Receiving stations in the 480 MHz band

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lanbergld

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Hello, I live in Richmond VA. I regularly receive transmissions in the 480 MHz band (e.g. 485.2375). These are definitely local taxis, hotels, banquet staff, apartment security and various other utilities. But obviously nothing is licensed for that in that sub-band. I thought that maybe I could subtract 20 and 30 MHz, and ID the stations that way. But still nothing even close to what I'm logging, according the FCC licenses for my city.

Not only do I log these stations on my Pro-2022, but I also did exactly the same with my FRG-9600 and my BCD-996T when I had them. So its not a radio-specific issue.

Can anybody tell me why I receive local utilities & businesses in this sub-band? Thanks.

Larry Lanberg
 

RKG

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Sounds like bootlegging.

Take a look at 10 C.F.R., Part 90, Sub-part L for the rules on licensing Part 90 radio systems in the spectrum range 470-512 MHz in selected geographic regions.

Note that this range is UHF-TV chs. 14-20, which is why it is sometimes colloquially referred to as "T-Band."
 

lanbergld

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Thanks for the reply. Its difficult to believe that security agencies would bootleg, but I suppose anything is possible. I logged well over 20 different agencies last night just between 484 - 486 MHz alone. One of them is a longtime, established taxi company that is listed as using trunked frequencies in the 800 Mhz band.

Also, when I had (both) the BCD-996T and FRG-9600, I was picking up our University police on the 440 Mhz band. They actually use APCO-25 on the 800 MHz band and are trunked right along with our city police. But I was getting their voice transmissions in analog mode around 446-448 Mhz. So this is a longtime mystery for me.

Now I live pretty high-up in the air; way up in a high rise. Maybe its silly, but I don't suppose that would have anything to do with it (?).

Larry Lanberg
 

N8IAA

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Thanks for the reply. Its difficult to believe that security agencies would bootleg, but I suppose anything is possible. I logged well over 20 different agencies last night just between 484 - 486 MHz alone. One of them is a longtime, established taxi company that is listed as using trunked frequencies in the 800 Mhz band.

Also, when I had (both) the BCD-996T and FRG-9600, I was picking up our University police on the 440 Mhz band. They actually use APCO-25 on the 800 MHz band and are trunked right along with our city police. But I was getting their voice transmissions in analog mode around 446-448 Mhz. So this is a longtime mystery for me.

Now I live pretty high-up in the air; way up in a high rise. Maybe its silly, but I don't suppose that would have anything to do with it (?).

Larry Lanberg

Only on the reception end of it. When you heard the university pd in the ham portion of the 440Mhz area, did you also hear them on their trunked system? You would be amazed how many companies don't care about where they trasmit when they can get cheap radios. I am sure that some radios bought at hamfests end up transmitting on frequencies not meant for them to be on. I have heard taxis broadcasting on the 2m portion of the ham band and on 440Mhz where I live. It doesn't last long, they get caught by the local hams and are warned about what they are doing.
Larry
 

ecps92

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485.2375 would be an input [based on normal use] are you hearing this as a REPEATER or simplex?

I'm guessing it's an Image Frequency, altho you hear them on multiple radios.. When they are talking, use another radio to search the 450-455, then 455-460, then 460-465, bands [better to chunk them up than search 450-470] after ruling these out, try the 470-512 band, it might be an upper image vs the lower

Hello, I live in Richmond VA. I regularly receive transmissions in the 480 MHz band (e.g. 485.2375). These are definitely local taxis, hotels, banquet staff, apartment security and various other utilities. But obviously nothing is licensed for that in that sub-band. I thought that maybe I could subtract 20 and 30 MHz, and ID the stations that way. But still nothing even close to what I'm logging, according the FCC licenses for my city.

Not only do I log these stations on my Pro-2022, but I also did exactly the same with my FRG-9600 and my BCD-996T when I had them. So its not a radio-specific issue.

Can anybody tell me why I receive local utilities & businesses in this sub-band? Thanks.

Larry Lanberg
 

W4KRR

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Hello, I live in Richmond VA. I regularly receive transmissions in the 480 MHz band (e.g. 485.2375). These are definitely local taxis, hotels, banquet staff, apartment security and various other utilities. But obviously nothing is licensed for that in that sub-band. I thought that maybe I could subtract 20 and 30 MHz, and ID the stations that way. But still nothing even close to what I'm logging, according the FCC licenses for my city.

Not only do I log these stations on my Pro-2022, but I also did exactly the same with my FRG-9600 and my BCD-996T when I had them. So its not a radio-specific issue.

Can anybody tell me why I receive local utilities & businesses in this sub-band? Thanks.

Larry Lanberg

Try programming 463.5375 and see if you hear the same transmissions that you hear on 485.2375. If you do, it's because 463.5375 is a harmonic of 485.2375, at least on some models of scanners.
 

ecps92

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Also the image does work the other way, also try 506.9375 IF that works you can always use +/- 21.7 Mhz as your image

Try programming 463.5375 and see if you hear the same transmissions that you hear on 485.2375. If you do, it's because 463.5375 is a harmonic of 485.2375, at least on some models of scanners.
 

