ElfnetCommunications
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Posts posted by ElfnetCommunications
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I found a GOLAY paging system on 42.180 MHz yesterday. I though all that was dead.
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They are smaller and do run warmer than my others (All my SDR's run warm).
I got two of these small SDR's for my NOAA HRPT dishs so I can conceal them in the LNA arm easier.
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Yes, That be CB Radio!
Normally uses AM, Upper Sideband (USB) Lower Sideband (LSB), there should be approx. 40 channels in that space.
There's actually something like 8 banks of 40 channels globally. The US uses band C or D, I cannot remember.
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This is interesting. So could I use part of my old DirectTV dish to make one of these and if so what part(s) would I use. Thanks.
No the new dish's usa an LNA (Low Noise Amplifier) that requires 24 V phantom power to drive it from the receiver box. The down converter I have came off an old C band type dish (Big black mesh type)
Now you can use the actual parabolic dish of course but the head LNA or LNB as some call it is somewhere in the 25 GHz area i think and your DTV box receives it as-is and converts it all internally.
I am no direct TV expert in fact I hardly ever watch TV.
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What freq. range are you trying to get? I know for 2.4GHz there's a fairly inexpensive wifi web cam set up that has a 2.4GHz dongle that comes with it and you can use there for that freq. range. I'd like to go the other way, down to the AM radio and HAM bands but those boards are in the $50-$60 range so it's not going to happen any time soon.
Look on ebay for the "Ham It Up" board. I saw it there for $30 and free shipping last week.
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also..... most of the small jumpers from MCX to SMA...even the "F" are made with RG316 cable... which is also 50 ohm.... Why does everyone use 75 ohm cable to make antennas for 50 ohm radios (DVB-T Dongles) ?
Because TV cable can be literally found anywheres for free.
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One USB SDR mod I did was internal shielding to lessen the outside RF from getting into the radio. Second thing I did was remove the USB connector and put in a pig tail without a shield braid in it. This also keep computer side RF out of the radio. A design flaw in most all SDR's is the USB shield ground and the USB -5 VDC lead are tied together electrically and this in turn turns the whole USB cable shield along with shield grounds in your PC into an antenna thar feeds direct into the radio thus causing a high noise floor and random spurs from PC clock interference.
Easy shielding can be done by wrapping the sdr in plain tin foil and using an extension USB cable that has no shield braid.
As for the antenna connectors I left mine intact and just purchased some adapter pigtails to take it to an "N" type connector.
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I think a transmitter that is able to transmit over a wide area of the spectrum and will be available to Joe Public is a terrible idea.
I know responsible people will buy them and those will only transmit where they are allowed to but we all know their are those out there who will but it just to cause issues.
For example you cannot transmit on the aircraft band 108 - 137 MHz but their will be someone who does it anyways and next thing we know the FCC with Homeland security is banning the boxs and dongles all together in the US.
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Found one more thing:
http://www.instructables.com/id/How-to-Make-a-19-Police-Radio-Scanner/ - this build uses SDR# and some trunking software to work with police radio better.
Police radios use trunking. In this case trunking refers to system that allocates different calls to different frequencies automatically. Think old style telephone systems where pretty ladies were plugin telephone jacks but automated =). This software puts it all back together. Hopefully, folks will mention trunking in their next video if there is one.
not all public services use a trunking system. True most in cities do but if your in a small town chances are they do not.
To track a trunking system you have to first understand what your going to be dealing with.
Depending on what type of system it is will depend on how you will need to configure your radio.
Their are several different types of trunking systems here are a few:
LTR
EDACS Analog
EDACS Digital
Passport
MPT1327
SmartNet
SmartZone
OpenSky
In the actual 2-way radio the police carry. Normally their will be 2 - 10 frequencies programmed in. these are control frequencies. These channels tell the radio to sync up, authenticate and emulate the voice traffic frequencies. The actual talkgroups are also programmed by the radio shop and not emulated.
To me it is less headache to just buy a police scanner and set it up than to try to trunk track on an SDR dongle.
