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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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Johnny B Good:

--- Quote from: DaveR on November 23, 2018, 03:13:02 am ---
--- Quote from: Johnny B Good on November 21, 2018, 08:45:04 pm ---
 Thirdly, if you feel the need to match the existing 50MHz 100ppm frequency reference to the counter's display resolution, then install a 50MHz 0.1ppm TCXO (if you're going to bother at all, why only take half measures with a mere 1ppm rated TCXO when you can get hold of a 0.1ppm ROJON part from a Chinese supplier on Ebay for as little as 15 or 16 quid?  :)).


--- End quote ---

I bought one of these not long ago:
https://www.ebay.co.uk/itm/External-TCXO-clock-PPM-0-1-for-HackRF-one-GPS-Applications-GSM-WCDMA-LTE/173432677234?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

and have just looked up the spec in the seller's listing: I thought it was 1ppm, but it's shown as 0.1ppm in the headline, and referred to as 0.1 - 0.5ppm in the description.  It's Rojon, but only half the price of those referred to earlier.  I wonder how much confidence you can have that 0.1ppm means anything like that accuracy, or that the £15 and £22 TCXO cans contain anything different to this £8 one?  The answer, of course, is "none".  Caveat emptor, again!

--- End quote ---

Hi Dave,

 That would require the addition of a 5 times pll multiplier since it's the all too ubiquitous 10MHz 0.1ppm TCXO that I kept bumping into in my search for a 0.1ppm 50MHz unit. That £15.53 JYEC TCXO on a handy test board is worth shelling out the extra 7 quid for imo in order to avoid the extra cost and work of adapting a 10MHz reference to the requirements of the FY6600 so, as I mentioned in my reply to Soundtec just now, I've got that module winging its way to me as I type.

 A point I was making in the original posting attempt that fell foul of the refresh button was my observing that every picture of a 0.1ppm TCXO I'd looked at showed a trimmer adjustment access hole in the can. Since I didn't observe any such hole in the cans of the 1ppm TCXOs I'd seen pictures of, I think one can safely conclude that if there is such a hole, it's got to be a 0.1ppm part.

 That discrepancy between the headline +/-0.1ppm and the wider +/-0.5ppm accuracy/stability figures is just a matter of the wider -10 to +60 deg C range compared to the less arduous room temperature range of 0 to 25 deg C.

 In the case of the part I've just ordered, I notice a degradation of temperature stability over the -10 to +60 deg C range to just +/-0.2ppm versus the more typically quoted 0.5ppm value. Hopefully, the TCXO module is actually as good as this. The internal temperature of the FY6600 is more likely to be 40 to 50 deg C rather than the 25 degrees C upper limit on its 0.1ppm rating and I can't see any easy way[1] of ensuring it stays at or just above typical room temperature.

 Since the degradation of temperature coefficient in this case would appear to be only an extra 0.1ppm rather than the more usually quoted 0.4ppm worsening, it shouldn't be too difficult to trim it to better than 0.1ppm at the elevated temperature in any case.

Regards, Johnny B Good

[NOTES]
 
[1]  I can see a hard way to achieve 'room temperature' operation for the TCXO which involves cutting a 47mm diameter hole in the base, fitting a slimline fan[2] and adding a deflector to divert the incoming fresh air straight towards the TCXO end of the main board. This would probably be a good thing to do regardless if only for the sake of everything else in the box but I suspect a tweak of the trimmer to compensate for the higher temperature will produce a result almost indistinguishable from that of the 0 to 25 deg C operational temperature range.

[2] Yep! A footnote to a footnote.  :)

 I just found a neat little 50mm square 10mm deep 12v 120mA cooling fan in an icecream tub marked "Fan Cooler Bits" that's been sat on a cupboard shelf in my 'Office' for probably the past two decades. A quick test with a 5v wallwart proves it will run reliably (and, of course, almost silently) at this low voltage and draws just under 43mA so won't be any strain for the under-utilised 5v rail. If anything, the extra 43mA on the 5v rail should provide a small but welcome boost to the 12v rail voltages.

