¿ªÔÆÌåÓý

  1. BITX20
  2. Messages
Single Messages Topics Expanded Polls

Re: Rx Radio #ubitx-help

 

I did not really do much in the way of calculating.? I do have the equipment to check it our.? One way was to feed in a 1000 Hz audio tone into the mic input.? Then measure the output power.? Then go up and down in frequency to where the power makes a big drop off.??

I know that by lowering the value of the capacitors the filter gets wider and going up in value the filter gets narrower.? The first attempt was around 68 pf (or whatever the standard value is near that).? That made the filter way too wide,so I put in the 80 some and that put it close enough for me.

Even going into a hifi amp it will be difficult to make the music sound very good.? If the filter cuts out the highs and lows before it gets to the demodulation part, about all you can do is use an? equalizer and run the audio from less than 500 hz way up and the audio above 1800 way up as there is almost no audio outside 500 hz to 1800 hz.

As the ubitx is, it is a great piece of engineering, but it is also easy to make changes to for anyone that has a bit of equipment and know how.? Many have published their modifications so that people like me only need to do them.

de ku4pt


On Fri, Jun 22, 2018 at 5:41 PM, Mike aka KC2WVB <rb5363@...> wrote:
Ralph,?
Thanks, you did the calculations so a change is now simply swap out. I knew the filter was narrow but not that narrow. I guess they aimed at between ideal for CW and SSB by selecting as is.?
I don't have the stuff required for guaranteeing success when swapping out surface mounted capacitors. If I did I might make the change.?
I run my audio into the line in on a hi-fi system and can make the AM sound well enough to listen to by making audio adjustments, but I can see where it would be a pain in the arse to listen to the AM off a tiny 8 ohm speaker especially when it's frequency range is limited like it is.

On Jun 22, 2018 4:16 PM, "Ralph Mowery" <rmowery42@...> wrote:
While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.? The music will sound clipped or somewhat distorted as it often has higher audio frequencies than? most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.? I changed out the 5? 100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).? That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.? Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .? So around 3 khz would be good for AM.

de ku4pt


_._,_._,_
Join [email protected] to automatically receive all group messages.