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Author Topic: Amazon RF amplifiers  (Read 2143 times)
K2OWK
Member

Posts: 1071




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« on: January 03, 2013, 04:17:28 PM »

A Quick question. How good are the RM Italy and the SainSonic linear amps? They have good specifications cover the complete ham HF bands, and are reasonably priced. They are available in a number of configurations up to and including commercial with multiple fan cooling systems. I would guess they they are FCC type
accepted as they are being sold by a large US chain.

Thank you.

73s

K2OWK
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N4CR
Member

Posts: 1688




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« Reply #1 on: January 03, 2013, 05:01:50 PM »

Listed on Amazon and sold by Amazon is two way different things.

These are not sold by Amazon. Amazon is playing the part of web advertising and shopping cart.

The seller is DNJ Radio and they have a web site that you can find in a search. Their reviews seem to be astroturfed with the engrish in the reviews looking about the same as the engrish in their own ad copy.

That doesn't make it bad, but it is what it is. In other reviews over the years, it has been noted that many RM Italy amps don't have any output filtering to control harmonics to legal levels in the US. That may have been corrected but a little investigation might be in order.

Go to their main web site and look at all the CW transmitters for a good laugh.
« Last Edit: January 03, 2013, 05:04:00 PM by N4CR » Logged

73 de N4CR, Phil

Never believe an atom. They make up everything.
N3LCW
Member

Posts: 152




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« Reply #2 on: January 04, 2013, 08:50:21 AM »

RMITaly makes a series of HF amps with output filtering.  I have one of the HLA-150 Plus amps bought used here.  My spectrum analyzer shows the output to be very clean harmonics-wise.  I found driving it past 90W starts to show distortion problems on the signal.   This is consistent with Tom W8JI's report on this amp found on his web site.  I am certain I could clean it up by tweaking the amplifier biasing but just have not had the time nor incentive to do so.  It's a good QRP amp for the used price I paid and I use it with a K2 and Argonaut V. 

I would NOT drive it to 150W.  It can do it but the output will be severely distorted.

Andy
N3LCW
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VE7DQ
Member

Posts: 177




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« Reply #3 on: January 04, 2013, 03:04:06 PM »

Therein lies the problem, 'LCW.  Many would purchase the amp as a '150 watt' amp, and by god, they're gonna get what they paid for!  Their on-frequency buddies, in their equal ignorance, say it sounds great, and it must be yer reciever (sic).  They don't take criticism well.

(Shaking head now... Sad)
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N3LCW
Member

Posts: 152




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« Reply #4 on: January 04, 2013, 06:28:28 PM »

'DQ, that's why I said it starts to distort past 90W, the real top end of these amps.

I wouldn't worry about the longevity of these, I suspect these amps don't survive long driven to 150W, and I have yet to hear one of these on the air.

I hear more problems with people driving their regular tube QRO amps non-linear. That I hear every night.

Andy
N3LCW
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ZENKI
Member

Posts: 980




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« Reply #5 on: January 04, 2013, 09:56:44 PM »

Unfortunately filters dont filter out the poor IMD products from these amps.   Just because an illegal CB amp has filters does not mean that its automatically clean in all regards to its operation performance.
Clean in my book would mean using proper RF devices meant for linear RF service. Clean would also mean a well designed bias that keeps the amplifier clean IMD wise and stable. Most of these RM amplifiers are poorly designed regardless if they have filters installed in them or not, they garbage cheap CB products.

These days with the SDR receivers its very easy spotting hams   who are using these garbage CB amps. They simple to out on the air because even the worst IMD performing legal ham radios even with all knobs cranked to the right
will not produce a filthy signal  like that produced from a bad CB amp design.

If  i bought any solid state amplifier I would want to be sure its clean in the harmonic and spurious products and departments. They should also be clean in their IMD performance. You wont find IMD specifications on any of these
amplifiers because the manufacturers probably dont know  what they are.  They assume anyone who is buying their products are dumb CB'ers

There so many good ham solid amps on the market why any ham would want to buy this  CB garbage is  beyond understanding.


RMITaly makes a series of HF amps with output filtering.  I have one of the HLA-150 Plus amps bought used here.  My spectrum analyzer shows the output to be very clean harmonics-wise.  I found driving it past 90W starts to show distortion problems on the signal.   This is consistent with Tom W8JI's report on this amp found on his web site.  I am certain I could clean it up by tweaking the amplifier biasing but just have not had the time nor incentive to do so.  It's a good QRP amp for the used price I paid and I use it with a K2 and Argonaut V. 

I would NOT drive it to 150W.  It can do it but the output will be severely distorted.

Andy
N3LCW

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N3LCW
Member

Posts: 152




Ignore
« Reply #6 on: January 06, 2013, 10:05:10 PM »

Where did you read here anyone claiming the band pass filters clean up the IMD's? 

As sold, they are as Tom W8JI described in detail.  Put an hour or two into re-engineering the bias and making some component changes and it becomes a good clean amp.  To an RF engineer or experienced RF experimenter it is not brain surgery.

Brand new, they are way overpriced for their mediocre performance and dirty output.  Used and cheap, they could make someone a good project.



Unfortunately filters dont filter out the poor IMD products from these amps.   Just because an illegal CB amp has filters does not mean that its automatically clean in all regards to its operation performance.
Clean in my book would mean using proper RF devices meant for linear RF service. Clean would also mean a well designed bias that keeps the amplifier clean IMD wise and stable. Most of these RM amplifiers are poorly designed regardless if they have filters installed in them or not, they garbage cheap CB products.

These days with the SDR receivers its very easy spotting hams   who are using these garbage CB amps. They simple to out on the air because even the worst IMD performing legal ham radios even with all knobs cranked to the right
will not produce a filthy signal  like that produced from a bad CB amp design.

If  i bought any solid state amplifier I would want to be sure its clean in the harmonic and spurious products and departments. They should also be clean in their IMD performance. You wont find IMD specifications on any of these
amplifiers because the manufacturers probably dont know  what they are.  They assume anyone who is buying their products are dumb CB'ers

There so many good ham solid amps on the market why any ham would want to buy this  CB garbage is  beyond understanding.

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