View Full Version : Does anyone use 70cm/440 MHz?

02-15-2008, 11:48 AM
We all have dual band radios but it seems that 2m gets all the attention. Why wouldn't we want to do simplex in the 440 range? Are there any repeaters on 440? Just wondering.

I wanted to get a higher gain antenna for my truck and a wondering if a dedicated 2m mast would be better than a dual band.

Uncle Ben
02-15-2008, 12:16 PM
I have played around a tad on 70CM. Basically, the same as 2M but less folks. Using it would cut out those folks with only 2M radios. Also, most radios put out less power on 70cm so there might be some range issues....I don't know....but I am very willing to play!

02-15-2008, 03:21 PM
I did it one time to access one of those Expedition Portal nets, because that's the repeater that Blake set up on IRLP. Haven't been back since.

Would be in to trying it some time on a trail run though, just to see what the performance is like. Maybe in June when we're all on I-70.. ;)

02-15-2008, 03:31 PM
Actually speaking of that (and going off topic in two different directions)

1. Would not the best (fastest) route west to Rubithon be to go up to I-80 then across?
2. What about 6m and 1.25m? Are those accessed by the standard rigs we in the club have been buying up? And are those accessible bands by a technician and/or general license?
3. Okay a 3rd - wouldn't Moab be a likely time to maybe try it first? Doesn't matter, just trying to jump the gun :D

02-15-2008, 03:49 PM
UHF is good for caravans because it's somewhat more immune to interference, because... Anyone? Anyone?

What are a couple of the propagation properties that make UHF nice for simplex talk groups? It's not a mistake that FRS radios were put on UHF, for example.

Also, UHF can be interesting because of what environmental phenomenon? Anyone? It happens over large geographical features, like oceans and near mountains often.

02-15-2008, 03:54 PM
a. higher freq

b. Shorter distance propagation ?

c. It'll bounce off of stuff.

02-15-2008, 04:03 PM
a. more energy, so electromagnetic field is harder to disrupt.

b. ?

c. critical angle of incidence for reflection is higher so it reflects off terrain features better?

02-15-2008, 04:22 PM
Hey Bruce, you already have your ticket, no cheating.
a. higher freq
It is absorbed more readily by vegetation and objects and does not bounce well. UHF doesn't really experience tropospheric bending and sporatic-E & F-layer skips or meteor reflection like lower VHF. It also does not favor sky wave propagation like VHF, so it tends to be even more line of sight than VHF and much more so than HF. With UHF generally if you don't have a good LOS, you probably aren't gonna communicate.
b. Shorter distance propagation ?
Higher frequency means shorter antennas and longer antennas tend to be more directional. But see (a) for why the FCC put FRS there, it tends to stay more local and so you get less interference using a Talkabout at Copper from people talking in Vail.
c. It'll bounce off of stuff.
Sort of. It's called tropospheric ducting and it happens here because of temperature inversions. Over the ocean they say you can talk between Hawaii and the West Coast with VHF with the right conditions. This is one (probably the only) type of propagation anomaly where UHF can have odd propagation. Otherwise just about everything reduces the range of UHF, which means your little traveling group is likely not to interfere with other people and you experience less interference other than localized noise and close stations.

All of this (with the exception of the rare tropospheric bounce) is why the UHF, EHF and SHF bands are so much in demand. Cell phones in particular want to be as high in the UHF band as possible so that each cell does not interfere with its neighbors.

02-16-2008, 01:04 AM
OK, so I just read this article:
Dumb and Dumber: Are Americans Hostile to Knowledge? (http://www.nytimes.com/2008/02/14/books/14dumb.html)

This in particular struck me:
Ms. Jacoby, dressed in a bright red turtleneck with lipstick to match, was sitting, appropriately, in that temple of knowledge, the New York Public Library’s majestic Beaux Arts building on Fifth Avenue. The author of seven other books, she was a fellow at the library when she first got the idea for this book back in 2001, on 9/11.

Walking home to her Upper East Side apartment, she said, overwhelmed and confused, she stopped at a bar. As she sipped her bloody mary, she quietly listened to two men, neatly dressed in suits. For a second she thought they were going to compare that day’s horrifying attack to the Japanese bombing in 1941 that blew America into World War II:

“This is just like Pearl Harbor,” one of the men said.

The other asked, “What is Pearl Harbor?”

“That was when the Vietnamese dropped bombs in a harbor, and it started the Vietnam War,” the first man replied.

At that moment, Ms. Jacoby said, “I decided to write this book.”

I immediately thought of this very intelligent, in-depth thread.

I'm proud to call you all friends.

02-16-2008, 07:46 AM
“That was when the Vietnamese dropped bombs in a harbor, and it started the Vietnam War,” the first man replied.

"Over? Did you say 'over'? Nothing is over until we decide it is! Was it over when the Germans bombed Pearl Harbor? Hell no!" -John Blutarsky, U.S. Senator

02-16-2008, 01:18 PM