 There is room between the back panel and the PSU board to mount this fan onto the base of the case but, just to present myself with a bit of a quandary, I also found a 60mm square 13mm deep cooling fan which only draws 35mA from the 5.15v wallwart despite its higher 170mA at 12v rating. Obviously, its larger size provides more airflow per mW but the only place it could be installed would be the top cover just over the area between the heatsink and the TCXO location. This would have the bonus of eliminating the complication of ducting but would spoil the top cover with a wire finger guard covering a 57mm diameter hole.

 This leaves me with the choice of style over function versus function over style - decisions, decisions. This is something I'll have to give some consideration to. Oh, and BTW, I found yet another 50mm square 10mm deep fan that draws just 28mA from the wallwart ( a mere  144mW) and seems to offer about the same CFM. I don't seem to be short of cooling fan options at any rate.

DaveR:
Hi Johnny,

I wasn't suggesting that you could use one in the FY6600, just alluding to the same item being on sale for wildly different prices from different suppliers.  As for the 10MHz one I bought for £8, I've tested it against RWM on 9996kHz and it comes in at 0.2ppm, which I'm not going to complain about, and I've had a look in the trimmer hole and the trimmer is there, so it's identical to the £18 version here:
https://www.ebay.co.uk/itm/TCXO-10MHz-10-000000MHz-0-1ppm-Ultra-precision-Crystal-Oscillator-DIY-AUD-GC1-XH/381746677180

I've also put a piece of kapton tape over the can, so now I've got the golden version as well!  ;D

Regards,
Dave

Johnny B Good:

--- Quote from: DaveR on November 27, 2018, 02:18:39 am ---Hi Johnny,

I wasn't suggesting that you could use one in the FY6600, just alluding to the same item being on sale for wildly different prices from different suppliers.  As for the 10MHz one I bought for £8, I've tested it against RWM on 9996kHz and it comes in at 0.2ppm, which I'm not going to complain about, and I've had a look in the trimmer hole and the trimmer is there, so it's identical to the £18 version here:
https://www.ebay.co.uk/itm/TCXO-10MHz-10-000000MHz-0-1ppm-Ultra-precision-Crystal-Oscillator-DIY-AUD-GC1-XH/381746677180

I've also put a piece of kapton tape over the can, so now I've got the golden version as well!  ;D

Regards,
Dave

--- End quote ---

 Actually, Dave, that would have been a better idea. I could have used Arthur Dent's technique of using an NB3N502 14 MHz to 190 MHz PLL Clock Multiplier to generate the 50MHz clock from the 10MHz OCXO that he'd installed into his Fy6600[1]. In my case, substituting the OCXO with the less power hungry 0.1ppm 10MHz TCXO instead.
 
 I've taken another IR thermometer survey of the main board, in particular the area adjacent to the 50MHz clock chip packed out with three linear voltage regulator chips raising the board temperature to circa 70 deg C, leaving the clock chip, as best as I can determine, at a rather toasty 50 deg C. My airflow deflector idea just ain't gonna fly in this case.

 Closer inspection of the picture of what I've ordered  suggests a circuit board size of 50 by 35 mm which will sit nicely over that 28mA @5v 50 x 50 x 10 mm fan that I plan on fitting into the bottom of the case in the space adjacent to the main board between the PSU and the rear panel. It looks like I won't be recycling that little PCB as a test mount for other XO clock generators after all since I've decided that, in this case, it'll be easier "To bring Mohamed to the Mountain".

 JOOI, I'm looking at a 3N502 chip right now on Ebay for £3.49 delivered from a London based warehouse <https://www.ebay.co.uk/itm/NB3N502DG-Frequency-Multiplier-8-Pin-SOIC/173385949750?epid=648417593&hash=item285e9ba236:g:psUAAOSwxDtbNlVW:rk:3:pf:0>

(https://preview.tinyurl.com/y8mosmkv).

 Of course, now that I've ordered the 50MHz part, the die is set and there's little point in my ordering a 3N502 frequency multiplier chip. However, since a 10MHz 0.1ppm TCXO is a damn sight cheaper to buy than a 50MHz TCXO, plus the fact that it's better to relocate the replacement TCXO away from the heat of those three voltage regulators anyway, for anyone else contemplating a similar TCXO upgrade, the 10MHz TCXO plus freq multiplier chip is not only cheaper, it's also the better option imo even if you aren't planning on fitting a small cooling fan.

