Batboard

"No, you can't use the XTS stubby on a MotoTRBO, it's not rated for TDMA. It's only rated for FDMA and analog. You need the TRBO antenna since the TRBO antenna is rated for TDMA"

Your thoughts???

Jeff,

Are you sure you want to go there? The remark speaks for itself.

Regards,

Frak! Now I need to order a boat-load of TDMA antennas.....

Just when I thought I had everything under control.


Just sayin'


Jack

Can I use a CDMA antenna then?

"No, you can't use the XTS stubby on a MotoTRBO, it's not rated for TDMA. It's only rated for FDMA and analog. You need the TRBO antenna since the TRBO antenna is rated for TDMA"

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OK, so here's the story.

Radios like the XTS use conventional analog and FDMA modulation formats. These radios use very simple class C PA circuitry which is very tolerant of load mismatch up to VSWR 2:1 whereas the MotoTRBO product uses TDMA modulation. The PA circuitry in these radios must be much more sophisticated in order to process the TDMA signal with optimum power consumption efficiency and in order to minimize spectral regrowth and thus be compliant with the narrow band emission mask.

An unfortunate consequence of this specialized PA circuitry is that it must operate into an antenna with VSWR 1.75:1 or better in order to fulfill these technical objectives, therefore, because the XTS stubby antenna cannot meet the VSWR requirement, it should never be used on the MotoTRBO transceivers.


So now you know.

Wait a minute - did I see someone throw a BS flag?

OK, so it's a total fabrication [remember - I did say is was a story], but who knows? Maybe there is a reason....

xmo wrote:"No, you can't use the XTS stubby on a MotoTRBO, it's not rated for TDMA. It's only rated for FDMA and analog. You need the TRBO antenna since the TRBO antenna is rated for TDMA"

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OK, so here's the story.

Radios like the XTS use conventional analog and FDMA modulation formats. These radios use very simple class C PA circuitry which is very tolerant of load mismatch up to VSWR 2:1 whereas the MotoTRBO product uses TDMA modulation. The PA circuitry in these radios must be much more sophisticated in order to process the TDMA signal with optimum power consumption efficiency and in order to minimize spectral regrowth and thus be compliant with the narrow band emission mask.

An unfortunate consequence of this specialized PA circuitry is that it must operate into an antenna with VSWR 1.75:1 or better in order to fulfill these technical objectives, therefore, because the XTS stubby antenna cannot meet the VSWR requirement, it should never be used on the MotoTRBO transceivers.


So now you know.

Wait a minute - did I see someone throw a BS flag?

OK, so it's a total fabrication [remember - I did say is was a story], but who knows? Maybe there is a reason....

ALL BOW BEFORE THE BULL$#!7 MASTER!!!

(I wonder if we can sell TDMA-compatible test cables for more $$$....

Nawww. Don't be Evil, Wowbagger.
)

It has to do with the bandwidth requirements, since FDMA separates the signals by frequency (Frequency Division Multiple Access) the antenna needs a wide frequency bandwidth, which the XTS antenna is fine for. TDMA is Time Division Multiple Access, so it needs an antenna with a wide time bandwidth. It's hard to explain, let's just say there's quantum mechanics and string theory involved. Also, to adjust a TDMA circuit properly you need to go get your Sonic Screwdriver out of the TARDIS.

One note,

There is a standard now that some of the Mototrbo equipment comes standard with GPS where before it was an orderable option. Can you order a Trbo portable without GPS?, I have to ask as there is not a completed listing in E cat yet.

May be there is a GPS difference, but do not quote me, I know the RF difference is negligible.

Bend the antenna and transmit, you just changed the output pattern of the transmitter and the VSWR with the loading from the object used to bend the antenna.

CoM

It's like the cellular dealers that capitalized on the switch to digital years ago.

They made a killing scraping off the old on-glass "analog" antennas and changing them to "digital" antennas.

