|
you can and that's how it's done at HF in like the little LDG auto-tuners and poo poo. but try keeping a filter network sane when the relay contacts have enough inductance to become a filter element diode switching (because we're pretty much talking rx-only so can use low bias voltages) would be the best answer i think
|
#
?
Apr 1, 2014 17:21
|
|
|
|
| # ? May 27, 2024 03:14 |
|
|
yeah but even then getting a ~2 MHz wide BW in to the SDR would be impossible over the entire band, i was thinking the only way to do it would be a set of broad pre-selection filters, followed by a mixer, but then tuning would be annoying unless you wrote a new driver to control it just been doing some at-home RFI tracking, found that the broad pockets of noise around 220 MHz was caused by leakage from the chassis of my computer, adding some strategic aluminium foil to the unshielded bits helped a bit but i'll need to buy some metal tape to get a good seal technique is simple, just a small electrically shielded loop at the end of a coax using some coax and part of a curtain-rod as a handle, it's not very sensitive and responds to magnetic fields so putting the loop along a wire will generally tell if current is flowing, moving it along seams in chassis will tell you if there's RF leakage there also need to order a pile of ferrite cores to wind chokes from
|
|
#
?
Apr 1, 2014 18:03
|
|
|
longview posted:
i seriously need, like NEED NEED NEED to spend about 70 bucks on ferrites for transformers and chokes and baluns, but i cannot crack the formulation/type thing. this beard says only use type 50. this guy says no he's an idiot, use only 43. no no, says greybeard 3, type 31 is the best! trying to spec parts via all-caps eham.net forum threads is maddening the best i can figure out is that the USB cable chokes seem to be ok for vhf/uhf coax chokes e: and i assume that the box full of toroids i've snagged off motherboards are iron or something and thus near-worthless for rf
|
|
#
?
Apr 1, 2014 18:05
|
|
|
the ARRL RFI guide i ordered had a table with specific recommendations, i can get a picture tomorrow, but there's at least two kinds you need for HF and VHF
|
|
#
?
Apr 1, 2014 18:06
|
|
|
this is kind of fun, i got a noise source that carpeted the entire 40-60 MHz region, turns out it was a cable bound emission from a cheap LED power supply (EMC tested my rear end), could measure it in all the house electrical wiring which made hunting it down more fun image dump:  frequency response of the discone preamp with filters  the upgraded FM+GSM+TETRA filter  loop probe using one of the smallest SDR dongles and a laptop
|
|
#
?
Apr 1, 2014 18:46
|
|
|
I found a new prison radio that I'm craving. i think i'm going to start collecting penitentiary sets after I move. http://www.ebay.com/itm/NEW-OFFICE-...=item3cdee276ad  They double as instructional/demo units! 
|
|
#
?
Apr 2, 2014 16:57
|
|
|
Jonny 290 posted:I found a new prison radio that I'm craving. i think i'm going to start collecting penitentiary sets after I move. are they regular units that get modified or are there special prison versions?
|
|
#
?
Apr 2, 2014 17:15
|
|
|
they're usually production radios with simple designs. every one i've seen has a clear case from the factory. pretty sure that's a requirement of the prison boards thing about them is, an AM/FM radio that sucks is going to suck bad inside a cell block, think 20 feet of concrete and 1000 fluoros in between you and freedom. So these things are actually considered sleeper radios with really good performance and noise rejection
|
|
#
?
Apr 2, 2014 17:17
|
|
|
Jonny 290 posted:they're usually production radios with simple designs. every one i've seen has a clear case from the factory. pretty sure that's a requirement of the prison boards quote:thing about them is, an AM/FM radio that sucks is going to suck bad inside a cell block, think 20 feet of concrete and 1000 fluoros in between you and freedom. So these things are actually considered sleeper radios with really good performance and noise rejection
|
|
#
?
Apr 2, 2014 17:20
|
|
|
oh no they're all factory jobs. think of how many inmates there are in the US. if you're one of the four models they approve, you're about to make some stacks. so far i've only found sony and sangean, both have a long history of making well designed radios
|
|
#
?
Apr 2, 2014 17:26
|
|
|
so why is it clear, so inmates can't hide things in them, or so they no people aren't using it as a science kit that will help them escape?
|
|
#
?
Apr 2, 2014 17:44
|
|
|
Crankit posted:so why is it clear, so inmates can't hide things in them, or so they no people aren't using it as a science kit that will help them escape? yes. the answer is yes.
|
|
#
?
Apr 2, 2014 17:50
|
|
|
i'm thinking of the pain one would experience were they to take the splintered end of a shattered AM antenna ferrite in the side ow yeah it's probably a little from column A, a little from column B
|
|
#
?