 Nice touch BTW, using kapton tape to 'upgrade' your TCXO to a 'Golden' version. :-)

 I noticed that the 10MHz TCXO you linked to is from the same trader that sells those three 50MHz TCXOs I mentioned earlier, ranging from £17.90 (9p cheaper than that 10MHz example you mentioned) to a top end of 22 quid for one in a square can. When it comes to 50MHz 0.1ppm TCXOs on Ebay, it's a very small world indeed.

 I had to google "RWM". I'm more familiar with WWV which operates 4KHz above RWM's frequency allocations at precisely 5, 10 and 15 MHz with the additional frequencies of 2.5 and 20 MHz. I've used the 10MHz WWV signal in the past (some 20 odd years ago now) to calibrate my Kenwood TS140S HF transciever which I recently rescued from a damp and neglected basement radio shack come workshop.

As far as I can tell, its frequency calibration appears not to have suffered in spite of the decades of neglect but I no longer have an external antenna by which to tune into the 10MHz WWV signal to confirm this. Even with a good antenna, it wasn't always possible to get a good enough signal from WWV to perform such calibration checks.

As far as I remember, I only had to recalibrate it the once shortly after I'd purchased it. Aside from the initial warm up from cold, it remained within one or two hertz of the 10MHz signal, demonstrating remarkable frequency stability for a late 80s example of radio technology.

 Regards, Johnny B Good
 

[NOTES]

[1] Reply #151 Posted just over a year ago (page 7).

[2] I've just had another look at the description of this "oscillator clock power supply". The dimensions given are "size: 20.8 x 13.2 x 15mm" which is clearly a nonsense unless they're that of the bare TCXO itself which, now I think about it, seems more likely. Double checking against the 74HC04D chip on the board to get a sense of scale confirms I was in the ball park with my original size estimate.

 My new estimate of the board's dimensions are now ever so slightly revised downwards to 45 by 30 mm which gives me a touch more leeway on exactly how I'll be mounting it over the fan to catch the incoming airflow without creating unwanted turbulence near the fan blades (which is a sure fire way to drastically reduce the efficacy of these high volume/low pressure axial fans).

 I'll want to provide ducting to divert the incoming air past the oscillator board and towards the front in order to minimise losing too much of that hard won cooling air straight out of the rear panel vents which I don't want to block off. I need all the exhaust venting cross sectional area I can recruit to exhaust the warmed over air, hence the ducting so that what does escape via the rear panel vents has already managed to pick up and carry away some heat from the innards of the box.

 I've got a few more weeks to install the fan before that TCXO board arrives anyway so I might as well do some testing to make absolutely sure there's not going to be a problem in stealing power from the 5v rail to drive the fan before I start cutting holes in the bottom of the case. I rather doubt there will be a problem but you can't take this stuff for granted. The most likely side effect I'm expecting is a slight boost in the 12v rail voltages which, in moderation, will be no bad thing in this case.

Johnny B Good:

--- Quote from: Johnny B Good on November 29, 2018, 03:36:22 am ---
=====bulk of previous reply snipped====

[NOTES]

[2] I've just had another look at the description of this "oscillator clock power supply". The dimensions given are "size: 20.8 x 13.2 x 15mm" which is clearly a nonsense unless they're that of the bare TCXO itself which, now I think about it, seems more likely. Double checking against the 74HC04D chip on the board to get a sense of scale confirms I was in the ball park with my original size estimate.

 My new estimate of the board's dimensions are now ever so slightly revised downwards to 45 by 30 mm which gives me a touch more leeway on exactly how I'll be mounting it over the fan to catch the incoming airflow without creating unwanted turbulence near the fan blades (which is a sure fire way to drastically reduce the efficacy of these high volume/low pressure axial fans).

 I'll want to provide ducting to divert the incoming air past the oscillator board and towards the front in order to minimise losing too much of that hard won cooling air straight out of the rear panel vents which I don't want to block off. I need all the exhaust venting cross sectional area I can recruit to exhaust the warmed over air, hence the ducting so that what does escape via the rear panel vents has already managed to pick up and carry away some heat from the innards of the box.

