Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: Prev 1 [2] 3 Next   Go Down
  Print  
Author Topic: Elecraft KPA 1500 High Cooling Fan Levels  (Read 2309 times)
K6BRN
Member

Posts: 1234




Ignore
« Reply #15 on: May 02, 2019, 05:01:12 AM »

Hi Jim:

Thanks for the info on the Icom IC-9700 master oscillator circuit and for quantifying the drift.  Yes, it is pretty small if its 10-100 Hz.  But if its REALLY causing problems on FT8, this is strange, because the TX and QSO periods are quite short, which means the drift is pretty fast.  And Icom seems to have known there was a problem - no other reason for the thernal padding - and tried to "patch" rather than fix it.

Regarding the VCTCXO... ummm... still have to look at it.  If this is really how they built the M.O. and did NOT compensate the DAC voltage reference (which would be VERY odd), THAT would be a brain-fart.  BTW, are you SURE this is an XO?  I only ask because I've seen similar behavior (rapid but short excursion drift) from "voltage stabilized" non-XO VC M.O. s when the designer attempted to use the control loop in a clever way to stabilize a less expensive and drifty bulk resonator (or even an inappropriate crystal cut could cause this).  Which would ALSO be unexpected in this design.

Either way, I agree with you.  Sounds like Icom DID misjudge the user community for this radio and then tried to fix the problem at nearly zero cost using thermal padding, after setting high performance exectations. (THUD)

Seems like an "A" version is likely to be issued.  Perhaps with an external reference INPUT.  Still have not really looked at this and not likely to until this weekend.  But it will be interesting to see what conclusions the community has come to.

Best Regards,

Brian - K6BRN


Logged
M0HCN
Member

Posts: 566




Ignore
« Reply #16 on: May 02, 2019, 07:28:21 AM »

No real way to know, but another common trap with modern VCXOs is that they quite often use a built in temperature sensor and digital lookup table to do the temperature compensation, this works sort of (and is cheap), but can add measurable steps in the output frequency if not done well.

There is something to be said for old school SC quartz in an oven (That stays on 24/7) and a real narrow PLL to lock to the external reference.
I almost suspect a digital guy doing the design (Clocks are digital, right???!).

73 Dan.
Logged
W9IQ
Member

Posts: 3077




Ignore
« Reply #17 on: May 02, 2019, 08:03:39 AM »

As a point of reference, the specifications call out:

      Frequency stability    Less than ± 0.5 ppm (–10°C to + 60°C; 14˚F to 140˚F)

That would yield less than +/- 72 Hz on 144 MHz and +/- 648 Hz on 1296 MHz. Perhaps they are meeting spec but the spec is inadequate for the intended use.

- Glenn W9IQ
Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K6JH
Member

Posts: 508




Ignore
« Reply #18 on: May 02, 2019, 07:13:19 PM »

I should mention this is what my recollection was of posts at the groups.io IC-9700 site. I have no firsthand knowledge of the IC-9700, have no access to the service manual to see schematics, may have gotten the numbers off a little, etc. YMMV. ;-)

As an EE 5wpm Extra Ham, I just find it interesting.
Logged

73
Jim K6JH
NO9E
Member

Posts: 873




Ignore
« Reply #19 on: May 03, 2019, 07:58:06 AM »

It seems that stability is just a function of price. Digikey sells IQOV-162/IQOV-164 Oven Controlled Crystal Oscillators. The first one is SMD mount, has  ±5 ppb stability and costs $80. The second one is larger, has <±1 ppb stability and costs $200. Seems the cheaper would have been good enough but perhaps it costs what is a profit margin for ICOM.
Ignacy, NO9E
Logged
K6JH
Member

Posts: 508




Ignore
« Reply #20 on: May 03, 2019, 06:28:23 PM »

Yeah, it's that price issue. Otherwise why not just be done with it and put in a GPS disciplined rubidium standard for $2119? So what if the price of the radio doubles?  Grin

https://www.digikey.com/product-detail/en/iqd-frequency-products/LFRBXO059244BULK/1923-1563-ND/8633850

Frequency10.0MHz
Frequency Tolerance±0.05ppb
Frequency Stability±1.50ppb

Short Term Stability (AVAR):
1s      0.08ppb
10s    0.03ppb
100s  0.008ppb

Ageing:
Day       0.005ppb
Month   0.05ppb

Or maybe a GPSDO module with built-in GPS, stable to 1ppt?
It's only $1090.
https://www.digikey.com/product-detail/en/iqd-frequency-products/LFOCXO065760BULK/1923-1544-ND/8633831
https://www.iqdfrequencyproducts.com/products/details/iqcm-110-2-30.pdf

This is FUN as long as I can spend other peoples money! Wink
« Last Edit: May 03, 2019, 06:33:38 PM by K6JH » Logged

73
Jim K6JH
K6BRN
Member

Posts: 1234




Ignore
« Reply #21 on: May 03, 2019, 08:40:44 PM »

Quote
Otherwise why not just be done with it and put in a GPS disciplined rubidium standard for $2119? So what if the price of the radio doubles?

Or, perhaps Icom could have just put in an external 10 MHz frequency reference, just the way most lab equipment does.  And a user could simply buy whatever added stability they need.

