The best station monitor you can buy or own is a SDR receiver.
A SDR receiver especially a direct sampling receiver captures every piece of trash that comes out of your transmitter. Most of the good SDR receivers have better dynamic range and speed that exceeds the performance of the
mega buck name brands spectrum analyzers. They excel in station monitoring applications. You wont go wrong adding a SDR receiver to your station as a monitor.
Oscilloscopes work OK on AM however for SSB and CW use they just about useless unless your signal is badly over driven. Oscilloscopes do not work in the RF domain!
It always amuses me hearing comments from stations like " i am looking at my oscilloscope and I cant see any splatter"
You really need some kind of FFT storage analyzer if you going to see flat topping however you wont see any splatter unless you have a faulty spectrum analyzer!
Most of the splatter that you hear on the air comes from radios with poor ALC designs that causes excessive IMD and buckshotting. A SDR receiver gives you a perfect picture of what damage your radio is doing.
Its also a great tool for monitoring your transmitter audio quality. SDR receivers are to as close to perfect as you can get for assessing audio frequency response and transmitter audio quality.
A SDR receiver can also tell you if you have holes in your audio frequency response or whether you are concentrating your voice energy and power in the wrong end of the audio spectrum(excess bass)
If you moderate ALC and dont use selfish inconsiderate modes like ESSB audio you will be ok 99% of the time when using a stock factory radio and mic.
The worst station monitor you can have is a ham buddy. Most dont know what splatter is, most dont know how to do a proper splatter assessment, and most good ham buddies dont want to hurt your feelings. They will tell you deliberate lies. I hear this kind of behavior all the time when some other ham gives a station a report that he or she is splattering. The buddy will say " i hear no splatter here, you S9 and and I hear nothing. Most people who live in the city have noise floors that are too high or the signal strength from the offending hams is not strong enough to give an indication of signal quality. The worst station to ask for a splatter report is a DX station, yet we hear many stations asking DX stations if they can hear any splatter. Most splatter products are below legal QRP power levels. If you have confidence in a DX stations ability to give you a honest splatter report, just reduce your power down to 1 watt and see if he can hear you. If cant hear a 1 or even a 5 watts signal how is he ever going to able to hear your splatter products from the other side of the world.
If someone gives you a report that you are splattering you should always ask for the signal S-meter level rather than screaming its your stinkin receiver. Then you simply get of the air, plug in the SDR into a dummy load or attenuator and transmit into the SDR receiver at the signal level that the reporting station gave you. You will instantly know if you splattering if you are using a good SDR receiver. You can see the splatter signal signature there on the screen.
When you look at the waterfall display you will see a nice brick wall signal. Signals with excessive splatter will have the distinct buckshotting lines being emitted from the waterfall pattern. In the spectrum domain if you narrow the span and scale you can see the 45 degree IMD shoulder as it falls away from the signal. Many stations have that really broad 45 degree shoulder indicating IMD problems. Good radios like the FT5000 even when the signal is 50 over S9 dont have this characteristic IMD 45 degree shoulder. The signal is essentially clean. Anyway you will learn all these signal traits as you monitor many stations.
My view is these days, is that the louder and more a station protests about receiving a splatter report the more technically incompetent that station is. You never hear the big mouths say look OM I have a second receiver monitoring here and I cant hear anything. Its always your crappy receiver or that you have the noise blanker on. Most stations are aware of the receiver issues and noise blankers etc etc these days. Its really hard to cause any modern receiver real problems from simple overload from a single single. Even a basic radio like a IC706MK2 is a good enough receiver to use as a station monitoring receiver. Its a bad receiver if you have the noise blanker on!
Anyway every ham station should use a SDR as a station monitor rather than a close to useless oscilloscope. Its even more important to use a SDR receiver if you using one of the Russian tetrode amplifiers with a modern radio. This combination is the biggest cause of splatter we see on the ham bands! Even a simple Softrock receiver is better than any oscilloscope as a station monitor. Its a real pity that the available pan adapters on most radios cant even monitor the TX signal. Rather than adding useless features on transceivers the manufacturers should add things like TX monitoring from the bandscope, a -40db tap or a simple 40 Db attenuator dummy load for these tests. These features would be easy to add to radios these days.
With a SDR receiver in the shack any ham can have a true professional signal quality monitoring system in place that rivals the best commercial spectrum analyzers, what more can you want?
The next best thing would be to have IMD laws like commercial SSB radios so that you know that you can never splatter or over drive. You certainly would not need SDR monitor receiver if the ham services had
proper transmitter IMD laws. It always amazes me when I take my old Icom Marine radio and put it on the air, perfect audio and no splatter regardless of what I do, this is how ham radios should be designed!
Well, I've been building my station now for a while (as "play funds" allow) and think I have a decent set-up.
My transceiver is a TS-940S, Al-80B linear, AT-2500 Tuner (in repair process). Backup is my TS-530S and MFJ-993B.
In consideration for other operators, I want to set-up a station monitor so that I can see what I'm putting out and not contaminate the band with needless splatter, noise etc.
I have a Tektronix 2336 100Mhz scope from the days when I was playing with CB and TV repairs, I believe this should do ok.
I'm also toying with the idea of a spectrum analyzer....
All probably complete overkill? but I want to make sure I'm "true and clean".....
I've found two companies that offer interfaces: CleanRF (
www.cleanrf.com) and PreciseRf (
www.preciserf.com) both offering similar products.
The other alternative was to software/pc based by Virtins Technology (
www.virtins.com), this would be scope/analyzer in one package.
What else is out there...what are you using and works effectively...?
Any comments and or suggestions are greatly appreciated.
73
Bart