W4KRR

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Also the image does work the other way, also try 506.9375 IF that works you can always use +/- 21.7 Mhz as your image

Yes, but there are no licensed users on 506.9375 in Virginia, but there are licensed users on 463.5375. There are also no licensed users on 485.2375, so I'm guessing the actual transmissions are in the 463MHz band, and the OP is just receiving an image. I guess bootleggers are possible, but not for so many different users on one channel. I would further guess it could be part of an LTR trunked system in the 463MHz UHF band, which are common all over the country.
 

lanbergld

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Ken and Bill: Thank you for +/- info on the harmonics & images. There has to be rational explanation outside of bootlegging. I will try this tonight when I come home. I will let you guys know.

And thanks also N8IAA for your response. But I can definitely rule-out our University police force bootlegging on cheap radios. I do pick them up on the 800 MHz trunking -- or at least I did when I had the BCD-996T which I no longer have. Plus our school (which I'm an employee of) is a state funded university with over 34,000 students. No mom & pop pirates here. :)

To answer another question: I receive both the mobile & base on the same transmission -- just like a normal operation. And its the same frequency by the same agency every time. Furthermore, these are fantastic sound quality for images. Usually I can tell an image right-off just by its slightly distorted sound.

I will check-out all of your suggestions later. You all have a great day.
 
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LMR use in the 470-512 band is authorized in the state of Virginia. Search the FCC database for Virginia from 470 to 512 MHz, you will find quite few licensed systems most are trunked.
 

lanbergld

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Well, the ( +/-) 21.7 MHz test did not pan out. It doesn't even jibe with the FCC licenses issued for this area. I actually thought that would be the most likely explanation. One of these stations sounds like a heliport for MedFlights ("The crew is on the pad waiting for your arrival" 2045 hrs EST 09182008). The others are hotels, taxi companies (2) and security agencies. I just haven't yet ascertained which business these are, with the exception of one of the taxis. And there are no local licenses for the 480 MHz band whatsoever.

They definitely sound like Txs one would normally hear on the 460 Mhz band. But a mathematical pattern of offset escapes me right now.

I am getting ready to monitor this band again & log. All I know is that this 480 Mhz band is very interesting to listen to all of a sudden :).
 

n1das

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Well, the ( +/-) 21.7 MHz test did not pan out.

Try 21.4 MHz instead of 21.7MHz.

I had a PRO-2022 years ago. I still have it actually but no longer use it. The 2022 the base/mobile version of the PRO-34 handheld and were made by GRE for RadioShack. They use a 10.7MHz 1st IF, with low-side injection of the local oscillator, so your image freq will be 21.4MHz above the actual freq and probably what you're hearing.

The 2022 is an old double-conversion receiver and is poorly shielded and has VERY POOR image rejection. In the 800MHz band, the local oscillator is injected into the 800MHz front end 10.7MHz ABOVE the desire freq instead of below it. That means in the 800MHz band, the images will be 21.4MHz BELOW the actual freq. In the 800MHz band, I found it next to impossible to listen anything in the 851-868 range because a VERY busy portion of the 800 band now censored from newer scanners had its images fall in the 851-868 range. Not only that, the received signal strength was as strong as if you were listening on the actual freq instead! This scanner was rendered USELESS for monitoring anything in the 800 band except to listen to the "censored" band!

I think the fact you're also hearing it on other receivers too may be a coincidence because they may also have the same 1st IF freq. I would not trust a Yaesu FRoG-9600 either. A good sanity check would be to listen on a newer scanner that has a triple conversion IF system.

I'd say the only positive side effect of the cell phone frequency censorship is it forced the scanner's receiver design quality to improve. That's why I say listen on a good ham portable or a newer scanner that's not more than about 5-6 years old. The scanners have an image rejection spec they have to meet (enacted by FCC rules in Feb 1999) in order to comply with the cell phone frequency censorship requirement in federal law. The quality of the receiver's design had to be improved a LOT in order to meet the new spec.

Good luck.
 
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lanbergld

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Ok guys -- its solved. In my case its (+/-) 21.4 MHz. This is why I hear the transmissions on the 480 MHz. I amazed that the images come in so well -- they literally are spitting images of the actual. So cased closed. Thanks a lot guys for all your advice. This gives me an added bit of knowledge I didn't previously have.

Larry Lanberg
Richmond VA

Yaesu FRG-100
Realistic Pro-2022
various homespun antenna systems
 

lanbergld

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David, I got your post just after I posted my last. We must've submitted at the same time. The specifics you provide are right on cue with what I observed a little while ago.

Just as an aside, I also had a Pro-2022 in the late 1980s. This one here is my second. Its not that I like this scanner very much (sound quality is horrible), but family necessity, a few months back, dictated that I sell my good ones. I found this model for $50 and saw a golden opportunity to at least continue monitoring VHF/UHF. But anyhow thanks for the specific info Dave.

Larry Lanberg
Richmond VA

Yaesu FRG-100
Realistic Pro-2022
various homespun antenna systems
 

ecps92

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Each of the Manuf's uses different IF's, even different models. It's RARE to find the bootlegger but they are there, most within common channels [my experience] not outside the band-plan for your region [attracts FCC attention that way], except some of the LP [Low Power] Police usages [try the inputs]

Glad to see it worked.

Ok guys -- its solved. In my case its (+/-) 21.4 MHz. This is why I hear the transmissions on the 480 MHz. I amazed that the images come in so well -- they literally are spitting images of the actual. So cased closed. Thanks a lot guys for all your advice. This gives me an added bit of knowledge I didn't previously have.

Larry Lanberg
Richmond VA

Yaesu FRG-100
Realistic Pro-2022
various homespun antenna systems
 
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