[rfeenstra]

In a post in Ron's 70 modifications, I mentioned that I compared the sound of the 570 with my 96 TRF radio.  The TRF has much better high frequency response as the there are no highly selective IF transformers to kill the side bands.  As a result, cymbals and snares sound a bit dull on the 570.  I decided to play with tuning a bit to see if i could broaden out the IF response to improve the high frequency response.  I used only the three compensating caps to play with that.  At the expense of sensitivity and selectivity, I was able to improve the high frequency response enough to actually get a little shimmer on cymbals and some snare sound rather than just a thud.  Here are some shots of the band pass characteristics taken from the output of the second IF transformer at the detector diode.

First, the curve with the radio properly tuned.  The side markers are at +- 5 khz.  Notice that a 5khz signal is attenuated by about 7 db. 

   


The second photo shows the curve with the IF compensators slightly detuned plus and minus.  Notice that peak signal level is down by about 6 db.

   


In this photo, the markers are at +- 8 khz and the IF compensators detuned a bit more.  Peak signal level is down about 10 db.

   


Then for fun, the curve with an RF signal modulated at close to 100% with a 8 khz sign wave.