On 1/29/07, Christopher Hodgdon <[EMAIL PROTECTED]> wrote: > The main setup that we received a quote for is the follow: > > 1 TKR-750 VHF Kenwood Repeater - $1350 > 1 KPG-91D Repeater Programming Kit - $119 > 1 TKR-PS1223 Kenwood Internal Power Supply - $169 > 1 PC24-NN Patch Cable (Repeater TX to Duplexer) - $31.50 > 1 PC24-NB Patch Cable (Repeater RX to Duplexer) - $26.35 > 1 PRD-1556 6 Cavity Pass-Reject Duplexer - $1859 > 1 PC95-400-NN Patch Cable (Duplexer to Polyphaser) - $54 > 1 IS-50NX-CI Polyphaser (Lighting Protection) - $62 > 100 feet of LMR-400 Feed Line $82 > 2 CC4-NM Coax Connector Type N Male - $25 > 1 ANT150D6-9 VHF 4-Bay Folded Dipole Antenna - $995 > 1 Setup, programming, and bench testing before shipping - $105 > > Total For Project - $4877.85
I applaud you "doing your homework" ahead of time, Chris. Countless people have shown up here on the list over the few years I've watched and learned from people here smarter than myself, who think that slapping something together will warrant them years of service and good performance. Some comments on your list above: - I don't know who's part numbers those are on the list, so it's hard to see exactly what you're purchasing there. Do you have the real manufacturer's names of those products. Those are the names most of us know these things by. - Patch cables: Make sure they're at a minimum double-shielded silver teflon or better -- you want all the RF to stay INSIDE those cables. I can't stress enough how much good quality RF cabling is needed in repeater service. - Great job thinking about lightning protection ahead of time! More comments on that below. Polyphaser is good, if the grounding system in place is correct at the site. That is a topic too broad for this reply, but look in the RB website for more information from a lot of sources on proper grounding techniques for lightning protection. If you're planning on installing in racks (you don't say here -- and that's another expense you might need to think about), you'll need to know how the site grounding system works to properly ground the cabinets or leave them floating, etc... for example, at one of our sites, we purchased the equivalent of "Trex" decking material and made a platform for our three rack cabinets to get them off the concrete floor so there would be both less chance that they could arc over and damage the floor/via grounding to the concrete itself in a lightning strike, and also to provide an inch or so of "water ingress" protection in case the room ever flooded for any reason. All cables to those cabinets come in through the top of the cabinets, and the grounding system is extended to have the cabinets themselves rise and fall with the voltage potential of the tower itself, if the tower were to take a direct strike. Will your polyphaser be mounted on a dedicated RF entrance panel (typically made out of copper plate and grounded via very wide copper strap or connected to an overhead "halo" system, or will it be mounted in the cabinet or elsewhere? Again, too much detail to go into in one message -- but something to think about. - I see you have LMR400 listed. Now this will always start a debate here, but for the sake of completeness -- there are many people here who've had bad problems with the LMR series of cables when used in duplexed radio service (transmitting and receiving at the same time on the same antenna/cable system). The gist of it is that unlike more "traditional" hardline, the LMR cable uses a braid-over-foil technology that in at least some people's viewpoint, can become loose/noisy enough (especially if it's moving at all -- make sure you budget for high quality tie-downs or at least UV-insensitive tie-wraps to secure ALL cabling on the tower) to create crackling, noise, desense and/or other issues. I would recommend (and others probably would also, but some would disagree) that the "safe" approach is to use a more traditional hardline for your tower run. LMR might be "do-able" from the duplexer to the polyphaser panel or similar... you might "get away with it" up the tower too... but generally if you want NO problems... buy 1/2" or larger hardline and run that instead of LMR400. Others can, and probably will, comment on this, but if I were putting together a nice system like that, I would avoid LMR cables like the plague. Spend a little more money on good hardline and connectors. Cost for new will be about triple your estimate for the LMR400 and connectors. I feel it's a "you get what you pay for" type of thing. Good hardline can be found on the used market, but you may need to test it and make sure it has never had a water ingress problem, and/or has never been bent beyond its designed maximum bend radius. (Hardline recovered from towers is typically brought down in such a way that it's damaged internally by hanging it by itself.) - The Kenwood repeater isn't really a very high-powered repeater. After duplexer/cable losses, you're not going to have a whole lot of RF left. Think carefully about your desired coverage area and if you don't want to do the math to come up with a "semi-real" number, decide if 10W at the antenna is enough to cover where you want to cover. The easiest rule-of-thumb for that repeater might be close to visualizing that if you hooked a 10W mobile rig directly to your 4-bay antenna and tried to talk on FM to someone in your desired coverage area, would it be full-quieting solid copy? If not... you may need to invest in a power amp and have the Kenwood drive that. At some point, of course, you get negative return on your investment above a certain power level, and you're just building an "alligator" but it is all very dependent on what you're designing for... are you designing such that at the fringe coverage of the repeater, a 50W mobile will be full-quieting? Noisy? Are you expecting a lot of HT users? Will they be indoors? On rubber ducks? Etc. Some thought needs to go into that to get the right combination of antenna, feedline, receiver sensitivity, and transmitter power -- which then dictates whether or not the duplexer has enough isolation... etc... it snowballs into a complete design -- all you have to do is to start with a known given set of data: What performance are you expecting will be sufficient for your end-users? - Speaking of receiver sensitivity, I'm not familiar with the factory specifications on the Kenwood, but you may want to consider some pre-amplification of the receive signal. Someone with more experience on the Kenwood can comment on the typical receiver sensitivity numbers, and then you would have to customize from that baseline information and possibly a site survey with a spectrum analyzer (if you're going for MAX performance) what the noise floor at the site looks like and just how close you want to get to it. Perfect performance is (of course) being able to "hear" signals all the way down to the site noise floor... again, this gets back to your end-users. If you have a lot of rubber-duck HT's a long ways off... you're going to want to "hear" really really well. Even if you're catering to mobiles, if you're going for max performance on receive, you may need added bandpass filtering, pre-amplification, etc. Something else to think about. - Other miscellaneous items: You may want to remember to purchase a hardline grounding kit if the ground system at the site properly includes the tower system, etc... they're inexpensive and it shows a level of "done right" to have the hardline outer shield bonded properly to the tower if that's the type of ground system you're working with. Okay, 'nuff said for now - plus I need to get back to working on other things here. Hopefully that's helpful. Nate WY0X