Brian - K6BRN
Logged
KX2T
Member

Posts: 1013




Ignore
« Reply #22 on: May 07, 2019, 01:08:28 PM »

I thought this post was about fan noise in the KPA1500 amp not the IC9700 but maybe I'm wrong. It seems that most all of the solid state amps require up graded cooling or either a very large heat sink and re designed cooling chamber like what Acom does on the 600 and 1200 SS amps. Not sure on the Palstar SS amp but the Ameritron ALS 1300 and 1306 are noise boxes as well, even with can's on you still hear that wine which as we get older just might drive one crazy. You are either forced to go with a SS amp around the 500-600W level or back to a good old tube amp like one of the Acom's or Alpha's which use a blower which is shock mounted and the noise is a hell of allot lower or like some who buy the OM power amps that sound like a 747 in your shack during take off.
I have used the KPA 500 and its not too bad but even the Acom 1000 I have makes less noise and put a solid KW to the antenna plus in most cases doesn't need an external tuner if the SWR is 3:1 or lower. I do believe that SS amp's are still in there infancy stages, time will tell if they can use some kind of liquid cooling heat sink system with some type of extra cooling that doesn't bother once shack noise level.
The SPE amp's are so far the ones that seem to be less noisy plus they have a built in tuner for up to a 4:1 swr, the KPA 1500 seems to handle a higher SWR at reduced power but you pay for that in noise level.
Logged
K6AER
Member

Posts: 5663




Ignore
« Reply #23 on: May 20, 2019, 06:00:55 PM »

 "or like some who buy the OM power amps that sound like a 747 in your shack during take off."

My OM2000+ is 57dBa 12 inches away with the A weighted sould meter. Which model are you referencing?
Logged
NO9E
Member

Posts: 873




Ignore
« Reply #24 on: May 27, 2019, 01:56:47 PM »

Did anybody do MTBF studies for SS amp as a function of sink temperature?

My Expert 2k-fa reaches 50C when running SSB or CW. This most likely means that the heatsink temperature is slightly higher, say 60C and temperature differential with ambient temperature of 25C is 35C. If the heatsink was allowed to go to 100C, the flow requirements would be one half.

Everybody says that SS amp needs to be cooled well. MTBF of BLF188XR is 10,000 years when the module case temp is 100C, but drops down to 100 years when the case temp is 170C. For me 10 years is enough.

Ignacy, NO9E

Logged
K6AER
Member

Posts: 5663




Ignore
« Reply #25 on: May 28, 2019, 07:58:42 PM »

Years? Or did you mean hours.
Logged
K6BRN
Member

Posts: 1234




Ignore
« Reply #26 on: May 28, 2019, 08:35:59 PM »

An MTTF between 30 and 500 years is often claimed for LDMOS devices in marketing materials.  We'll see.  Maybe Ignacy will pull out the fan from his amp and we'll have at least ONE data point.  Smiley

Brian - K6BRN
Logged
M0HCN
Member

Posts: 566




Ignore
« Reply #27 on: May 29, 2019, 04:19:35 AM »

The trap with that is what happens under fault conditions....

Sure, steady state a heatsink at 100c is not that big a deal as long as junction to heatsink is not too high (Doubling up the output devices helps here, as does the use of the modern plastic package (instead of ceramic air cavity) parts), but what happens when the aerial snaps at the centre insulator?

100% reflected power, and instant massive dissipation in the output device if the phase angle is unfortunate, and you are into a race between the reflected power trip getting the bias and drive removed and the die melting. If you can trip in say 10us then yea, not too much of a problem, but 10us is just 20 cycles on topband, 0.1ms and I would be starting to worry, and certainly 1ms is way too slow.

Note that those times are short enough to make relays untenable, it needs to be a pin switch or similar, and then there is the drain voltage trap, in that if you trip too fast and hard you can end up with the power stored in the feedline coming back and over volting the part, again there are ways to deal with it, but you do need to deal with it.

Finally, a heatsink at 100c, will if it is an efficient one result in exhaust air not that far off 100c, which will strip paint off the wall behind the amp (Speaks from experience).

73 Dan.
Logged
NO9E
Member

Posts: 873




Ignore
« Reply #28 on: May 31, 2019, 07:03:09 AM »

Quote
Maybe Ignacy will pull out the fan from his amp and we'll have at least ONE data point.  Smiley

I used to have a 400W solid state amp without a fan but a big sink on top. When running, the sink temperature was above the boiling point. No problem in 10 years except occasional adjustment of idle current.

I am not advocating getting rid of fans (except for really innovative products like class D with envelope restoration). Have a fan but let the internal temp be higher. Also have a $30 Arduino controller with sensors that will shut the amp down in milliseconds when dangerous conditions are sensed. 

Sometimes we think that we should go soft on equipment (and hard on our backs and hearing). Perhaps some remember comments by W8JI on treating 3z500 lightly that it was counterproductive as gettering was not activated.

Ignacy, NO9E
Logged
K6AER
Member

Posts: 5663




Ignore
« Reply #29 on: June 14, 2019, 03:29:00 PM »

Quote
Otherwise why not just be done with it and put in a GPS disciplined rubidium standard for $2119? So what if the price of the radio doubles?

Or, perhaps Icom could have just put in an external 10 MHz frequency reference, just the way most lab equipment does.  And a user could simply buy whatever added stability they need.

Brian - K6BRN

Brian is spot on. A GPS 10 MHz reference chip is less than $20.00 from Digikey:

https://www.digikey.com/product-detail/en/antenova/M20048-1/627-1099-2-ND/7931494

Noone is going to be using this unit without an outside antenna.
Logged
Pages: Prev 1 [2] 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!