Look, it's real simple - just like when CB went from 23 channels to 40 channels.

Lots of folks were told that they had to have a second antenna on the vehicle and attached to the CB so they could use the newer, higher frequencies....

Sort of like that.


Just sayin'......


Jack

Wowbagger wrote: "I wonder if we can sell TDMA-compatible test cables for more $$$...."
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Here is a draft of our new test cable white paper. You may be familiar with our Mr. Harden as he hold numerous patents relating to cables, primarily the interconnect cables used to significantly improve the listening experience for so many owners of high end audio systems.

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TEST CABLES FOR TDMA

By Rod Harden, IDRT Corporation

One of the most overlooked facets of testing TDMA digital radios is the quality of the test cables used between the instrumentation and the DUT [Device Under Test]. Here at IDRT [Instruments for Digital Radio Testing] we have become the industry leader in affordable field instrumentation for the testing of digital radio systems. First with our 9275 and now with our 9320 series TSOW [Test Set Of the Week], we have incorporated all the features necessary to confidently verify the performance of digital two-way radio products with innovative features such as our Modulation Fidelity With Integrated Constellation [MFWIC]

While developing MFWIC our lab engineers noticed occasional anomalies in the display results. Laboratory grade signal generators create the test signals used in our product development. After returning several of these generators for calibration without resolving the anomalous readings, our engineers decided to investigate further. Using the latest simulation and vector modulation analysis tools from Agilent Technologies, we were able to eliminate every aspect of the test system as a potential cause – except for the test cables.

Because test cables normally affect measurements only in the sense that they introduce loss, we were very interested as to how these particular cables could affect the MFWIC. After considerable research it was determined that there are two significant factors in the construction of test cables that can introduce error into digital signal measurements. These are specifically PIM and SRL. PIM refers to Passive Inter-Modulation while SRL refers to Structural Return Loss.

Passive intermodulation is simply the creation of intermodulation products in a passive device such as a cable or connector. SRL occurs in cables because of non-uniformities which cause minute reflections of the incident signal. These reflections are too small by themselves to cause a problem but can sum together coherently to create significant issues.

SRL is defined as the ratio of incident signal to reflected signal in the cable referenced to the cable’s impedance. In the cable industry, a cable’s impedance is usually defined as an average impedance that actually gives the minimum value for SRL.

At first one might conclude that a test cable is only passing a single frequency and thus there can be no IM, however, that is incorrect. In all modulation formats the modulation added to the RF carrier causes the creation of a composite signal which contains many frequency components. These components can interact with each other in a non-linear device causing additional frequency components to be generated. Of course, these IM products are at extremely low levels and are masked by the modulation envelope itself in such a way that they are undetected in a traditional analog system analysis.

Unlike an analog system, in a digital system, the complex modulation format is demodulated into specific combinations of amplitude and angle to determine the data points defined in the particular format’s constellation [polar demodulation]. This demodulation process “unmasks” the hidden signal distortions caused by PIM and SRL with the effect that these aberrations cause a smearing of the data point locations within the demodulator and thereby degrade the effective modulation fidelity.

As a result of having determined the importance of quality test cables in the digital test environment, IDRT is proud to announce a new line of test cables specifically engineered to support accurate measurement of TDMA systems.

These test interconnects are constructed using the highest quality cable available for the purpose, Flexco F182. This cable is phase stable to 40 GHz, thus you can be sure that SRL will not be a problem. Further, only the highest quality low PIM connectors are used in the test cable construction. Fortunately, IDRT’s sister companies have considerable experience in the connector field. As a matter of fact, our test cables are constructed in their state-of-the-art facilities and every cable is certified on the industry’s most stringent PIM analyzer from Summitek Instruments. Each new cable is provided with an NIST traceable Certificate of Test and warranted for a period of one year to the original purchaser.

xmo wrote: TEST CABLES FOR TDMA

someone had waay too much time on their hands!

OK OK Its April Fools......