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Do any of you bother with RF Baluns? Trying to figure out exactly when they are necessary. Also, is there a good way to find the impedance of some black-box component? I have no idea about the impedance of my rtl-sdr or how to find it.
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May 23, 2019 18:08
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| # ? May 9, 2024 15:59 |
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The Scientist posted:Do any of you bother with RF Baluns? Trying to figure out exactly when they are necessary. Baluns can do many things, one common type is a 1:1 balun (or just a "choke"). They can be either common-mode chokes (with a DC connection) or a transformer. Transformers are also used for impedance matching, i.e. with a 50/100 ohm transformer you can match a 50 ohm line to a 100 ohm load without reflections. A 1:1 balun will, within its ability to do so, force the current flowing through the center conductor of a coax to return through the same coax shield. This reduces the effects of ground loops. It's probably the most useful where your antennas are grounded together with other stuff, if there's a reasonable return path through the literal ground, a PE bonding connection or another coax running back to the radio then some current will flow. This can (among other forms) act as a loop antenna. This is sometimes referred to as the cable shield radiating or other weird terms describing the same concept, it typically manifests itself as a lot of noise and RFI. Here's a picture from a Wurth common-mode choke data sheet (not usually used for RF, but this one would be ok for LW/MW reception). A current-balun is the same thing.  The coupled inductors act as a massive inductor for signals running in common mode (or unbalanced current), when all the current flowing in the top inductor is equal to the current going through the bottom but in opposite directions, the inductance is very low (ideally it's zero). If you put a current balun in series with your coax near the antenna then you avoid any current going back through other paths than the coax shield since any current attempting to do so would cause an imbalance and would have to go through the big inductor. Current returning through the cable shield and balun would have a much easier time since it's balanced and the magnetic fields inside the balun will cancel out. Same sort of thing applies when using an RF transformer. Sticking some ferrite cores on the outside of the coax also works, but ferrite cores are optimized for different frequency ranges so using them requires at least knowing the core material. Twisted pair gets a similar effect wrt. current balance as well. -- To measure the input impedance of an RF device you need something like a Vector Network Analyzer (VNA), unless your device has a literal resistor across the inputs the input impedance will be variable over frequency as well. With a fast pulse generator, a scope, and some coax connectors you can also do an approximate measurement using TDR. For the RTL-SDR I'd just look up the R820T (or whatever tuner your dongle had) data sheet and see what it says for input impedance there.
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May 23, 2019 18:49
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The Scientist posted:Do any of you bother with RF Baluns? Trying to figure out exactly when they are necessary. I've used a 9:1 with an rtl-sdr when direct sampling hf. I've never used a balun with the rtl for its normal frequency range.
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May 23, 2019 19:01
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Yeah, baluns are extremely important for sure. i have at least one choke balun on every single one of my antennas, and the HF ones have a lot more than one core.
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May 24, 2019 06:12
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This makes sense, thanks for the info. I was starting to hatch a plan to use a Raspberry Pi as an arbitrary waveform generator so that I could calculate the impedance of my rtl-sdr's receiver, or just take it to one of the Electronics labs at school and do it there, but from what I read it started to sound like impedance matching was of most importance when maximizing tx power and less so when receiving. I'm sure I will get to this stage at some point. I was considering building a custom antenna tuner circuit, but all the ones I have seen for sale are specific to HF and VHF, and less UHF, where all the interesting signals I am messing with are. As for the balun, it will be worth it for me to invest in at some point. For now, the dipole antenna T-connector that came with my SDR has a ferrite core on the lovely "coax" cable (and the UHF monopole I have has an inductive winding built right in to the mast, which I assume is for this purpose), so I think that will be good enough for now.
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May 25, 2019 21:06
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I have started ordering parts for ES HAIL 2 U satellite use and i was wondering if anybody have used a transverter that goes from 144ish to 2.4 ghz and can tell me if there is something i should know before i try to buy on. (mods change thread name to ES'HAIL 2 U, u know u want 2) edit: while checking for airspy firmware at https://airspy.com/airspy-hf-plus/ i did a double take at the title Big Mackson fucked around with this message at 13:58 on May 27, 2019 |
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May 27, 2019 13:07
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I suspect that my connection from balanced ladder line to unbalanced coax should have had a proper balun on it, but so far I've just had some ferrites on the coax to dampen the common mode. I've worked only lower power, so I haven't had to consider the safety implications yet. I just got an MFJ antenna analyzer and feel ready to try building a vertical. Vir fucked around with this message at 21:22 on May 27, 2019 |
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May 27, 2019 21:09
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199 for an sdr.. seems Pricy.. but also probably seems like it'll have less noise maybe than the hubk o poo poo I was using before.
