[Local DE] 2m and 70cm reception near Frankfurt - Page 1
Forum section: electronics / rf-microwave

author: brainwash
author_rank: Frequent Contributor
timestamp: August 18, 2017, 09:06:49 pm
content: Just asking as an enthusiast, this post is focused on Germany and esp. Frankfurt.I've been using my RTL-SDR to listen in on airband (works fine with standard antenna), also just bought a UV5R which is rated for 70cm and 2m.I don't have a license, probably will in the future, but for now I just want to monitor the waves.I'm near Frankfurt and the airport, sitting quite high above the ground, with an unobstructed view to the TV tower (~10km) and Taunus Berg (~25km?).I've entered the local relay station frequencies, 145.750MHz and 438.925MHz, was expecting quite a chatter but just get some static noise (~1s) every minute or so. Managed to catch a CW reception two times, been doing this for about 3 hours, set up in dual-frequency monitor mode.My questions are:- should I use other frequencies? I thought relays would output the most traffic- should I try other bands? Right now 70cm and 2m is what the Baofeng offers- is the included antenna so bad? AFAIK, elevation beats SWR, and I'm pretty high off the ground with no obstructionsThe radio works, I've tested it with my small PMR transceivers on 446.00625MHz. So small in fact that they are watches, they barely get a 50m range.EDIT: I realize the first suggestion would be to upgrade the antennas. But with my RTL-SDR I get 90% of the traffic approach conversation (from planes, tower is 100%). Also the FM signal is so strong that I get all the IF superhet combinations in my  receivers. Perhaps I'm just not on the right frequencies or the ham activity on these bands is so low.EDIT 2: I'm using the freq list from relaisliste-qrg.pdf, fromhttp://www.amateur-funk.de/andhttps://www.funkamateur.de/tl_files/downloads/hefte/2008/FM-Kanaele.pdf- that's as far as my extent of German language was able to find.

author: babysitter
author_rank: Frequent Contributor
timestamp: August 18, 2017, 09:39:24 pm
content: Hi Brainwash,activity on the repeaters depends on the time but is quite lowish. A portion of the traffic migrated to digital voice, too, but as i also don't have a radio for it i can't tell exactly how much is going on there, I would have to check from our club station at Schaffenburg.On direct FM your best chance is using a scanner and note the time when some activity is on air - some of it are regular networks, say the local one here every wednesday around 19 o clock.Most of it is random traffic.You can try the 70 cm band of course, some activity there, way more repeaters available for you.Still, Antenna can always be improved. Remember that the planes are transmitting down from above with line-of-sight.BRbabysitter

author: brainwash
author_rank: Frequent Contributor
timestamp: August 18, 2017, 10:18:37 pm
content: Thanks for the reply.I did make a makeshift 1/4 antenna with a length of wire but the reception was only marginally better. I intend to buy the ultra-wideband antenna (forgot the name) which looks like a tripod with many legs, but it's a risk that you get the fake one.The planes are either on the ground (below LOS) or a lot of times behind a few walls of concrete. Still, even 30km LOS is impressive, with a thermally-insulated window in-between. I don't know what their transmitter power is but I assume 50-150W.Any specific frequencies I should scan on? I expected at least someone every 15 minutes, at least, should I expect much less than that?

author: cdev
author_rank: Super Contributor
timestamp: August 19, 2017, 01:28:52 am
content: You can make a fairly decent high gain antenna out of 300 ohm twinlead and a small bit of RG-174, plus whatever you use for feeding it.Look up "ed fong antenna" or "DBJ-1" or "DBJ 2"For reception you can also make something out of two pizza plates called a planar disk antenna.The antenna they come with is nearly useless. The wire it comes with isnt even coax (although it sometimes is marked coax, it isnt)

author: abraxa
author_rank: Frequent Contributor
timestamp: August 19, 2017, 04:52:36 am
content: You could also compare your results withhttp://sdr.homeip.net:8901/and see if you miss traffic when there is some.

author: brainwash
author_rank: Frequent Contributor
timestamp: August 19, 2017, 11:29:15 am
content: Thanks for the link, yeah, I got essentially the same traffic with both my SDR stick and the Baofeng.So does this mean I have to scan channels constantly or keep an eye on the spectrum? Just curious as to what would be the equivalent of a 'chat room', most connections I could catch were peer-to-peer.

