At 1/4/2007 05:57 AM, you wrote: >n9lv wrote: > > I am in need of at least five 131.8 versatone boards for the following > > GE tone board. Also, I need to know, are these board just encode, and > > is there a way to make them decode. I put one in one of the radios, > > it does send pl out the transmitter, however I do not get any audio > > from the speaker out of the receiver. > > > > Problem I am having is that the GE converted radios will not allow the > > PL tones to pass through them. I can take the repeater out of PL and > > the radios work just fine, and the audio is just fine. > > > > Any sugesstions? Thanks > > > > Mathew > >I think you are you using these radios for voting remote receivers? If >that's the case, are you sure you want to introduce yet another PL >response time into the equation? If not, consider FM'ing the >transmitters, and installing some sort of audio processor designed to do >the job of clipping and HPF'ing that fits the situation.
While FMing definitely improves the low-frequency modulation performance of PM exciters, I've experienced good performance with my stock MVP PM exciters. I know from Dave Karr's experiments (or was it Virgil at S-Com, can't quite remember who did the tests a while back) that the harmonic distortion at low modulating frequencies and high deviation levels is a bit high. However, CTCSS deviation levels are quite low in practice (should never be more than 1 kHz). If the output from the RX discriminator is de-emphasized so as to "match" the pre-emphasis curve of the phase modulator, a very flat audio response that includes the CTCSS frequency range can be obtained. Basically this means lowering the "break point" of the de-emphasis network from the usual 300 Hz to just below the low end of the CTCSS range (40 Hz or so). > The AP-50 is one such animal. Most commercial equipment audio chain in > good from only 300 to 3000 cycles; it won't pass PL and it won't pass the > high-end audio that the voter relies on to properly vote. The phase > modulators that most of this equipment utilizes won't properly follow > audio that is recovered from the discriminator, and is why I choose to > install a real FM modulator in the radio set. A better sounding, better > working radio >will result; one that is transparent to the system. I have never tried >to FM a EXEC II; we've always used MASTR II's for remote satellite >receiver - link-back transmitter combo's, but, I don't see why it can't >be done. IMO the AP-50 is an excellent "final output" processor that enables a near-perfect balance between keeping the output clean and preserving repeat audio fidelity. However, for a remote receiver link I think you'd want to make it a 1:1 link with no limiting or filtering whatsoever. For that you could simply FM your TX, or use the CG HI (direct to the PM modulator) & apply the de-emphasis as described above. I've done this for my system which has a total of 3 links in the repeat path & have been told by some local FM "purists" that it sounds quite respectable. My ears do detect a bit of subtle low-pass filtering taking place somewhere; I believe it's due to the combined low-pass roll-off of each RX in the system as a result of the IF filtering but I could be wrong. Bob NO6B
