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Author Topic: RM Italy Amplifiers  (Read 91032 times)
SWL2002
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Posts: 895




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« Reply #135 on: August 14, 2015, 05:03:14 AM »

You can clearly see the problems on a SDR panadpater and it will clearly show how many dB down that splatter is.  There is an amazing number of splattery transmitters on the Ham bands and most guys have no clue to the crap they are spewing out... some do have a clue and do it intentionally - especially when they think that someone is encroaching near to their own personal frequency.
« Last Edit: August 14, 2015, 05:07:08 AM by SWL2002 » Logged
G3RZP
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Posts: 1213




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« Reply #136 on: August 14, 2015, 09:44:04 AM »

The 1.3K-FA was reviewed recently in the RSGB RadCom magazine: at full output, the 3rd order IPs were 20dB rel PEP or -14dB relative to one tone of two tone signal. At about 1kW, they were about -24dB relative to tone or -30dB rel PEP. Not very good......
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JS6TMW
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Posts: 1255




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« Reply #137 on: August 14, 2015, 05:07:43 PM »

Is there a good reference that will explain all these terms to me? I am confused between IMD, IP, and harmonics as applied to HF amplifiers. Harmonics, as I recall, are generated because of the inability to reproduce a perfect sine wave from a single frequency (let's say CW). My bargain amp will consist of a barebones pushpull SS pair (operating at Class that I do not know but supposedly "linear"), followed by the filter design shown here (just the one for 14, 18, and 21 MHz since those are the bands my QRP CW rig covers) http://www.w6pql.com/a_1.5kw_lpf_for_160-6m.htm. I don't have the rated 10 watts input power to drive the amp to full output either, so it will be loafing at about 150 watts out if I am lucky.

So where do the IM products come from if not the same kind of nonlinearity that makes harmonics? And aside from key clicks, what would I have to be concerned about for CW operation?

Thanks for your informed answers.

Steve in Okinawa (waiting for my JA license to come through)

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KA4WJA
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Posts: 1098




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« Reply #138 on: August 14, 2015, 05:49:35 PM »

Steve,
While there are great papers and tutorials on-line from Rohde and Schwarz, Texas Instruments, etc....those have a lot of math and assume a bit of RF knowledge as a prerequisite....
And, while I think the ARRL Handbook will be your overall best bet (and every ham should have at least one copy in their shack!!)...here are a few on-line sources that should help...

Is there a good reference that will explain all these terms to me?

Lloyd, VK5BR has a great write up...
http://users.tpg.com.au/users/ldbutler/Intermodulation.htm

And, so does David Hall...
http://electronicdesign.com/communications/understanding-intermodulation-distortion-measurements


And, also this...
http://gs35b.com/imd.html


And, once you've read those....have a look at these...
http://www.ni.com/white-paper/4384/en/

https://www.arrl.org/files/file/Technology/tis/info/pdf/Procedure%20Manual%202010%20with%20page%20breaks.pdf

http://cdn.rohde-schwarz.com/pws/dl_downloads/dl_application/application_notes/1ef79/1EF79_1E.pdf


I hope this helps...

73, 
John,  KA4WJA

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SWL2002
Member

Posts: 895




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« Reply #139 on: August 14, 2015, 05:58:47 PM »

Is there a good reference that will explain all these terms to me? I am confused between IMD, IP, and harmonics as applied to HF amplifiers. Harmonics, as I recall, are generated because of the inability to reproduce a perfect sine wave from a single frequency (let's say CW). My bargain amp will consist of a barebones pushpull SS pair (operating at Class that I do not know but supposedly "linear"), followed by the filter design shown here (just the one for 14, 18, and 21 MHz since those are the bands my QRP CW rig covers) http://www.w6pql.com/a_1.5kw_lpf_for_160-6m.htm. I don't have the rated 10 watts input power to drive the amp to full output either, so it will be loafing at about 150 watts out if I am lucky.

So where do the IM products come from if not the same kind of nonlinearity that makes harmonics? And aside from key clicks, what would I have to be concerned about for CW operation?

