[RTTY] Dealing with High-Pitched Background Noise?

[Joe Subich, W4TV]

> One caveat is that the reason 2125/2295 became a "standard" is that
> any mixing artifacts are outside the passband of a typical SSB
> transmitter. When you go lower those artifacts start to come into the
> passband.

It's no so much mixing products as it is harmonics of the tones.

In general one should *never* use tones less than 1/3 of the transmit
bandpass (e.g. 1 KHz for a transmitter with 200 - 3000 Hz audio) to
allow the transmitter to eliminate third harmonic energy from clipping
in the audio stages.  In practice, because all distortion is not third 
harmonic, it is advisable to keep the audio tones above to 1400 - 1500
Hz if possible.

73,

    ... Joe, W4TV


On 2014-07-25 2:24 PM, Jeff Stai wrote:
> Using lower tone freqs like Bill suggests is one answer, but I usually just
> turn down the volume to just the threshold where I can hear to tune. That
> may sound flip but I used to keep the volume a lot higher than I needed to.
> Once I started experimenting with how low I could go with it I found I
> could use a lot lower volume than I thought after some practice. You may
> also find after lowering the tone freqs lets you choose a lower volume than
> at a higher freq.
>
> One caveat is that the reason 2125/2295 became a "standard" is that any
> mixing artifacts are outside the passband of a typical SSB transmitter.
> When you go lower those artifacts start to come into the passband.
> Something to check on.
>
> Have fun! jeff wk6i
>
>
>
> On Fri, Jul 25, 2014 at 10:11 AM, Bill Turner <dezrat at outlook.com> wrote:
>
>> ORIGINAL MESSAGE:          (may be snipped)
>>
>>> However, I noticed an annoying disadvantage when I did this.  With the
>>> narrow filter engaged, the background noise becomes much higher in pitch,
>>> to the point that I find it quite uncomfortable to listen to.
>>
>> REPLY:
>>
>> Perfectly normal. The default tones for RTTY in most transceivers and
>> software are 2125 and 2295 Hz. When you narrow down the receiver's filters,
>> the white noise falls into that range and that's what you are hearing -
>> high pitched white noise.
>>
>> One alternative is to use lower frequencies if your transceiver and RTTY
>> software support them. Many hams use tones in the range of just above 1 kHz
>> which may be easier to listen to over a long period of time.
>>
>> Consult your owner's manual to see if it possible with your present rig.
>>
>> 73, Bill W6WRT
>>
>>
>> _______________________________________________
>> RTTY mailing list
>> RTTY at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rtty
>>
>
>
>