[R-390] Receiver noise

[Roy Morgan]

> On Oct 9, 2018, at 10:15 AM, dog <agfa at hughes.net <mailto:agfa at hughes.net>> wrote:
> 
> When I don't have an antenna on the balanced (or unbalanced) inputs, the noise level is quite low on the RX. ... I can hear the rx internal noise with no antenna, and when I attach an antenna, I hear an increase but nothing like the R390A. Is this typical? 

Is this an R-390/URR (the non-A)? (That should not matter it seems to me.)

Have you set the IF gain?  On an R-390A, it is often found that the IF gain needs to be adjusted. The procedure is simple, though I don’t remember the details.   I would put a resistor on the input (125 ohms on balanced input), no antenna, gains all the way up, and set the IF gain pot for modest noise - a low level on the line output meter.  (AGC on or off should not make a difference.). Then see if most bands give the same amount of noise.

You might want to do a rough sensitivity check if you have a signal generator.  Note that the calibrator signal is introduced at the very first stage of the radio, and gives a quick rough check of overall sensitivity.

Also you may want to go through the set with known good spare tubes one at a time, replacing the original at each step, to see if you have a weak tube.

Roy


Roy Morgan
k1lky68 at gmail.com <mailto:k1lky68 at gmail.com>