 I've got a few more weeks to install the fan before that TCXO board arrives anyway so I might as well do some testing to make absolutely sure there's not going to be a problem in stealing power from the 5v rail to drive the fan before I start cutting holes in the bottom of the case. I rather doubt there will be a problem but you can't take this stuff for granted. The most likely side effect I'm expecting is a slight boost in the 12v rail voltages which, in moderation, will be no bad thing in this case.

--- End quote ---

 Apropos of installing the whole "oscillator clock power supply" PCB into the case as a sort of airflow deflector rather than just transplant the actual TCXO onto the main board in place of the original XO chip, I completed the electrical tests with both the 28 and 43 mA at 5v fans to check the effect on voltages and power consumption.
 
 As expected, the 12v rails enjoyed a modest 30 to 40mV boost with the 28mA fan whilst the 5v rail dropped about 10mV with the overall consumption rising by just under half a watt to the 9.5W mark when driving 50 ohm loads at the 20MHz 20v P2P amplitude setting (maximum consumption conditions). Thus encouraged, I've cut out the hole and fitted the fan exactly as I described in NOTE 2 above (except, of course, for the fan ducting).
 
 With the lid perched loosely to allow convenient test access, the temperatures do appear to have dropped a good 10 deg C all round despite a lot of the incoming air getting blown straight out of the rear panel vents. I've now clipped the lid into place to seal up the gaps and, for the time being, I've taped over the rear vent slots to increase the cross flow air circulation over the main board.
 
 The "Hot Spots" on the top of the case are now merely perceptibly warm spots and even the underside hot area is now significantly cooler than before and I'm now inclined to permanently block the rear vents and open up the RHS vent slots to increase the airflow across the main board rather than faff around with additional fan ducting. Those rear vent slots are now more trouble than they're worth (and they were pretty worthless to begin with imho).
 
 I'm still planning on mounting the oscillator board over the fan to both keep it at little more than ambient and to act is a deflector to direct the incoming air towards the front panel. I think this is likely to prove just as effective a solution as the more fiddly ducting idea I'd had to prevent the rear vents from exhausting incoming cooling air straight out the back.
 
 It can be all too easy to overthink things when trying to find an optimum solution. Initially, it seemed a shame not to put the rear vent to good use but they were a horrible half hearted exercise in passive ventilation to start with, being as they are in a far from ideal location, especially considering the built in tilt to the case before it's made even worse by being propped up by the pull out front support stand.
 
 The kindest thing I could do after addressing the woefully inadequate passive ventilation with a cooling fan was to block this vent and look to improving the existing right hand side vent (the LHS one is perfectly fine as it is). However, I'll deal with that when I finally get hold of the oscillator board.
 
 As things stand right now, simply adding a  five volted 50mm fan and blocking the rear vent slots has considerably reduced the internal temperatures so yet another upgrade that's well worth adding to the list. There's no need to be concerned about 'fan noise' since it's barely audible against the louder fan noise of the Siglent SDS1202X-E DSO which is whisper quiet just as had been remarked upon by most, if not all, of the reviewers who'd checked it out.
 
 IOW, I had to shut the Siglent down before I could ascertain the level of fan noise coming from my modified FY6600. Even then I had to pick it up to place it close to my ear before I could hear any noise. Unless every other bit of kit in your workshop is passively cooled, you'll be hard pushed to detect fan noise from the FY6600 (assuming, of course, that you haven't used the crappiest 50mm fan from your Junk Box collection).
 
 Now that I've had it running for a good half hour or so since I clipped the lid back into place, I can no longer detect any warm spots other than on the underside of the case. That, I have to say, is a remarkable improvement for a relatively simple modification. Opening up the RHS vent slots as a final touch should noticeably improve the effectiveness of this forced ventilation modification to the benefit of significantly improved reliability and an extended service life.
 
 It looks like it's going to be several weeks before I'll have anything new to report so I'll take this opportunity to wish everyone still monitoring this thread a Merry Christmas and a Happy New Year. :-)
 
Johnny B Good.
 

Johnny B Good:

--- Quote from: Johnny B Good on November 29, 2018, 11:04:21 pm ---
====snip====
 
 Now that I've had it running for a good half hour or so since I clipped the lid back into place, I can no longer detect any warm spots other than on the underside of the case. That, I have to say, is a remarkable improvement for a relatively simple modification. Opening up the RHS vent slots as a final touch should noticeably improve the effectiveness of this forced ventilation modification to the benefit of significantly improved reliability and an extended service life.

