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I have some old antennas my grandpa gave me for VHF, UHF and so on use, I need to find mounting brackets for them, so I wonder if anyone here can tell me what they're called and possibly who supplies them? First is this:  It's an Allgon brand antenna, I have a couple of them for 2m and NMT 450 MHz. The screw mount is similar to some eBay brand magnetic mount antennas but much thicker. I measured the internal diameter at 4.7 mm, so the screws are probably 4.5 mm or 5 mm.  The other is this, which is similar to some old AM car antenna mounts I remember seeing once, inner diameter around 7 mm, one of them had a wing-nut attached that was 6 mm so it probably screws into that. Outer diameter of the ring is 2 cm. The antennas are apparently from a danish company called Scan Antennas. I'd prefer to buy on eBay or another site that offers cheap shipping to Norway.
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Nov 11, 2012 20:40
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The greybeards inform me that the second picture I posted is called a DV mount. I'm still studying for my exam, I was thinking a quiz with the Q-codes might be helpful, so for example it would show QRM and ask me what it means in a multiple choice fashion. Does anyone know of a quiz like that? If not I'll have to write my own like I did to learn the phonetic alphabet.
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Nov 13, 2012 15:54
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Pukestain Pal posted:Are you studying for the Tech exam? I think there is only 1 or 2 questions involving q codes. Still good to know them though. Not sure what it's called in English, but I don't have a callsign yet so I think that's technician. I'm pretty much done modifying my NATO trainer for Q-codes, basically it picks a Q-code, then asks you either to pick the meaning or a proper reply from a list of four slightly random choices. When I learned the phonetic alphabet using a similar system (had to type the phonetic name) it took me about two days to learn it for good.
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Nov 13, 2012 16:35
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The phonetic alphabet is also far more useful in day to day life than Q-codes, unless you only talk to hams. I learned it properly when I took my maritime VHF certificate, but really I think it should be taught in middle school. Interestingly I don't think it was required to pass that test either, but it's highly recommended to be at least proficient.
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Nov 13, 2012 20:11
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I agree, but the local hams seem to use a bit of slang and some phrases are on the test. Standard phrases are good since they make it easier to understand you on poor quality links but Q-codes seem almost counter productive. In maritime use you have several standard procedures but no special names or codes outside of securitè, pan pan and mayday. So my suggestion would be to drop Q-codes and instead make phonetic alphabet knowledge required.
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Nov 13, 2012 21:24
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We've already got a list of changes to the textbook, our teacher is pretty experienced. There are some changes that take effect in 2013, so we will apparently have to show how to calculate some basic EE stuff rather than just multiple choice. At least we don't have to learn morse.
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Nov 13, 2012 22:24
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Unless they want AC node analysis I think the EE stuff is well under control. What I have realized is that I don't know poo poo about antennas or antenna grounding however. I don't care for "simple" explanations of what is definitely a complicated situation, I know some transmission line theory and wave propagation is not unfamiliar, just not the realization of the antenna outside of "make a dipole, here's how" which did seem to work well for OTA TV.
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Nov 14, 2012 09:49
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There is the Per Vices, I only know it from the Ars Technica article but it sounds like a very sophisticated solution for SDR, you could implemented all sorts of fancy communications hardware using that solution, including super high bandwidth spread spectrum stuff.
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Dec 20, 2012 00:55
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Playing around with my RTL-SDR receiver I picked up the weirdest thing, a narrowband FM transmission at 123.593 MHz which appeared to be the soundtrack from the movie "Christmas with the Kranks" I picked up some unreadable AM airplane chatter on a frequency nearby (not a tower frequency) at the same time.
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Jan 8, 2013 18:23
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I suspect it was a mirror frequency, my guess: wireless rear speakers in a surround system broadcasting somewhere below the commercial FM band, or some kind of unlicensed transmission. If I'd thought about it then I would have looked at a lower frequency. I'm using a UT-108 antenna since it fits the magnetic base that came with my radio, it seems to pick up most of what I'm expecting to hear, including broadcast FM, air-band and GSM signals. Another weird thing is there's a 440.550 MHz station broadcasting a 1 Hz square wave that sounds like a heart beat in AM. I should probably start looking into demodulating the packet radio systems on the air, a lot of industrial sites in range have UHF digital links that are probably running some common packet radio protocol.
