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Kuhne QH40A crystal heater problem

on6ab
 

I tried the QH40A crystal heater mod as presented all over the internet. However, it did not work out for me ( my FT847 is a 2004 model).
I can't quite figure out how it is possible that for some people this mod actually DOES work.
The FT847 is using a reference crystal especially cut to be stable at or around room temperature (25C).?
What you actualy do with the QH40A crystal heater is bringing your crystal to a very stable 40 degrees, a temperature on which the FT847 crystal itself is ...unstable.
What you gain (at best) is...nothing.
On the contrary, with the QH40A installed, the frequency on my FT847 is continuously increasing at a 1Hz per minute rate (on 144Mhz)? for hours on end.
Without the mod, at least it more or less stabilize after a while.
Crystals to be used in an oven are cut very differently.
 

Hello,

I see one modif for FT847 for better stability, it is simply to put isolation of foam or plastic on quartz. I never have the stability?problem with my 847, who I use for monitoring some sats. With programm Sat32 ant connecting CAT to Com1 (rs232), who is very good combination for following satellites.

Vy 73 Yvan HB9CSM




--
Yvan
on6ab
 

Hello Yvan,
Indeed, putting foam over the quartz is a far better solution. Looking at the foam that is over the crystals in my 2004 unit, I suspect it was done at the factory.
Meanwhile I improved the stability a lot by mounting a TCXO-9 reference oscillator in the FT847.
I wanted to add my TCXO mod to the files on this group but apparently I'm not aloud to do so.
 

I tried the TCXO 9 mod, and even though it improved stability, on 2 metres FM it generated an awful tone for some reason. Output was clean, and no amount of decoupling would cure it. So I used a bit of foam with a slot cut in it, and wedged by the case.?
on6ab
 

Hi Andy,
Interesting...
I tested my FT847 (with TCXO-9 mod) on FM today but I can't find any tones as you describe.
I did the TCXO-9 mod a bit different as to what is available on the internet and I made a detailed pdf file of it.
I wanted to add it to the files menu but that seems to be impossible.
If you're interested, drop me a mail bruno.beckers@...
 

i made the sleeping bag for both of my 847s


keeps the swing down to pretty low numbers
I made a homebrew crystal heater for my TEN-TEC 526
out of a little metal clip and a 40C Positive Temperature Coefficient Thermistor
Amphenol #?YQS5745PTO? ?it has a 3C temp swing around 43C

just did not find that necessary on the 847
maybe if one was driving a transverter it might require more help

on6ab
 

Hi, as stated before, a crystal, manufactured to be used at room temperature is not very well suited to put in an oven.
Below you see a typical stability range of such a crystal.
image.png
If you put this crystal in an oven at 40 degrees, you're trying to keep it stable at a non-stable temperature. Not exactly a smart thing to do.
Crystals to put in a 40 degrees oven are MADE for this, they will show the flat part of the curve at 40 degrees, not at 20 degrees.

Op wo 5 jan. 2022 om 17:47 schreef k9wkj <k9wkjham@...>:

i made the sleeping bag for both of my 847s


keeps the swing down to pretty low numbers
I made a homebrew crystal heater for my TEN-TEC 526
out of a little metal clip and a 40C Positive Temperature Coefficient Thermistor
Amphenol #?YQS5745PTO? ?it has a 3C temp swing around 43C

just did not find that necessary on the 847
maybe if one was driving a transverter it might require more help

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