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Nose to the windows
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"Philip"
Slippery slope John....
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Now you'r addicted and there's no known cure .. I blame Hans :) Philip G4JVF --- In QRPLabs@..., "m0els" <m0els@...> wrote:
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John Randall
It did arrive as well,? in what looked like a margarine tub...hi. Good idea I must add. Now just clearing some space on which to start assembling it. I opted for the 80m/160m LPF, as this kit will replace my HF rig which is currently an IF on 80m for for the G3XBM 475Khz transverter kit. Getting it all in a metal box within the existing enclosure should be easy. I will also change the 20Mhz xtal for a more stable oscillator. John ? Digitally signed mail - M0ELS From: Philip <pcteee@...> To: QRPLabs@... Sent: Thursday, 25 July 2013, 15:11 Subject: [QRPLabs] Re: Nose to the windows
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Slippery slope John....
Now you'r addicted and there's no known cure .. I blame Hans :) Philip G4JVF --- In QRPLabs@..., "m0els" wrote: > > As the postman approaches down the road, I h. One had is holing the soldering iron and the other is pecking away at the keyboard. > > > 73 > John > |
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Barry Chambers
开云体育On 25/07/2013 15:56, John Randall
wrote:
?John I'm playing with using a U2 to drive a30 watt class E PA directly at 475KHz and using WSPR. The PA driver circuit needs a 0/5V square wave input signal so I've removed Q1 and Q2 from the U2? and am feeding the pin 7 output from the DDS module through a 4066 switch. The control signal for the 4066 is taken from pin 19 of the ATmega168 since I want the PA driver signal to be at 0V during the WSPR off period. If I take the PA driver signal from Q2 drain of the U2 kit, it's 'high' when I want it low! -- 73 Barry, G8AGN |
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John Randall
Ok Barry, I will check it all once I get it all into a screened box. The tvtr is 10w out, but also need to build a 100w amp as I am not getting signal reports at the moment bar one local station. Cable loss according to my MFJ259 @ 475 kHZ is OVER 4dB PLUS THE ANTENNA LOSS. 73 John ? Digitally signed mail - M0ELS From: Barry Chambers To: QRPLabs@... Sent: Thursday, 25 July 2013, 16:15 Subject: Re: [QRPLabs] Re: Nose to the windows
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On 25/07/2013 15:56, John Randall
wrote:
?John I'm playing with using a U2 to drive a30 watt class E PA directly at 475KHz and using WSPR. The PA driver circuit needs a 0/5V square wave input signal so I've removed Q1 and Q2 from the U2? and am feeding the pin 7 output from the DDS module through a 4066 switch. The control signal for the 4066 is taken from pin 19 of the ATmega168 since I want the PA driver signal to be at 0V during the WSPR off period. If I take the PA driver signal from Q2 drain of the U2 kit, it's 'high' when I want it low! -- 73 Barry, G8AGN |
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Graham
开云体育Mmmm, might not as easy as that.
I had the same idea. I haven't yet rechecked but I seem to recall in my perusal of the Atmega data sheet that in order to use an external oscillator rather than a crystal you need to set a specific bit or two for that purpose when the chip is programmed. Something else became a priority before I pursued the U2 kit built any further. It is still patiently waiting it's turn on the workbench. cheers, Graham ve3gtc On 13-07-25 02:56 PM, John Randall wrote:
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Hans Summers
John & all Regarding the food container: the kits usually ship in a small cardboard box but they must have run out! So while waiting for replacements, the plastic box substitutes are used. It's not a matter really of margerine though. The containers are new, available in small quantities from the local equivalent of our UK poundshop or the US dollar store.?
Regarding replacing the 20MHz crystal: technically, Graham is correct, there are "fuse" settings in the chip which control what kind of external oscillator is used: external oscillator, or crystal, and whether it's low (e.g. 32.768kHz) or high frequency, and what start-up characteristics and stuff. If the fuse is set for "external oscillator", connecting a crystal will never work.?
However, in THIS case, I think everything will be fine. The fuse setting specifies high frequency crystal. But if you have an external oscillator and you feed it into pin 9, in my experience, everything will work fine. The AVR won't know it doesn't have a real crystal.?
73 Hans G0UPL On Thu, Jul 25, 2013 at 4:15 PM, Barry Chambers <b.chambers@...> wrote:
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Graham
开云体育Thanks for the info Hans.
I will be sure to give a try. Unfortunately someone else is likely to beat me to trying it. I will keep an eye open or such reports. cheers, Graham ve3gtc On 13-07-25 10:35 PM, Hans Summers wrote: ??? |
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Barry Chambers
开云体育On 25/07/2013 19:53, John Randall
wrote:
?John I also have a 472kHz 'XBM transverter which works well - about 13W output to an inverted L (6m vertical section). Actual eirp is very small hence QRP operation. My class E PA for the U2 kit? is roughly based on the "Design Notes" article by G4JNT in May 2013 RadCom - see his refs 3 and 4. The paper design from the software needed quite a lot of tweaking "on the bench" to get the class E waveforms right. A good explanation of this is given in Nat Sokal's QEX article in the Jan/Feb 2001 issue. When correctly adjusted, a class E PA can have an efficiency of 80-90% but will only work for digital modes not SSB. The 4066 mod to the U2 kit that I mentioned yesterday does work but in the "not transmitting" state, the 4066 still leaks too much so I'll next try either a small c/o relay driven from the original Q2 or another digital solution based on an AND gate. The U2 kit is certainly versatile. One minor mod I'd like to see on the PCB is slightly larger tracks in places and more robust pads for making connections - larger diameter so that pcb pins/header could be installed? -- 73 Barry, G8AGN |
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John Randall
Graham, I thnk with these processors if the internal fuses are not burned for an internal oscillator, then the default is an external one. I used an ATMEGA-8 for a freq counter project and it was the same with that. If you can get hold of a 1ppm ocxo or better, then you will be smiling. 73 John ? Digitally signed mail - M0ELS From: Graham To: John Randall Sent: Friday, 26 July 2013, 10:56 Subject: Re: [QRPLabs] Re: Nose to the windows John,
Agreed. My recollection of reading the appnote for the Atmega328 was that you "needed" program the correct fuse otherwise an external clock source would not work. As Hans pointed out, that is indeed technically true however his experience was that it did not make that much difference and that when programmed to use an external crystal (or say 20Mhz), replacing the crystal with an external clock source would also work without having to reprogram any fuses. I started down this path wanting to use a more precise clock source for the U2's micro just as you are intending but also with a though to using a higher precision oscillator (i.e. 10Mhz OCXO) to drive the micro for some timing experiments. Due to higher priorities, both of these little projects have been temporarily set aside but now having Hans' comments to hand, I will probably be able to move a bit further ahead with both a little sooner than anticipated. I look forward to your report to the QrpLabs list your comments and results of replacing the U2's crystal with an external clock source. cheers, Graham ve3gtc ? On 13-07-26 05:15 AM, John Randall wrote:
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Hans Summers
Hi John The default fuse setting on the AVR is for the internal 8MHz RC oscillator, and the divide-by-8 fuse is set. So the effective internal clock speed is 1MHz.? 73 Hans G0UPL On Fri, Jul 26, 2013 at 11:26 AM, John Randall <m0els@...> wrote:
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