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Jan 8, 2013 22:13
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APRS greybeards  I've mentioned my project in the electronics thread but this is a question about APRS tracker modules: We need a tracker with high power output, good power saving and the ability to data-log the GPS position locally as well as transmitting it. Batteries will be external so we have the option of putting in a pretty big cell. I looked at the Byonics Micro-trak RTG or similar solutions, the option with external GPS module would let me use a micro-controller to store the NMEA data to an SD card for later processing, does anyone have experiences with these? The 50W power output would be good for reaching across the sea in choppy conditions, otherwise we could find a small PA stage and use the smaller options.
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Jan 15, 2013 12:26
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I found some on eBay once through a chinese ham radio supplier, IIRC the power was around 500mW. Fake-e: Yup you can get 500mW on eBay easily enough. Looks like the kit-site linked has pretty cheap RF amplifiers kits that could work with a small modulator.
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Feb 1, 2013 08:54
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My 5R is already losing the paint on the buttons after a single weekend of normal field use, the battery life is quite good though. Transmit audio is very low on the stock 5R but I think they've fixed that in later hardware revisions. Get the extended battery. The 5R is also pretty sensitive to intermodulation so it frequently picks up noise, and the squelch doesn't actually support changing the level so there's not much to do about it when it happens. But for the price it's pretty good.
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Mar 17, 2013 23:06
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I figure ham radio operators will know the answer to this one: if I can't afford a good linear supply for my HF rig, can I take a regulated 13.8V lower power supply and connect it to a lead acid battery? I figure if current is shared correctly then as long as the average current of the HF rig (duty cycle) is less than what the supply can deliver then the battery will maintain a decent charge?
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Apr 1, 2013 08:37
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Ok thanks, my plan was to make a regulated linear supply since I have some fairly powerful transformers to use as a base, then I can get some big linear regulators and a nice heatsink. I have already experienced the devastating effects of my laptop charger when not grounded on pretty much everything from 5-15 MHz so I definitely want to limit the amount of switching supplies where possible. As a follow-up question what's a good size battery to use for a 20A peak-load? I started with a 20Ah SMF battery since that lets me receive all day and I can just charge at night, I was thinking I'd go up to 50-70Ah for when I get the antenna up and want to start transmitting?
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Apr 1, 2013 18:59
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nobody- posted:The prices of the Baogeng UV-5Rs have me spoiled. Is there a way to get into HF SSB for similarly low prices? The only cheap HF stuff I've found so far is all CW and I just don't have the time to learn Morse right now. I found a nice a FT-747GX with a brand new rotary encoder for nearly nothing, 100W SSB, CW, AM and optional FM, but the rotary encoder is usually hosed and it's nearly impossible to source new ones so that's something to watch out for on that model. Expect to do a bit of repair on radios of that vintage though, even if its mostly cleaning connectors and dry solder joints.
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Apr 9, 2013 21:42
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Don't use magnet mounts on your car for long though, it traps moisture and dirt and destroys the paint and then rusts from what I've heard. I have a Nagoya RB-CLP which is a window mount for a SMA/BNC antenna, just put a reasonably long whip like the SRH-536 on that for a quick temporary mobile antenna. Alternately if you have rails on the roof you can get all sorts of PL-259 mounts.