author: cdev
author_rank: Super Contributor
timestamp: August 19, 2017, 12:56:40 pm
content: Is the signal you are listening to going through two meters or so of "coax" as supplied with RTLSDR, or something else? (preferably double shielded RG-6) also is it a semi upgraded antenna or the stock "antenna", meaning is it seven inches long or a telescoping mag mount antenna longer than that?What metal object is its base anchored to? If you're inside, refrigerator, top of turned off major appliance, or non-operational computer works, bigger and flatter the better. A metal file cabinet makes a good ground plane. Metal radiators work too, but try to attach base of mini mag mount to a flat point to get more capacitance. then run loose wire vertically. Ideal antenna length varies but is more than seven inches. Try a meter to start out.(replace the little wire with any other wire some length long to give it more range- also you're hopefully giving it it something to work "against" ground wise, that is also is super important, see above)Are you using a USB extension cord to get the dongle away from your computer?Are you using some ferrite RFI reducing beads on the USB cable from computer to RTLSDR ? (This is very important for best results, start with one at each end, it may already have one or two)

author: cdev
author_rank: Super Contributor
timestamp: August 19, 2017, 01:14:17 pm
content: Save your money on buying an antenna, you can make areally good antennafor reception from two pizza tins.If your main interest is ham radio I would build a replica of ed fong's DBJ-1 j-pole, which has quite a bit of gain on both 2 meters and 70 cm. You can also make a slightly modified version, the dbj-2 which rolls up and which can hang from a hook on your ceiling when you want to use it. You can use the same hook for the planar disk when its in use.But a few feet of decent coax, with copper braid and center conductor you can solder to. its a good investment. There are virtually no broadband antennas on the market that are worth what is charged for them.Many scammer antennas are ludicrously overpriced.A discone is broadband and works but a planar disk or biconical will give you a better radiation pattern out to the horizon. A discone has a skewed pattern that develops most of its gain upward at an angle and for land mobile use that largely wastes it.For those two ham bands check out the ed fong dualband j-pole. Cant beat it for any price unless you want to spend >$100 on specialized single band antennas (or use a yagi, i.e. beam) .Which reminds me, you should figure out where the repeaters you want to listen to are, build a simple beam out of coat hanger wire to see if you can get them with a directional antenna.Directions to make a super cheap 15 minute Yagi are on the same site that the Planar Disk antenna is on.If you have a $10 radio and $0.025 antenna wire its not worth spending money until you have done the few basic things that are necessary to use an rtlsdr effectively.Get some decent coax. The wire that comes with those radios is only useful for lower frequencies.Its a tribute to the value of those devices that it even works at all.Invest a bit of money in a barrel adaptor so you can use regular coax.Dont spend more money until you know your QTH has a line of sight path to the repeaters you want and have your ham ticket.Build your own antennas first to get a better idea of what you need.You may need a dedicated Yagi - if they are some distance away or behind some obstacles.Ask your local hams what the popular repeaters in your area are, there are also likely online listings.There is a free program, "chirp" which can be used to program Baofengs. It allows importation of several frequency lists, those lists are likely a good place to find your local repeaters. I forget where they are.Also, many of your local hams may not be online except on weekends, evenings and when driving to and from work.Quote from: brainwash onYesterdayat 16:18:37

author: babysitter
author_rank: Frequent Contributor
timestamp: August 19, 2017, 01:53:55 pm
content: DONT EVER BUY A RECEIVING ANTENNA!Its easy to make your own antennas, e.g. groundplane antenna out of wirehttps://wiki.schaffenburg.org/Projekt:Groundplane_f%C3%BCr_70cmDont use a lot of cable, put the RTL-SDR stick on the antenna immediately.Also when you gained some experience you can try to get antenna preamplifiers for broadcast and modify them. This is mainly to compensate for cable losses, not really "improve reception", or get a LNA. Any improvement will be small, about "lifting a bad rtl-sdr to baofeng quality."If pay a visit to my Makerspace "Schaffenburg" and leave a little donation you can build such a amplifier there.https://wiki.schaffenburg.org/Projekt:Gainblock_Schaffen1105

