[AMRadio] AM Transmitter Advice??


James M. Walker chejmw at acsu.buffalo.edu
Tue Jan 31 07:55:11 EST 2006


I would like to jump in here,
I have a converted solid state rig on 20 meters.
It runs an adjusted level output of 100 to 650
watts on that band. It uses a derivative of the MRF-150
only requires 100 milliwatts of drive over the whole band.
The only drawback if you can call it that is this unit is
water cooled.
YMMV
Jim
WB2FCN

----- Original Message -----
From: "Jim candela" <jcandela at prodigy.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Monday, January 30, 2006 8:36 PM
Subject: RE: [AMRadio] AM Transmitter Advice??


>
>
>    Guys,
>
> I just looked up the MRF150. For the moment look at the characteristics
> below with a big AM final amplifier in mind.
>
> With a 300 watt Pd rating, this thing might do well as a efficiency
> amplifier (modulate the gate bias) to make 100 watts AM, and do so with
room
> to spare. So with say 33% efficiency (SWAG), 300 watts DC input, you get
100
> watts RF output with 200 watts Pd. With modulation the efficiency improves
> (doubles @100% modulation from sine wave tone input).
>
> If you do a conventional Class C high level modulated amplifier with say
150
> watts Pd, and 75% efficiency (SWAG), that gives you 600 watts DC input X
.75
> = 450 watts RF output! There are tons of hi power solid state audio
> amplifiers around, so there is your modulator too!
>
> Sure, the application notes dwell on SSB linear usage, but heck if it
works
> on SSB, you can make it work on AM!
>
> Regards,
> Jim
>
>  So how much do these things cost? :-)
>
>
> MRF150
>
> MAXIMUM RATINGS
> Drain-Source Voltage VDSS 125 Vdc
> Drain-Gate Voltage VDGO 125 Vdc
> Gate-Source Voltage VGS ±40 Vdc
> Drain Current - Continuous ID 16 Adc
> Total Device Dissipation @ TC = 25°C
> Derate above 25°C
> PD 300
> 1.71 W/°C
> Storage Temperature Range Tstg -65 to +150 °C
> Operating Junction Temperature TJ 200 °C
>
>
> MOTOROLA RF DEVICE DATA
> ELECTRICAL CHARACTERISTICS (TC = 25°C unless otherwise noted.)
> Characteristic Symbol Min Typ Max Unit
> OFF CHARACTERISTICS
> Drain-Source Breakdown Voltage (VGS = 0, ID = 100 mA) V(BR)DSS 125 - - Vdc
> Zero Gate Voltage Drain Current (VDS = 50 V, VGS = 0) IDSS - - 5.0 mAdc
> Gate-Body Leakage Current (VGS = 20 V, VDS = 0) IGSS - - 1.0 mAdc
>
> ON CHARACTERISTICS
> Gate Threshold Voltage (VDS = 10 V, ID = 100 mA) VGS(th) 1.0 3.0 5.0 Vdc
> Drain-Source On-Voltage (VGS = 10 V, ID = 10 A) VDS(on) 1.0 3.0 5.0 Vdc
> Forward Transconductance (VDS = 10 V, ID = 5.0 A) gfs 4.0 7.0 - mhos
>
> DYNAMIC CHARACTERISTICS
> Input Capacitance (VDS = 50 V, VGS = 0, f = 1.0 MHz) Ciss - 400 - pF
> Output Capacitance (VDS = 50 V, VGS = 0, f = 1.0 MHz) Coss - 240 - pF
> Reverse Transfer Capacitance (VDS = 50 V, VGS = 0, f = 1.0 MHz) Crss -
40 -
> pF
>
> FUNCTIONAL TESTS (SSB)
> Common Source Amplifier Power Gain f = 30 MHz
> (VDD = 50 V, Pout = 150 W (PEP), IDQ = 250 mA) f = 150 MHz
>
>
> Full data sheet:
>
> http://www.twhrf.net/mkic/mrf150.pdf
>
>
>
>
>
>
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net]On Behalf Of Jim candela
> Sent: Monday, January 30, 2006 6:54 PM
> To: Discussion of AM Radio
> Subject: RE: [AMRadio] AM Transmitter Advice??
>
>
>
>
> Larry,
>
>    I am interested in what your friend Jim, KR1S has in mind for that 100
> watt AM solid state exciter for 75 meters. Is that carrier output, or PEP?
> In thinking about it, this could vary from a "scaled up CB" rig with a
tuned
> class C final with high level modulation, or maybe a small AM exciter with
a
> solid state push pull linear, or maybe a class E setup. We seemed to get
> side tracked on the 813 amp idea, and glossed over the exciter concept you
> laid out.
>
>   How about a nice juicy MRF-150 with high level drain modulation, or low
> level gate bias modulation? I bet no one has ever tried it either way..
>
> Regards,
> Jim
> WD5JKO
>
>
> [mailto:amradio-bounces at mailman.qth.net]On Behalf Of Larry Keith
>
> My friend, KR1S (Jim Kearman) is designing an AM
> transceiver, for me.  We plan for this to be a
> solid-state unit that will deliver about 100 watts
> out. It will be single band (75 meters) and I have
> been considering using that to feed a homebrew linear.
> I have the makings of a 2 x 813 amp thanks to my and
> Jim's hamfesting efforts.
> Larry
> KQBY
>
> Larry Keith
>
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