--- In [email protected], "skipp025" <[EMAIL PROTECTED]> wrote: I've had DCI make a number of repeater window filters for me. > > It took a bit of time on the phone with Sean to find out what > they could do vs what trade offs I would allow in the specs. > The end result UHF 10 pole filters they made to my specs work > just killer. VHF is another animal...
Ralph from DCI suggested either a 4-pole or an 8-pole filter. Here's a link he sent, and I must say that it looks pretty good. http://www.dci.ca/html_commercial/graph_158-4-8_wo219.htm >From that I gather from the response curve of the 8-pole unit, we could then expect to get something in the order of -90db (or more?) isolation at 4MHz off-center (where our Tx carriers are located), with only 1db insertion loss. Price is quite reasonable, only delivery of 4 weeks (or maybe less), is a bit of a problem as we ideally would need to return to the site in about two weeks time. In regards to the added insertion loss of 1db of the filter, to compensate for this maybe we could probably bypass the stock Preselector that came with the multicoupler, and/or just remove a 2db pad that is now installed between the output of the multicoupler preamplifier and the power divider. Would you say this is a viable option? Using the 8-pole might probably seem like a bit of overkill, but given the critical need to not only solve the problem, plus the difficult access (it's very distant) to the site where the system is installed, we would like to have the peace of mind of an additional margin of safety. For this reason maybe we might also consider filtering the TX path as well, also with another 8-pole filter, or maybe just 4-poles. The only other Preselector option that we are considering at the moment is the Telewave TPCP-1546C 6-cavity Preselector, as it seems to offer between -70 to -80db isolation at 4-5MHz off center, although we don't like much the 2.5db added insertion loss. If you care to take a look at it, the datasheet is here: http://www.telewave.com/pdf/TWDS-2006.pdf Telewave (posted their full response at the bottom) suggested the TPCP-1544C Preselector, but it seems we could only expect 45-50db isolation with that one. A bit tight, if adequate at all in this case. http://www.telewave.com/pdf/TWDS-2005.pdf > > I've taken a look at the DCI site, and also contacted them. They > > promptly responded and seemed very eager to help. Have you had any > > previous experience with their products and so forth? > > Excellente' you will luck out by having all your receivers > within a same window. Imagine doing receive preselection when > the FCC gives you "pop-corn picked receiver input frequencies". > > My VHF rx pre-selection system is a very special network made > for use with non-sequencial (mixed spaced) receiver inputs. Oh > the joy it was to make... I can imagine it was a bit of a pain to make, but glad to hear is humming along nicely now. both your positive comments on DCI, and their prompt and helpfull responses actually made me want to include them in our short list of possible solution providers. You might be able to ask for a possible sales commission... ;-) > You don't mention if the system will be mostly mobile or > combo mobile and portable operation. If you don't have any > portables, bypass the preamp right away... you don't really > even need it at this point in the game. It has to handle both portables and mobiles, although portables will only be used for close range communication well within view of the tower (2-5 miles). Still as it is, portables have been proven to be still usable further away, but for reliable communications they will have to use the mobile radios, as the very dense vegetation around the site, plus the mostly small winding roads that where cut between small hills have proven to be a big factor in attenuating RF signals. On the open we managed to place a reliable call from about 30 something miles away. Probably still good for another 10-15 miles, but with some gray areas. > There's a really killer Dubus Magazine Phempt Preamp > article available for free on my www.radiowrench.com/sonic > web page, which well describes some of the problems with > preamps and example noise floor levels of a location. Well > worth a look if you have time... Yesterday I downloaded the PDF, but didn't have a chance to read it. Indeed it looks like a real killer preamp. > Some of us only dream of a low noise floor... but then there's > that city of 1.2 million just down the mountain and that [EMAIL PROTECTED] > military radar and eplers system nearby. I hear you. We have that problem here in Caracas. VHF is basically so congested that it is almost unusable at any of the good mountain top sites. BTW, yesterday the Telewave response came in. See bellow. Well its about lunch time, at least around these parts. Bon Apetit eveyone, specially you Skipp. We also take our lunches VERY seriously. :-)) Alex ========TELEWAVE RESPONSE============ I have just finished with our engineers and they told me you have done all the proper tests and the problem is on the receive side. The mobile duplexer you have is not providing enough attenuation and you need to knock down the transmitters more than that can provide. We have a TPCP-1544C preselector that will do the job for you. Your price is $ 865.20 USD. You can just bypass the mobile and connect right to the input/output. The connectors are N-female. If you would like to purchase this unit please email me and let me know the particulars of the transaction. We take Visa/MC or wire transfer. Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
