@n5ims : The aim is to have full duplex voice communication between two buildings connected by the RG 58 coaxial cable. The distance between the two buildings is 30000 feet. The attenuation of the RG58 cable is very high about 2034dB. I need a repeater to extend the signal and also serve the full duplex purpose. Im kinda lost on how to calculate by how much the repeater will boost the signal. I want to use FM Modulation in VHF highband.
I think you need to reassess on a systemic level. Start with the requirements document and work from there with no predetermined solution in place.
9+ kilometers is a significant amount of coax, even cheap coax like RG-58, is there no other way to get the signal between locations? How about fiber? Sure, the cost of the fiber is slightly higher, but that distance can be run with no support equipment other than the launch and receive sites, so it might be a lower total cost effort.
If it is just voice why use RF at all, why not just base-band audio (think telephone system)? If the bandwidth requirements are not large, and you want RF based for the full duplex then why use VHF-Hi? Why not HF or MW where losses are much lower in any coax you select? For example changing from 250 MHz to 5 MHz reduces the loss by more than 1800 dB, you would be able to get away with significantly fewer bidirectional amplifiers, going to 1 MHz would get the loss down to around 100 - 110 dB, and might mean you could get away with only one or two amps.
What is the purpose of putting it on a cable for such a distance, why can’t it go as RF in space?
If you want security look at a digital spread spectrum encrypted over-the-air RF link, you should be able to purchase one with antennas for less than the cost of 9 km of coax and associated amplifiers.
Direct burial fiber can be purchased for less than $500 USD per kilometer, meaning the entire 9+ km run could be purchased for under $4500 USD, roughly the same cost as a 30000 foot run of RG-58.
Or look at point-to-point laser systems, unless you are in the path between the two points it can be hard to tell when the link is active. If you want to deny someone the intelligence of when you are active leave the link up all the time with bogus data/audio on it in discrete channels.
By the way, speaking of security, leakage from such a long run of coax cable will mean that someone can tell when you are using it, if they really want to, so if security is a driver it might not be as tight as you think. Fiber would be the way to go here if security is a concern.
A lot more thought needs to be given this project for it to come to a successful and fiscally responsible conclusion. Also, the existing factors and limitations need to be known.
T!
(edit) Ooops, sorry, I see N5IMS already brought up several of the points I made. I did not see that until after I posted.
