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Author Topic: Amplifier  (Read 2814 times)
KJ4DHI
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Posts: 57




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« on: October 22, 2017, 01:00:27 PM »

I am almost exclusively QRP, but sometimes in a contest 5w just ain't enough. My equipment consists of MFJ 9420, 9040, and 9320. Can anyone recommend an amplifier for use on those difficult contest weekends?
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KM4DYX
Member

Posts: 63




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« Reply #1 on: October 22, 2017, 04:03:43 PM »

The Hardrock-50 kit is well spoken of. https://hobbypcb.com/products/hf-radio/hardrock-50-hf-power-amp

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KC4ZGP
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Posts: 1637




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« Reply #2 on: October 22, 2017, 05:53:03 PM »


Kraus recommends the EB-104, EB-27A or EB-63. You'll have tons of fun affixing the relay,
power supplies and heat sink.

Be safe.

Kraus
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KC2QYM
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Posts: 860




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« Reply #3 on: November 07, 2017, 06:02:37 AM »

Buy a cheap 100 watt rig and save yourself the extra costs and efforts of amassing all the extra accouterments.  Unless you like building everything or almost everything which is the other side of the QRP appeal. 
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OZ8AGB
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Posts: 345




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« Reply #4 on: November 07, 2017, 06:19:14 AM »

I built one of these (180W version) for my K2.

http://www.communication-concepts.com/an762/
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K8AXW
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Posts: 6361




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« Reply #5 on: November 07, 2017, 11:35:00 AM »

Since you have built stuff, perhaps you might consider the W6JL 40m homebrew amplifier that was in QST a few years ago?  This amp construction article can be Googled and the whole thing can be build for less than US $50.00.  I built one and it worked right off. 

Since it requires very little drive, I built an attenuator into the same box to provide the correct drive from my homebrew transceiver.

The original W6JL article also provides component values for other band output circuits.
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KU3X
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Posts: 432




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« Reply #6 on: November 23, 2017, 03:55:36 AM »

The Hardrock-50 kit is well spoken of




I have to agree with KM4DYX, the Hardrock-50 is a great little amp and well priced.

But, what do you have for an antenna. Please don’t tell me you are putting 5 watts into a G5RV and then wandering why you are having poor results !

It’s all in the antennas. Put your focus there first. This year, NB3R and I ran field day, from my back yard, using a KX3, at 5 watts out and we ended up fifth in our class (1E) in the country. One guy ahead of us was running 100 watts. If you take him out because of the high power, we actually ended up forth place all running QRP. We are on the east coast and on 20 meters, I worked Hawaii with the OCF40 at 35 feet.

http://www.ku3x.net/p

Yes, the amp will really give you an edge, but first focus on the antenna(s). Remember, an amp will increase your signal strength but that is only one way. Gain in using a good antenna is a gain in signal strength both ways.

Barry, KU3X
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AC7CW
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Posts: 1002




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« Reply #7 on: November 23, 2017, 10:58:57 PM »

Currently amplifiers are limited to 15dB of gain. That means you can take your 5 watts up to about 165 watts. If you are buying new then you want something near that power output, perhaps a good bit more so you can underwork the amplifier and make it last longer... There are some kits on eBay that are stunningly inexpensive and might be fun to work up.
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Novice 1958, 20WPM Extra now... (and get off my lawn)
KB1GMX
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Posts: 1505




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« Reply #8 on: November 24, 2017, 10:17:22 AM »

Some things:

The 15DB gain limit applies to commercially made and sole amplifiers.

Most bipolar designs are about 9-13db gain (typical).

Most designs based on 12V MOSfets are lower gain in the 12--16db range
while those that run 28 to 50v devices can easily have gains greater than
16db to 24db,   For that higher gain its often a build it rather than buy it,

Based on the above if you need a lot of power the gain is important.   If
your shooting for 30-60W then the amplifier gain is likely not an issue and if
its higher  than needed its simple enough to add attenuation or turn the
drive power down.

There are few clean amps out there and it also possible to build a good amp.
What you want is at the intersection of skills, cash, and desired features,

Allison
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