Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Power on VHF vs UHF  (Read 576 times)
K3DC
Member

Posts: 88




Ignore
« on: December 19, 2007, 12:02:29 PM »

Great idea having a place to put up questions.  Especially since I'm a new ham (KI4YMD).  I've purchased a few VHF radios and I have one Dual-bander (2m/70cm).  In looking at these I've noticed the the UHF power is less than the VHF power.  I would like to know why it can not be the same?  It also seems to me that propagation and attenuation is worse for UHF than VHF and more power would actually benefit.

Chris,
KI4YMD
Logged
WA3SKN
Member

Posts: 5434




Ignore
« Reply #1 on: December 19, 2007, 12:19:14 PM »

Congratulations!
You can have the same power out, if they use more expensive finals!
Yes, the loss is greater at UHF, but the noise is actually less.  You just don't notice the difference, because you are using FM, not one of the "weak signal" modes.
Get on the local repeaters, make contacts and friends, join local clubs... then you can expand your horizons!  
Remember, it is a journey, not a destination.  There's still plenty to learn out there!
Hope to make contact soon!

-Mike.
Logged
K1CJS
Member

Posts: 5855




Ignore
« Reply #2 on: December 19, 2007, 12:39:11 PM »

Exactly.  There are some rigs out there--few and far between--that have the same power out at both VHF and UHF.  Those rigs are more haevily constructed and have parts (finals and associated circuitry) that will withstand the extrs power added to UHF to equal the VHF side.

Todays rigs are getting back to that, but the rigs of approximately 1994 to 2004 were made lighter and more cheaply.  Just to let you know, you'll hear a lot more activity on 2 meters than you will on 70 cm, but its nice to have at least one rig that will work the 70 cm band.
Logged
K1CJS
Member

Posts: 5855




Ignore
« Reply #3 on: December 19, 2007, 12:40:53 PM »

Oops! Clumsiness strikes again.  Should have typed 'heavily', not 'haevily'.  Oh, well.....
Logged
KB9CRY
Member

Posts: 4284


WWW

Ignore
« Reply #4 on: December 19, 2007, 12:58:14 PM »

It would take more stuff to create equal power outputs for both bands and therefore the rig would be much larger.
Logged
KZ1X
Member

Posts: 3227




Ignore
« Reply #5 on: December 19, 2007, 01:09:04 PM »

"In looking at these I've noticed the the UHF power is less than the VHF power. I would like to know why it can not be the same?"

Cost.  For a given amount of money, as you go up in frequency, gain drops off.  ;-)  Seriously, it IS about cost.

"It also seems to me that propagation and attenuation is worse for UHF than VHF and more power would actually benefit."

Maybe; maybe not.  For example, building penetration at 445MHz is generally a lot better than at 146 MHz.  It's all about what you're doing with what you have.

And another thing:  ERP matters in determining ability to overcome path loss, not just transmitter power.  You can get a LOT more gain on a UHF antenna than with a VHF antenna, all size matters being similar.

UHF FM is good enough where I live that I only have one 2 meter radio, and hardly ever use it.  Don't miss it, either.
Logged
K3DC
Member

Posts: 88




Ignore
« Reply #6 on: December 19, 2007, 01:15:41 PM »

"Just to let you know, you'll hear a lot more activity on 2 meters than you will on 70 cm"

You are correct.  I live in Atlanta and am a member of GARS (Gwinett Amateur Radio Society).  The have a VHF repeater at 147.075 and UHF at 444.525.  I have a TN-V7A in my office that I bought used and have been playing with it to connect MY 2M Radios (VX-170 and FT-2800M) to the UHF repeater.  In the few days I've been doing it I've heard no one on that repeater.  However it has been fun figuring out how to do this and I can see a real use for cross-band repeat with a UHF mobile going to a VHF repeater. Like in the mall.  Or in a stadium, etc.  I'm doing a presentation next month on IRLP vs Echolink in the basement of a church.  I plan on using a UHF HT to connect to the Kenwood in my van to try and demo IRLP during the presentation.  Hopefully it will work well.
 
Logged
N3OX
Member

Posts: 8852


WWW

Ignore
« Reply #7 on: December 19, 2007, 01:38:53 PM »

I would say you're NEVER going to find a dual bander that has equal power  out on VHF and UHF.

Why?

The same final transistors are probably used for both bands in most designs, and as other posters have said, the gain is lower on UHF (and efficiency is lower too, I *think*)... but this means that a rig with equal power out on both bands would probably have the VHF side *turned down* just to equalize the power.

Output power is a big seller... lots of 50W/35W 2m/440 rigs out there... a rig that could safely do 50W on UHF could probably do 70W on VHF and the manufacturer would probably rather sell a 70W/50W rig instead of a 50W/50W rig.

I would guess that designs will always use the finals to their maximum safe output and that sort of makes sense, but it means UHF is always going to be a hair lower.

It *is* sort of about cost ... but I think it's more about transistor characteristics and marketing... the cost comes in when you want *more* power overall.

73,
Dan
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N2IK
Member

Posts: 220




Ignore
« Reply #8 on: December 19, 2007, 04:29:32 PM »

That was true for some time, but check out the new TM-V71A and TM-D710A from Kenwood that are the same radio with different control heads. Both VHF and UHF put out the same power.

Never say never, I guess.

73 de Walt N2IK
Logged
N5YPJ
Member

Posts: 642




Ignore
« Reply #9 on: December 19, 2007, 05:13:17 PM »

And it gets even lower at 1.2 Ghz where the highest powered rigs seems to be outputting 10 watts.

Just my .02 cents worth - on FM phone (voice) after doing tests for 4 years from my home I found it hard to justify running more than 5 - 10 watts simplex or repeater qsos. On packet (ah the days) it was worthwhile to run the extra power.

73

Tichard
Logged
WA9SVD
Member

Posts: 2201




Ignore
« Reply #10 on: December 19, 2007, 05:36:10 PM »

A major consideration isn't just price, but EFFICIENCY.  For the same DC power input, the UHF (higher frequency) circuits are not as efficient.  many of the mobile dual band radios use hybrid modules in the output circuit, (different modules for the different bands) and the modules do not operate at the same efficiency.  Even with discrete devices in the output stage, for a given DC power input, the higher frequency circuits will not have the same power output, but will be lower.
Logged
W4DL
Member

Posts: 182




Ignore
« Reply #11 on: December 20, 2007, 03:45:08 AM »

Look up "gain bandwidth product" in the handbook or other RF treatise.  
Logged
W1VT
Member

Posts: 809




Ignore
« Reply #12 on: December 20, 2007, 05:46:17 AM »

You might enjoy the "magic" of a large Parabolic Dish Antenna.  If used on transmit and receive, signals actually get louder as you move up in frequency, while keeping the power the constant!  I used to regularly operate a QRP portable setup with 2' dish antennas on 3.4, 5.7, and 10GHz--signals were best on 10GHz if there was no tree or foliage attenuation.  
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!