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Author Topic: New Legal Limit SS Amplifier coming soon  (Read 16375 times)
NO9E
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Posts: 880




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« Reply #30 on: November 30, 2015, 10:33:32 AM »

I compare the specs for this amp to Expert 2k.

Expert has 6 x 300W modules and this amp has 3 x 500W transistor pairs.
Expert has full power on 6m and this one does not.
Expert has a few small fans (noisy at high level) and this one has one big for PA. 
The commercial PS in the Expert has an annoying fan. Not sure whether this one has the same problem; same if same type of PS.
Expert has 2 radio input and this one has 1.
Expert has 6 outputs and this one has 2.
Expert has an extremely useful AT with pretune by band and antenna.
Expert has a similar price (from W5UQ) and has room to lower price because of volume and low pricing in EU.

So considering that the Expert has a few years of experience, the only advantage of this one is possibly greater reliability (still untested), which will appeal to very few (like Prometheus).

It would be nice if a SS amp has 2 Microsemi KW modules for headroom over 1.5KW and lower parts count.

It would be nice if a SS can be warmer but quieter. My Expert 2k reaches 50C (120F) when running, with the case of the amp cool. Perhaps one can let the amp reach 60-70C with lower fan noise. Lower reliability would makes one angry possibly every few years, but a loud fan makes one angry every day.

It would be nice if the amp has some design for increased efficiency especially on CW. 66% efficiency requires half the cooling of 50% efficiency and uses 25% less power. 

Many would compare this amp to Expert 1.3K-FA, which is less power but also less than half weight. Its EU price is about half of this one. 



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M0HCN
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Posts: 566




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« Reply #31 on: November 30, 2015, 02:21:15 PM »

They look to be aimed at subtly different markets, and to have traded things off a little differently.

Cooling is the elephant in the room with all SS amps, but hotter is seldom the way to go, unless you can lower the junction to heatsink thermal resistance  (Solder the device package to the heatspreader?) or lower the difference between the heatsink and the case.
There are some very interesting new heat-sink designs out there that manage spectacular numbers with relatively low airflow and small size at large static pressure, which favours blowers rather then fans, I have one specified to 0.04C/W (We will see, I am not at all sure I buy it, going to try for a kW with a BLF188XR).

One downside of the big fan and pressurised case design is that there is no filter (and plenty for dust to plate off onto), tunnel cooling is better but hard to design in (Laser power supplies never seem to learn this lesson).

3 * 500W for 1,500W at the socket does seem to be stretching a little (Combiner and LPF losses), 4 pairs would have been safer, but I suspect BOM cost is a huge issue.

Efficiency is a tough nut unless the amp has WAY more information about what is going on then just drive and key signals, but even feeding |Z load| back to the power supply so it can adjust to the actual drain load impedance would help some.

Regards, Dan.
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WA7PRC
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Posts: 2315


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« Reply #32 on: November 30, 2015, 04:34:30 PM »

In the RF Lab or the world's larges OEM of RF-driven sealed CO2 Lasers, I learned a few things...
Lasers are horrid loads. Efficiency is around 15%, and between off and on, they're all over the Smith chart. We would've killed for ONLY 2:1 worst-case VSWR!

Thus, our RF drivers HAD to be built like brick outhouses, and we ran them in Class E to (try to) improve overall efficiency. A single board would deliver up to about 1KW. Higher power was done using combiners. Average power control was done using PWM.

I'm wondering what kind of loads this new amplifier can handle while delivering full power and w/o self-destructing.

vy 73 es gl,
Bryan WA7PRC
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K6AER
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Posts: 5689




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« Reply #33 on: November 30, 2015, 07:29:50 PM »

The elephant in the living room with high power solid state amplifiers is the FCC compliance. Being the impedance on the amplifier stages is very low the harmonic content will be very high. In the case of a normal amplifier the harmonics have to be 43 dB plus 10 dB log of the power out to the third harmonic. This is not only being measured at the RF output but as a case radiation as well on an antenna range. This means the PTT keying line, AC input, case and all panels must not radiate above this level.

Now for the killer. Being the amplifier is going to work above 30 MHz the readings now go out to the tenth harmonic.  Harmonics up to 300 MHz will be sampled at an antenna range on a table turnstile at 0, 10, 20, and 30 degrees from the Device under test. In addition for no gain being exhibited from 26-28 MHz the amplifier must meet part 15 radiation requirements. This goes up to 1000 MHz.  It is very hard to get enough cooling and RF shielding in place of a cooling fan. The AC cord will be a significate antenna. LCD panel readouts have to be intrinsically shielded. At 62 dB below the 1500 watt level is the maximum radiation level. Poor RF connectors can fail an amplifier. The RF connection lines have to be superflex or better.  A lot of dummy loads will not meet this requirement. The amplifier testing can take up to 3 hours of continuous testing with the spectrum, angles of antenna and table azimuth readings.

Most amplifiers fail the first 3-5 times on the range. Addition shielding has to be redesigned in most cases. The cooling applications in a lot of cases are fine for heat dissipation but fail in shielded applications. Interconnection coax has to be double shielded.