Thanks for your informed answers.

Steve in Okinawa (waiting for my JA license to come through)



Non linear devices cause mixing... Now just think of mixing two frequencies very close together - you get product and difference signals which were not there before... You create new frequencies that can also mix with the original frequencies...
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JS6TMW
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Posts: 1255




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« Reply #140 on: August 14, 2015, 06:51:11 PM »

Thanks for those references, John. I think I got the gist of it now, and my takeaway is that transmission of IMD is primarily an issue for voice transmission, not CW.  I think the filter I plan to build will go a long way to reducing harmonics to a low level.

I have seen lots of discussions in this thread about why some amplifier designs are worse than others for IMD. One of these days I'll try to catch up on that matter as well, but I am strictly CW until further notice.

73,

Steve
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G0OQX
Member

Posts: 20




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« Reply #141 on: May 18, 2019, 02:43:04 PM »

I recently bought one of their linear HF amps and much of what is said on this thread is true - they do not deliver what they claim. However, my 300W (claimed) RM amp is giving me up to 180W on most HF bands on data, and it only cost a couple of hundred pounds new. It has performed faultlessly so far, so even though I'm not too happy with the output, I've gained 6dB on my signal for very low cost, and my more expensive transceiver is likely last much longer now it is only asked to deliver 5-10W. For what I paid I'm happy with the result as I could never afford the several thousand pound price tag of a good quality linear.
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WY7CHY
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Posts: 953




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« Reply #142 on: May 20, 2019, 08:40:11 AM »

I tested an HLA-300v a few years ago. I thought it was a little expensive, but for a Solid State amp; capable of mobile use; it wasn't too bad. I tested it, and I was somewhat impressed with it. Not jumping up and down with joy impressed; but enough. I've not tried any of the newer HLA-305v models. "Basically, the only difference is the 300v is open to all frequencies, and the 305v blocks the 11m band. Also, the 305v purposely limits the output power so it doesn't overdrive. The 300v, you have to be smarter than the amp not to overdrive it.

A couple years back, a friend owed me, and was moving, so he gave me his HLA-300v as partial payment. I've used it on and off regularly for the last few years. I don't put more than 15 watts into it. It produces 300-325 watts continuous no problem. (Depending on the band). In SSB mode it gets about 350-375 watts PEP. (Depending on the band).

Would I spend $500 for a new 300v? No, not really. Not when for about $100 more, you can get a good used AL-811, SB-200, FL-2100B or other amp. Would I spend $700 for a new 305V, simply because it had a silly FCC sticker on it, and LESS POWER than the 300v? No, not at all. BUT.... if you picked up a 300v used, at a decent price, and you don't over-drive it; it's a decent amp for 5db+ gain. Especially in a mobile/field day type environment where it works on 12vdc. And it performs decently; as long as you don't try to 400 or more watts out of it. But for 300w cont; or 350w PEP it's fine.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W1BR
Member

Posts: 4177




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« Reply #143 on: May 20, 2019, 11:36:18 AM »

You might be surprised by how many of us have spectrum analyzers and facilities to run two tone tests.

Allowing or not reviews of kit sold legally in non US markets is of course a decision that only the site owners can make, and I can see arguments both ways, especially given the problems in America with 10/11M kit, and the FCCs subsequent rather heavy handed clamping down on RF amplifier sales to the point that it sometimes takes extra electronics to stop the things working there.....

Regards, Dan.



I hate to dig up an old thread... but this begs a question. I have several 141T analyzers fitted with all of the heads, etc. and a very capable Tek 497P that has 10 and 100 Hz RBW.  Where I would into a problem is being able to generate a very clean two or three tone test.  None of HF SSB rigs (JRC, Ten Tec)  are clean enough to do meaningful measurements.

How do you guys, with average home labs, do these measurements?

