Gents: While one may wish the elegance of a variable speed fan, doing so will likely adversely affect your tuning accuracy. I find that with the flex supplied fan installed in a "full" unit sans xverter (i.e. PA, ATU & full board stack), the unit becomes extremely temp stable in 30 minutes with 0Hz drift afterward (1 -2hrs) when spot checked repeatedly with WWV on 20MHz. The cal setting is repeatable in that the unit drifts into the same point. This is because I use the same relative TX/RX duty cycle and my shack is in my basement, which is seasonally isothermal at about 56F this time of year.
When I used to have the cover off during the more experimental days, the drift was erratic and calibration factors unrepeatable. The stock flexfan is more quiet than the PC's HDD and PS fan combo. I really don't know what gain a variable cooling setup would offer. As to comments regarding DDS installations without a heat sink - that thing boils without it. Also, the drift is much more accentuated without the additional thermal mass to damp slight ambient variations, such as those created by the PA, if installed. If one is using a DDS without a sink, by all means add one immediately for these and other reasons. Regards, Lee Pedlow NG6B San Diego, CA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tim Ellison Sent: Wednesday, February 22, 2006 9:29 AM To: Lee A Crocker; FlexRadio@flex-radio.biz Subject: Re: [Flexradio] How much cooling Lee, See my comments below. We basically agree on most of the points brought up here with the exception of turning off the fan rather than operating it at a very low speed during times where a lot of cooling isn't necessary. 73 -Tim --- Integrated Technical Services "You can't close the door when the walls cave in" --Robert Hunter -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lee A Crocker Sent: Wednesday, February 22, 2006 10:09 AM To: FlexRadio@flex-radio.biz Subject: [Flexradio] How much cooling Tim You have an elegant solution, but probably overkill for this application. I also removed the metal around the area of the fan to reduce resistance. Why did you choose the values of 105 and 150? TE> For a primarily RX application of the radio, yes this would be overkill, but I run a lot of digital modes, so I get those little PA transistors toasty especially running RTTY. The fan controller settings were chosen because they were the default settings that the board was designed to. You can change them by swapping out a few resistors. I chose not to. I left the max fan setting at 105F because I did a little test to see how hot it gets in RX with no cooling. I turned off the fan, left the radio in RX mode and replaced the cover. After About 30 minutes I removed the cover and took the temperature of the PA transistors (on the ceramic top). They were at about 95-100F degrees (I am not so sure about the accuracy of my thermocouple) definitely very warm to the touch. So I decided that 105F was close enough to run the fan at full speed. Could I have set the temperature a little higher? Probably, but more cooling is always better than less. The amp transistors only generate heat when they are drawing current, so the fan running to remove all the "latent heat" during RX is just extra fan noise for no real reason, and waiting for the heatsink to cool down to 105 is kind of arbitrary. It would seem to me that if you decide to transmit you know you are going to need increase cooling so the intention to transmit should be what turns on the fan, not an oscillation around some arbitrary temp. TE>When the radio is on (RX or TX) the transistors are drawing current. Even with the radio off and the power supply on it draws some bias current and without the fan blowing, they do get a little hot. With the fan controller, in RX mode, the fan is rotating at such a low speed that the fan is inaudible and it is at ear level about 2 feet away. The fan does not "oscillate" around some arbitrary temp - the fan speed responds linearly with temperature increase up to 105F. You can hear the fan increase its speed within a few seconds of beginning to transmit. After transmitting, it runs at full speed until the temp drops to 105F. >From that point to ambient, the fan speed is slowing down. The 150F high temperature alert was left the way it was designed because the specs on the PA transistors indicates the max operating temp is 175F so I just didn't see the need to change it. I did not want to use a system that actually turned off the fan completely. The continuous action of turning a fan off and on can lead to the fan seizing up and not coming on when needed. Most computer fan failures are not when they are operating, but when they have been turned on. I wanted to significantly reduce the possibility of that failure scenario by using a solution that does not turn the fan completely off during the time it is operating. The heatsink/fan combo are designed to provide enough heat transfer for digital modes, so the real cooling need only take place during transmit periods, and for a little while longer to take care of any thermal inertia in the system. The idea is to devise a system that is smart enough to run at max cap only when needed. TE> And the fan controller accomplishes that task perfectly. I do not want to make an arbitrary time decision on how long the fan should stay on. I want it to stay on until I know that there is no more thermal inertia in the system that need to be expelled. With a thermostatically controlled controller, the guess work is eliminated. The ideal system would be a combination of my idea and your idea in a 2 stage system. I have been running my SDR-1000 with some series diodes in the fan line to drop the voltage so the fan runs more quietly. The fan runs all the time at a moderate speed, and I have had no problems with overheating. I am adding a second SDR-1000 to my station and the last thing I want is 2 of these puppies cranked up in the war mode. Add to that a couple of amplifiers a whoop tee doo computer system and all its fan noise, and the noise will be intolerable. OSHA will probably come and shut me down. TE>Those 70 dBa earplugs in combination with Bose noise canceling headphones really do the trick :-) I spend most of my time listening, and the reason I am adding a second SDR is to play around with spatial diversity on very weak signals with multiple antenna choices, so even a moderate speed fan is annoying when you are trying to copy someone several dB under the noise, and will prove to be worse when I get 2 boxes running. It would be useful to either shut off completely or to really slow it down to absolute minimum during RX. TE> In RX mode, with the fan controller, the fan noise is inaudible. An on demand system that would turn on the fan to a medium level at key closure and then time out would take care of 90% the cooling needs. A second system that monitors temp and would kick to high would be ideal if you happen to be using digital modes, or you are doing a lot of tuning up etc. This would make a dandy little project for this fine radio. TE>The fan controller essentially does this, but rather than just timing out and shutting off the fan completely, it is getting direct feedback from the actual temperature inside the chassis. I do use a lot of digital modes, so I have a higher comfort level knowing that the fan is going to be running at full speed (max cooling) when the PA transistors are at 105F and no where near their higher operating temperature range. 73 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! 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