Here's a sysop's-eye view of the KIDDER packet router (left) and GB7PZT BBS (right) consoles.
There is nothing much of interest, they are simply a pair of very old computers and even older monitors (the right-hand one is EGA). The unlit monitor is part of the spare node.
The sysop rarely sees this view, as the systems are operated remotely via TCP/IP links
All the radio equipment is located elsewhere, linked by RS232 cable.
Some of the TNC's and radio equipment are located in the loft, the rest in a metal roadside cabinet outdoors. This was done partly to reduce the QRM and partly to reduce the fire risk.
The large blue units occupying the top half of the cabinet are the Pye R460/T461 transmitters and receivers, used on the 70cm links.
The untidyness is due to the fact that the system was thrown together using whatever equipment was to hand. Link partners come and go, and equipment frequently has to be redeployed in different configurations to cope with this. And when things break down, sometimes this re-configuration has to be done in the dark, in the freezing cold or pouring rain!
This is a bandpass filter, of the type used on the 144MHz and 70MHz ports.
They give good rejection of out-of-band signals such as pagers and other local transmitters, which might otherwise swamp the receiver front end.
On transmit, they help to ensure that the station does not radiate spurious signals.
There are several of these UHF cavity filters used on the 70cm ports.
As with the lower frequencies, these protect against spurious out-of -band receive and transmit signals, but they also have considerable selectivity within the band, allowing several 70cm systems to co-exist.
They can provide a bandpass or notch response depending on how they're connected, and KIDDER uses both modes. In bandpass mode, the signal is fed into one of the two BNC sockets and taken out of the other.
In notch mode, only one socket is used, the cavity being fed by a coaxial "T" piece. This results in a deep notch which can be used to "suck out" the carriers or noise sidebands of co-sited systems.
These two pictures show a UHF duplexer similar to those used on KIDDER.
The aerial is connected to the middle socket, the transmitter and receiver to the two outer sockets.
Inside the unit, a number of helical resonators (in this case 5) are connected via BNC "T" pieces, providing deep notches in the transmit and receive signal paths. Those in the receive path are tuned to suck out the transmit carrier frequency, and those in the transmit path are tuned to suck out the receive carrier frequency, thus eliminating noise sidebands from the transmitter, which would otherwise swamp the receive signal.