====snip====
 

--- End quote ---

 One final final post for this year (unless that oscillator board arrives early). I couldn't resist taking another look at improving the RHS vent slots this afternoon. Although there is the potential to open them up without altering their external appearance, the job looked just too fiddly and time consuming to be worth all that effort, not to mention the risk of spoiling the appearance of the case, so I decided against it.

 However, I did spot the gaps where the front panel clips onto the bottom half of the case so, with careful application of a small file, I bevelled the inside of the RHS engagement slot to increase the effective CSA without obviously altering its external appearance and used BluTak(tm) to seal the gap in the LHS engagement slot.

 This represents a compromise between riddling the base under the opamps with a dozen or so 4mm holes to encourage additional airflow under the main board as I'd suggested in an earlier post and improving the existing airflow accidentally provided by the gap in the RHS securing slot.

 Having applied BluTak(tm) to seal up the LHS securing slot in order to favour the improved RHS with more airflow, you might well ask why I didn't block or partially block the LHS vent slots to favour the RHS slots. Well, the answer is that you can overdo this balancing act when restricting airflow in one part without reducing the restriction elsewhere since the increased back pressure can significantly reduce the efficacy of a high volume low pressure axial fan to such an extent as to become counter-productive not just to the total flow of air through the whole box but also to the targeted areas of concern.

The LHS vents might be letting out cool air, seemingly in an unproductive fashion but it's still allowing a higher speed of airflow within the confines of the box to encourage better heat transfer to the circulating air some of which heat energy, whilst diluted, will still escape via the LHS at a reduced temperature whilst the air exhausted via the RHS vent will be carrying more energy as a result of its higher temperature, courtesy of the improved energy transfer from the faster air speed within the box around the heatsink and the main board and its components.

 One might also wonder why I agonised over drilling a dozen 4mm holes in the base after cutting out a whacking great 47mm diameter hole for a cooling fan. Well, TBH, the 47mm hole is an inescapable consequence of blessing the box with a much needed active cooling system, aka, a fan and, as such, is as much a statement as a necessity whereas a bunch of 4mm holes, let's face it, just looks a little naff.  :)

 I reckon I've done about as much as I can to reduce component temperatures short of lending the case a 'Swiss Cheese' look. Installing the oscillator board (once it finally arrives) over the fan location at a jaunty angle to better deflect the airflow towards the front panel should offer a further, if modest, improvement in the efficacy of my active cooling modification.

 Before I forget, I think it's worth noting that despite the optical illusion, that little heatsink is actually square (19mm by 19mm in my case). Whilst I'd had the main board out to modify the retaining slot, I'd thought to check the dimensions with a view to reorientating it to favour the anticipated cross flow of air.

 When I'd first refitted it after the opamp upgrade, I'd replaced it in its original orientation with the fins aligned front to back, thinking it might not completely cover the opamps if I did otherwise (yet another ASS U ME moment). It now sits on the board with the fins parallel with the front and rear panels which should improve heat transfer under the new regimen of my active cooling system.

 Indeed, I think it can even be fitted at +/-45 deg without fouling anything and still cover the opamps if that gives a better alignment with the airflow direction wherever you might choose to locate a cooling fan. Obviously, you need to determine or guestimate which direction the airflow will be taking in order to make an effective choice but at least you have room for manoeuvre to maximse the heatsink's efficacy. In my case, I've simply guestimated that, on balance, an east west orientation rather than the original north south one is the better choice for my setup.

 Anyhow, that's the latest development for the time being. As modifications go, it's been one of the most satisfying ones I've done so far (it's right up there with the opamp upgrade with the PSU mods not too far behind - all vital and worthwhile improvements imo).

 Not only does this mod improve reliability and extend component life, it's also an essential part of the 50MHz clock oscillator upgrade since it should hold the temperature of the TCXO to within a degree or two above room ambient rather than have it subjected to 50 or 60 degree temperatures. There'll be virtually no warm up delay from switch on as a result which is a nice touch to my mind.  :)

 Well folks, that's all for now. Have a Merry Christmas!

 Johnny B Good
 

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