Batboard

I'm trying to do the whole maxtrac to maxtrac poor man's P25 repeater thing but with a couple of spectras. The receiver would be a mid power and the transmitter is a Hi power deck with the pins jumped for power.

I'm trying to locate a good place inside or out to tie in to the flat transmit audio path. I tried searching the board but it keeps kicking out the term "spectra". I've found references to the regular filtered audio repeater configurations but nothing showing a way to transmit using flat audio input.

nobody.......?

I have not seen any postings here on this. I will see what I can find on a Hi Power in the shop.

I just got back from vacation, so I'm late answering.

The flat audio input is the Option Tx Audio, but the trick is the Spectra microprocessor will not activate this input unless a programmed radio option (like Securenet) is activated.

http://www.onfreq.com/syntorx/spectra/b ... tml#sprmib

Unless you can trick the Spectra into using Option Tx Audio in the flat audio mode, the connection is useless. For dedicated repeater use it might be possible to bypass the pre-emphasis and make the microphone input permanent flat audio. On the other hand, if you install Securenet hardware and activate it, except use custom wiring to the Option Tx Audio pin you would have selectable flat audio on Tx.

Excellent... so you are saying that I would basically have to enable internal securenet and then intercept the audio exiting the module/carrier board in to that internal pin?

I wonder what the radio would do? Would it fail out due to an improper secure hardware setup during the start up self test routine?

BTW, I was exploring the idea of an IMBE repeater using two astro spectras in true digital mode. I lifted the lines feeding the digital data to and from the secure module and routed them out on flying leads that I could work with. The radio would stop working when I allowed one of the digital lines to go open. I know it's a different animal but I wonder if it's somewhat the same? The astro seemed to continually sense what was going on with the digitized data leaving and exiting the DSP. Once it sensed and error it emitted a horrible whine and shut off.

As for rooting around looking for ways to bypass the emphasis circuitry, I've had no luck. Will helped with some points to go after but nothing seems to work. It just doesn't seem to be a very "flat" audio no matter what I tap into.

Thanks for the reply on the securenet idea. I will look into it when I get some time.

In a normal Spectra (not a Spectra E) the U400 Audio Filter IC takes microphone audio through external components R420 and C419. These external components set the actual pre-emphasis. From inside U400 the microphone path goes through a Limiter and Splatter Filter. The Limiter sets the maximum deviation audio level (not the actual deviation out) and the Splatter Filter cleans up any clipping effects from the limiter. In a conventional Spectra the Splatter filter has around a 3000 Hz upper frequency. For passing a digital signal either the Limiter or Splatter Filter could possibly affect a digital signal and kill it.

The Option Tx Audio op-amp U401C and enters U400 through a different path Aux. Tx In. This path bypasses the entire microphone path with its Limiter/Splatter circuit and is also used by U700 Signaling Filter (DTMF, MDC, etc.).

Looking through the detailed manual description, there is no evidence of any microprocessor controlled switch to control the Option Tx Audio path, however that doesn't mean no such switch exists (it could be inside U400). Try just feeding the Option Tx Audio with an audio signal, press the PTT and see if it modulates the Tx output. If it does work, then you will not have to trick the Spectra by using Securenet hardware or anything else. To get an approximate audio voltage level for the Option Tx Audio, try sending internally programmed Tx DTMF while looking at the voltage on U401C pin 9 with a scope. This will give you a starting place for an external Option Tx Audio level. Be careful, because this audio path has no Limiter/Splatter circuit, so it has no maximum deviation limit control. The deviation will be set by the audio signal level and will go as high as U400 allows (possibly +- 7.5 KHz or higher for a maximum level). Another thing about digital, is you cannot invert the digital signal polarity between what your receiver gets and what your transmitter puts out. This type of repeat connection uses an audio connection to try and pass digital signals.

Using Astro equipment in digital mode will incur an audio delay from the repeater codec (the repeat connection would be decoded non-digital audio passed between radios as a real audio signal using the microphone connection). However, it will have the advantage of cleaning up the digital signal and doing error correction at the repeater site.

Mike B wrote: Try just feeding the Option Tx Audio with an audio signal, press the PTT and see if it modulates the Tx output.

It does not work, the signal is gated off except when the radio is transmitting DTMF, MDC or Securenet. Even tried different PTT inputs. Maybe the data mode would allow the TX Option audio to work, have not tested this.. yet.