Apr 2, 2014 17:53
|
|
|
turns out we had a surplus of 100 MHz toroids at work, so won't be hurting for those any time soon also decided to set up a ADS-B receiver using the space SDR dongle, just using a SRH805S (yes, that tiny little dongle) and a short 316 run taped to the window and i get about the same performance as the discone (not unexpected, the discone system isn't set up for GHz reception) gonna try to build a high-pass filter tomorrow, then set up another LNA board so i can put the antenna where it can see the sky as a bonus i now have premium flightradar24
|
|
#
?
Apr 2, 2014 18:10
|
|
|
adsb seems neat to goof with but there's too much DLL hell and weird middleman program overhead for me to care right now. maybe i'm reading bad tutorials from 2 years ago and it's super simple now, idk. maybe once i get spare dongles, like yer doin. really i dont even have a computer that can run an SDR dongle for more than 2 minutes without overheating - let alone that hackrf 
|
|
#
?
Apr 2, 2014 19:01
|
|
|
With RTL1090 and the FR24 feeder program it took me about 10 minutes to get a signal out so that's been made absurdly simple, once they verify two flights received (automatic) the feeder program gives you an api key and you can register and get free premium for as long as your station is active seriously amazed at the performance now, picking up flights like 100 km away, if i get a better antenna setup and some filter+gain i should be able to plug a small hole in their coverage area, already picked up several flights were just too weak to get a GPS signal and that werent on the map
|
|
#
?
Apr 2, 2014 19:10
|
|
|
radio secrets: this whip antenna which is $18 on amazon prime gets decent reception, and unscrews from the base it comes with and onto the one for the antenna included with SDR dongles, so you don't need to use an adapter
|
|
#
?
Apr 2, 2014 21:26
|
|
|
volunteer FD sure does have a lot more activity on the radio than the city FD. wonder if radioreference is out of date
|
|
#
?
Apr 3, 2014 01:34
|
|
|
PuTTY riot posted:volunteer FD sure does have a lot more activity on the radio than the city FD. wonder if radioreference is out of date it'd be cool if you could submit a rating for relative channel activity sdr# has a plugin that will monitor a slice of band and log all detected activity and count the number of seconds it was active i'd run that in the background for a week and scale it to 1-10 and submit it, that'd be useful info
|
|
#
?
Apr 3, 2014 01:38
|
|
|
ya that sounds like a rly good idea. u could even set it to monitor all radio ref submitted freqs for ur area. if radioreference wasn't a uniden shill i mean also what's up with CW on the county fire freq
|
|
#
?
Apr 3, 2014 01:55
|
|
|
PuTTY riot posted:also what's up with CW on the county fire freq station id probably
|
|
#
?
Apr 3, 2014 02:42
|
|
|
yeah you can get a cw IDer that spits out audio on an IC, or program an arduino or w/e commercial/law enforcement has to ID too, its less stringent tho
|
|
#
?
Apr 3, 2014 02:44
|
|
|
OOH this plugin looks good http://rtl-sdr.ru/page/timeshift-sdr lets you just click on anything in the waterfall, it's like tivo for your sdr
|
|
#
?
Apr 3, 2014 02:47
|
|
|
uni cops play by the rules, i like it there apparently was someone of interest black cop lady on foot saw. dispatch says 'make sure you get a violation on him' 3 mins later 'i'm 10-82 on a black chevy cruz. violation no turn signal'
|
|
#
?
Apr 3, 2014 05:09
|
|
|
did some experimentation today, managed to make a pretty alright bandpass for 1090 MHz: i started with straight 1/4 wave whips, this gives a broad response, winding them into large helixes increases the Q factor and shifts frequency slightly, having them touch each other reduces the Q a lot the middle segment is shorted at one end, and is tuned by varying the capacitance to ground (i.e. distance), it provides a notch around 930 MHz  frequency reponse, tuning for minimum insertion loss was very important, both shape and capacitance mattered  i put it inside a brass shield and soldered it along the ground plane, adding the shield required a slight retuning of one of the coils, i made the shield large on purpose to minimize the impact on the tuning one side has a brass cover, the other is just copper tape to allow retuning if it's ever needed, tomorrow i'll build a preamp stage to go after this, which should make a pretty drat good ADS-B receiver i also tested this design at VHF frequencies and it did work, but iirc it was harder to get a decent Q factor at lower frequencies
|
|
#
?
Apr 3, 2014 18:01
|
|
|
When this article says that the RTL-SDR, LNA, and upconverter should be shielded separately, does it mean having them in separate, electrically isolated enclosures, or just physically blocked off (so that the components are all physically isolated in sub-boxes or whatever) but electrically in the same box? edit: this is cool as hell Maritime Historical Radio Society posted:Each year the Cornish Amateur Radio Club organizes International Marconi Day (IMD), an on-the-air event to celebrate the birthday of the Great Man, Guglielmo Marconi, born on 25th April 1874. The IMD event is not a contest: it is an opportunity for amateurs around the world to make point-to-point contact with historic Marconi sites using HF communications techniques similar to those used by Marconi, and to gain an attractive Award for achieving the requisite number of Marconi stations worked. quote:KSM will also be on the air, keyed at various times from the Bolinas transmitter site and from the Marshall receive site. Do you hold a commercial radiotelegraph license? Visit us to exercise the privileges of your license and have it endorsed for operation at KSM. We expect that SS RED OAK VICTORY/KYVM will be operational on MF so you might get the chance to work a ship on 500kc! atomicthumbs fucked around with this message at 20:30 on Apr 3, 2014 |
|
#
?
