My HF rigs act weird during the weekends. In some mysterious way both my Kenwood TS-570DG and Yaesu FT-920 are suddenly way more sensitive than normal. I hear stations I never heard before, for no apparent reason at all.
“Well, more sensitive, that’s a good thing” you might say. Unfortunately there’s a con too: my SSB filters suddenly fail miserably. It proves to be impossible for my receivers to separate a number of stations; some of them are up to 25 KHz(!) wide and a few are causing horrible crackling noises way beyond those 25 KHz.
Weird. Only during the weekends. While there are contests going on. Just a coincidence?
“Clearing The Frequency”
Not really. While 99% of the contest stations won’t mess up my receivers is any way, there are a few who do – sometimes on purpose. “Clearing the frequency” one station called it, while laughing. It’s a practice often done just before a contest begins. Just make your linear amplifier non-linear by overloading it in some way, and combine this with a really dirty sound compressor set to max.
Linearity is a desirable property, the station argued, but it comes at the cost of reduced efficiency when clearing a frequency. I’m glad we’re talking about a very small minority here, but it’s still annoying to say the least.
Almost no weekend passes or there is a contest. I’m not a contester, but to each his own. I can’t compete with big guns anyway; I simply switch off HF and limit activities to VHF/UHF.
It’s not the sheer amount of output power bothering me during contests — it’s the sometimes insane amount of splatter. If I take a look at the spectrum, some signals changed into plain double sideband, and are sprinkled with numerous spikes up and down the working frequency. The spectrum looks a bit like a lawn that hasn’t been mowed for months.
Under normal circumstances I can filter out neighboring stations stations quite well, even if they’re only 1 or 2 KHz up or down. Not the most comfortable working conditions, sure, but my brain somehow filters out the rest. Not during a contest though.
Splatter on SSB transmissions is in fact nothing else than high-order intermodulation distortion (IMD), caused by gross overdriving on speech peaks. Any so-called “linear” amplifier will generate IMD if it is driven too hard.
Speech processors are usually advertised as giving your signal more “punch” or “talk power”. That can be true – but a speech processor can also help to eliminate splatter. If you adjust your speech processor correctly you can have a more “punchy” signal that gets the DX, and also a cleaner signal that doesn’t offend local stations.
Also keep an eye on your ALC. Please!
There’s nothing on the receiver’s side you or me can do about splatter. The solutions, as simple as they are, can only be done at the transmitter side. Just turn some of those pots down, thanks!
How the hell do I know? Suffering from memory loss? Lost the Yellow Pages, too? Oh wait, yet another contest….
Fortunately there’s always someone available for a decent ragchew. Finding a frequency that’s not in use isn’t a problem, but that’s not enough. This weekend I found out the hard way that empty frequencies are claimed too. A certain (probably very rare) breed of contesters might be visiting the bathroom, or busy lubricating their throat in the kitchen. When they return after five minutes or so and find out that ‘their frequency’ is occupied, you’re in trouble.
OK, OK, I got the message! I’m outta here!
Don’t you love…
… events like the current CQ WW SSB contest? No? Wait, not so fast.
QRM is great!
It’s the ideal moment to put receivers, filters and antennas to the test. A mediocre receiver will crumble like a cookie made by a 1-year old. A filter with pathetic characteristics will be exposed faster than the Lewinsky scandal. Crappy front ends will relieve themselves, forcing you to wipe their behinds with toilet paper before the stuff hits the PA fan. No testing equipment known to man can beat the interference created by some hams.
One station, 20 KHz of space occupied
How do they do it? I have no idea. A crackling noise, still perfectly readable 10 KHz down and 10 KHz up. All my filters proved as effective as a paper coffee filter (No. 4 size, cone shaped). DSP’s don’t process. Noise blankers don’t blank. Roofing filters are leaking like a sieve. Where’s my roofing contractor when you need him? Decreasing the sensitivity didn’t help much either. I’m stunned. These stations, by the way, were all located in certain parts of Europe.
Could it be that they’re just strong? Nah. UK, US and Canadian stations were sometimes just as strong, or even stronger, but their signals were gone within 3 KHz up or down. These (polite, patient, receiver-friendly) hams were the ones who got points from me. They deserved it.