Digital Modes Meanderings
The Equipment – Part 3
The Alinco DX-70TH was now “repaired” and the power supply and leads were supplying clean and proper amounts of voltage and current. The Alinco was happy and responded with superb performance. The transmitter of the DX-70 TH was found to provide a minimum of 60 clean watts of digital mode power. Without anyway to know the ALC level that was the most I dared to run and keep the transmit signal clean. On the air checks with other stations confirmed clean operations. Typically I ran 30 to 40 watts as that was found to be sufficient for most QSOs and put less stress on the transmitter final amplifier from the heat dissipation. The DX-70TH is a very good digital sound card mode rig considering it was designed in the pre-digital sound card mode era. It has two supplied I.F. filter selections for USB and LSB mode of operations, a standard width filter (2.4 kHz) and a narrow width filter (1.0 kHz). Those filter width selections seemed a bit narrow for most SSB operations to me but they were a godsend for digital mode operations. For a non-DSP I.F. filter radio, that 1.0 kHz position is fantastic for peaking up the S/N on digital mode signals. The DX-70TH also has an I.F. shift function, which when coupled with the 1.0 kHz filter option, is a powerful QRM fighting duo. For local QRN (noise), the noise blanker was generally a moderate performer but did help some. Unfortunately, when the noise blanker was in use and a strong CW station was within 1 kHz of the dial frequency, loud clicks were produced in the receiver passband and made receiving problematic. Many times I was forced to choose QRN rather than the clicks. Fortunately this interaction with CW stations primarily only happened on 40 meters.
The Alinco DX-70TH was now “repaired” and the power supply and leads were supplying clean and proper amounts of voltage and current. The Alinco was happy and responded with superb performance. The transmitter of the DX-70 TH was found to provide a minimum of 60 clean watts of digital mode power. Without anyway to know the ALC level that was the most I dared to run and keep the transmit signal clean. On the air checks with other stations confirmed clean operations. Typically I ran 30 to 40 watts as that was found to be sufficient for most QSOs and put less stress on the transmitter final amplifier from the heat dissipation. The DX-70TH is a very good digital sound card mode rig considering it was designed in the pre-digital sound card mode era. It has two supplied I.F. filter selections for USB and LSB mode of operations, a standard width filter (2.4 kHz) and a narrow width filter (1.0 kHz). Those filter width selections seemed a bit narrow for most SSB operations to me but they were a godsend for digital mode operations. For a non-DSP I.F. filter radio, that 1.0 kHz position is fantastic for peaking up the S/N on digital mode signals. The DX-70TH also has an I.F. shift function, which when coupled with the 1.0 kHz filter option, is a powerful QRM fighting duo. For local QRN (noise), the noise blanker was generally a moderate performer but did help some. Unfortunately, when the noise blanker was in use and a strong CW station was within 1 kHz of the dial frequency, loud clicks were produced in the receiver passband and made receiving problematic. Many times I was forced to choose QRN rather than the clicks. Fortunately this interaction with CW stations primarily only happened on 40 meters.
Timewave DSP-59+
I found that my Timewave DSP-59+ audio filter helped in the QRN area and became an essential piece of equipment in my digital mode station. While not an absolutely required piece of equipment for digital mode operation, a good DSP audio filter unit can offer useful additions to your digital mode station. This is especially true for non-DSP radios and ones without a “Data” mode interface connection (e.g. the DX-70 TH). They can assist in combating static and noise which can help boost S/N figures. It can also provide a more ear pleasing audio reception of the desired signal if the audio filter has an adequate selectable audio passband control. However, be aware that removing an offending signal from your final audio passband will NOT remove it from your RF passband. Just because you do not hear it in the speaker or see it on the waterfall does not mean it will not affect your reception. That is why DSP I.F. based rigs have become so popular among digital mode (and CW) operators. The Timewave DSP-59+ has given me excellent service in my digital mode operations.
