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UHF Linear LD MOSFET RF Amplifiers - RF Cafe Forums

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 Post subject: UHF Linear LD MOSFET RF Amplifiers
Posted: Thu Aug 07, 2008 4:16 pm 

Joined: Mon Jul 07, 2008 9:42 pm

Posts: 7

Location: Northern, IL

Hello Everyone,

I've been pondering and researching Military Surplus UHF Solid State Linear LD MOSFET RF Amplifiers for the last six (6) months to increase my signal above 10 Watts Output.

I've found two amplifiers on Mike Murphy's Website Link:


And then scroll down to the MOTOROLA URC-7175 / URC RF AMP for $2,500.00.

And the KALMUS M200U-BA and BP versions which cost $795.00 EA & $695.00 EA respectively.

Both RF Amplifiers are rated at 200 Watts Output and have selectable Power Output levels, both operate on +28V DC @ 20A.

Have any of you hams purchased either the MOTOROLA or the KALMUS RF Amplifiers and used them on the 430~450 MHz portion of the UHF Band? How Linear are these RF amplifiers as far as Spectrum purity and Sideband Noise either side of the operating Fc?

These RF amplifiers operate CW/FM/AM/PULSE with 2 Watts Maximum RF Drive level buit I intend to operate USB Class AB1 for Terresterial UHF contacts and FM simplex. I've already got a 120' Rohn SSV Tower with 15' 2" O.D. Chrome Molly Mast Pipe, 7/8" Heliax cable and a Tailtwister rotor with a Bearing Shelf to satbilize the Antenna / Mast Pipe. The transceiver is an older YAESU FT-726R. My ASL is roughly 915' and I'm just getting back active again.

So do any of you guys have experience with the two types of UHF Amplifiers?

Or any thoughts regarding the station set up? :roll:




 Post subject:
Posted: Fri Aug 08, 2008 11:42 am 
User avatar

Joined: Tue Dec 26, 2006 5:39 pm

Posts: 58

The entire state of Florida is limited to 50 W transmit output.

I didn't look it up in the fine print of the Federal Register, but many of us are limited on 70 cm.

http://www.arrl.org/?artid=5864 is a brief summary of the power limitation.

 Post subject: UHF Linear LD MOSFET RF Amplifiers
Posted: Mon Aug 11, 2008 12:20 am 

Joined: Mon Jul 07, 2008 9:42 pm

Posts: 7

Location: Northern, IL

WB9JTK Wrote:

The entire state of Florida is limited to 50 W transmit output.

I didn't look it up in the fine print of the Federal Register, but many of us are limited on 70 cm.

Perhaps you didn't read the current USAF, FCC & ARRL Interference / RF Power Reduction requirements. Any Amateur Radio Stations located within 140 miles of the three (3) USAF PAVE PAWS Sites or close to the U.S. Coastal Boundries and/or Borders are required to reduce their RF Power Output Level to 50 Watts Maximum. This conirms the State of Florida is required to comply which is too bad for the Ops living down there.

Apparently you must have considered that I'm a new Ham and not able to understand the current FCC Rules & Regulations related to this hobby. If you looked at my call sign, then you could have easily looked at my data and found I'm currently located near Elgin, Illinois Grid Sq. EN52.

I have been licensed since October, 1968 roughly 40-years in Ham Radio. Since I'm located 45 air-miles northwest of downtown Chicago, IL., I think I would qualify for being well over the 140 air-miles from any three (3) of the USAF PAVE PAWS installations but I could be mistaken.

I'm intending to call the local FCC Commissioner in Park Ridge, IL on Monday morning August 11, 2008 and confirm or deny the RF Power Limits for Northern, Illinois.

I've been all over the Internet looking for a website like this one, assuming there are "RF Engineering" personnel to answer technical questions related to Ham Radio, Land Mobile Radio and/or Electronic Hardware but now I question if those technical people really exist here. :roll:

Now back to my original request, "Does anyone have experience Pro or Con on (HF/VHF/UHF) Linear LD MOSFET Amplifiers?




 Post subject: Re: UHF Linear LD MOSFET RF Amplifiers
Posted: Wed Apr 08, 2009 9:44 am 
User avatar

Joined: Wed Apr 08, 2009 7:53 am

Posts: 19

Do you have any data sheet of these amplifiers? (I did a quick search and I couldn´t find some)..

From what you wrote, the amplifiers have 35.7% efficiency so you have 2 options: they can be a Class AB or fair Class B amplifiers.. if they are Class AB, you will have a low 2nd harmonic and a filtered 3d harmonic.. that is all I can say for now..

Any way, for that cost and power, you could have for sure a better eff LDMOS Class AB Amplifier with the best possible linearity given by the latest generation LDMOS amplifiers.


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