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Apr 14, 2013 12:35
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As an update to my question a page or three ago about a DC-UPS, using a power supply at 13.8V to power a battery, I have now completed an implementation of this power supply: http://ludens.cl/Electron/Ps20/Ps20.html with a few additions, mainly a short circuit/overload shutdown using a second opamp, 4-wire output sensing (important for the battery charging!) and electromechanical thermal control (thermostat switches for the fans). Somewhat surprisingly, the warmest components outside of the current sense resistor (wound from resistor wire) is the rectifier and Q2, the base-driver transistor. If anyone else wants to build it as a battery charger, note that when mains is lost the opamp will drive Q2 from the battery and pull about an amp from the battery unless something blocks current from flowing through the base. In my case this is implemented with a relay that's powered by the auxillary fan power supply (which exists to let the fans run after the supply is turned off), when power is turned off or a brownout or complete outage occurs the relay disconnects the base from the opamp output. It's simple to add 4-wire sensing to the output, this is important since a typical wire might have a few hundred mV drop at several amps load, this will negatively affect the battery when it's loaded. The 4-wire sensing just means connecting the output opamp+reference+pot thingies output-ground and V+ leads to a BNC socket on the output. When no sensing is happening the voltage will drop instead of increasing, when you connect the second set of wires to the battery it will regulate based on the battery terminal voltage instead of the output terminals. For mine I added a switch to select 2 or 4 wire regulation, the 4-wire option means the battery terminal voltage is rock solid even when transmitting, where it would drop about 50mV per amp drawn (I know, my wires are too thin) in 2-wire mode. Over all I'm very happy with it, once I had the current regulator adjusted and compensated (driving a UPS tends to make things difficult) it now supplies 10A continuously and allows peaks of 20A+ for about a second before regulating it down. Short circuit current is in the order of a few tens of mA, making it fairly safe to work with. The only things I would consider improving is using an opamp (LF 356H) and voltage-reference (LM336) with a lower tempco, as built it will drift by something like 1mV per degree, meaning it's not exactly a precision supply over temperature. longview fucked around with this message at 22:22 on Apr 18, 2013 |
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Apr 18, 2013 22:16
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Those cables are really problematic on Windows 8 too, Prolific has dropped support for by far the most common USB-Serial adapter chip on the market (definitely within their product lines), the only official fix is to downgrade to Windows 7 (the best solution, honestly) or to crack open every device you have with a Prolific chip in it and solder in a new chip that's impossible to find anywhere since nobody has it yet. This affects genuine chips too, my Agilent multimeter interface cable is also affected. It sort of makes sense with the hardware piracy costing them a ton of sales but it sucks for the end user.
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Apr 26, 2013 23:52
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Well it might get slightly more complicated when mixing in parity modes and stop bits and it's still not a good reason. Of course the whole scenario is a little silly when good USB-Serial adapters put a MAX232 at the output and the very first thing it meets is another MAX232 (or a 3.3V version) at the device end. Not that I'm anti-RS-232/422 but it's pointless when most devices are 1 meter away from the host.
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Apr 27, 2013 11:33
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I meant that using a +-15V spec when most devices don't need the robustness that the higher voltage offers is silly, most of the time straight TTL serial would be completely adequate. To clarify: the MAX232 takes a 0-5V TTL signal up to a +-15V (I think, maybe +-5), and back down again on the receiving side, there's still a USB-TTL serial interface chip that does all the hard work. Really though comparing RS-232 to USB is perhaps a bit like comparing a HF radio to a D-star or GSM network, RS-232 is from a simpler time and it's still super reliable, but it's going to have some quirks. USB is much easier for the end user but when the network falls down (or Prolific stops providing drivers) you're SOL and that old fashioned serial link is still chugging along. E: so is anyone in here familiar with the FDK Multi-2700 internals? I have the schematic and service manual, I've readjusted it for 5/2.5 kHz deviation but I'm not sure how to increase the AF gain to make up for the lower deviation on receive. I also wanted to modify the Receive lamp to only light when the squelch was opened but it's looking like the squelch is a very analog system... Second edit: if anyone wants to help, the schematic here: http://www.concept9.co.uk/NoBackup/FDK2700/KLM2700schematic1.pdf (tilt your head I guess  )If I'm reading it right the audio amp is on board X-16, to the middle right, that's fed through the AF gain knob (front panel knob) on a bus from boards X-12, the AM receiver and pin 8 on X-11 (bottom left). I can't see any adjustment for the FM receive deviation and the AM receive audio is actually almost too loud. I'm thinking I'll use a LF356H (since it's a vintage radio you see) opamp and stick a little AF gain board between pin 8 on X-11 (FM AF out) and the rest of the AF bus, then I could adjust the FM gain separately from AM. There will be slightly less audio on narrow but with the gain stage that shouldn't be a problem. Third edit: yup that worked, a tiny TL072CN board with adjustable gain longview fucked around with this message at 21:49 on Apr 28, 2013 |