I found that my Timewave DSP-59+ audio filter helped in the QRN area and became an essential piece of equipment in my digital mode station. While not an absolutely required piece of equipment for digital mode operation, a good DSP audio filter unit can offer useful additions to your digital mode station. This is especially true for non-DSP radios and ones without a “Data” mode interface connection (e.g. the DX-70 TH). They can assist in combating static and noise which can help boost S/N figures. It can also provide a more ear pleasing audio reception of the desired signal if the audio filter has an adequate selectable audio passband control. However, be aware that removing an offending signal from your final audio passband will NOT remove it from your RF passband. Just because you do not hear it in the speaker or see it on the waterfall does not mean it will not affect your reception. That is why DSP I.F. based rigs have become so popular among digital mode (and CW) operators. The Timewave DSP-59+ has given me excellent service in my digital mode operations.
Rear panel of the DSP-59+ showing the “Line Output” jack
As a bonus it has a fixed audio level “Line Output” jack which helps to provide an audio source which will not overdrive the audio input of the computer’s soundcard. This helps to ensure proper decode of the received digital signal. The Timewave DSP-59+ also provides a LED indicator to let you know when you are over driving the DSP unit’s audio input. Having a “Line Output” jack gives you control over the monitoring of the receiver audio too. Personally, during my digital mode operations I like to hear a low level amount of transmit and receive audio in the background rather than complete silence. It helps me stay connected to what is going on. By using the DSP audio unit’s gain control it will allow you to adjust the audio going to the external speaker while not affecting the audio that is being provided to the sound card input via the “Line Output” jack.
While on the subject of DSP audio units, a word of caution is needed concerning CW carrier removal features offered by most DSP audio units. You will not be able to utilize any carrier frequency removal feature while operating most (if not all) digital modes because it will see the digital signals as carrier signals and try to remove them too, sometimes quite effectively! PSK modes are the most susceptible. If you encounter interference from a nearby CW station you will have to use a tighter I.F. filter selection or a manual notch filter. If you do not have these options in your QRM fighting toolbox then a judicious juggling of dial frequency and I.F shift control may alleviate the QRM situation. If you have two CW stations, one on either side of your QSO frequency causing QRM, then you may have to just grin and bear it. If you are fortunate, you may be able to remove one CW station and reduce the other one to a more tolerable interference level. With today’s new radios you should have enough QRM fighting tools available to take care of just about any typical QRM situation. Learn to use whatever tools you have available and the experience will take you far. The knowledge will come in handy when you upgrade your radio for a newer model that has better QRM combating features. Believe it or not, you will be a better ham for the experience and get more out of your future newer radio.
As a bonus it has a fixed audio level “Line Output” jack which helps to provide an audio source which will not overdrive the audio input of the computer’s soundcard. This helps to ensure proper decode of the received digital signal. The Timewave DSP-59+ also provides a LED indicator to let you know when you are over driving the DSP unit’s audio input. Having a “Line Output” jack gives you control over the monitoring of the receiver audio too. Personally, during my digital mode operations I like to hear a low level amount of transmit and receive audio in the background rather than complete silence. It helps me stay connected to what is going on. By using the DSP audio unit’s gain control it will allow you to adjust the audio going to the external speaker while not affecting the audio that is being provided to the sound card input via the “Line Output” jack.
While on the subject of DSP audio units, a word of caution is needed concerning CW carrier removal features offered by most DSP audio units. You will not be able to utilize any carrier frequency removal feature while operating most (if not all) digital modes because it will see the digital signals as carrier signals and try to remove them too, sometimes quite effectively! PSK modes are the most susceptible. If you encounter interference from a nearby CW station you will have to use a tighter I.F. filter selection or a manual notch filter. If you do not have these options in your QRM fighting toolbox then a judicious juggling of dial frequency and I.F shift control may alleviate the QRM situation. If you have two CW stations, one on either side of your QSO frequency causing QRM, then you may have to just grin and bear it. If you are fortunate, you may be able to remove one CW station and reduce the other one to a more tolerable interference level. With today’s new radios you should have enough QRM fighting tools available to take care of just about any typical QRM situation. Learn to use whatever tools you have available and the experience will take you far. The knowledge will come in handy when you upgrade your radio for a newer model that has better QRM combating features. Believe it or not, you will be a better ham for the experience and get more out of your future newer radio.
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