Batboard

Does anyone know what Invert DPL means in the MTsx RSS? If I remember it is under Channel options (F9)

Outa here

In some radios, inserting a +.1V signal into the modulator will offset the radio's output some +N kHz above the carrier, resulting in a higher frequency.

In some radios, inserting a +.1V signal into the modulator will offset the radio's output some -N kHz below the carrier, resulting in a lower frequency.

The spec for DCS states that a 1 shall be a positive frequency offset from nominal carrier, and that a zero shall be a negative frequency offset.

The problem is, that for many systems created by adding an after market encoder to an existing radio, if the radio is of the second type (inverted), the resulting signal will NOT follow the DCS standard, and will have a 1 bit resulting in a negative frequency offset.

Also, for some radios a signal of 1 kHz above nominal carrier (that is, higher frequency than nominal carrier) will yield a +N Volt output at the discriminator tap.

For other radios, a signal of 1 kHz above nominal carrier will yield a -N volt output.

Again, adding an aftermarket decoder to the second type of radio will result in the decoder getting a signal that does NOT follow the DCS spec, but is inverted.

Now, the standard DCS codes are chosen so that the are equally valid (e.g. the check bits correctly match the signal) when the signal is inverted, but the code word will be different - so in the inverted cases above, the DCS code will be valid, but different from the intended code.

Hence the "invert" setting on DCS encoders and decoders - to correct for the cases where the radio is backwards, or cases where the system is backwards.

Alternatively, you could look up the corrisponding inverted code and program your en/decoder for that.

raymond345 wrote:

A second use of inverted DPL is on
a Repeater when they have a great number
of paying people.

By using inverted DPL then it is harder
for normal hackers to get to steal free
air time .(Like on a Phone Patch).

Most phone patches and repeaters keep track
of used air time. This is one more use out there.


.

DPL makes it marginally harder for people to get on the repeater (ie: they need to spend a few dollars more on equipment capable of decoding DPL)...using inverted DPL is no different. If you were to use inverted DPL 026 for instance, a person with a scanner capable of DPL decode would show it as DPL 464. They would then just program their radio with DPL 464 & they can access the repeater. The 'security' level is the same.

Todd

wavetar wrote: DPL makes it marginally harder for people to get on the repeater (ie: they need to spend a few dollars more on equipment capable of decoding DPL)...using inverted DPL is no different. If you were to use inverted DPL 026 for instance, a person with a scanner capable of DPL decode would show it as DPL 464. They would then just program their radio with DPL 464 & they can access the repeater. The 'security' level is the same.

Todd

In the same vein are the people who use "nonstandard" DCS codes rather than the approved standard codes, thinking that will make them secure. Of course, a code scanner will still report the nonstandard code, and most radios will happily accept the nonstandard code, so all that you are doing is making the system less reliable.

the reason motorola gave that option originally had nothing to do with other types of radios, etc. but the fact that in certain situations, to get rid of certain receiver interference problems (via image response) (which is not much of a problem now 'cause they finally got the bright idea that if you put the 1st i.f. high enough in freq you put the image way out of the front end passband) you could do something called changing "i.f. injection" from either "low side" to "high side" or vice versa....make a short story long, when you do this, everything coming out of the discriminator ("rx") is inverted, and you have to correct for this...you think they would have logically fixed this at the source (the rx that you changed injection on) but in the big M's wisdom they used to flip the tx dpl codes on all the mobiles, say...thank god there were not too many of these systems out there as when equip was added later, invariably it was forgotten that the rx was "custom".....