I wish Dan and his team well for bringing this kind of device to a limited market. This is no easy task.
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M0HCN
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Posts: 566




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« Reply #34 on: December 01, 2015, 01:23:41 AM »

In the RF Lab or the world's larges OEM of RF-driven sealed CO2 Lasers, I learned a few things...
Lasers are horrid loads. Efficiency is around 15%, and between off and on, they're all over the Smith chart. We would've killed for ONLY 2:1 worst-case VSWR!
Ah yes, plasma startup, I always wondered why they did not place a little stripe of Am241 or similar along the inside of tube to help the thing ionise.
1/4 wave coax lines between the exciter and the tube so that the open circuit at the tube turned into a low Z at the exciter seem to fit my memory of laser shenanigans.

I am guessing Coherent, or maybe Synrad? Home of the water cooled 8 * MRF151 as a generator on 80 odd MHz (I have a couple of those modules)?

I was under the impression that below 30MHz the harmonic suppression requirement was (43 +  10 log p), but not to exceed 50dB?

Case radiation? Interesting one, glad I don't play in the US market (I would expect that all that black painted steel would be a problem lots of potential slot radiators there).

Regards, Dan.
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G3RZP
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Posts: 1222




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« Reply #35 on: December 01, 2015, 04:38:28 AM »

Quote
I was under the impression that below 30MHz the harmonic suppression requirement was (43 +  10 log p), but not to exceed 50dB?

That's the level from the ITU Radio Regulations, CEPT ERC Rec 74-01 and the ETSI standard for conducted emissions. Incidentally, a transmitter at 30.001MHz has to meet 43dB + 10 log P  not needing to exceed 70dB: 2kHz lower and it's not required to exceed 50dB. I did ask about this informally at ITU TG1/5, and was advised by the head of the UK delegation to 'let sleeping dogs lie'! FCC managed to leave out the '+10log P' for frequencies below 30 MHz.....

The ETSI EMC standards for commercially available amateur radio equipment do have radiation standards from power lines and the like, but aren't as expensive as the in US, especially as the self certification route can be used, which is a LOT cheaper.

I do wonder if the costs involved will ever be truly recovered by sales, but there may well be tax offsets from any excess costs that can be applied to profits elsewhere in the company........A very brave attempt at getting a new product out.
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M0HCN
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Posts: 566




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« Reply #36 on: December 01, 2015, 08:35:48 AM »

What about a transmitter on 29.999 with a 2 Khz modulation bandwidth running USB .... ?
I know, don't ask things like that at ITU meetings!

I didn't think self cert applied to commercially available transmitters in this power range (Something about there being no applicable product standard?).

Regards, Dan.

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G3RZP
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Posts: 1222




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« Reply #37 on: December 01, 2015, 08:58:46 AM »

Quote
I didn't think self cert applied to commercially available transmitters in this power range (Something about there being no applicable product standard?).

Not sure what the official line is now, or what the new product standard will include - it's being updated to meet the RED. The argument originally was that there was no IEC standard, but I don't know if that's the case, or what is done about 400 watt marine transmitters. If there's no standard, then I suspect that there is no Test House or notified body registered as competent to judge compliance of amateur equipment, so a manufacturer could go down the route of claiming self certification and producing a good quality technical file. There is a slight complication that the Administrations don't have the staff or budget to do any real market surveillance and the amateur market is so small and the users supposedly technically qualified that again, sleeping dogs are left in peace....I believe that only Germany does much market surveillance and even they are budget constrained.....
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M0HCN
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Posts: 566




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« Reply #38 on: December 01, 2015, 09:12:05 AM »

Yea I don't see the European market doing anything except self cert in reality any time soon, there are lots of little specialist markets where the approach to CE is to buy a reel of stickers and call it good, and for the most part there is seldom a real problem with that (These tend not to be markets that do £1.99 cell phone chargers).

Certainly I would not be at all phased by designing a rig or amplifier that I was happy with, taking it to a field miles from anywhere and having a poke around with a spectrum analyser, rogowski coil and yagi, then slapping a sticker on it and selling it on the European market (Worst case, I would eventually be told to knock it off).
It would probably be close enough that I would be very unlikely to get any comeback (You would be very surprised how much of that goes on, often without the niceties of a open field test, or even any test).

Regards, Dan.
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G3RZP
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Posts: 1222




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« Reply #39 on: December 01, 2015, 12:26:06 PM »

Dan

Quote
(You would be very surprised how much of that goes on, often without the niceties of a open field test, or even any test).

NO, I wouldn't!!!

Not that I am cynical.....who me?


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ZENKI
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Posts: 1621




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« Reply #40 on: December 04, 2015, 02:57:35 AM »

Good IMD numbers, if that figure holds across all bands it will be a specifications winner. The nice drop off of all the higher order IMD products indicates a stable design. If it holds across the bands it will be a benchmark solid state amplifier. The company should be congratulated for having such good specifications. With pre-distortion applied it would be ultra linear and certainly put the SPE and other solid state amplifiers too shame.
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W4AMP
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Posts: 3




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« Reply #41 on: December 05, 2015, 01:37:03 PM »

They had me until I saw the I designator.
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KB4MNG
Member

Posts: 350




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« Reply #42 on: December 10, 2015, 10:55:31 AM »

Gosh, that's a lot of money. Don't have that much for ham radio Huh
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