Does anyone have any idaes on how to lower the nf in a uhf preamp?

In article .com,
" wrote:

Does anyone have any idaes on how to lower the nf in a uhf preamp?


1. Lower then temprature of the device, by dumping it in Liquid Nitrogen.
2. Use a device with a lower Noise Figure, as the active element.

Daaa.....

3a. Tune (match) the input for lowest in-system noise figure.
This is in general not a match for maximum power transfer.
3b. Be sure the active device(s) is/are biased for optimum
noise figu collector/drain voltage and standing current.
4. Be sure there are not any unnecessary noise
contributions from components other than the
active devices in the amplifier.
If you want to consider the system as a whole,
4. Lower the loss between the antenna and the preamp
(eliminate feedline, for example).
5. Be sure that the preamp has enough gain that it
sensibly sets the system noise figure. (Be sure
that its gain gets the signal seen at the next stage
high enough that the next stage contributes
insignificant noise to the system.)
.... etc.

But beware of trading other things for noise figu beware of
poor intermod or desense performance, for example.

Cheers,
"Me" aka Tom


"You" wrote:
In article .com,
" wrote:

Does anyone have any idaes on how to lower the nf in a uhf preamp?


1. Lower then temprature of the device, by dumping it in Liquid Nitrogen.
2. Use a device with a lower Noise Figure, as the active element.

Daaa.....

As a point of reference, a typical NE3508M04
(http://www.cel.com/pdf/datasheets/ne3508m04.pdf) can give you a device
noise figure under 0.4dB, operated at room temperature, at any
frequency across the entire "UHF" frequency range (300MHz to
3GHz)--better than that at the lower end of the frequency range.

Cheers,
Tom

Thanks for the website, my problem was i had a factory cellular preamp
from surplus equipment, it had a ceramic filter on the input set
824-850 mhz. When i removed the filter the noise figure was terrible
but the bandwith very wide, im trying to get it to operate in the 33cm
band with decent noise figure. The only thing i can figure is that by
removing the banpass filter i raised the NF?

How are you measuring noise figure? Describe your setup?

wrote:

Thanks for the website, my problem was i had a factory cellular preamp
from surplus equipment, it had a ceramic filter on the input set
824-850 mhz. When i removed the filter the noise figure was terrible
but the bandwith very wide, im trying to get it to operate in the 33cm
band with decent noise figure. The only thing i can figure is that by
removing the banpass filter i raised the NF?




--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

In article .com,
"K7ITM" wrote:

As a point of reference, a typical NE3508M04
(http://www.cel.com/pdf/datasheets/ne3508m04.pdf) can give you a device
noise figure under 0.4dB, operated at room temperature, at any
frequency across the entire "UHF" frequency range (300MHz to
3GHz)--better than that at the lower end of the frequency range.

Cheers,
Tom


Nothing like a Ruby Maser dumped in Liquid Nitrogen and pumped at
-12 DBm to bring in those extremely small signals........

all it takes is cold......

Im guessing at the noise figure, im running a low level 1mv fr0m a
cushman service monitor to the preamp input. Im using a uniden 898t
scanner as a receiver because it has a digital S meter. When i turn on
the preamp jumps up 3-4 bars
but the modulation tone stays the same volume level. By this im
guessing the noise level has increased, the preamp had a ceramic
filter with the 50ohm input going directly into it and its output thur
cap to the 1st amp, the seller on ebay said just remove the filter and
move the input to the filters output trace, thats what i done but
results are poor even thou this is a commercial preamp pulled from
analog cell site. It looks to be a very well made preamp so it should
work if i figure out the
input match?

You wrote:
In article .com,
"K7ITM" wrote:


As a point of reference, a typical NE3508M04
(http://www.cel.com/pdf/datasheets/ne3508m04.pdf) can give you a device
noise figure under 0.4dB, operated at room temperature, at any
frequency across the entire "UHF" frequency range (300MHz to
3GHz)--better than that at the lower end of the frequency range.

Cheers,
Tom



Nothing like a Ruby Maser dumped in Liquid Nitrogen and pumped at
-12 DBm to bring in those extremely small signals........

all it takes is cold...

It still takes cold but InP HEMTs perform much better than ruby masers
these days...

"Extremely Low-Noise Amplification with Cryogenic FET's and HFET's:
1970-2004"
http://www.gb.nrao.edu/electronics/edir/edir314.pdf


Happy reading!
-Galen, W8LNA