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May 27, 2019 21:11
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I have a regular airspy as well as an hf+. Despite the much smaller bandwidth I prefer the hf+ since it doesn't need a transverter to see hf. I also have the airspy branded transverter but somehow haven't ever gotten it to work properly outside of sdr#. It might also just be broken, I had previously turned one of the washers holding a connector to the housing too tight and the connector popped loose. Mashed it back on and seemed fine but could still have busted something via that.
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May 27, 2019 22:03
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Hey all, a friend wants a 20m band radio to radio home. Any suggestions?
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May 28, 2019 01:09
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Any HF radio could work. A lot depends on how much they want to spend, and whether they plan to use it at a desk or on the go. In my opinion an IC-7300 is great value for money (among new radios) but not everybody wants to spend that much up-front.
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May 28, 2019 02:08
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https://twitter.com/pwguru65/status/1133254042174590976 The old site of Hamvention (Hara Arena in Dayton) was hit by a Tornado this evening.
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May 28, 2019 07:34
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Dehry posted:https://twitter.com/pwguru65/status/1133254042174590976 Wasn't it already collapsing in on itself before? I imagine the owner is cashing the insurance checks as we speak.
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May 28, 2019 08:18
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I was wondering about this place. RIP Hara Arena.
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May 28, 2019 14:15
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Someone just flew a drone over it: https://www.daytondailynews.com/news/local/hara-arena-roof-blown-off-trotwood-schools-closed-after-tornadoes/5W7NpDohYwDBNwu9fp59bK/ It's hosed
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May 28, 2019 15:12
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Vir posted:I suspect that my connection from balanced ladder line to unbalanced coax should have had a proper balun on it... That would be the exact use case for a balun. For ladder line, you will probably want a manual tuner anyway, which usually has a 4:1 balun inside. FYI, balun is a portmanteau of balanced-unbalanced. You can have an unun too, an unbalanced input and output.
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May 28, 2019 16:10
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Today i got an 80 cm dish for SATELLITE COMMUNICATIONS! SPACE! SCIENCE! I hope calibrating the dish against eshail 2 wont be a long and tedious job.
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Jun 6, 2019 14:52
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Big Mackson posted:Today i got an 80 cm dish for SATELLITE COMMUNICATIONS! SPACE! SCIENCE! from what twitters i follow es'hail is incredibly easy to work and i think you'll have a pretty straightforward job. What are you using for a feed?
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Jun 7, 2019 02:17
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Jonny 290 posted:from what twitters i follow es'hail is incredibly easy to work and i think you'll have a pretty straightforward job. What are you using for a feed? I think i will use rg214 with Goobay universal twin lnb. I wonder if i can supply 12v in one port and get signal from the other, so i dont have to biastee. edit: Here you see how i done it (u also see HF and VHF/UHF solutions)  edit2: I have an F male to N Female adapter so if you know of a more suitable coax that commonly use N connectors then i must know. Big Mackson fucked around with this message at 22:41 on Jun 7, 2019 |
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Jun 7, 2019 21:47
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we used LMR400 for uhf to low micro when doing WiFi dish work. When I dealt with Ku satellite there was a block convertor so RG6 worked - not like there’s a suitable transverter to use with RG8. You can get Times LMR 400 or equivalent in preterminated lengths N-N for sure , I have a belkin version I think in 100’ in storage
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Jun 7, 2019 23:59
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Partycat posted:we used LMR400 for uhf to low micro when doing WiFi dish work. When I dealt with Ku satellite there was a block convertor so RG6 worked - not like there’s a suitable transverter to use with RG8. [Google results] Attenuation (dB per 100 feet) MHz: 30 50 100 146 150 440 450 1000 2400 RG-214 1.2 1.6 1.9 2.8 2.8 5.1 5.1 8.0 13.7 LMR-400 0.7 0.9 1.5 1.5 2.7 2.7 6.6 Hmmm, i am gonna use about 26 feet of cable so lets say 1/4 of 100 feet. If i use LMR-400 for uplink 2.4 ghz i will get 1.65 db loss compared to 3.425. If i use Yagi grid antenna thus getting 3db loss due to vertikal/horizontal polarization instead of circular i will have a total of 4.65 db loss for LMR-400 6.425 db loss for RG-214. LNB downconvert to about 700ish mhz so i i guess LMR-400 have half the loss of RG-214 on the RX side. edit: we live in modern times so 0 loss cable when? Big Mackson fucked around with this message at 17:09 on Jun 8, 2019 |
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Jun 8, 2019 17:05
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Big Mackson posted:edit: we live in modern times so 0 loss cable when? Was going to say ladder line but from playing with this calculator it might actually be worse than good coax in 2.4ghz territory
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Jun 9, 2019 00:00
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G-line to the rescue! single wire that uses cone launchers at either end to impedance transform and set up a traveling wave Downside: gotta be more or less a straight tensioned line.
