UHF Offsets

[massarmyguy2]

i was wondering if anyone would know the frequency offset on 440 ham radio the offset is 5000

 

[N0IU]

I am not quite sure I understand the question you are asking...

On 440 (or 70cm), the offset is + or - 5 MHz... which would be 5,000 KHz or 5,000,000 Hz.

 

[ka3jjz]

Actually it's +5 Mhz below 446, above that it's - 5 Mhz. There are areas, however, that use their own unique offsets. These are sometimes referred to as an 'odd split'

You could check our database, or your local coordinator's site (sometimes they publish the freqs of all the coordinated repeaters in their area) to find out whether they're using a plus or minus offset. The links for which (always blue) are below...

Massachusetts Scanner Frequencies and Radio Frequency Reference

NESMC - New England Spectrum Management Council

Mike

 

[kayn1n32008]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9900; en-US) AppleWebKit/534.11+ (KHTML, like Gecko) Version/7.1.0.1047 Mobile Safari/534.11+)

+5 below 445MHz -5MHz above 445MHz 446.000MHz is the Call channel and is not paired, although the - offset may also be used for simplex, or other use. Although band plans are very local in nature, and is not universal.

 

[zz0468]

i was wondering if anyone would know the frequency offset on 440 ham radio the offset is 5000

You just said what the offset was, only you're missing a decimal point...

5.000 MHz.

I am not quite sure I understand the question you are asking...

On 440 (or 70cm), the offset is + or - 5 MHz... which would be 5,000 KHz or 5,000,000 Hz.

Or .005 GHz.

 

[N8IAA]

Or, 5,000,000 Hz :lol:
Larry

 

[KK4TTR]

i was wondering if anyone would know the frequency offset on 440 ham radio the offset is 5000

Hmm, considering this is your first post, did you leave off **TEST POST** from the subject line?

Welcome to the forum!

 

[Plum47]

I took the question to mean why is it a 5 MHz offset when VHF is only 0.6 MHz offset. I was thinking the same thing last night while programming 65 repeaters into my new HT.

 

[zz0468]

I took the question to mean why is it a 5 MHz offset when VHF is only 0.6 MHz offset. I was thinking the same thing last night while programming 65 repeaters into my new HT.

Running duplex, as in a repeater is a tradeoff. It's a tradeoff between transmitter power output, receive sensitivity, receiver bandwidth, available spectrum for separation, and cost.

As you go higher in frequency, it becomes more difficult to build filters and cavities with sufficient Q to provide the necessary isolation to allow a radio to run full duplex without desense. At UHF, the frequency allocations allow a 5 MHz split, which is sufficient for simple and inexpensive duplexers. The amateur split follows the commercial split, because the commercial equipment is all designed around a 5 MHz split.

At two meters, there isn't enough spectrum for a really wide split, and because VHF high band doesn't have a standard frequency pairing, amateurs settled on 600 KHz, because it was workable. It's a reasonable compromise between cost and available spectrum.

I've worked on a VHF repeater system that used 240 KHz frequency spacing, but it took a combination of generous antenna spacing, and lots of filtering on both the transmitter and the receiver. It worked great, but few amateur operators would have put up with the number of cavities that had to be purchased to make that system run. In that case, the compromise was between available frequencies, performance, and cost. The frequencies were what they were, performance would not/could not be compromised, and cost was no object. We made it work.

 

[W8VFD]

There's a 6 meter repeater in my area with a legal limit transmitter and a 240KHz offset, needless to say, there's no receiver at the transmitter site.

 

[Project25_MASTR]

I'm surprised there isn't an official allocation in the band plan for field expedient VHF high band repeaters with a 3 MHz offset.

Reminds me of Texas 6m repeaters. Band plan calls for 500 kHz offset but nearly all of Texas' are at a 1 MHz offset.




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[WB4CS]

I'm surprised there isn't an official allocation in the band plan for field expedient VHF high band repeaters with a 3 MHz offset.

Reminds me of Texas 6m repeaters. Band plan calls for 500 kHz offset but nearly all of Texas' are at a 1 MHz offset.




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In terms of amateur radio I'm not sure what you mean by "VHF high" but if you're referring to 2 Meters, how would you do a 3 MHz offset? There's not enough bandwidth to do so.

A repeater with an output at 145 MHz would need an input of 142 MHz (out of band) or 148 MHz (out of band.) A repeater output on 146 MHz would need either 143 MHz or 149 MHz (out of band.) A repeater output on 147 MHz would need either 144 MHz (technically in band, but would conflict with SSB/CW/Weak Signal allocations) or 150 MHz (out of band.)

 

[nd5y]

Reminds me of Texas 6m repeaters. Band plan calls for 500 kHz offset but nearly all of Texas' are at a 1 MHz offset.

The Texas 6m band plan is for all repeaters to have a -1 MHz offset.
See Band Plans

 

[Project25_MASTR]

The main question, why not go with the arrl band plan?


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[nd5y]

The main question, why not go with the arrl band plan?

I'm not a TXVHFFM member and I don't know their reasons for doing that and other things differently here.

 

[AK9R]

Guys, the thread is about the 440 MHz amateur band and the OP's question was answered two weeks ago.. If you want to discuss the offsets for other bands or localized spectrum management issues, please take it to another thread.