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+--- Thread: 70cm Noise Floor (/thread-501.html)
70cm Noise Floor - VK2FAK - 31-01-2018
Hi all..
I seem to be seeing more and more crap turning up inside the 70cm Sat segment of the band, where I was in the past having no issues gathering the TLM form Sat's its now getting harder and harder.
Using HDSDR the floor was around -111dB as indicated . with intermittent bounces in the Floor level.. and also with intermittent bursts of other TX .
Would be interested to hear from other on there situation, and if they managed to clear it up and how.
One issue of mine is, using a wideband preamp up front, this really cant be helping, was looking at tossing in some filters, or coax stubs to see the effect of block noisy signals lower down in Freq.
John
RE: 70cm Noise Floor - VK1JA - 31-01-2018
I found that our wireless weather station and wireless energy monitor use the 433MHz band to transmit data between their remote and head units.
While the weather station isn't to bad, the energy monitors output is very dirty/broad and I can noticeably hear an increase in the noise floor 1 to 2MHz away from the freq it's transmitting on !!!
It seems there aren't many rules around devices in this band
RE: 70cm Noise Floor - VK2FAK - 31-01-2018
Hi....
I was reading ACMA had approved the use of 433-434 (from memory) for these type of devices, but there was a limit of about 25mW allowed........even so, that would be easy to hear with an antenna on 70cm from some distance away. No mention of how clean the signal had to be, which is typical here.
RE: 70cm Noise Floor - VK4ADC - 31-01-2018
Remember that almost all LIPDs at 434 MHz are a digital FSK or spread spectrum and either will occupy a significant band of frequencies across the 430-440MHz segment of the amateur band, the closer you are physically then the worse the QRM becomes. I suspect the SAW oscillator devices aren't necessarily right on frequency either, the cheaper they are then the poorer the tolerances.
I have also run across car entry keyfobs/systems on 434 as well as the wireless weather, wireless doorbells, etc - the list is long.
LIPD : Low Interference Potential Devices
https://www.acma.gov.au/Industry/Spectrum/Radiocomms-licensing/Class-licences/lipd-class-licence-spectrum-acma
RE: 70cm Noise Floor - VK2FAK - 01-02-2018
Hi all....
further to my looking for signals that could mess up the SDR input on 70cm.......scrolling down the freq....I have come across a booming FM radio source playing music. its way outside the FM broadcast band, its not inside the digital radio band, its on 152.124 MHz.
Anyone have an idea what this station is, or at least confirm that its there.....in the Sydney area.
John
RE: 70cm Noise Floor - VK3QI - 01-02-2018
John,
The ACMA register is your best friend here.
Cheers
Peter VK3QI
A quick search 100 kms radius from central Sydney reveals:
Searched From Location: SUITE 2001, LEVEL 20, 15 Castlereagh Street SYDNEY NSW 2000
ID
Frequency
Emission Designator
Authorisation Date
T/R
Client
Licence
Site
Distance
Elevation Profile645985
152.125 MHz
16K0F3E
12/Apr/2006
T
Apostolos Vasilopoulos (1138673)
John,
I should have added that if you go to the ACMA register and enter the name or licence number, you can find the address of the particular assignment and can make a judgement as to how strong the signal would be in relation to your location.
I had a quick look and the location is Heckenberg 2168 and I see that you are Ashcroft 2168
Me thinks you are neighbours! That would explain a lot.
Regards
Peter VK3QI
RE: 70cm Noise Floor - VK2FAK - 01-02-2018
hi
Thank you for that, saved the address of the ACMA Register..
That guy is not to far away, probably only a dozen or so streets, how would he get a broadcast Lic, to play music, the area already has an FM broadcast station.
Besides who would have a radio to pick up his Broadcast....?
John
RE: 70cm Noise Floor - VK3YCQ - 01-02-2018
Hello John,
FM transmitters like the ones near 150 MHz have been around for decades. They generally seem to be narrowband (read 'crap audio quality') and often confined to particular ethnic groups or audiences with specific interests. A very quick search on Google gave me this example http://www.radioena.com.au/
Some of these transmitters have been known to use strange methods to stop general listeners tuning in, extracting money from listeners for a suitable decoder box.
cheers,
Ian
RE: 70cm Noise Floor - VK4ADC - 01-02-2018
(01-02-2018, 01:47 PM)VK3QI Wrote: 16K0F3E
The emission mode is the same as our old 25KHz channeling on 2M so one wouldn't really expect wideband FM (88-108) quality. Only Narrowband transmissions are allowed in that section of the spectrum given that it is surrounded in frequency by normal high-band radiocom facilities (most likely still also all using "25KHz modes").
RE: 70cm Noise Floor - VK2FAK - 01-02-2018
Hi all,.
Well blow me down, learn something every day. Thanks for that info, if I was not searching for problems with an SDR I still would never had known, And yes this is an Ethnic broadcast, and I must say the music being played is not bad at all, quite enjoyable.
John