author: brainwash
author_rank: Frequent Contributor
timestamp: August 19, 2017, 02:57:24 pm
content: Quote from: cdev on August 19, 2017, 12:56:40 pmThe RTLSDR has a stockR-SMAMCX antenna with 1m of thin cable. It has a screwable wire "top" that's 12cm and a magnetic base. I tried a flat metallic base but I got the best reception by keeping it as high as possible. A makeshift 1/4 length wire instead of the small top made little difference, tried different lengths just for fun.The SDR is plugged directly into the laptop, that's a limiting factor which I will detail below.Quote from: cdev on August 19, 2017, 01:14:17 pmAll are valid points, which is why I've listed the location and the frequency listings I have and have gotten great replies so far from people in the area.I've also not invested anything extra until I collect enough information. I was contemplating the discone but the various versions on amazon.de have mixed reviews. The planar antenna looks like a good project.Quote from: babysitter on August 19, 2017, 01:53:55 pmThanks for the link, I might give the space a visit sometime - during open hours -it's about a 30 mins drive from my place. If you think I can also collect some parts - for a price - or decent DIY stuff from the members please let me know. I don't have a stock of coax or connectors or anything RF-related.My plan is to set up an antenna (or more) on the balcony, I already have the holes for the cable pre-drilled. I have a great view with lots of LOS (>25km, 180 degrees). Then to set up a semi-permanent instalation (laptop or rPI) with the SDR inside the house. Since the cable run would be at least 3 meters, it would probably require an LNA as well.I don't mind going outside to switch the antenna, but I might have an antenna switcher around. I might even have some LNAs, but those are for satellite dishes and not even tested. I'll gladly give some stuff away if someone can make use of it.The SDR has a horrible thermal drift, if this hobby sticks I will invest in the improved units, those are not even that expensive.The Baofeng is mainly intended as a portable device since it kind of duplicates what the SDR can do. Not interested in the transmitting portion for now as I don't have a license and am not a prepper. But it would be nice if I can get a decent antenna for it that's at least semi-portable. I mean, for the money, it's a surprisingly good device and it might provide some entertainment while hiking or camping.

author: brainwash
author_rank: Frequent Contributor
timestamp: August 19, 2017, 05:41:39 pm
content: As another question, what connector should I consider for the RF system? Was thinking SMA-male on the antenna side, female on the receiver side.Or should I go with N-Type or even BNC?

author: cdev
author_rank: Super Contributor
timestamp: August 19, 2017, 07:12:15 pm
content: whatever connector works for you as long as its not "uhf" (pl259 and so239 which really have a lot of loss.)SMA works well up to several GHz on patch cords and short runs between equipment, BNC seems to be the old standard on test equipment up to a GHz or so. Be aware that MMCX (?) is not made for lots of use so if your radio has (M)MCX I would buy an adapter to something else and just leave it on, all the time so as not to destroy the plug by repeated insertions. They are meant to live inside equipment and be left connected, only good for a few dozen changes. u.fl are even worse. (but very small)Because of value for money, decent quality CATV coax and connectors are a good choice for many people. Also being a "TV" receiver the RTLSDR's input is nominally 75 not 50 ohms.However the wire they use on its antenna is crap because even the smallest coax is fairly expensive compared to silicon chips. So for example, with GPS they put an LNA at the antenna and then use crap coax and that works.. but it works far less without an active antenna.So use real coax and connect it to a planar disk or whatever you choose, and get some ferrite split beads and a USB extension to reduce the noice coming up the USB line from the computer, and you'll be hearing tons of stuff in that great location in no time. The way the RTLSDR works it desensitizes due to noise so your dongle will be relatively deaf until you effectively filter broadband computer noise out.Make sure to correct your PPM so you are able to tune in stations by dialing them up. Some RTLSDRs are as much as several dozen ppm off frequency. I correct it using a known station, and adjust it until the frequency agrees with the dial. You may have to go up or down. Then write that down on the dongle. +6 or -15 or whatever. I have one that only needs -1. It was 0 when I got it. (over time they age but also the rate of aging slows) Here in the US I use vHF weather broadcasts to tune them. You can also use an FM station.

author: cdev
author_rank: Super Contributor
timestamp: August 19, 2017, 07:31:01 pm
content: If the wire was not so thin I would tell you to just chop the antenna off and instead connect two wires to the end. the center one continuing and the shield wire going back down again. But that would just disintegrate as the wire used in the wire is way too thin to solder anything to.Hopefully you get the idea.

