Author Topic: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz  (Read 1528 times)

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Offline rcbuck

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #25 on: July 27, 2019, 08:43:58 am »
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If you need a schematic to work with a linear RF amp, you probably shouldn't be working with one.

I didn't say I couldn't reverse engineer and create a schematic from the board layout. I just meant it would have been nice to see the schematic for a quick glance at the circuit.

I have a 20 wpm Extra Class license. I have been licensed since 1962. I have built transmitters, receivers, transceivers, tube amps (811, 813), and solid state amps. Last year I built a 50 watt amp for my uBitx. I had to add external bandpass filters between the uBitx and amp since the uBitx has issues with harmonics and spurs. The amplifier was based on the Hardrock 50 design.

I can certainly build a HF amp but I don't think I would use a single output device to do it. A push-pull output stage is always better since it significantly reduces even harmonics. Although I must admit I built several transmitters with single 6146 output stages in the 60s and 70s.

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Online langwadt

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #26 on: July 27, 2019, 09:16:27 am »
Quote
If you need a schematic to work with a linear RF amp, you probably shouldn't be working with one.

I didn't say I couldn't reverse engineer and create a schematic from the board layout. I just meant it would have been nice to see the schematic for a quick glance at the circuit.

I have a 20 wpm Extra Class license. I have been licensed since 1962. I have built transmitters, receivers, transceivers, tube amps (811, 813), and solid state amps. Last year I built a 50 watt amp for my uBitx. I had to add external bandpass filters between the uBitx and amp since the uBitx has issues with harmonics and spurs. The amplifier was based on the Hardrock 50 design.

I can certainly build a HF amp but I don't think I would use a single output device to do it. A push-pull output stage is always better since it significantly reduces even harmonics. Although I must admit I built several transmitters with single 6146 output stages in the 60s and 70s.

AB7HE


and since it is available in mirrored pinout it seems made for push-pull
 

Offline rcbuck

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #27 on: July 27, 2019, 10:05:32 am »
Yes, and the price is certainly right. Mouser has them for $21.87 each in single lots. A pair of them for $44 gives you the capability of building a 200 W amp.

But, do you really "need" more than 100 watts? I guess it would be needed if you are fighting the California kilowatts ;) in a DX pileup.
 

Online langwadt

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #28 on: July 27, 2019, 10:18:02 am »
Yes, and the price is certainly right. Mouser has them for $21.87 each in single lots. A pair of them for $44 gives you the capability of building a 200 W amp.

But, do you really "need" more than 100 watts? I guess it would be needed if you are fighting the California kilowatts ;) in a DX pileup.

or triple the power with MRF300AN, $35.17 in singles from Mouser
 

Online OwO

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #29 on: July 27, 2019, 02:50:58 pm »
MRF6S9125N/MRFE6S9125N is still my go-to transistor for VHF and below. Over 100W and you can get refurbished ones for $4 each from taobao. I've used 5 of these and haven't encountered any duds yet.
つぁおにずぞんしばだい。
 
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Online Lord of nothing

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #30 on: August 06, 2019, 08:53:58 am »
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But, do you really "need" more than 100 watts?
a guy claim to use a 1kw amp so what do you think?  :-//
Made in Japan, destroyed in Sulz im Wienerwald.
 

Offline jujun

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #31 on: August 16, 2019, 10:04:27 pm »
Thank you all for all this interesting readings.


There is one thing that I dont understand in the design of a matching network: Ciss and Coss are given a 1Mhz in the datasheet, so how you can know it at the frequency you want to use it ? Is it needed that you measure it yourself ? but how ?


Also it seems that Vds have an effet on Ciss and Coss, so to my eyes it seems hard to do it without any mesurements.
Maybe because after 20V it's near flat it's not a big problem if you have at least Vds at more than 20V.

The complex impedance at 13.5Mhz and at 27 Mhz dosent seems very far. I'am currious to know how they get this data. Simulation ? Measurement ?


Any pointer are very apreciated :)

« Last Edit: August 16, 2019, 10:08:47 pm by jujun »
 

Online Kalvin

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #32 on: August 16, 2019, 10:11:09 pm »
But, do you really "need" more than 100 watts? I guess it would be needed if you are fighting the California kilowatts ;) in a DX pileup.

For 2m EME you may want to use 1 kW. Probably for HF contesting and pileups 1 kW may be "the thing".
 

Online OwO

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #33 on: August 16, 2019, 11:32:01 pm »
The datasheet load/source impedances come from experimental measurements, or "load pulls". Basically the transistor is put in a test jig where the load and source impedances are swept over a range and the "optimal" (usually in terms of efficiency or power output) impedance is recorded. You would not want to design an impedance match based on input/output capacitance at >100MHz because other parasitics (bond wire and lead inductance) also come into play.
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Offline jujun

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #34 on: August 16, 2019, 11:51:10 pm »
I don't understand how you avoid to blow the transistor when you sweep the impedance : it must oscillate when the match is very bad ?

It would be great if a simulation model of the transistor was avaiable and enable us to do all this measurements in a simulation, but I don't think it exists.

Do you mean that the capacitance input and output at 1Mhz (in datasheet) is enough to calculate the matching at for example 7 Mhz ?
« Last Edit: August 16, 2019, 11:53:30 pm by jujun »
 

Offline jujun

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Re: Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz
« Reply #35 on: August 17, 2019, 12:02:14 am »
Wow I just downloaded a MRF101AN s2p file on the NXP website !!

EDIT : unfortunately the file start at 30Mhz :(
« Last Edit: August 17, 2019, 12:52:38 am by jujun »
 


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