FYI. Cross-posting to IllinoisDigitalHam list and Repeater-Builder list from the [EMAIL PROTECTED] list.
Thoughts folks? Thanks to Mark N5RFX for doing real testing. First real attempt I've seen at really quantifying the performance of the receivers. Would love to see tests of the repeaters themselves now. But this is a good start! Nate WY0X -------- Original Message -------- Subject: [dstar_digital] DStar Channel Spacing Date: Fri, 31 Aug 2007 09:53:54 -0500 From: Mark Miller <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] To: [EMAIL PROTECTED] The discussion about DStar channel spacing made me interested in looking at the channel spacing. I looked at the 450 kHz IF in an ID-800 just before detection to see what the attenuation is at certain frequency offsets. My receiver was an ID-800, and the transmitter was a 91AD modified for very low power. The 450kHz of the ID-800 with normal receiver noise looks like this http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450.jpg> The power within that bandwidth is about -70dBm on the spec an. This can be used as a reference, but does not represent the absolute power, as my test setup requires buffering of the 450kHz IF before it hits the spec an. I used a Tektronics 465B to provide that buffering. I supplied an on channel DV signal at -71 dBm to the antenna port of the ID-800 and here is the result http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_cf.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_cf.jpg> The channel power is around -9 dBm or 61 dB above the noise floor. Here is the result of Moving the ID-800 up 5 kHz http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_5.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_5.jpg> The channel power falls to around -17 dBm which is 8 dB below the on channel signal. Moving the ID-800 down 5 kHz gives this result http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-5.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_-5.jpg> . The channel power is around -20dBm. 6.25 kHz offset http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_625.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_625.jpg> . http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-625.jpg <http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-625.jpg>10 kHz offset http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_10.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_10.jpg> . Moving down 10 kHz gives this result http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-10.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_-10.jpg> . 12.5 kHzoffset http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_125.jpg <http://home.roadrunner.com/%7Emdmiller7/images/dv/ch_sp/id-800_450_125.jpg> . http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-125.jpg <http://home.roadrunner.com/~mdmiller7/images/dv/ch_sp/id-800_450_-125.jpg> . I am not sure how much the ID-800 IF bandwidth is similar to the repeater receiver bandwidth, but this does show that 10 kHz channel spacing is probably adequate, but 12.5 kHz spacing between local systems is ideal. 73, Mark N5RFX
