Daily image
Dual Channel RF over Fiber
© Lesley Goudbeek
https://www.astron.nl/dailyimage/main.php?date=20170112
A couple of years ago a special module was developed for Ingram Networks, situated in England.
The Ingram module operates from 20kHz to 800MHz (not a typo) and over a hundred optical links have been shipped to Ingram. The modules are destined to be used for a railway project, where base stations connect to moving trains providing wireless internet to the passengers. The RFoF modules provide signal transport between base stations.
A dual channel RFoF module has been suggested and if it is easily achievable. As a Friday afternoon test, a dual channel RFoF module was made using previous developed single channel PCB’s (shown in upper picture). Instead of using a single laser, a dual laser module was used. This dual laser module is connected to 2 separate PCB’s (without any additional modifications). The same is done on the receiver side were a dual channel detector is connected to 2 separate PCB’s. The graph on the left show an old “normal” single channel RFoF module, and the right graph shows the modified dual channel RFoF Frankenstein (shown in the picture), where 2 separate signals are visible. And without any additional modifications, the results are not that far off of the original module. Reducing pin length and removing the unused detectors should improve stability.
This shows that a dual channel RFoF module is quite feasible and existing designs can be used. Plus the costs of a dual channel laser or detector is not significantly higher than 2 separate laser or detector modules. A dual channel can, for example, be used for transmitting both antenna polarizations and reduce the number of fibers needed by half. With a small PCB redesign, the total PCB size used can also be reduced. Sometimes a Friday afternoon can give insight into a lingering question.