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Apr 28, 2013 07:57
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Caesar Helge Adam Rudolf Ludvig Ivar Erik 
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Apr 29, 2013 12:54
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Technical question: if I want to fit some gas discharge tube type fuses on my antenna outputs to prevent ESD, in theory lightning strikes (though extremely uncommon where I live) and things like mains entering the socket, what kind of voltage rating should I put on them? For my 10W VHF, the RMS output voltage should be around 22V, peak voltage is then close to 32V. In the case of total reflection from the output, I would have as much as double voltage on my antenna output? In that case it should be acceptable to use my 90V (~70V minimum trigger) protection devices, correct? Or perhaps it would be safer to just install an output fuse and put the protection on the receiver only and stop my protection from destroying my transmitter I have some 90V Littelfuse double pole devices intended for telecom, so I'd put one side to the RX antenna line and the other to the 12V input. longview fucked around with this message at 17:16 on May 11, 2013 |
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May 11, 2013 14:29
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SoundMonkey posted:Other technical question: how long would it take to transmit two characters via RTTY in baudot (ie, 10 bits)? As a followup, does anyone know of any commandline things (using an SDR) that will just detect and spit out decoded RTTY data in real time? It would depend on the baud rate but for 10 bits using ham standard 45.45 baud it would take 10/45.45 or 220 ms. I don't know how much synchronization is required to set up a RTTY link, but that would be the actual transmission time for 10 bits.
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May 11, 2013 22:15
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Thanks for the advice, yes it's a GDT made by Littelfuse, hence my confusion about what to call it It's a double tube, designed for dual supply applications so I was going to use the second tube to protect the 12V in case some idiot were to connect mains voltage to it. Dumping a transient into the supply rail won't necessarily cause bad things to happen since at AC it is close to ground anyway, but obviously it's good practice to suppress to ground instead of a supply rail. Looking at that graph it looks like I should have checked my ratings more carefully before buying, since I had initially hoped to protect my 100W HF rig as well, but based on the table you linked I'd actually need at least 350V rated tubes. I think I'll settle for protecting the receiver inputs on my FDK and the RX+12V on the Yaesu using the existing tubes.
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May 12, 2013 23:01
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I'm having a problem with my FT-747 FM module, it essentially isn't modulating properly, deviation is around 2-300 Hz at full mic gain + deviation adjust. Here is the relevant schematic section, the signal path in yellow:  The AF output from the opamp is present and working, and at the junction between the varactor and crystal there is a clear FM signal on the scope, but this is not present any further into the signal chain. At the base of Q04 there is a severely distorted sine wave (bottom period crushed, rest looks to be approaching a triangle wave). A distorted IF signal is present on the IF out pin, but this is basically unmodulated and looks like the bottom half of the sine is clipped though less severe than the Q04 base. The power supply is fine, I've checked for bad connections between components and reflowed the more suspect areas but no dice, tapping or flexing the board makes no difference and input control signals seem fine from the radio. I'm starting to suspect the crystal is bad, there's no DC continuity. Since the signal is severely distorted after the crystal and the remaining stages seem to be working correctly with the signals present I'm not sure what else would be wrong. It would suck though since it looks like that frequency is used pretty much only by this type of radio.
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May 20, 2013 23:34
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I don't think a reactive load would cause a problem with SWR readings, but the antenna analyzer would let you measure at the antenna instead of at the transmitter where return power will have been attenuated and you wouldn't have to fire up the transmitter to test. I think the antenna analyzer would tell you if the load is reactive or capacitive? That would help in designing matching networks as well.
