Modulation Uniden UBC125

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Modulation Uniden UBC125

Postby spaceman76 » Sat Aug 19, 2017 11:15 pm

Hi, im new to scanning and since i got my scanner yesterday im not really sure what im doing, however have found that London Busses are are busy around 239.6700 FM. Anyhow what I need to know about is when im searching (usually through every bank), is how to know what modulation to use (FM or AM), for the bandwidth. Are the preset modulations for the widths all well and good ?? Like say im searching a bandwidth on AM (and picking up channels), is it possible that im missing other(FM) channels on this same frequency ? I cannot get my head round this. What are the (rule of thumb) modulations for widths, if that makes any sense ? Or am i missing something. Thanks BTW anyone have any frequencies for the Bromley, Kent area ? Im getting alot of London Bus activity in North London area and thats more than 20 miles away, which is good !
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Re: Modulation Uniden UBC125

Postby alpha_india » Sun Aug 20, 2017 12:04 am

I'm pretty sure that in Search mode modulation doesn't apply, you're searching between a lower and upper frequency and the scanner will identify the correct modulation.

But.. although I'm a UBC125 user, I very rarely Search. I'm almost always in Scan mode against frequencies I've loaded into the scanner using Scan125. My main interest is airband, but I'll also have a scan through the standard 433/466/SUKL/Events and the default Baofang channels.

Limiting your Search to a narrower frequency range or your Scan to fewer banks will be more efficient.
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Re: Modulation Uniden UBC125

Postby spaceman76 » Sun Aug 20, 2017 12:18 am

Okay thanks, noticed that im not recieving any Ham, is this because the aerial (Watson 881) is not up to it, or the UBC125 is not powerful enough ?
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Re: Modulation Uniden UBC125

Postby alpha_india » Sun Aug 20, 2017 1:14 am

If you're listening to the right frequencies and it's all quiet, it's more likely that it's because nobody is broadcasting.. at least round here there's not a lot of ham activity, just a couple of old boys chewing the fat on a Saturday morning.
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Re: Modulation Uniden UBC125

Postby m0lsx » Sun Aug 20, 2017 8:59 am

spaceman76 wrote:Okay thanks, noticed that im not recieving any Ham, is this because the aerial (Watson 881) is not up to it, or the UBC125 is not powerful enough ?



If you are listening to simplex frequencies, then with a handheld antenna don't expect any great distances. Maybe a mile or two at the most. With repeaters maybe 10 miles. You could hear people from further afield, but don't expect it.
What you hear will depend upon both your antenna & the other antenna & the path between you. So at the top of a tower block which is on high ground expect many miles, in a bungalow at the bottom of a hill expect very little.
Buildings, hills, trees almost everything will attenuate a VHF/UHF signal.
What you hear will also depend upon the time of day & the day of the week. A commercial airport is all day, 7 days a week, all year round. But a small club airfield may be very quiet mid week & during the winter months. While a shipping frequency could be just once or twice a week for a few minutes each time. And a business may not use a radio at all at the weekend or evenings, while a tourist attraction may mainly use the radio at weekends.
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
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Re: Modulation Uniden UBC125

Postby Minus1 » Sun Aug 20, 2017 9:19 am

London Buses do NOT transmit on 239.67, that is in the NATO military band!
You must be very close to a transmitter and picking up a ghost signal.

London Buses previously use frequencies between:
Base: 139.5-140.5 MHz, 12.5 kHz channels, 6.25 kHz offset
Mobile: 148-149 MHz, 12.5 kHz channels, 6.25 KHz offset

Now they use:
Base: 152.5 - 152.9875 MHz, 12.5 kHz channels
Mobile: 147.5 - 147.9875, 12.5 kHz channels (i.e 10MHz below the base frequency)

Plus a few other VHF channels.

The scanner does not necesssarily "identify the correct modulation".
It uses preset the modulation defined in "Band Plan 1" (which is vaguely set for 'Europe' and not specific to the UK).
Adjustable under under [Func Hold].
Most of the time it is correct.
Most transmissions these days are FM, the notable exceptions are civil and military air.