Pete
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KD8MJR
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Posts: 5529




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« Reply #144 on: May 20, 2019, 01:25:41 PM »


I hate to dig up an old thread... but this begs a question. I have several 141T analyzers fitted with all of the heads, etc. and a very capable Tek 497P that has 10 and 100 Hz RBW.  Where I would into a problem is being able to generate a very clean two or three tone test.  None of HF SSB rigs (JRC, Ten Tec)  are clean enough to do meaningful measurements.

How do you guys, with average home labs, do these measurements?

Pete

Pete I use an IFR 1500 service monitor which allows me to generate any set of tones i need.  I then use an attenuator and run the signal into an Siglent SA.  If it's 100 watts or less power I directly measure it with the IFR 1500

You can buy or make a two tone generator, they are all over the internet and kits are on ebay etc.
Here is one https://www.qrpkits.com/twotonetest.html


73s
Rob
« Last Edit: May 20, 2019, 01:28:09 PM by KD8MJR » Logged

“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
W1BR
Member

Posts: 4177




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« Reply #145 on: May 20, 2019, 01:49:36 PM »

Hi Rob

I wasn't very clear.... my problem would generating a 100 watt two tone signal with clean IMD to test an external power amplifier.  The Ten Tec exciters are pretty poor IMD wise, and the results would be confusing if used for test exciters.

Pete
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KD8MJR
Member

Posts: 5529




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« Reply #146 on: May 20, 2019, 02:15:13 PM »

Hi Rob

I wasn't very clear.... my problem would generating a 100 watt two tone signal with clean IMD to test an external power amplifier.  The Ten Tec exciters are pretty poor IMD wise, and the results would be confusing if used for test exciters.

Pete

My fault Pete I did not read the last line. Duh... Smiley
A clean 100 watts is not going to be easy to get.  I know there are radios out there that are very clean but do you really want to spend that kind of money for casual testing?  If you find something cheap let me know.

Rob
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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
K6AER
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Posts: 5688




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« Reply #147 on: May 20, 2019, 02:52:20 PM »

Why not use to exciters set 5 khZ apart and combine them through a power combiner/splitter. It is easy to get a two tone signal that the third is down 55 dB. Put a 6 dB pad on each input. Port A and Port B isolation should be t least 55 dB.

An amplifier will never better IMD than what is fed at the input.
« Last Edit: May 20, 2019, 03:11:02 PM by K6AER » Logged
VK6HP
Member

Posts: 500




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« Reply #148 on: May 20, 2019, 07:00:52 PM »

You can certainly do that and I have done it successfully using two TS-830Ss.  But be aware that there is a substantial amount of devil in the implementation details.  There is a lot written in T&M application notes but a good account of some experiences in the amateur context is included in an article by W0QE at https://www.w0qe.com/Technical_Topics/imd_testing_of_amplifiers.html.

I find that an effective and quick alternative way is to just use my 50 year-old Collins 32S-3 in conjunction with a low-distortion two-tone audio system; it's still the cleanest exciter around.  Mind you, for the amplifiers under discussion in this thread you won't have to try very hard to see the added IMD products.

73, Peter.
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G0OQX
Member

Posts: 20




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« Reply #149 on: July 01, 2019, 01:05:20 PM »

I recently bought one of their linear HF amps and much of what is said on this thread is true - they do not deliver what they claim. However, my 300W (claimed) RM amp is giving me up to 180W on most HF bands on data, and it only cost a couple of hundred pounds new. It has performed faultlessly so far, so even though I'm not too happy with the output, I've gained 6dB on my signal for very low cost, and my more expensive transceiver is likely last much longer now it is only asked to deliver 5-10W. For what I paid I'm happy with the result as I could never afford the several thousand pound price tag of a good quality linear.

Update. A few weeks ago I accidentally drove my RM Amp with the full 100W output from my rig for 2-3 seconds before realising what I'd done. I assumed the linear would have been cooked, but when I reset the drive to 10W all was working perfectly, and now several weeks later all is still fine. This RM amp appears to be idiot proof, or at least able to cope with this particular idiot. I now have a big red warning sticker on my rig so hopefully I won't repeat my mistake.
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