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May 23, 2013 09:53
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Find the greyest beard around and befriend him, he will most likely offer you lots of cheap old gear, it's how I've ended up with an Azden PCS-4000 mobile, the FDK Multi-2700 base station and the FT-747GX HF before even getting my license. Also I'd definitely make sure I had the 20 meters band, I think 40 meters is used a fair amount too but someone else will have to comment on that. --- I've now received confirmation that I've passed the license test (all or nothing in Norway), so my callsign will be official in a few days. I am interested in advice on what kind of antenna tuner to get for the FT-747 though, there's the LDG models that seem to be brand agnostic automatic tuners, or should I just get a manual tuner? Will probably be using either a G5RV or a long-wire with a 9:1 balun. longview fucked around with this message at 08:00 on May 30, 2013 |
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May 30, 2013 07:57
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Jonny 290 posted:Manual tuner to be sure. They have wider range, are infinitely tunable (versus just having stepped values on autos) and are generally built tougher. You don't need to band-hop at lightning speed just yet, which is auto tuners' main benefit. I didn't know auto-tuners had a more limited range, that's good to know, thanks. It looks like the 20 meter band is the most actively used in Europe anyway (or maybe my antenna is just too lovely to hear the lower bands) so except for the QST-LA transmissions on 80 meters I would probably stay on one or two bands yeah. We have a pretty active local group here so I don't think finding a used tuner from a local ham shouldn't be too hard. One had an anecdote about window shopping for a new HT and finding a nice Kenwood that looked familiar, turned out he had one on the shelf behind him collecting dust. Speaking of HTs, I think the Icom T70E dual band 5W IP54 HT looks like a decent FM radio, I refuse to buy anything that can't use a Li-Ion battery (T70 comes with nickel but it supports lithium), any comments? I know it lacks D-Star, but I'm not looking at that price range now (I will in the future though!). My current HT is a Wouxun KG-UV6D and I think the input filters are a little poor (better than the Baofeng though), seems like it picks up noise from mirror frequencies and probably other noise that radios like the FT-270 don't even read a signal for, let alone breaking the squelch.
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May 30, 2013 20:06
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longview posted:Thanks for the advice, yes it's a GDT made by Littelfuse, hence my confusion about what to call it I've just gotten around to mounting these on the FDK and the Azden: Azden 25W: It doesn't trigger at all at 25W with a resonant antenna, when I substituted it with a lovely dummy load giving about 15W return power it activated and clamped the output as designed, no damage to the transmitter. A nice aspect is that when it's engaged the PO meter reads far less than normal, which will let me see that there's something wrong pretty easily. The tube glows a nice orange when it's lit. I put the tube right at the antenna socket and used the other half of the tube to protect the 13.8V in against transients. On the FDK (10W) it didn't light at all, because the APC system shuts down the output if the SWR goes above a certain adjustable level (it actually drops the output to zero, and won't reengage until you re-key the transmitter). So over all I'd say that 90V GDTs are a good way of protecting at least up to 25W transmitters, unless you need to run at a very high SWR it won't be a problem at all, and the devices I used (PMT8 series) are designed to provide fast protection. E: I'm positive now that the tube did not trigger during the Azden test, but it was glowing. Has anyone here tried using a coaxial quarter wave stub arrestor? It's an interesting concept for mono-band antennas and the Wikipedia article claims it's one of the most rugged ways of protecting a RF transmission line... Basically a T-joint with a quarter wave shorted stub that will present a DC short, I'm a little unsure if how effective it will be against lightning since lightning would be like sending an extremely high energy pulse, not a DC signal. longview fucked around with this message at 09:26 on Jun 2, 2013 |
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Jun 1, 2013 17:58
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Thanks for the advice, if I buy new I'll get an automatic tuner, but I'll keep my eye open for a cheap manual. Now, for mounting a mobile VHF in my car, I've got a temporary setup which uses an external mount mobile antenna, there's 5 meters of RG-174 that goes through one of the doors (RG-174's thin enough that it passes without issue). I calculate that I have about 2 dB of loss there. I probably only need around 3 meters of cable at the very most, but to further reduce loss I was thinking I might just do a 0.5m RG-174 run out to the antenna, then run normal RG-58/RG8X inside the car to the radio. What sort of connectors should I be using for the splice from RG-174 to RG-58? I could get BNCs, N-connectors, PL-259/SO-239 or some specialized splice-connector? Obviously the insertion loss in the splice needs to be lower than what I'll lose by keeping the RG-174.
