VHF amps

[2M Guy]

Why so expensive? I have no problem with my little 65-75W, but to have 300 would kick ass. Hearing a repeater, and reaching it are very different.

 

[Highlander_821]

You don't need power for VHF/UHF. You need antenna gain and height.

Put up a pair of Cushcraft 13b2's on a 100 foot tower. (Or something similar) You'll hit any repeater you want to.

 

[2M Guy]

A 100' tower isn't cheap, either. More than the more expensive amps. I'm getting a Cubex quad ( made a homemade one, it sucked lol), just was curious about the high cost of amps.

For mobile, it would help alot. I use Larsen antennas, they do the job, I just wonder why 300W costs so much.

 

[KingCobra_CDX882]

hi..

why are some amps (VHF & UHF)
rated not in power as in watts..
but rather in Dbd..

how many watts to Dbd (or vise verser)

 

[2M Guy]

Never saw that. Db's are relative. I guess to input. A 1 Db gain amp would have to put out four times the input.

Dbd is using a dipole for reference.

 

[KingCobra_CDX882]

yes i realise that..

but..

how many watts equal say an 18 Dbd VHF or UHF amp

seems this is how most amps are rated by cell companies
who typiclly make amps for VHF UHF and SHF frequency's

there is a formula that is easy i simply forget it

 

[Beetle]

engr.nmsu.edu/~etti/fall96/communications/db/db.html

 

[Captain Kilowatt]

When we talk about power output (not gain) in terms of dB we must also state the referance.That referance is usually dBW,or decibels over one watt.This would mean that an amp with a power out of 19 dBw would be rated for 80 watts.Calculations involving power output and received signal strength are all done with dB's as they are much easier to work with,sort of like converting fractions to a common denominator.Received signal strengths are usually referanced to dBmv (dB above one millivolt) and power out dBw,dB above one watt.Note that these dBw ratings do not mean the amp has that much gain, it is referance to the power it will deliver.

 

[KingCobra_CDX882]

so this amp is designed for 18 Dbm
(i had assumed Dbd we know what assume means right...lol)

now i need to figure the math..

Thanks Beetle

 

[CDX1220]

hey 2mguy what larsen do you run and do you run 6m in the mobile.

 

[Moleculo]

dbd = decibels referenced to a dipole; used in antenna calculations

dbm = decibels referenced to one millliwatt

VHF/UHF amps are expensive in part because everything has to be much more precise at those frequency levels. Every little thing in the amp can affect something else, even case design.

 

[C2]

da pills be costing more too

dBd
dBm
dBc - relative to the carrier

dB - gain

an 18 dB gain amplifier will amplify the signal 64 times---that is 1W in means 64W out. 10W in means 640W out, assuming it is rated for that input level.

If it's rated 18 dBm input and 18 dB gain, then you would have 36 dBm output at that drive, which is just a hair under 4W output.

30 dBm = 1W and 40 dBm = 10W

 

[2M Guy]

hey 2mguy what larsen do you run and do you run 6m in the mobile.

An LM 150 and an NMO 150. No 6M, Waiting 'till I take ele. 1 to get a 706.

 

[Captain Kilowatt]

da pills be costing more too

dBd
dBm
dBc - relative to the carrier

dB - gain

an 18 dB gain amplifier will amplify the signal 64 times---that is 1W in means 64W out. 10W in means 640W out, assuming it is rated for that input level.

If it's rated 18 dBm input and 18 dB gain, then you would have 36 dBm output at that drive, which is just a hair under 4W output.

30 dBm = 1W and 40 dBm = 10W

When an amplifier's POWER OUTPUT is speced in dB it is ALWAYS (at least as far as I have ever seen) in dBW,or decibels over 1 watt.I don't mean gain I mean power output,thus an amp with a power rating of 18dBW would be rated for 64 watts output MAX.An amp rated for 20dBW would be rated for 100 watts.It is just another way to express the maximum power output available from the amp and has nothing to do with the gain it provides.That 20dBW amp may require 10 watts drive to get the 100 watts out and thus it would only have a GAIN of 10dB but is still rated for 20dBW.Some may be rated as providing a certain amount of dB gain and state a maximum power output level as well.An example would be an amp that provides a gain of 10dB with a maximum output of 150 watts.That amp would provide 150 watts out with 15 watts in and with 5 watts in it would provide 50 watts out etc.

 

[C2]

I'm just more familiar with transitor amplifier spec's...

While dBW may be a valid specification for "amps," I've never seen them rated in terms of dBd.