Welcome to PE1RAH.
On AMSAT-BB I often seen that amateurs having problems
with their 13cm down convertors. I had also some problems with getting the
local oscillator correctly tuned. The problem is that not everyone has expensive
frequency counters till the 2400 MHz area.
I have here an self-made frequency counter, but is
stops till 1800 MHz. Measuring the crystal was what I wanted to do, but it gave
to less signal to drive my counter L Then I thought out some even more simple and more easier way to measure
the oscillator frequency.
The frequency of the oscillator is 8.8125 MHz. When we
take the 49th overtone, then we have 49 x 8.8125MHz = 431.8125 MHz
When we use an reciever that can measure the
center-frequency, than we can also measure the local oscillator of the NORSAT
(Or maybe other) convertor. I have tuned my NORSAT convertor by using my FT847.
The 2m can be used to feed the convertor with 12Vdc via coax. At the 70cm I
connected an portable 70cm antenna and placed it close to the crystal of the
convertor. The signal is weak but well detectable by the FT847. An FT726, FT736
can also be used, and many other types what are able to measure
centre-frequenty. Below you can see an simple drawing how it can be done :
Making the LO more stable:
Below you can see how I made the local oscillator more
temperature stable. It is done by using an MURATA heat-clip. The heat-clip is
an metal clip that can be put over the crystal. At the metal clip an PTC
resistor is glued. When an stabalised voltage is supplied over the PTC, it will
warm up to an constant temperature. I used the 9V internal stabalised voltage
of the NORSAT.
Here an close-up of the heat-clip:
This page is designed and created by PE1RAH. (William Leijenaar).