Hi,
We had an interesting occurrence on 3947 last night. That being during the late edition of the Virginia Fone Net, which starts at 7:30 PM eastern.
Someone broke in asking: 'Net control, why is your signal so wide?' No call sign, so this person was ignored. And, we had some bleeding over from 3950 and 3945 ourselves. No big deal from my point of view. I just twiddle the filter controls to cut some from the Lo and Hi sides of my bandpass and so narrow down my receive bandwidth and minimize it. I was operating with 1.6 kHz myself.
Now, this is super easy with the modern rigs which have DSP filtering. It was pretty easy with my old Kenwood TS850s as it has filters in both IFs and so I could perform this Lo Cut and Hi Cut even without having a DSP. Even my older TS430s can do this by selecting the 1.8 kHz filter and shifting the IF up a bit to a happy point between 3945 and 3950. The old 430s has only one IF with filters in it. Heck, the old Collins and Drake tube receivers could do this, pretty much the same way. Narrow the IF bandpass and shift it some if necessary.
If one bought the optional narrow SSB filter, that is. This is one place where it costs one to be cheap. The modern DSP equipped radios don't need extra filters as the DSP mimics filters and usually does a better job at it. Of course, I have no idea what Mr NoCall had by way of a radio. But, I bet whatever kind it was, he doesn't know how to use it.
What happens is a strong signal appears to be really wide if one doesn't use their attenuator and RF Gain control to reduce the strong signal down to where one is hearing it at s2 to s3 and then tune up and down to obtain an approximation of occupied bandwidth. That's best measured on a Spectrum Analyzer or with a calibrated Measuring Receiver where we have no RF amplification and a step attenuator in our front end. Precisely set the peak of the signal and then measure it.
We need to be able to get a peak reading without swamping the front end and then find the -6 dB points on the slope of the signal and the measure the bandwidth between them. I happen to have some older RF test equipment in the shack because I have mostly old radios and I like to periodically check them without having to tote them downstairs to my RF Lab (where newer equipment lives).
I also use the old TS430s as Diversity Receive, especially on nets, hooked to a longwire. This often times hears better than the dipole which I use for transceive. The longwire is only happy as a transmitting antenna on 160m, which it is now an end-fed full-wave.
So, now it was simply a matter of hooking the longwire to the spectrum analyzer and performing a measurement. The net control was occupying 2.6 kHz. So, not wide.
I find where so many hams never get a good understanding of how a signal looks like a pitched tent between the peak of the signal and the noise floor. A spectrum analyzer shows this clearly, but so few hams ever become exposed to such an instrument. Sadly. An understanding of how all this works helps to avoid the situation which occurred last night. Someone tuning way too far down the slopes of the signal and so thinking it was too wide.
73
Stan - w2ck
We had an interesting occurrence on 3947 last night. That being during the late edition of the Virginia Fone Net, which starts at 7:30 PM eastern.
Someone broke in asking: 'Net control, why is your signal so wide?' No call sign, so this person was ignored. And, we had some bleeding over from 3950 and 3945 ourselves. No big deal from my point of view. I just twiddle the filter controls to cut some from the Lo and Hi sides of my bandpass and so narrow down my receive bandwidth and minimize it. I was operating with 1.6 kHz myself.
Now, this is super easy with the modern rigs which have DSP filtering. It was pretty easy with my old Kenwood TS850s as it has filters in both IFs and so I could perform this Lo Cut and Hi Cut even without having a DSP. Even my older TS430s can do this by selecting the 1.8 kHz filter and shifting the IF up a bit to a happy point between 3945 and 3950. The old 430s has only one IF with filters in it. Heck, the old Collins and Drake tube receivers could do this, pretty much the same way. Narrow the IF bandpass and shift it some if necessary.
If one bought the optional narrow SSB filter, that is. This is one place where it costs one to be cheap. The modern DSP equipped radios don't need extra filters as the DSP mimics filters and usually does a better job at it. Of course, I have no idea what Mr NoCall had by way of a radio. But, I bet whatever kind it was, he doesn't know how to use it.
What happens is a strong signal appears to be really wide if one doesn't use their attenuator and RF Gain control to reduce the strong signal down to where one is hearing it at s2 to s3 and then tune up and down to obtain an approximation of occupied bandwidth. That's best measured on a Spectrum Analyzer or with a calibrated Measuring Receiver where we have no RF amplification and a step attenuator in our front end. Precisely set the peak of the signal and then measure it.
We need to be able to get a peak reading without swamping the front end and then find the -6 dB points on the slope of the signal and the measure the bandwidth between them. I happen to have some older RF test equipment in the shack because I have mostly old radios and I like to periodically check them without having to tote them downstairs to my RF Lab (where newer equipment lives).
I also use the old TS430s as Diversity Receive, especially on nets, hooked to a longwire. This often times hears better than the dipole which I use for transceive. The longwire is only happy as a transmitting antenna on 160m, which it is now an end-fed full-wave.
So, now it was simply a matter of hooking the longwire to the spectrum analyzer and performing a measurement. The net control was occupying 2.6 kHz. So, not wide.
I find where so many hams never get a good understanding of how a signal looks like a pitched tent between the peak of the signal and the noise floor. A spectrum analyzer shows this clearly, but so few hams ever become exposed to such an instrument. Sadly. An understanding of how all this works helps to avoid the situation which occurred last night. Someone tuning way too far down the slopes of the signal and so thinking it was too wide.
73
Stan - w2ck
