[Boatanchors] General Coverage for Ham Receivers

[Robert Nickels]

On 11/11/2023 9:51 AM, Keith Densmore wrote:
>   curious if anyone has played around with using a DDS generator to expand frequency range of  receivers of this type.

Hi Keith,

I've done that quite a lot, using both programmable oscillators for a 
single frequency, and the Si5351 clock generator IC.    The logic-level 
output has always been sufficient when used to drive a mixer or balanced 
modulator, as I've used them extensively to add frequency agility to 
crystal-controlled military and commercial radios.   An additional stage 
of amplification is usually needed to drive tube type transmitters to 
full output.

But the application you mentioned is ideal since the mixer is always 
followed by a tuned circuit that will eliminate any harmonics or other 
spurs from the digital oscillator.   Your mention of the Drake FS-4 
reminded me that maybe I ought to do something with the "FS-4 Lite" that 
I designed a few years ago - it was put aside when the "global supply 
chain meltdown" made it impossible to get the parts needed but that's no 
longer the case.   I used an Arduino Pro-Mini to control the Si5351 and 
a small OLED display and encoder to select the desired injection 
frequency.    Power is supplied via a 5V USB charger/power supply.

Here's a photo of it connected to a Drake R4A, tuned to receive WWV on 
10 MHz: https://i.imgur.com/Z6RnFlE.png

The Drake manual includes a table that shows which bandswitch position 
to use for proper preselector tuning, but to eliminate the need to 
constantly refer to it,  I programmed the OLED with that information as 
well.    I sent one to Drake expert WA8SAJ to test and he pronounced the 
output when it was used to drive a T4X transmitter to be as clean as 
with a crystal.     The Si5351 is used in many QRP rigs now on the 
market as well.

New technologies can breathe new life into old radios in many ways!

73, Bob W9RAN