Most business bands use 12.5 kHz channels (so x.0125, x.025, x.0375, etc), a few have channels offset by 6.25 kHz (so x.00625, x.01875, x.03125, etc
It doesn't handle 12.5 kHz channels offsets by 6.25 kHz properly (it's a daft OFCOM notion), so you have to scan twice as many freqs as you actually need to.
Again defined under "Band Plan 1" and adjustable under [Func Hold]

So whatever you think you are getting on 239.67, you will actually find around 152 MHz, with many similar transmissions.
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.
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Re: Modulation Uniden UBC125

Postby spaceman76 » Sun Aug 20, 2017 5:27 pm

Thanks for the response; can you recommend any good books for someone (like myself) new to scanning; explaining the principles of wavebands ect. Its all greek tome this MHz, KHz, offset ect ect. With my Watson 881 aerial im picking up mostly airbands, and London Buses, although i did chance upon a Ham this morning when I went to a (Greenwhich) park with a big hill. I have noticed thou that im not getting any marine atall, even though I walked along the Thames at Greenwhich earlier, Im thinking maybe the Watson 881 is no good for marine, they are mostly still analouge right ?

Regards

James
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Re: Modulation Uniden UBC125

Postby alpha_india » Sun Aug 20, 2017 10:09 pm

How are you using the scanner James?
- are you scanning or searching?
- when are you listening? remember that marine activities are tidal with most ship movements occurring either side of high tide

If you're Scanning..
- what frequencies do you have installed in the memory banks?
- have you got any empty memory banks at the moment?

If you're Searching..
- what are the frequency bands your searching?
- how many are you trying to search at once?

And where are you in relation to likely marine traffic? You need height to get a signal path, if you're a ground level trying to pick-up ground lever transmissions (by definition marine users are at or close to sea level) then you're not going to have much success over distance. Air band is easier because one half of the conversation is being broadcast at altitude. Get high or get the antenna higher. I switch between a Nagoya whip (similar to your Watson) and a loft-mounted bowtie antenna. Just going to the first floor with the whip antenna gives me a huge improvement in reception, switching to the loft antenna gets me an even greater improvement principally because it's higher.

The marine bands are known frequencies, it's easiest to follow these by Scanning but you must have them programmed. If you're in London the Port of London Authority publishes their contact procedures, so which frequencies will be in use at different point on the river - https://www.pla.co.uk/assets/London_VTS ... mation.pdf
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Re: Modulation Uniden UBC125

Postby Minus1 » Mon Aug 21, 2017 8:07 am

OFCOM's spectrum map is a start
http://static.ofcom.org.uk/static/spectrum/map.html
but it's very poorly designed, is not to scale (a single channel can look as big as an entire band), does not show frequency steps nor modulation, does not show users in much detail.
So it needs much deciphering to extract anything useful.

Marine channels are between 156.0 and 163.5.
They are all FM, 25 kHz channels.
There is a 4.6 MHz split between base and mobile, some channels are simplex.
Start at 156.8 (Channel 16).
See http://coastalradio.org.uk/vhfchann.htm
Yes, most, if not all are still analog, channels allocated for digital are new, and probably little used yet.
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.
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Re: Modulation Uniden UBC125

Postby spaceman76 » Mon Aug 21, 2017 3:10 pm

Thanks for replies, ive got the hang now of searching individual banks, and understand now that I can only scan entered frequencies. While at the River Thames yesterday at Greenwich, I did not specifically scan from 156.000 to 163.000 as advised, maybe thats why I did not pick up any marine; but i will try again in the future on that (is it called a range ?).

A couple more questions for you thou if you dont mind; why/how is channel 16 related to frequency 156.8 ?? This frequency is located in bank 7 on my uniden125 !
What are channel numbers ? I was assuming a channel number was a certain frequency ?? Can I search channel numbers (is this possible) ?

Also, would i receive a better reception by entering an exact frequency (via the quick search function) and toggling through, than if searched an entire bank (frequency range) ? I get the feeling that searching an entire range will miss things.

Im well aware that my "radio" nomenclature is virtually non-existent, any good books anyone can recommend to explain the basics (for a beginner like myself) ??

Thanks all
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