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Jun 5, 2013 09:56
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I was considering maybe trying to run RG-214 I'll look around for SMA connectors then, since I'd like to keep the joint small. It's temporary since I'm moving in a month or two and the car won't be going with me, otherwise I'd be punching a hole in the middle of the roof for a SO-239/NMO, so I think some RG-58 will be fine for now (RG-174 is actually working just fine). Unfortunately using a mast mount on the roof rails isn't providing a big enough ground plane for the 1/4 wave whip antenna I have on now though and I'm getting a SWR of 2:1 unless I put my hand on the base of the antenna. I tried mounting one of those in-line ground-plane things with the three rods, but it made no difference. Not sure what else to do, the rail is bare metal and I've put it as close to where it joins the roof as feasible. Running with 2:1 seems to work but it's not great and I can't really move the antenna to where it has a better ground plane anyway. If the height allows it I'll try putting a 1/2 wave antenna on there, I tested one and it was pretty much dead on resonant on the same mount. Slightly related I actually had my first QSOs today on 2m, first on the local repeater then later SSB which was pretty fun (SSB is more radio-like with the noise and my stereo acting as monitors even at 1W with the antenna outside.) It turns out the hot weather has detuned the FDK LO by about 2 kHz so I was way off frequency at first, but it only required two tiny readjustments in about 45 minutes (still, I need to order a TCXO for it). Afterwards I tested the mobile rig out in the field, which worked perfectly even with the poor SWR. E: I "solved" the antenna problem by winding a current balun from the spare coax underneath the antenna mount, brought the SWR at the transmitter down to around 1.2:1, I also ordered SMA connectors for RG-174 and RG-58 + a female-female adapter. longview fucked around with this message at 19:48 on Jun 7, 2013 |
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Jun 5, 2013 22:46
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Update: I figured out the correct way of getting cables into the car, so I ran some high quality RG-58 directly to the HT under the carpets and such. The price of doing anything to a VW is blood sweat and tears, but I got it done and it looks very nice compared to a pile of loose RG-174.Crankit posted:Antenna coax and various other things are supposed to be grounded, how does this work with stuff like HTs, or vehicle radios where there is no connection to earth? For whip-antennas you need a ground plane, normally on a HT your hand and arm provides the ground plane through holding the chassis/touching the battery terminals on the back, this is why you might notice the HT suddenly perform much better when you pick it up. When you're not holding it the metal chassis inside (even the cheapest HTs have a metal frame inside) provides the ground plane, but it's not as good. On cars the roof normally provides the ground plane, sort of like how a GP antenna works, it's why mobile antennas are supposed to be mounted in the middle of the roof instead of on the rails like I did. Some antennas like 1/2 waves are not supposed to need a ground plane, and my experience seems to confirm that the 1/2 wave is less picky than the 1/4 wave about how much of a ground plane you have. For example my 1/2 wave mobile is a perfect match on the mount that the 1/4 wave gives a 2:1 SWR, too bad it's 10" too tall to fit inside a parking garage. longview fucked around with this message at 00:15 on Jun 10, 2013 |
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Jun 10, 2013 00:11
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APRS tracking my car has been pretty fun just using a FoxTrack and a UV-5R as a transmitter. Now to use this IC-25E mobile rig as a digipeater out in the boonies where I spend the summers, I always wanted to build infrastructure and this is the next best thing.
