Metropolitan Crossband Relay - This just adds additional remote 2 meter receive sites that all link back to the WEB site still on the same UHF channel, or multiple UHF channels depending on popularity of the system. The web page can operate a scanner to capture images on all crosslink channels. Voice Repeater Relay - This simply takes advantage of existing 2 meter voice repeater inputs by adding only the crosslink UHF transmitter at existing repeater sites. A mute circuit mutes the output of the repeater while an SSTV link is in progress. It is doubtful that there is any technical advantage to this arrangement since it will in most cases be politically unacceptible.
Frequencies are a local issue only.
Typically, only one frequency is needed and it can be shared with other applications. ALso, since only mobiles or remotes uplink on the channel in simplex to the APRN receiver, any simplex frequency can be used. There is no need for the APRN site to transmit anything on the channel back to the user other than a brief 1 second acknowledgment. Thus it is consistent with simplex shared use. These pages are NOT yet automatic.