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Why are cellular bands blocked on receivers?

Aug 3rd 2011, 15:28

ka9wgn

Joined: Apr 4th 1998, 00:00
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Note: This topic was moved here from the Welcome to ARRL forum.

I've had this question for a while and been meaning to ask this. But I don't see a particular forum for this kind of question.

Since cellular telephone service on the unencrypted cellular frequencies has ended, why is it that wideband radio receivers still need to have the cellular bands blocked?
Aug 4th 2011, 22:05

WD9EWK

Joined: Apr 4th 1998, 00:00
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Quote by ka9wgn

Since cellular telephone service on the unencrypted cellular frequencies has ended, why is it that wideband radio receivers still need to have the cellular bands blocked?


Because the FCC rules haven't kept up with the
technology. Not only are the two 800 MHz band
segments get blocked, other frequencies in the
receivers that can receive images of signals in
the blocked 800 MHz band segments also get blocked.
Many VHF/UHF FM transceivers that have receivers
that cover into the 900 MHz range have some of
our 902-928 MHz band blocked for that reason.

73!




Patrick WD9EWK/VA7EWK
Aug 4th 2011, 23:51

ka9wgn

Joined: Apr 4th 1998, 00:00
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If someone were to petition for a rulemaking to remove the blocking requirements for those unencrypted cellular frequencies, who would object? Would the cell phone companies still file objections for some reason? Is there a reason such a petition should not be done?
Aug 5th 2011, 16:46

WD9EWK

Joined: Apr 4th 1998, 00:00
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Hiagain!

Quote by ka9wgn
If someone were to petition for a rulemaking to remove the blocking requirements for those unencrypted cellular frequencies, who would object? Would the cell phone companies still file objections for some reason? Is there a reason such a petition should not be done?


In theory, with mobile telephones in the USA now operating on digital networks, our receivers should not have any ability to receive and decode those signals. Maybe a rulemaking petition should be submitted to FCC to remove that requirement. Then again, the mobile-phone carriers may object to changing the rule since it has been in place for so long - "if it ain't broke, don't fix it".

In comparison to how it has been done in the USA, Canada never had rules or regulations that required receivers to block reception of the 800 MHz mobile phone bands. You could purchase receivers, and some ham transceivers, that had the 800 MHz range - and other frequencies, like those at 900 MHz I mentioned before - unblocked. Those radios would generally be more expensive than the USA versions, which would have those ranges blocked.

73!





Patrick WD9EWK/VA7EWK (I live in Arizona, but traveled to Canada often enough to write the ham exams up there in 2002)

Aug 7th 2011, 02:08

ka9wgn

Joined: Apr 4th 1998, 00:00
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I think we have a technical reason to receive at least some of that blocked 800 MHz spectrum (in addition to the image reception that can impact 902-928 MHz). Consider the 869-894 MHz range that is blocked. 869-888 is the 6th harmonic of 144.833333-148 MHz. 888-894 is the 4th harmonic of 222-223.5 MHz. And the entire 869-894 is the 2nd harmonic of 434.5-447 MHz. While even harmonics tend to not be so problematic, I do think it would be good that hams be readily able to get receiving equipment that can pick up these frequencies, to help in our compliance with the technical standards rules.

Also, this blocking is usually implemented in embedded firmware. This probably further encourages manufacturers to keep the control logic of the radios closed. If we are to encourage manufacturers to make radios with more openness (so we can do more independent innovations and carry on our traditions in the more advanced context we have today), having no impediments from regulations that are no longer needed would help. I would include SDR in this, as well, since these rules could also complicate SDR in the marketplace (where we get radios when our innovations involve higher levels of control and automation).
Aug 28th 2011, 13:38

jrincayc

Joined: Apr 3rd 2011, 22:32
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What is the specific FCC law or ruling that prevents receiving the blocked spectrum? (It is rather hard to petition to remove a rule with out knowing which rule we want to remove.)
Aug 28th 2011, 14:07

jrincayc

Joined: Apr 3rd 2011, 22:32
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The law seems to be 47cfr15.121 2(b): (b) Except as provided in paragraph (c) of this section, scanning receivers shall reject any signals from the Cellular Radiotelephone Service frequency bands that are 38 dB or lower based upon a 12 dB SINAD measurement, which is considered the threshold where a signal can be clearly discerned from any interference that may be present.
http://edocket.access.gpo.gov/cfr_2010/octqtr/47cfr15.121.htm

and the Cellular Radiotelephone Service is described at:
http://wireless.fcc.gov/services/index.htm?job=service_home&id=cellular
Jan 29th 2012, 20:44

K8WHB

Joined: Jan 11th 2011, 19:02
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Even if the FCC wanted to change those rules they could not do so UNLESS Congress modifies the Telecommunications Act of 1996 to remove the requirement that the FCC promulgate these rules.
May 25th 2012, 13:02

AF4RZ

Joined: Apr 14th 1999, 00:00
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It is quite interesting that general receivers and expanded receive transceivers have part of the frequencies in the 33cm band blocked but those units designed to operate on that band do not. Obviously those units must receive the frequencies that are blocked on other units. I just doesn't make sense that one type of radio can receive in that range but another type cannot. Are 33cm radios designed in such a way that they would not be able to receive the signal images the rule is trying to protect?
May 25th 2012, 20:40

AA6E

Joined: Apr 4th 1998, 00:00
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I think all you need to know is the principle: "The Law is an Ass".

It seems we need an act of Congress here, so no need to hold your breath.

73 Martin AA6E

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