"Stephen"

#91

Greetings from sunny England,

Those of you who have built the beacon kits will have noticed that we do not use NP0 caps. In fact I cannot remember the last time I used them. Yet these beacons are very, very stable in output frequency as are my other projects. Which makes me wonder if modern caps are much less temperature sensitive than they were in times of yore and question why people still use them.

What do you guys think?

Regards,

Steve G0XAR

"hanssummers2000"

#92

Hi Steve et al

Greetings from sunny England,Speak for your own part of England! Here in London, the sun has disappeared behind some thick clouds.

Those of you who have built the beacon kits will have noticed that we do not use NP0 caps. In fact I cannot remember the last time I used them. Yet these beacons are very, very stable in output frequency as are my other projects. Which makes me wonder if modern caps are much less temperature sensitive than they were in times of yore and question why people still use them.

What do you guys think?Personally I think NPO caps might be useful sometimes, but generally are over-rated. There are a lot of other temperature-sensitive parts involved in an oscillator, including of course, the crystal itself.

In past QRSS work, I have used the DB6NT crystal heater, see  . I found that it completely removed any observable drift, even though I didn't trouble with NPO capacitors. So I believe that, in the case of crystal oscillators for QRSS, the main freuqency-drift-determining component is the crystal itself. The DB6NT crystal heater is very nice. It typically goes on an HC49 crystal, whereas the crystal in the QRSS Beacon kit is a 1/4 height crystal. So I'm not sure how well it would work, or maybe need adaption. Beware too, that it will cost you somewhat more than the QRSS beacon kit cost you!

73 Hans G0UPL

"Paul Daulton"

#93

开云体育

my experience is not all npo caps are created equal. I suspect many are mismarked as happens with nuts and bolts. Mono caps or cog as they are sometimes called exhibit better stability.

?

My beacon is mounted at the center of my dipole, temp here has been from 100 degrees F daytime to 75 or so at night. My beacon will shift about 25 to 30 hz. this fall I may have to take it down and reset it. I have a 7805 regulator down in the shack, power is fed to beacon through rg59 coax and? f? connectors. I could replace the 7805 with an LM 317 and limit the voltage to 6v and trim the freq by adjusting the voltage. also the led may shift somewhat due to temp change, I have found this the case when using varactors to tune vfo's. Those in cooler climates may want to put a heat source in the case if the beacon is to be remote mounted. a small incadesent lamp or led or resisor? and lots of insulation on? the beacon. would help.

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Drift is a minor problem.

?

Paul k5wms

Show quoted text

----- Original Message -----

From: Stephen

To: QRPLabs@...

Sent: Thursday, June 17, 2010 11:24 AM

Subject: [QRPLabs] NP0 Caps

?

Greetings from sunny England,

Those of you who have built the beacon kits will have noticed that we do not use NP0 caps. In fact I cannot remember the last time I used them. Yet these beacons are very, very stable in output frequency as are my other projects. Which makes me wonder if modern caps are much less temperature sensitive than they were in times of yore and question why people still use them.

What do you guys think?

Regards,

Steve G0XAR

"Charlie , W5COV"

#94

开云体育

I have to agree with Hans . NP0 caps are fine in some applications , but not all . I just changed a pair of them out in a filter and replaced them with some high quality "glass" capacitors , which work much better in this application.

?

I am on the waiting list for a beacon , but while waiting and having worked with QRSS60 for many years , know the crystal and oscillator are the areas of real concern .

?

I built my 10.140 MHz.?oscillator on a very small board?separate from the transmitter . I soldered a thermistor to the crystal to maintain a constant temperature . The entire board is then encapsulated in a small container and filled with thermal conductive epoxy .Only the leads for hookup to the transmitter come out of the package .

?

I haven't yet had time to run many tests with it . I'll post my results once I can run it for a few days under different temperature conditions .

?

Charlie , W5COV

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Matt Palmer

#95

NP0 caps become much more important when going cold... not such an issue for ham electronics which will likely never see temps below 0C

Matt
W8ESE
sent from my VIC-20

Show quoted text

On Thu, Jun 17, 2010 at 12:33 PM, hanssummers2000 <hans.summers@...> wrote:

?

Hi Steve et al

> Greetings from sunny England,

Speak for your own part of England! Here in London, the sun has disappeared behind some thick clouds.

> Those of you who have built the beacon kits will have noticed that we do not use NP0 caps. In fact I cannot remember the last time I used them. Yet these beacons are very, very stable in output frequency as are my other projects. Which makes me wonder if modern caps are much less temperature sensitive than they were in times of yore and question why people still use them.
>
> What do you guys think?

Personally I think NPO caps might be useful sometimes, but generally are over-rated. There are a lot of other temperature-sensitive parts involved in an oscillator, including of course, the crystal itself.

In past QRSS work, I have used the DB6NT crystal heater, see . I found that it completely removed any observable drift, even though I didn't trouble with NPO capacitors. So I believe that, in the case of crystal oscillators for QRSS, the main freuqency-drift-determining component is the crystal itself. The DB6NT crystal heater is very nice. It typically goes on an HC49 crystal, whereas the crystal in the QRSS Beacon kit is a 1/4 height crystal. So I'm not sure how well it would work, or maybe need adaption. Beware too, that it will cost you somewhat more than the QRSS beacon kit cost you!

73 Hans G0UPL

Mike-WE0H

#96

I use that Lyle K0LR style thermistor crystal heater in my freq counter. It has maintained better than 1hz stability for over a year now.

Mike
WE0H

Charlie , W5COV wrote:

Show quoted text

 ...
I built my 10.140 MHz. oscillator on a very small board separate from the transmitter . I soldered a thermistor to the crystal to maintain a constant temperature . The entire board is then encapsulated in a small container and filled with thermal conductive epoxy .Only the leads for hookup to the transmitter come out of the package .
 I haven't yet had time to run many tests with it . I'll post my results once I can run it for a few days under different temperature conditions .
 Charlie , W5COV