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Jun 20, 2013 10:26
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Half drunk eBay shopping strikes again, picked up a used Icom IC-T70E for about $180 shipped (new price in Norway is close to $350). Of course I'll have to buy li-ion batteries for it, but the nickel based one should work fine for the summer months when it's warm out. Now unfortunately all my other equipment is Kenwood-style so I'll have to buy a nice hand microphone, any recommendations? I'd prefer something that's at least IP54 or better to match the radio, if it has some buttons on it that would be nice but I managed just fine without it before. It uses the standard two-prong 2.5/3.5mm system. Best bet seems the HM-131.
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Jun 21, 2013 09:32
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RF amplifiers aren't really broad-band so no, I think what might happen if you try to run 2m on a 70cm amplifier is the filters would only let the harmonics of your carrier through, so your third harmonic might be amplified a few dBs and then everything else would be very much blocked by the various filters and tuned circuits on the input. Or as Vir said, you might run 2m in and find that the amplifier produces horrible harmonics and other spurious radiation since the output filters are designed for the harmonics of a 70cm signal. I hadn't actually though of how to feed a rotating antenna before, a circular waveguide is the obvious choice, but for target acquisition radar they need four signals in, I wonder how that works...
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Jun 24, 2013 09:33
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Icom IC-T70 has been really good so far, it does pretty much the same as a UV-5R but it does everything right, and the UI, scanner etc. are all fast as poo poo compared to the chinese rigs I've tried. I would definitely recommend it as a solid brick-like dual bander (only single channel, though it has a priority channel watch feature). I like how the Icom antennas always end up with a slight bend to the right after use. Unsolicited on-air reports said it had a very good microphone, and RX audio is pretty excellent too. Previous owner did the extended RX mod, seemingly with a set of tongue and groove pliers to remove the SMA nut which looked like it had been run over with a car a few times (fortunately I had a replacement one in my junk drawer). No real damage to the plastics so it doesn't show but the SMA connector threads have been damaged a bit. The antenna still mounts just fine though, but definitely not a professional job. Emergency communications was one of the major reasons I wanted to become a ham operator, it's nice to know that when bad things happen, I'll be able to help instead of sitting at home wondering what's going on. So with that in mind I decided to try building a cross band repeater using two handhelds and VOX today. The wiring is so simple I won't even draw up a diagram, put a trimpot to reduce the volume levels going from the speaker and into the mic-input of the other radio, repeat and you're done. I also put coupling caps between the trimpot and microphone input. The cool thing is it actually works, using equipment for less than $100 and in theory being able to operate on internal batteries for hours with fairly heavy traffic. Of course it wasn't exactly perfect, first there's a problem that the Wouxun KG-UV6 (2m) and the Baofeng UV-5R (70 cm) radios have vastly different timeout times for vox, the Baofeng holds the output open for about 5 seconds making it pretty annoying to use. Using two identical radios would be better, but they should be models with adjustments on both sensitivity and timeout time. The second problem is that reliably and continuously keeping the VOX open means the input signal has to be loud enough that the noise floor of the receiver will trigger it, since otherwise it would just drop out whenever you stopped talking, confusing whoever you're talking to. I concluded that this isn't really a solvable problem without adding a continuous tone that won't be filtered out by the receiver (so a subtone won't work), or modifying the radio to gain access to the squelch lines, in that case it would of course be trivial to make this work. So anyway I ordered the Puxing PX-UV973 -- which is apparently the only hand held cross band repeater device on the market -- after futzing around with this MacGyver solution for a while, and I'll try using that in the future.
