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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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1st Sep 2018, 11:24 am | #1 |
Octode
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
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Airband receiver.
Hi Peeps. As a diversion to my Multiband SSB transceiver... I re visited my portable Airband receiver. As it is for "Local field" reception, i.e end of runway, it does not need to be "high spec". However the previous iteration, did not have a frequency read out, it had two specific channels which were set before setting out. This was / is a bit inconvenient.. so I rebuilt using a Frequency counter module from ebay. I replaced the two preset tuning pots with 10T external adjustment types... again sourced from China. This works ok and is reasonably stable........
I fitted a DC switch to turn off the display when not required, to conserve the batteries (120m/A)But one thing I noticed.. on the lower end of the band, 120.3 Mhz there was a definite reduction of noise. This is obviously being generated from the clock of the counter. I could go the total solution and EMC screen the display, and decouple to death the supply lines,,, but the switch works ok. Another problem... when I park at a location, there is a high noise level, and the Tower / Radar controll radio's are barely readable. I discovered that after 5 mins the noise disappeared completely....My Dashcam stays on for 5 mins after power off, i.e ignition power. Using my spectrum analyzer I found a heck of a lot of wideband hash from the camera.. With the radio in the car, using an extending rod aerial, it is / was impossible, but using an external vertical and magmount.. problem solved totally. Ah well back to the multiband.
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Should get out more. Regards Wendy G8BZY |
1st Sep 2018, 1:19 pm | #2 |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
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Re: Airband receiver.
Very interesting about the hash from the dashcam. I’d not thought that they might do that, perhaps there’s an SMPS running in there. I would not have thought the GPS would radiate, it’s a receiver isn’t it?
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Richard Index: recursive loop: see recursive loop |
1st Sep 2018, 1:40 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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Re: Airband receiver.
I once found a bit of GPS kit in a pond. It was IP68 and was dry inside.
Every power rail had a 1Mhz down converting chopper regulator across two PCBs. I know as I looked the chips up on line. |
1st Sep 2018, 7:25 pm | #4 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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Re: Airband receiver.
The dashcam I recently fitted in my wife's car radiates like a good 'un. Blots out the local FM radio station she normally listens to. I have tried all sorts to reduce the interference, as I originally assumed it was coming from the cigar plug regulator, but no, it's coming from the camera. My dashcam which I have had for a few years radiates spurious signals when powered up, one of which unfortunately falls on one of my local repeater channels. I managed to reduce that a bit by installing a clamp on ferrite choke and also wrapping the power cable round a toroid.
Alan. |
1st Sep 2018, 7:29 pm | #5 |
Octode
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
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Re: Airband receiver.
Hi Biggles... I also tried ferrite clamp cores on the DC Lead to no avail... I guess its the local clock for the camera cpu and the GPS clock... dunno which, but a mag mount sorts out the QRN
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Should get out more. Regards Wendy G8BZY |
1st Sep 2018, 7:35 pm | #6 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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Re: Airband receiver.
It's certainly an annoying problem.
Alan. |
2nd Sep 2018, 7:19 am | #7 |
Octode
Join Date: Jan 2004
Location: Southport, Merseyside, UK.
Posts: 1,156
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Re: Airband receiver.
My dashcam interferes with the car radio if it's powered from the cigar lighter, but when running it off a 'portable power bank' which I do almost all the time there's no problem.
John |
2nd Sep 2018, 10:32 am | #8 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
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Re: Airband receiver.
Isn't it QRM?
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....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
2nd Sep 2018, 11:12 am | #9 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
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Re: Airband receiver.
That's interesting John. Sounds like the interference is actually getting back into the wiring loom of the vehicle, rather than being radiated as I originally assumed. I have a 12V gel cell so I will try powering it up from there, although it will still be through the cigar plug gadget to the dashcam. Worth a try. Surely the "general public" must have experienced similar problems by now. I haven't heard much said about it though. Maybe nobody listens to analogue radio in the car any more.
Alan. |
2nd Sep 2018, 11:55 am | #10 |
Octode
Join Date: Jan 2004
Location: Southport, Merseyside, UK.
Posts: 1,156
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Re: Airband receiver.
I've just Googled 'dashcam interference' which I've not done before and there seems to be a lot of problems from dashcams with regards to DAB radios SatNav systems etc.
John |
2nd Sep 2018, 2:02 pm | #11 |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
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Re: Airband receiver.
Of course, a lot of modern cars use a networked wiring system which might be more susceptible to supply-bourne interference. My car is 46 years old so maybe doesn’t suffer so much.. and I have an old FM radio with minidisc player which is quite bomb-proof!
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