>A good example of where this comes into play is
>early in the morning on 75 meter SSB during the
>winter months. During the longpath opening at
>my sunrise, DX signals are typically right at the
>noise floor, whereas the big guns here in
>California just sit on the peg of my S meter. In this
>environment, the guys who are running setups
>with mediocre IMD can wipe out the entire DX
>window for everyone else, whereas the guys with
>clean rigs can park 3 to 4 KHz from a weak
>longpath signal without inflicting significant
>damage.
>
>This is a pet peeve of mine as some of the
>more well endowed big guns ought to know
>better, but don't really seem to care if they
>have wide signals (I sometimes wonder if they
>don't do it on purpose just to kick a little more
>sand in everyone elses face).
>
One treatment for rotten IMD is to measure the turkey's IMD and read his
IMD report to him whenever he is trying to listen. Putting it on a tape
loop helps. Be sure to ID. Under No circumstance use ad hominems or
expletives.
- "Yo' mama" shit is definately not going to help reduce interference
cheers, Mike
>----- Original Message -----
>From: "Tom Rauch" <w8ji@contesting.com>
>To: <amps@contesting.com>; "Zyg Skrobanski" <af4mp@mindspring.com>
>Sent: Tuesday, March 04, 2003 6:52 PM
>Subject: Re: [Amps] Why hasn't solid state replaced tubes?
>
>
>> > Looking at the ARRL graphs of transceiver IMD testing, and comparing
>> > different rigs by their 3rd order products, if one rig has poor 3rd IMD
>> > results it does not necessarily follow (according to the graphs) that
>the
>> > higher order products are also going to be worse. For example, for the
>> 160
>> > meter result at -4 KHz, the TS2000 has a spur at -55 dB, and the
>FT1000MP
>> > is at -50 dB. Both rigs are below 60 dB at 10 KHz. So, if the 3rd
>order
>> > distortion is not audible (not that I thought it would be;) and its
>value
>> > does not indicate the amount of the higher order IMD, then what is the
>> > purpose of having the 3rd order IMD specification?
>>
>> That's right, and that's an important observation most people miss Zyg.
>>
>> The important thing is how the rig rolls off on higher order products, not
>> the close-in stuff. I can hear a modestly strong IC756 or TS2000 on SSB
>> 15kHz away on a quiet band (my noise floor does not move my S meters
>much).
>>
>> It is the stuff that stick out 10kHz that is annoying.
>>
>> The ARRL and everyone else should start testing rigs in a meaningful
>manner,
>> instead of nearly useless two-tone tests. The FCC now requires landmobile
>> radios to be tested with voice modulation and a peak sample-and-hold
>> spectrum display used. That would be a useful test for ham gear. A
>bandwidth
>> test would weed out keyclicks and splatter.
>>
>> > That I understand, what I don't understand is how one rig is deemed to
>be
>> > "better" than another relative to transmitter IMD, when graphs show that
>> > each has its advantage but on different bands.
>>
>> You're right. The only thing I care about is the bands I work weak signals
>> on. Those are the rigs I notice. If I worked ten meters I suppose I'd
>> dislike some other models.
>>
>> The real important points are radios really are not tested in any
>meaningful
>> way, and what data we get isn't easily understood. I'm just as perplexed
>as
>> anyone else when trying to decide what to buy. You can't actually tell how
>> anything is until you use the rig for a year (or more) how it is. It took
>me
>> almost two years to get the first keyclick report on my FT1000D, and darn
>if
>> the guy wasn't right. The thing clicked like heck, and no one told me for
>> almost two years.
>>
>> Of course I learned a new 775DSP was a problem in two days, but that was a
>> receiver issue (and a 300 watt transmitter spike that showed on my power
>> meters and dumped the grid protect over and over in my triode amplifier).
>>
>> 73 Tom
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>_______________________________________________
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>http://lists.contesting.com/mailman/listinfo/amps
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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