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Jul 3, 2013 19:51
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The scenario I was thinking about it mostly for camping, I put the big antenna with the proper ground plane at the best spot to reach the nearest repeater, then I can talk on 70 cm anywhere there's line of sight using the lowest power setting. Kind of like a femtocell is used for mobile phones. This Saturday I was in the mountains and found that I could reach the repeater no problem in one particular spot, but move 100 meters further and I was in a shadow area, if I wanted to camp there I'd put the tiny hand held cross-band there, and I could go anywhere in the immediate area and have consistent coverage with no huge batteries and mobile rig to carry. We're also doing a emergency communications drill using several x-band repeaters next weekend to provide a reliable voice link to a remote mountain area (power company has a major installation and there's no cellphone coverage at all there). I was hoping to get my little toy before then so we could test if it would work as a tiny little fill-in link. The main uplink will be 2-3 mobile rigs strategically parked though, all running 50W or more. We're also going to set up a digipeater network for APRS tracking of any workers/rescuers in the area, this is all integrated into large suitcases with a proper battery and usually a high power mobile rig inside, but some of the digipeaters also use handhelds to fill in gaps in the network.
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Jul 3, 2013 22:43
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I wasn't part of the last test but I was at the briefing afterwards, for some reason they weren't able to get the I-gate link to work so while they were able to receive and log data locally, none of it made it out to aprs.fi. They also had the sort of failure that only happens in the field, both of the x-band repeaters failed due to corrosion in the antenna sockets and a bad cable (the x-bands are car-mount, the corrosion only shows up when the car is parked for a few hours, normally the vibration keeps it in contact). To make it worse they brought very few tools to measure and repair these things (it was -10*C out and they had to travel by snowmobiles for most of the trip, in all fairness). This time we're definitely bringing more tools, since we can drive all the way up to the camp-site I'll be bringing my stuffed service-suitcase which has everything needed to repair antennas and cables + any minor electronics repairs. There will also probably be a few mobile HF rigs there as a backup for voice comms, but that's not something we're expecting to rely on (not that I see any reason why 2/6/10m cross bands couldn't be set up for the backbone link, aside from equipment availability and antenna sizes). There's a fairly active D-star user's group here too, two simplex gateways on 2m+70cm cover the town. We're also working on installing our first regional repeater on 70cm on top of a mountain later this year, and we have just purchased a new 2m repeater that could be re-worked to act as a DV repeater in the future. There's a lot of old-fashionness here about 2m repeaters though, they only recently added subtone access, and there's no tone encoder on the main city repeater. The main method for opening is still supposed to be a 1750 burst (DTMF is supported and the future recommendation), and it's not been converted to the new 12.5 kHz band plan yet (and probably won't be, the repeater hardware is from 1970). I actually placed my order for the Icom ID-51E today, so I'll be joining the ranks of digital users in a week or two. I suspect I have a lot to learn about D-star operation in the meantime.
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Jul 4, 2013 11:04
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Vir posted:longview, if you're getting D-Star, perhaps you should get set up to exploit its digital data transfer abilities? That is, if your served agencies are interested in transfer of text and images over the air at all. D-Star voice helps to parially obscure the content of voice traffic from the casual scanner listeners, but apart from that I personally don't see the point of using voice-only D-star for emcomm. AMBE is an efficient voice codec, but isn't it better to use analog voice in marginal conditions? Yeah our emcomm stuff will probably be analog for a long time, but we did experiment with using DV last time we did a normal event (just some comms for a football tournament) and the improved voice quality was a plus. Especially since the cumulative distortion of all those repeaters tends to add up, if a DV link was set up it would still sound just as good. Another potential advantage is we could route over the internet, the area we'll be working in has internet normally, so we could in theory use an internet gateway to link some sites together. Obviously it's not a good emcomm strategy but for event coverage it would be neat. As far as I know the ID-51 can be used as a D-star data modem using a separate data port on it, but I haven't actually found any information on how this can be used for anything. If anyone knows what kind of protocols can be used over the 3600 baud link, I'm interested. Running IRC would be fun, but AFAIK most interpretations of the amateur radio rules prohibit internet traffic so it would have to be some kind of HamIRC. Transferring an image over that link would take a while, there is the 128 kbit link over 1.2 GHz but that's probably not practical to set up for the hilly environment we're dealing with.
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Jul 7, 2013 00:10
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