RE: [DSTAR_DIGITAL] Repeater stack
You folks in the UK do it up right. I paint all of my antennas. I lightly sand the fiberglass and paint with water based outdoor house paint. A sky blue color or grey helps camouflage the antenna. Paint tends to last longer than a clear varnish coating. If you want to go first class, use marine paint, made to use on fiberglass. For metal antennas, use Zinc Chromate or other metal primer, followed by a finish coat of sky blue or grey. This really extends the life of an antenna. Buddy Morgan WB4OMG On Apr 21, 2010, at 11:50:40 AM, Barry barrym...@ntlworld.com wrote: Another tip from the UK, is to paint the antenna(s) with Marine varnish several times, this prolongs their durability and certainly stops any rain or otherwise penetrating the fiberglass tube(s) over time. Might look ugly, but an ugly working antenna is better than a non working 'clean' one!
RE: [DSTAR_DIGITAL] Repeater stack
what is the lightning like in your area? If it is anything like it is here in Florida... go with a commercial grade antenna... otherwise your putting up a toothpick maker YES you can, but ask yourself, how many times you want to replace it when a storm rolls by. Some are lucky, others are not your call. Evans F. Mitchell KD4EFM / WQFK-894 Fla. D-Star Tech Support Group http://www.florida-dstar.info http://www.florida-dstar.info/ Polk ARES A.E.C. http://www.polkemcomm.org http://www.polkemcomm.org/ BB8330 PIN: 30965B58 _ From: dstar_digital@yahoogroups.com [mailto:dstar_digi...@yahoogroups.com] On Behalf Of Skier Sent: Tuesday, April 20, 2010 9:58 AM To: dstar_digital@yahoogroups.com Subject: [DSTAR_DIGITAL] Repeater stack If you are installing a D*Star repeater stack (2m 440cm modules) can you use a single dual band antenna for both modules or do you need separate antennas for every module in the stack?
Re: [DSTAR_DIGITAL] Repeater stack
If you are installing a D*Star repeater stack (2m 440cm modules) can you use a single dual band antenna for both modules or do you need separate antennas for every module in the stack? That somewhat depends on your preferences. If you are seeking decent performance then I would suggest not trying to combine them, but keep in mind that I would also suggest that you not use a Comet or Diamond antenna on a repeater. As long as you have the proper equipment to combine the signals there is no rule that says you can't do it, but I would warn you to that unless you are using gear designed specifically for the purpose of a repeater connected to a single TX/RX antenna system using two different bands you are going to have trouble. Take note of things like ham bands are all harmonics of each other and those little $60 duplexers are not designed to handle two 25W transmitters on two different bands operating at the same time. I think you will find this to be the sentiment of every repeater builder who has been around for the long run. None of them will tell you it won't work, as we have all had to scab something together in an emergency, but long term it is just grief. Dan Thompson d...@waycom.com
Re: [DSTAR_DIGITAL] Repeater stack
If you find that you must use a Diamond or Comet antenna, I would suggest that you at least solder each connection. The mechanical connections will cause you grief over time. Also, take the time to seal the antenna joints (including the top cap) as they will allow water to find a way in. Even doing all this, you will probably be back to change out the antenna in 3 to 5 years unless a lightning strike brings you back sooner. There is no substitute for a commercial antenna. __ Michael Murphy - KD8OK kd...@yahoo.com __ From: Daniel G. Thompson d...@waycom.com To: dstar_digital@yahoogroups.com Sent: Tue, April 20, 2010 1:53:32 PM Subject: Re: [DSTAR_DIGITAL] Repeater stack If you are installing a D*Star repeater stack (2m 440cm modules) can you use a single dual band antenna for both modules or do you need separate antennas for every module in the stack? That somewhat depends on your preferences. If you are seeking decent performance then I would suggest not trying to combine them, but keep in mind that I would also suggest that you not use a Comet or Diamond antenna on a repeater. As long as you have the proper equipment to combine the signals there is no rule that says you can't do it, but I would warn you to that unless you are using gear designed specifically for the purpose of a repeater connected to a single TX/RX antenna system using two different bands you are going to have trouble. Take note of things like ham bands are all harmonics of each other and those little $60 duplexers are not designed to handle two 25W transmitters on two different bands operating at the same time. I think you will find this to be the sentiment of every repeater builder who has been around for the long run. None of them will tell you it won't work, as we have all had to scab something together in an emergency, but long term it is just grief. Dan Thompson d...@waycom.com
