to the customer requesting more fault information. I hope if they do return I will have enough information to attempt repair if I have a way of testing the particular reported fault and if not send it directly to Motorola.

Thanks for the help everyone,
~Andy~