[ARC5] Reversibly modifying 1415kc IFTs

[Ian Wilson]

Hi Brian,

I had some project or another that (also reversibly) used an altered
RF coilset to move an ARC-5 receiver to some other frequency.
However, this was a fixed frequency - oscillator tracking was not
relevant since it only had to work at one frequency.

Not being able to recall what project is going to keep me awake
tonight, I can tell....

73, ian K3IMW


On Wed, Mar 25, 2015 at 4:58 PM, Brian <brianclarke01 at optusnet.com.au>
wrote:

> 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
>