25-08-2016, 09:38 AM
The two amplifiers we have are a Teleste CX100 and a Teleste CX101. They are virtually identical and are interchangeable in the museum system.
Gain is 39dB and the maximum output high enough for them to run at a healthy +50dBmV with it's three channel network, still with plenty of headroom available (distortion products increase with the number of channels in a network, which means that networks with lots of channels have to derate the permissible maximum output level). +50dBmV is actually much higher than required by the present system - note the 8dB pad on the output! - but allows lots of expansion potential if ever required in the future. Teleste data available here
If you are choosing an amplifier for a distribution system, the two important factors you need to know are maximum permissible output level and gain. Assuming the possible output level meets or exceeds your requirements, the gain will determine the input level required. If you need to combine several sources, the available level might be less than you are expecting, so always check your calculations first! You can, of course, cascade two amplifiers with different characteristics - amplifiers like the CX100 consist of two amplifiers in one box, anyway, the first is optimised for low noise and the second for low distortion.
You will note that the lower limit of the CX100/1 is stated as 47MHz (i.e. Channel E2) but Channel B1 is used in the museum, which needs a response down to 40MHz. However, those amplifiers are designed to include a return path amplifier for upstream communication which the museum examples don't have. This means that the diplex filters which separate the forward from the return signal and which roll of sharply below 47MHz are not fitted, leaving the B1 area free.
This usually means that, if you see a similarly specified amplifier, you should be alright - it is simply that, since the UK abandoned Band I, manufacturers see no point in advertising a response below that used in Europe. However, if an amplifier has a flat response from 47 - 865MHz, the chances of this not extending down to 40MHz is unlikely. The exception to this is an amplifier equipped with, or planned to be optionally equipped with, a return path amplifier but has the diplex filters permanently built in. I would expect this to be very rare, though.
You will note from the problem with the museum's diplex filter I mentioned in my previous post, that the new cut off in specs has risen to 85MHz since the abandonment of Band I for broadcasting, so it might be a gradually increasing problem in the future to ensure good Band I performance.
On the subject of the return path, because of increasing demands for upstream capacity for broadband internet and similar uses, there has been a tendency to raise the crossover limit over time. The first network I worked on only had a small amount of upstream telemetry traffic and a 30/50MHz split. Today it is 65/85MHz and, if cable operators abandon FM radio on their networks, it can rise even higher.
Gain is 39dB and the maximum output high enough for them to run at a healthy +50dBmV with it's three channel network, still with plenty of headroom available (distortion products increase with the number of channels in a network, which means that networks with lots of channels have to derate the permissible maximum output level). +50dBmV is actually much higher than required by the present system - note the 8dB pad on the output! - but allows lots of expansion potential if ever required in the future. Teleste data available here
If you are choosing an amplifier for a distribution system, the two important factors you need to know are maximum permissible output level and gain. Assuming the possible output level meets or exceeds your requirements, the gain will determine the input level required. If you need to combine several sources, the available level might be less than you are expecting, so always check your calculations first! You can, of course, cascade two amplifiers with different characteristics - amplifiers like the CX100 consist of two amplifiers in one box, anyway, the first is optimised for low noise and the second for low distortion.
You will note that the lower limit of the CX100/1 is stated as 47MHz (i.e. Channel E2) but Channel B1 is used in the museum, which needs a response down to 40MHz. However, those amplifiers are designed to include a return path amplifier for upstream communication which the museum examples don't have. This means that the diplex filters which separate the forward from the return signal and which roll of sharply below 47MHz are not fitted, leaving the B1 area free.
This usually means that, if you see a similarly specified amplifier, you should be alright - it is simply that, since the UK abandoned Band I, manufacturers see no point in advertising a response below that used in Europe. However, if an amplifier has a flat response from 47 - 865MHz, the chances of this not extending down to 40MHz is unlikely. The exception to this is an amplifier equipped with, or planned to be optionally equipped with, a return path amplifier but has the diplex filters permanently built in. I would expect this to be very rare, though.
You will note from the problem with the museum's diplex filter I mentioned in my previous post, that the new cut off in specs has risen to 85MHz since the abandonment of Band I for broadcasting, so it might be a gradually increasing problem in the future to ensure good Band I performance.
On the subject of the return path, because of increasing demands for upstream capacity for broadband internet and similar uses, there has been a tendency to raise the crossover limit over time. The first network I worked on only had a small amount of upstream telemetry traffic and a 30/50MHz split. Today it is 65/85MHz and, if cable operators abandon FM radio on their networks, it can rise even higher.