Re: [DSTAR_DIGITAL] Repeater stack
Bob, All good advice, however I would like to add that there are a number of duplexers out there that do both pass and reject such as TX/RX and Wacom (both the same company now I believe) and there are some other ones as well. I like the TX/RX vari-notch design where all cans in the duplexer have Pass/Reject capabilities. Another way to deal with this is to use seperate antennas at different heights on the tower. Vertical seperation gives an amazing amount of isolation. Right now we are running VHF and UHF on a combiner/multicoupler with 4 antennas involved, and of course we are sharing that with several other systems as well. For 1296 there is a single antenna and soon we will see the arrival of our Triplexer from TX/RX that is a cross between a duplexer and combiner that allows both the Data Voice modules for 1296 to operate on one antenna. Dan Thompson d...@waycom.com Also use Double shielded Coax (Like RG-214 or RG142B/U) or hardline for all connections between the antenna and the Repeaters (especially between the Duplexers, any preamps and the Repeaters). Remember 98% shield still has 2% Holes where RF can get in. Cheaper cables are even worse! Also keep in mind that the Duplexers only notch out the Transmit frequency - they allow many out of band signals in. We use DCI bandpass filters in front of the preamps to keep out signals that get through the Duplexers.
Re: [DSTAR_DIGITAL] Repeater stack
Daniel It is true that The band pass/band reject do offer some protection it is not as great as many believe. See http://www.anglelinear.com/repeaters/repeaters.html for a description of the limited filtering of most Cavity type Duplexers. We have duplexers from TX/RX and still needed additional filtering on 146 and 442. Our 1.2 and one of our 440 duplexers come from Angle Linear as do out PHMET Preamps. We had thought about a triplexer for the 2 1.2 modules but the wait was too long and we elected to go with 2 antennas (one for each module) and frequency separation 1285HHz - 12MHz for DV with a duplexer and 1255MHz for DD as of now we haven't had any problems - the 2 antennas are about 20' apart, The Duplexer on the DV module is a 7 section unit with PHME preamp from Angle Linear. Bob Cumming W2BZY (for K1XC W4PLB) At 03:50 PM 4/20/2010, you wrote: Bob, All good advice, however I would like to add that there are a number of duplexers out there that do both pass and reject such as TX/RX and Wacom (both the same company now I believe) and there are some other ones as well. I like the TX/RX vari-notch design where all cans in the duplexer have Pass/Reject capabilities. Another way to deal with this is to use seperate antennas at different heights on the tower. Vertical seperation gives an amazing amount of isolation. Right now we are running VHF and UHF on a combiner/multicoupler with 4 antennas involved, and of course we are sharing that with several other systems as well. For 1296 there is a single antenna and soon we will see the arrival of our Triplexer from TX/RX that is a cross between a duplexer and combiner that allows both the Data Voice modules for 1296 to operate on one antenna. Dan Thompson mailto:dan%40waycom.comd...@waycom.com Bob Cumming W2BZY
RE: [DSTAR_DIGITAL] Repeater stack
At 12:34 AM 4/21/2010, you wrote: what is the lightning like in your area? If it is anything like it is here in Florida... go with a commercial grade antenna... otherwise your putting up a toothpick maker If on a site where any weather extremes are possible - wind, snow, ice, lightning, whatever, spend the money on commercial grade antennas, they'll pay for themselves in the long run. I use a dual band antenna on my (analog) repeater here, but the environment is a domestic one. It's not an exposed tower on top of a mountain. 73 de VK3JED / VK3IRL http://vkradio.com
Re: [DSTAR_DIGITAL] Repeater stack
Bob, Yes, you are right. Many people have found that the D-Star systems need more isolation than a similar FM system especially the UHF units. There has been much discussion about that. I was only trying to add that the pass/reject type filters do offer far more protection from things outside of your pass filter. We had an instance with a Broadcast FM radio station on one of the towers killing a 220 MHz machine. One of the first things we did is switched to pass/reject and that knocked out alot of it. Their harmonic was at roughly 211MHz but they were so strong it just made everything deaf. To finish getting rid of the radio station we cut an open stub at a 1/4 wave of the radio station frequency and put a T in the feedline with the stub hanging down. That dangler