author: brainwash
author_rank: Frequent Contributor
timestamp: August 19, 2017, 07:42:02 pm
content: So standard tv antenna connectors are fine? I thought they have a high insertion loss and work only up to a limited frequency. Granted, I'm not shooting for anything above 1GHz and might end up using an LNA, except for the Baofeng.Regarding tuner trimming on the SDR - I wrote above that it doesn't make a lot of sense, as the temperature drift is quite high. I learned to just trim the frequency by hand to get the frequency in the middle (or edge, if on SSB). The drift also varies with sample rate, air drafts and a lot of other stuff that causes it to vary by more than a few hundred Hz.I found an MCX-SMA(female) patch cable in my junk box, so at least that part is sorted out. Also found a "wideband" (30-950MHz) active TV antenna, Thomson ANT1621, it's probably junk but probably better than the stock ones.Guess I now have to start stocking adapters....

author: cdev
author_rank: Super Contributor
timestamp: August 21, 2017, 01:48:34 am
content: Remember most of what you're likely hoping to listen to is vertical, not horizontal polarization (like TV and FM) .

author: brainwash
author_rank: Frequent Contributor
timestamp: August 21, 2017, 11:56:46 am
content: With some help from here, a bit of scanning and downloading a preset list for the Baofeng I was able to listen in on a few 'ragchew' discussions. The usual topics: kids these days and their smartphones, drivers using their phones in traffic, immigrants, ...Last night, really late, two completely plastered guys started in half-German, switched later to some other language (Turkish?). Neither of them gave away their callsign and they were using the same relay frequency (DB0FT) as the guys before. Not sure whether they were hams or just happening to be on the same frequency. Talking about car deals as stuffAnyway, just wrote the above as confirmation that: there is activity around the area and there is some stuff to hear. Regarding polarization, with the stock antenna the Baofeng sometimes receives better in a horizontal position, not sure why this happens, I wouldn't expect those kind of reflections at these frequencies.

author: babysitter
author_rank: Frequent Contributor
timestamp: August 23, 2017, 02:10:25 pm
content: Hey Brainwash,you're welcome at our club even when Frankfurt itself has some too, i dont know if there is any RF going on.(Full disclosure: I am the founder. We like memberships, starting at sqrt(2) EURO/month. )If you think that playing with radio waves sticks with you consider a ham radio license (incidentially, there is a free course starting at our space on september 14th, executed by local DARC ham group in our rooms.)Something I really want to point you to is applying RF filters. Your little stick gets a lot of broadcast and mobile phone signals and all that takes its toll, it might increase noise at the signals you actually want to measure. Simple filters can be easily made from quarterwave coax cables. Try it, its worth the effort.Don't wonder about unexpected antenna angles with polarisation losses. Stuff like that happens.Oh, and take care of the stock antenna of your baofeng, one of our licensed members gave me his to test, the connection of the SMA inner connector to the rest of the antenna broke.Talking about DIY: you might ask the local tv shop or scrap dealer for old antenna scrap and the old amplifiers, you might change them from broadcast to ham frequencies.

author: brainwash
author_rank: Frequent Contributor
timestamp: August 23, 2017, 03:03:44 pm
content: Many thanks for the warm reply, I will contact you on the PM.Regarding the license, just for my information I've looked up the sample exam questions. That is the exam which you can take without any membership - and the questions were quite tough!I know getting the license via club membership is the recommended and desired way, but what would be the difference? You stay in a club for 1-3 years and learn the same stuff as you would at home, but with someone standing by? Is the club exam just a formal procedure with a bit less tricky questions?I mean, it's a lot of stuff to memorize and the questions don't seem designed to be answered by elimination...(For reference, talking about these:https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/Fragenkatalog/BetriebVorschriftFragKlAuEId7830pdf.pdf?__blob=publicationFile&v=3https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/Fragenkatalog/TechnikFragenkatalogKlasseAf252rId9014pdf.pdf?__blob=publicationFile&v=3)

author: babysitter
author_rank: Frequent Contributor
timestamp: August 23, 2017, 07:46:35 pm
content: With club i was referring to our makerspace which has a small 5 person amateur radio community inside, about to increase numbers. The DARC is the national association which of course has a local group in AB, too. They do the course.(I didn't go to a course from the association, my neighbour teached me a bit. Also, my wife is a self-taught ham which entered DARC later.)The exam is independent of any club. Of course. Thats BNetzA stuff (Or BAPT in the time I did it.)Clubs are just a way to socialize and share, say if you like to build your own stuff you might easier find people with test equipment or knowledge or experience.