[Repeater-Builder] Re:N3SDO antennas / 6m collinear / Jpole
Im confused on the J-Pole calculations. I calculate mine was 3/4 y = 13.36' (About 14 feet, tip to mast) Phasing U = 4.45 feet, with a 8.91 foot stinger off one leg of the U. John, you wanted to know what I built, best from memory 10 years ago, with fresh calculations. What I made is a supersized Ringo Ranger II. 5/8 over 5/8 with 1/2 wave phasing, with ground plane 1/2 wave below. The donor was a 5/8 CB antenna that had the coil fried, but tapered tubing to nearly the exact length. I calculated 11.13 feet for each 5/8 wave segment. I used a fiberglass ski pole yard sale (2 for $1) along with fiberglass electric fence posts to make the center insulator and Plus sign shaped horizontal support bar for the hairpin phasing loop. I used aluminum radio shack wire for the phasing loop, 8.91 feet long, folded into a hairpin, spaced 1 apart on plastic milk jug spacers, then siliconed to the wire and spacers onto the support bar. Wound phasing hairpin into a @ looking circle. I wrapped 3 or 4 turns around each element end, then clamped with Stainless hose clamp. I fed it with a coil about a 1/4 wave of copper wire, wound on a mason jar, with coax center tapped 1 turn up from ground end at bottom of coil. Was supposed to be a first starting point, got lucky worked so good I never changed it. Provided a DC ground. I used about 1/2 wavelength (rf length internally) about 5.88 feet in RG8 coax, to the ground plane. Fed with 80' of RG8. Absolutely tops on 52.525 FM!!! After the lightning hit, 8 feet of aluminum wire was never to be found. Only a 6 chunk 150 feet away in the neighbors driveway. I suspect the hairpin made a whopper of a magnetic field just before the wire melted making it push away from itsself. (best theory I got) Good luck!
[Repeater-Builder] Re: DC Ground Lightning Protection / Concrete Electrode
I'm going to disagree with the following posting: If the tower is bolted to galvanized pipe that is embedded in concrete of which a significant amount is in contact with soil, you have a concrete-encased grounding electrode which is hard to improve upon. It is not likely that a ground rod would be worthwhile, since damp concrete (concrete in intimate contact with soil at grade level) is a fairly good conductor, and such a footing or foundation has hundreds of times the surface area of a ground rod. I have read Ericsson specs for cellular tower installation in that disagrees with the previous statement. Standard concrete without conductive enhancing materials can crack, pop or crumble if subjected to a direct lightning strike if ground rods are not properly installed. The water contained within the concrete will vaporize instantly causing the concrete to fail. There are types of conductive concrete mixes or additives that can be used, but the most common practice is to use a ground rod from each leg with a copper wire bonded to each tower leg. Our mfg building at work is made from steel I-Beams into concrete. I have noticed each I-Beam has its own ground connection. The strap is bolted to the beam about 1 above the concrete, then disappears into the concrete, and suspect there is a ground rod going into the soil beneath the concrete piling, but that's just a theory, as I dident see it before the mud was poured. Ed N3SDO
[Repeater-Builder] Re: Help with power supply
Charles Checkout the Astron page on the repeater builder website. There is a lot of info on general linear supplies using the LM723 regulator chip. You should be able to change the zener reference diode, and tune it down to 13.8v and deliver the same current. ***Danger, notice here *** You will NOT have the 13.8v overvoltage - crobar protection without changing that circuit also. You will have whatever it had at 28v. In my experience, regulator transistors seldom fail open, they often short, delivering the full transformer output into the crowbar circuit, Which if it fails to crowbar, frys your precious ham rigs. This supply will probably have 35 volts or more at the caps, even under load. If you dump 35v into your 13.8 rig, it will not survive!!! It might burst into flames!! If only the output voltage is lowered, the regulator transistors are going to dropping more voltage, and will get MUCH HOTTER!!! You will be dissipating 3 times more heat then it would have at 28v. Fans!! Several of them! My theory, ( without seeing this supply ) 120v input to transformer, transformer output 35v, bridge, Caps, 35VDC, regulated down to 28v. The transistors are dropping 7v. 7v @ 15a = 105 watts of heat. If you just tune the voltage reg down to 13.8, you will still have that 35vdc from the rectifier. The transistors are now dropping 21.2v 21.2 @15a = 318 watts of heat. That might be too much dissipation per transistor, and cause them to fail fast. You might gain an advantage by changing the 125 volt input to the 220v option. This will lower the voltage on the transformer secondary. You should still get around 17.5v or more at the secondary/rectifier-caps, which will reduce the heat generated in the regulator transistors. I use a junker automotive foglamp (free from junked truck) for load testing of unknown powersupplies. It pulls about 5 amps, and is tolerant of over voltage conditions and even runs on 12v AC. 73 Ed N3SDO
[Repeater-Builder] Re: W1GAN and square duplexers aka homebrew duplexer
I built a paint can 6 meter helical coil duplexer, and also built an 8 stub heliax 6 meter duplexer. The mechanics don't seem all that complicated, but getting the rejection and insertion loss you want can take a lot of messing with it. The heliax was difficult to find. Traded a large tray of donuts to a local electrical contractor for 6 pieces of 8 foot long scrap heliax. I found a partial tray of 3-30 pf trimmer caps at a hamfest. The paint cans didn't hold up to temp changes at all.- Drift all over the place like others said. I cut the heliax cable, drilled and installed BNC connectors, selected stubs resonant at the higher frequency then used ceramic piston trimmers to couple the coax to the stub, then a duplicate trimmer to tune stub down to desired freq. I have built a 1/4 wave heliax stub filter using same technique with a 1/4 wave phase line to a T connector to make a band pass filter for 2 meter APRS. I suspect heliax will make a more stable and smaller duplexer then oil cans. Happy tinkering! Ed N3SDO
[Repeater-Builder] Re: Remote receiver suicide control
Might I suggest a Shunt Trip Circuit breaker. I have used these in cases where power to an entire Mainframe Computer Room, was cut. This was linked to the fire alarm system, and killed the system outlets at the moment the Halon system siren sounded. It will remove your AC power and require a manual reset. I have seen these in 120v single phase, 208 3 phase, and up. $.02 Ed N3SDO
[Repeater-Builder] Re: Anyone got a Amp-meter Circuit to Repeater Controller for Telementry Readback?
Kevin, are you using a charge controller between the solar panel, rpt, and batteries? Does your controller provide any kind of monitoring of current or voltage or state of charge? The op-amp circuits can also be extended in range beyond the VCC by using a voltage divider on each side of the input voltage. 1k 1% resistors are my fave for this divider type of app. Keeps the impedance low enough you can get good gain on the op amp with reasonable component values. You might want to consider some sort of outboard microcontroller based data logger. It could tell you how many charge hours you are getting, and peak amps, total amps, and at what time of day your batteries reach full charge and when the charge controller begins to dump excess voltage. This can let you know your batteries are doing through the days / nights. I built an APRS digipeater some years back that ran solar. Low power short burst tx, It would fail in late December due to lack of sunlight, and be fine otherwise throughout the year. Enjoy tinkering! Ed N3SDO http://geo.yahoo.com/serv?s=97359714/grpId=104168/grpspId=1705063108/ms gId=90412/stime=1238701456/nc1=5349272/nc2=4836040/nc3=5191955