had such high voltage at the end of it, that I sustained a small RF burn when the end of the coax was up against my arm... yes it got covered very quickly after that. On the other hand, what I am actually using on D-Star is a combiner/multicoupler setup. Seperate antenna's with alot of isolation. On the UHF RX though the bandpass of the multicoupler was too narrow, so we used two tuned lines and a T so that one goes to the multicoupler and one goes to a 10 pole DCI filter (I think it's 10 pole) followed by a pre-amp and then pass cans for the indicidual receivers. So, I am with you on this one, as we actually do something very similar. Bob is definately correct that the typical 4 can setup used on the average FM repeater will cause you nothing but headaches, and that includes the ultra nice TX/RX stuff. You either have to go with a 6 can setup using pass/reject or like Bob said, throw an DCI filter between the duplexer and receiver. This is also true of the VHF as well. We fought with this problem for a couple of weeks before we went on the multiplexer with about 40' between the antennas. Bottom line I think for this thread, is repeaters are fussy when it comes to a good feedline and antenna system, and D-Star is even fussier. Dan Thompson d...@waycom.com It will save you alot of headaches. Daniel It is true that The band pass/band reject do offer some protection it is not as great as many believe. See http://www.anglelinear.com/repeaters/repeaters.html for a description of the limited filtering of most Cavity type Duplexers. We have duplexers from TX/RX and still needed additional filtering on 146 and 442. Our 1.2 and one of our 440 duplexers come from Angle Linear as do out PHMET Preamps. We had thought about a triplexer for the 2 1.2 modules but the wait was too long and we elected to go with 2 antennas (one for each module) and frequency separation 1285HHz - 12MHz for DV with a duplexer and 1255MHz for DD as of now we haven't had any problems - the 2 antennas are about 20' apart, The Duplexer on the DV module is a 7 section unit with PHME preamp from Angle Linear. Bob Cumming W2BZY (for K1XC W4PLB)
Re: [DSTAR_DIGITAL] Repeater stack
On Apr 20, 2010, at 5:43 PM, Daniel G. Thompson wrote: Bob is definately correct that the typical 4 can setup used on the average FM repeater will cause you nothing but headaches, and that includes the ultra nice TX/RX stuff. You either have to go with a 6 can setup using pass/reject or like Bob said, throw an DCI filter between the duplexer and receiver. This is also true of the VHF as well. We fought with this problem for a couple of weeks before we went on the multiplexer with about 40' between the antennas. The traditional 4-can setup often doesn't work well with Analog systems either, but the owners are too clueless to test it and see. :-) Most 4-can setups also really need a large hi-Q pass cavity on the Receive side to reject out of band and close-in crapola at multiple-transmitter sites. Bottom line I think for this thread, is repeaters are fussy when it comes to a good feedline and antenna system, and D-Star is even fussier. On D-STAR it's just damn hard to test it properly. So you do the pants+suspenders thing and over-filter it a bit. The receivers are more sensitive than what most analog repeater operators are used to working with (60's vintage through 80's vintage receivers that had nice tight front-end filtering built in, vs. a badly shielded aluminum box that blocks nothing, bad quality coax internally -- which can be fixed -- and a really sensitive but not very SELECTIVE receiver... inside the pretty D-STAR aluminum box). I'll take the front-end helicals of a MASTR II any day of the week -- even the loss! -- over the Icom RF design that looks like it was built out of two mobiles in a box... oh wait, it was... One was ENGINEERED, the other one was ASSEMBLED. There's a big difference between those two schools of thought. One doesn't require a school at all, in fact. ;-) Again I'll rant lightly that without real numbers for when the CODEC itself falls apart (bit-error rate) and a way to test it... testing these things properly is an exercise in a whole lot of ASSUMPTIONS and trial-and-error style antenna/filter system design. Sharing real-world stories of what works and what doesn't, kinda fixes that, but it sure would have been easier if it wasn't left to the users of the repeaters to beta-test them for the manufacturer. A couple of models of expensive as hell Service Monitors can now record an off-air digital signal and then play it back, so you add attenuation and reverse-engineer any type of digital repeater, but expect to be in the $40K range for them, list. Probably $20-$25K real-world, pricing. Not something we're going to see too many hams doing, I suspect. -- Nate Duehr, WY0X n...@natetech.com
