While I don't have any recordings for you, I can assure you that ALL machines I build have audio responses that sound as close to simplex as possible. When I am finished with a machine, I have a helper in another room talk into the repeater's input while I toggle my receiver between the receiver's input and output frequencies. If they don't sound REALLY close, the machine doesn't leave my shop.
There are many things that can lead to distortion in a repeater's audio path. Among these are discriminator response, PL filtering, (if used) controller bandwidth and distortion, and exciter frequency response. The most likely causes of audio response issues are the controller and exciter modulator. Since you describe the audio response as either 'tinny' or 'muffled' that tells me that the audio input response of the controller is not configured properly. *Most* controllers can be used with both discriminator audio or de-emphasized audio. This is often jumper selectable, but sometimes component changes are necessary. I will leave it to the reader to do further research on what these two type of audio are, but suffice to say that most controllers expect to see discriminator audio and have on-board de-emphasis circuitry to make the audio response "flat" again. If the repeater in question has a 'boomy' sound to it, this is likely a sign of too much low-end audio response. The audio is more than likely being de-emphasized twice inside the system. The best and easiest way to fix this is to remove the extra de-emphasis circuitry. This can sometimes be done on the input circuitry of the controller. If it can't be done there, you may have to look at your Rx audio source. It is common practice to those who don't know any better to use audio from the speaker. "It's convenient and it squelches when the repeater is not active." This is a BAD idea. Not only is the audio WAYYY to loud from a speaker's output, it's bound to the volume control. If someone is at the repeater site and decides he wants to listen in on a conversation, there goes the audio setting for the repeater!! Speaker audio is a good example of de-emphasized audio. If the repeater audio sounds 'tinny' it has too many high frequency components. In this case, an additional stage of de-emphasis is required. Again, the easiest way to add this is in the controller's audio circuitry. If the audio is 'muffled', it is probably being processed (compressed) too hard. Inside a transmitter there is circuitry that keeps the audio tamed down and in check to avoid overmodulaton and other band things from happening. This circuitry can only do so much. If it is getting hit with an audio source that is WAYYY to loud, it simply slams it to the ground, hence making it sound bad. This is an over-simplification, but more information on audio processing and how to *properly* set it up can be found in the repeater-builder.com site.: http://www.repeater-builder.com/tech-info/audioprocessing.html (This may be a bit over your head)[sorry Jeff] http://www.repeater-builder.com/tech-info/fmtheorydiscussion.html Sounded like a simple enough question didn't it!! Enjoy, Scott Scott Zimmerman Amateur Radio Call N3XCC 474 Barnett Road Boswell, PA 15531 tait700 wrote: > Hello, > Was Wondering if anyone had a link to a site that had samples of talk thru > Repeater traffic that would be considered good quality audio ? > Maybe i am expecting too much but any of the ones around here that i have > heard seem either Muffled or very Shrill, Listening on the input frequency > the Audio seems quite reasonable but the Transmit Audio doesn't sound the > same and seems a bit average. > I realize that the Audio will vary due to the normal constraints of Radio > atmospherics but i was hoping for something that doesn't sound like a very > cheap tiny AM broadcast radio > I would be really interested in discovering just how good normal Analogue > speech can sound when it is being passed through something that is properly > setup. > Apologies if this has been answered before, i searched but couldn't find > anything specific. > Any info gratefully received, > Cheers, > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.375 / Virus Database: 270.13.2/2214 - Release Date: 07/02/09 > 05:54:00 >
