Tuning a duplexer for a range of frequencies rather than just one pair
I'm in the process of building portable repeaters for use on the national interoperability channels. In UHF, that would include UTAC41-43. Those frequencies range from TX 453.4625-453.8625 and RX...
View ArticleCommScope DB404 vs. DB411
Hello all, I am looking at purchasing a DB-404 or DB-411 for a repeater site. I see that the DB-404 is much cheaper than the DB-411 and has less gain. Are there any advantages over one or the other?...
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Is Sinclair SD318-HF2P2LDF(D00) folded dipole shorted?
Good day. Is a single dipole of Sinclair SD318-HF2P2LDF(D00) 8 dipole antenna electrically shorted? I opened one today and discovered a thin wire seemingly connecting central pin of the inner coax to...
View ArticleComet CA-712EFC VS CommScope DB404
Hello all, I am looking at purchasing either a Comet CA-712EFC or CommScope DB-404 for a GMRS repeater site. I see that the DB-404 is much more expensive than the CA-712EFC and has less gain but...
View ArticleWill a passive antenna work?
Reliable portable radio comms in our station has always been difficult. The building construction is lightweight steel truss with tin wall studs and corrugated metal decking as the base for the roof....
View Article1/2 Wave Aviation / Airband Antenna
Looking for a half-wave antenna good down into the Aviation/Airband range. Installed an aviation radio into a full size John Deere tractor for an airport, and used a standard Q88 1/4 wave antenna....
View ArticleUsing a VNA to tune a band-reject only duplexer
I have a band-reject (notch filter) duplexer with low side at 462 MHz (transmitter) and high side at 467 MHz (receiver). I would like to learn on how to tune a duplexer, so I’ve watched many tutorials...
View ArticleMotorola UHF Preselector out of band rejection question
Question for the moto gurus or anyone else. Have an application with a UHF 460mhz repeater getting hammered / desensed by 700-750mhz cell tower that is 50'-75' ft away at the same elevation. Current...
View ArticleVHF Antenna Selection and Install Location
Looking for some advice on what antenna to use and where to mount it. Installing a Motorola CM300D for VHF use in a rural area. My vehicle is a 2022 F-150 with the panoramic sunroof and I would like to...
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Commercial Antenna Identification
I used to see a lot of these antennas in the late 70's and 80's, but not so much anymore. I'm wondering who made it and what the model is? I've also seen a black version that appears larger in diameter...
View ArticleFluctuating SWR reading
I’m having the issue where my SWR will not stay rock solid. If I get it just perfect, it does. Any other time it’ll start to climb excessively, then hold steady. Or it keeps increasing. The PA cuts...
View ArticleWhat NMO antenna is best for mobile VHF 150MHz-170MHz
I am new to HAM and am putting a MSC2000 Motorola with Emergency/marine VHF frequencies in my work truck (logger) I live in a commercial fishing community in Alaska and that's how we all keep in touch....
View ArticleMobile install - common mode problem?
Installing a 477mhz collinear antenna on the bull bar of my 4wd - opposite side to my 2m/70cm dual band. Testing off the car in the open it gives close to 1.1:1 Swr, but mounted on the car I can’t get...
View ArticleMulti Radio on one antenna system
I'm working on a in-building radio communication system and I want to use 2 or 3 mobile radios connected through one cabling/antenna system. Is this possible to do using either a combiner or some sort...
View ArticleWhat are these antennas for ?
I was at a convention in St Louis at the Americas center last week. About every 50 feet there was one of these arrays.. I don’t think it was wifi as there were wifi hot spots throughout the convention...
View ArticleHelp finding a Multi-band Low Profile Antenna
I have a public safety agency that is looking for a low profile antenna to be paired with a Motorola APX 8500. They are looking specifically for one manufactured by Laird Technologies, does anyone know...
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MSat satellite antenna
Was working on this guy today at our EOC. MSat antenna for their satellite radio/phone. Figured some of you might like to see what is inside one of these.
View ArticleInteresting Use of a Yagi
So my wife was in hospital in a nearby town... every day I parked next to this village water tower and was bemused by this yagi, pointed straight up, and apparently reflecting its signal off the curved...
View ArticleDB224 refuses to duplex
Greetings, I have a top mounted DB224 which doesn't want to duplex with any appreciable power anymore without receiver desense. Here are the specs: I have tried four different repeaters - Motorola...
View ArticleWas always curious about this.
I come to visit my mom in Los Angeles from Arizona regularly, and always have to pass the CHP/Caltrans office in Glendale. I’ve always wondered why this vertical beam antenna is on the top of this...
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