UHF Offsets

Status
Not open for further replies.

massarmyguy2

Member
Joined
May 31, 2014
Messages
1
i was wondering if anyone would know the frequency offset on 440 ham radio the offset is 5000
 
Last edited by a moderator:

N0IU

Member
Joined
Sep 26, 2009
Messages
802
Location
Wentzville, Missouri
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

Wiki Admin Emeritus
Joined
Jul 22, 2002
Messages
23,220
Location
Bowie, Md.
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

ØÆS, I put that shØt on everything.
Joined
Sep 20, 2008
Messages
6,172
Location
Sector 001
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

QRT
Joined
Feb 6, 2007
Messages
6,036
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.
 

Plum47

Member
Joined
Jun 14, 2014
Messages
5
Location
Texas
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

QRT
Joined
Feb 6, 2007
Messages
6,036
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

Member
Feed Provider
Joined
Jul 8, 2005
Messages
198
Location
Northeastern Ohio
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.
 
Joined
Jun 16, 2013
Messages
3,565
Location
Texas
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.




Sent from my iPhone using Tapatalk
 

WB4CS

Member
Joined
Feb 10, 2005
Messages
900
Location
Northern Alabama
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.




Sent from my iPhone using Tapatalk
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.)
 

AK9R

Lead Wiki Manager
Super Moderator
Joined
Jul 18, 2004
Messages
6,478
Location
Central Indiana
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.
 
Status
Not open for further replies.
Top