[ARC5] Reversibly modifying 1415kc IFTs

[Brian]

Hello Ian,

Great idea.

If you changed the oscillator frequency in a Command receiver to produce the 
1750 kHz, what did you do about tuning dial tracking?
Have you tried raising the BFO frequency the same way?

73 de Brian, VK2GCE.

On Thursday, March 26, 2015 6:09 AM , Ian said:

There are a number of ham receiver designs that use
a frequency of around 1750kc as a first IF. Several
80/40m "band imaging" receivers do this.

The 1415kc IFTs have 60uH coils which are tuned to
frequency by a parallel combination of a fixed 180pF
capacitor and an air-variable trimmer.

If you reduce the fixed capacitor value, the resonant
frequency increases. It turns out that 270pF in series
is about right for 1750kc (240pF would be better).

The fixed capacitors are those small metal tub thingies.
It is straightforward to remove the connection to the top
of the capacitor (the other end attaches the capacitor to
the mica top plate with a screw) and insert a small
ceramic capacitor in series. If you do this with some
thought, the operation could be reversed with no visible
signs. A piece of tape can be applied to the outside of
the can stating what has been done (also reversible).

Hope this is helpful. If the heresy content is too high,
please delete me.

73, ian K3IMW