Now tracking and listening in on a P-25 system may be worth it though
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Some frequencies that may be worth listening and/or decoding:
26 - 27-405 MHz - 11 meter CB Radio band
28 - 30 MHz - Generally the 10 meter ham radio band. With a good antenna you can hear voice and data communications between hams across the world
137.100, 137.500, 137.620, 137.9125 MHz - Weather Satellite APT, Receive live images from polar orbiting weather birds
144 - 148 MHz - 2 meter ham radio band. Local ham radio repeaters, beacons, etc
150 - 160 MHz - Commercial and public safety band. 154.600 for example is MURS green dot and also used by McDonalds drive thru.
157.740 MHz - US paging frequency using Pocsag formats
160 - 162 MHz - US Railroad band - Union Pacific is 160.740 MHz where I am
162.400 - 162.575 MHz - US NOAA weather 24/7 broadcast
220 MHz - 220 ham radio band (not sure of the exact spread of this band yet)
220 - 390 MHz - US Military bands. USAF is AM Mode and 220 - 300 MHz.
315 MHz area is used widely by remote controls for car alarms and garage doors
406 - 420 MHz - US government trunking systems. USAF security police use this also
420 - 450 MHz - 70cm Ham radio band
450 - 451 & 455 - 456 MHz - TV and radio station live remote units
451 - 455 MHz - Commercial Industrial business band and Public safety
460 - 465 MHz - Commercial Business and Public safety band
470 - 512 MHz - UHF "T" band
822 MHz area is /was old analog cellular NON GSM systems voice carriers.
850 - 869 MHz - Commercial and Public safety trunking band
920 - 1300 MHz area is ISM band along with another ham radio band or two
1420.50575 MHz - Hydrogen Line used by SETI
2400 + - Wireless ethernet systems, STL systems, satellite TV and Radio systems
NOTICE! When tuning frequencies from 1 GHz and up be aware that you may get a lot of spurs from your computers CPU clock.
Also you DO NOT want to run a usb SDR dongle on a desktop or laptop while it is powered by a 12 VDC to 120VAC inverter that is modifies sine wave. This will cause a lot of unwanted noise and interference in the radio.
Also same as above when you get in proximity of a power inverter you will pick up a lot of noise as well. proximity is estimated at least 50 feet from some inverters.
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Paging systems range in operating frequencies
in the 90's most operated in VHF-Hi band on 157.740 or 152.480 but traffic there is now very very rare.
800MHz systems are more likely to be police, fire, or ems related where 900MHz systems are general usage.
if you have a volunteer fire dept and know the frequency they use for radio comms then chances are they will have pagers on that frequency if they have a paging system. most fire type pagers are 2-tone voice with a Pocsag 1200 or 2400 piggyback. In house hospital and trauma dept pagers will most likely be pocsag 512, 1200, or 2400 or a mix of each including flex 9600.
back in the 90's radio shack marketed a private paging system that operated on 27.145 Mhz i think is what it was.
A good tool to have aside from you sdr is a pretty decent handheld police scanner so you can band search for things and make notes when you dont have your computer setup on hand.
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You can use microwave down converters from old system TV dish systems. One that I am using takes 3 - 15 GHz down to the 900 MHz band.
To go into HF ham bands you can get a USRP with the proper daughter board or build your own simple sdr to match which ham band you want to tune.
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Normally one would want to have a band related antenna that matches the frequency or band you intend to receive. But if you intent is a broad range reception then look into antennas for scanner radios that run from 30 MHz to 1.3 GHz for starters.
Think of a receiver antenna as an ear. The bigger the ear the more it hears.
Also the antenna is only half of a radio.
TV Antenna as an SDR Antenna?
in SDR - Software Defined Radio
Posted
The stock dongle antenna is whats called a "Unity Gain" antenna.
If you do not have a specific target frequency or band you can use a TV antenna or better yet a Discone scanner antenna.
For NOAA LEO APT on 137 MHz you need a Right Hand Circular Polarized Quadrifillar Helix Antenna or a Cross Dipole Antenna.