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Jun 10, 2019 17:53
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If you have tons of money to throw at the problem, you could always go with some hardline. https://www.commscope.com/catalog/cables/product_details.aspx?id=14710
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Jun 10, 2019 19:00
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Jonny 290 posted:G-line to the rescue! I'm calling it a G-string and none of you can stop me
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Jun 10, 2019 20:56
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Progressive JPEG posted:I'm calling it a G-string and none of you can stop me Only g-string a ham is likely to get.
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Jun 10, 2019 23:52
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mashed_penguin posted:Only g-string a ham is likely to get. Prostitutes are much less expensive than radios.
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Jun 11, 2019 00:08
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mashed_penguin posted:Only g-string a ham is likely to get. That's why we have SSTV.  
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Jun 11, 2019 02:44
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I should send two low resolution melons over SSTV.
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Jun 11, 2019 21:35
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Partycat posted:I should send two low resolution melons over SSTV. SSTV is fascinating but I don't know if I could resist the temptation to build a pirate radio rig to blast  at 6.995 for 10 minutes at a time on random Saturday nights
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Jun 12, 2019 02:23
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 I get a strong signal with rg213 i had lying around but the drift is insane lol
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Jun 12, 2019 19:26
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Earlier my comment was that I need to just have long wires and cases I guess. A slipmap mount for my iPhone or iPad and some loomed power distro. The rig runner with the USB looks good but no source switching so I’d need a diode arrangement or something. There are other manufacturers of similar parts that may be suitable. A small not annoying or shiftable speaker would be great with remoting the radio. But it’s still rough to put it into a pickup truck crew cab and have passengers and that for a drop and go operation. I have been using APRSPro on my iOS devices and it works great to see the map, doesn’t seem to support picking a point to Nav to which would be perfect. I’ll have to browse the new rigs and see if there’s any new hotness.
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Jun 12, 2019 22:25
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Got some work to do still, plugged a few frequencies in to the scanner, but here’s twitch plays 80meters. RSP1A and a long wire along the fence line. turned it off blugu64 fucked around with this message at 12:43 on Jun 13, 2019 |
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Jun 13, 2019 05:11
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I found this mod for my goobay so now i think i will be able to actually hear people instead of garbled wobble speak.
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Jun 13, 2019 16:15
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I destroyed my goobay with bad soldering skills, so i ordered an octagon twin lnb. https://www.passion-radio.com/lnb-pll/octagon-lnb-pll-759.html#/lnb-twin_2_outputs I got it now but there are no schematics for it  I have no idea where i am gonna put external reference signal in.
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Jun 29, 2019 18:11
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I think they just closed up for the evening, but since there's a tropical storm in the Gulf of Mexico, the Hurricane Watch Net is active for anyone who's interested. I don't have a 20m or 40m rig (for day and night, respectively) but you can pick it up via websdr, which is pretty neat.
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Jul 12, 2019 04:35
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Finally messing around with radio's again after getting my general ticket early this year and then getting busy with life. Ordered an antenna and mount to try and get mobile in the Raptor for off roading. Still waffling about whether I should get a fancy dual bander or just a no frills 2m for the task. Also I need to get my HF antenna up before the weather turns again. I bought a Comet CHA-250B quite a while back and it is still in the box. It is a compromise antenna for sure but I got it before I really knew anything. Should I even bother setting it up or try for some sort of dipole? Denver hams, what some good repeaters/nets to check out? I programmed a handful in my ft-60r but activity seems to be slim to none. Since there are plenty of ways to Dox me here already my call sign is KE0UBP
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Aug 11, 2019 21:31
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*wave* denver crew here. 145.145 is the big ragchew repeater here; 145.310 is also very popular. You can goof with the cha-250 but something tells me you'll be stringing a wire up a couple weeks later.
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Aug 12, 2019 01:21
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Jonny 290 posted:*wave* denver crew here. 145.145 is the big ragchew repeater here; 145.310 is also very popular. Those two do seem a bit more active!  Installed a mobile Kenwood TM-V71a and talked to someone briefly on the 310 repeater to make sure all is good and well. Also strung up a 10m dipole on the side of my house just to mess with HF a bit. Of Course 10m is the only band I haven't heard any activity on since I put it up. Messing around with FT8 and WSPR is pretty neat 20m and 40m are pretty packed. Of course I can only transmit on 10m which is dead so no contacts yet.
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Aug 16, 2019 23:08
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watch dxmaps.com for openings. You can sign up for email alerts when sporadic-e propagation comes within a couple hundred miles of us. Also listen 28.200-28.300 for CW beacons. The only one you will hear when there's no prop is going to be 28.236; i want to say it's down in Parker. If you hear them on any other frequencies, the band is open to somewhere. https://www.qsl.net/wj5o/bcn.htm is a relatively current list of who's on what freq in 10m beacon land.
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Aug 16, 2019 23:14
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