Apr 3, 2014 19:57
|
|
|
Wasn't APCO 25 crypto broken years ago anyways?
|
|
#
?
Apr 4, 2014 02:45
|
|
|
not the crypto, that's locked down afaik I'm teaching myself L networks today. they're not too complicated, but it's a little tricky and I'm back in Mathville. wish i brought my ti83 today
|
|
#
?
Apr 4, 2014 17:45
|
|
|
built a second preamp and bias-tee for 1090, much simpler since i didn't need a broad-band tee, 100-2000 MHz is fairly straight forward with a coilcraft 90 nH air-core inductor and a ceramic to ground decided to use 3.3V for the supply since that makes it easier to make a low loss protection diode, and the only downside is slightly worse intermod and lower power output (not a problem due to bandpass filters and being a antenna system, not a transmitter driver) i still have one PSA4 left, i might go for the gold and build a preamp for my DV repeater, that will require a T/R switch, making everything far more interesting, i suspect the easiest is to use a mechanical coax relay and run the relay off the bias-power, i think a diode matrix is a sexier solution so i'll look in to that
|
|
#
?
Apr 4, 2014 18:47
|
|
|
i designed a T network for a 5.5 meter vertical (a relatively magic length for upper HF) and hahhahahahaha it's got almost 20% 2:1 swr bandwidth magic i gotta build this now
|
|
#
?
Apr 4, 2014 19:09
|
|
|
BREAKTHROUGH: pi networks and T networks are just two L networks back to back with a shared element and a common impedance in the middle  oh and i designed a network by hand, no wizards or auto calculators, by finding out my antenna impedance at a freq, calculating the equivalent parallel circuit, figuring out how much extra capacitance i needed, etc etc. punched it into mmana-gal and it's accurate to like 1%. holy poo poo i'm learning this for real haha this owns Jonny 290 fucked around with this message at 21:48 on Apr 4, 2014 |
|
#
?
Apr 4, 2014 21:46
|
|
|
well this thread has inspired me to get my licence. test is in a few weeks so its study time i guess currently reading this  while listening to this https://www.youtube.com/watch?v=6Cd9YJvoQIg pretty excited not gonna lie
|
|
#
?
Apr 5, 2014 00:21
|
|
|
that's so amazing and i'm really glad that we could help motivate you. when you get down to it, getting your ticket means being given legal privs to play around with some pretty neat radio equipment, learn a bunch of things and talk to some cool people. the more of us that get on the air, the better it gets
|
|
#
?
Apr 5, 2014 00:33
|
|
|
i hope i don't get in trouble for copy/pasting listserv emails but ugh thanks for the notice. gonna try to get out there early unless landlord replaces stove tmw (lol) I apologize to everyone, Evidently I had typed the wrong email address in it for the listserv somehow. So my emails about tomorrows QSO party never went out. I would still like to do it if anyone else is interested, I will be bringing a radio, tuner, and logging laptop with me tomorrow if someone can bring the coax and antennas over! We have our normal spot at the county central fire station and the Party runs from 9am to 9pm tomorrow (Saturday). Please let me know and again I’m sorry for messing up the emails!
|
|
#
?
Apr 5, 2014 00:36
|
|
|
that sounds fun make sure to try to get up in a field day. last weekend in june. its the super bowl of ham radio, if you hit one thing a year you hit field day (#2 is the local hamfest)
|
|
#
?
Apr 5, 2014 00:42
|
|
|
Jonny 290 posted:that's so amazing and i'm really glad that we could help motivate you. you know you're the Official YOSPOS Elmer now right
|
|
#
?
Apr 5, 2014 00:47
|
|
|
haha i guess so well the official non-catte one
|
|
#
?
Apr 5, 2014 01:02
|
|
|
how many is that now who have passed or are studying to get their ticket since this thread started?
|
|
#
?
Apr 5, 2014 02:51
|
|
|
also i was wondering why the uni pd was so busy tonight then i remembered that nelly has a free concert in the grove on campus tonight. lol.
|
|
#
?
Apr 5, 2014 03:39
|
|
|
|
| # ? May 27, 2024 03:14 |
|
|
Well it looks like everyone is busy or out of town today so we are going to cancel the QSO party. I hope to see everyone at our regular club meeting Monday night at 6 maybe if u didn't wait till 6:00 the night before lol
|
|
#
?
Apr 5, 2014 15:38
|
|