Topband: Receivers, Noise Blankers and Key Clicks

[Brad Rehm]

"...I ran the numbers, and sure enough, an S-9 +30dB
signal from an FT-1000 would have composite noise sidebands
that would be 20dB above the rigs minimum discernable signal...."

"...I would sure hate to live close to someone using a rig like
this...."

73 de Mike, W4EF..............

Mike,

This is a perfect example of what concerns me about the off-the-air
testing we're doing.  And please understand that I'm not criticizing
your work.  What you have done is very much like the testing I've done
with equipment from my company's EMC lab.

The problem: In the 160 contests, I compete with a number of contest
stations in the Austin area.  Even though my QTH is 45 miles north of
Austin, N5TW and K5NA, for example, can both deliver full-scale
signals to my receiver when they direct their arrays toward me.  Yet,
I've been able to work relatively weak stations within 1 kHz of each
of them.  And I have never lost the use of large sections of the band
when they're active and beaming north.

In CQ WW 160, for example, to see if I could do it, I worked an S7
station that was only 750 Hz above Tom.  My rig is a Mk V with a full
complement of filters and the IRCI IF and click mods.  (Antennas: 3
Beverages & an inverted V for domestic 'tests.)  My band noise that
evening was about S3 on the Mk V meter.  I believe Tom (ten miles
south of my QTH) was running his Orion at the time with a linear,
although he could have been using his FT-1000D.  I had no trouble with
spurious stuff from his signal, which speaks well for both the Orion
and the Mk V, because phase noise affects both the receiving and
sending end of the circuit.  He hasn't mentioned having a problem with
my 500 W signal, so...where's the beef?

I could tell a similar story about Richard, K5NA's, signal in the ARRL
160 'test in December.  I helped put the IRCI click mods in his radios
and confirm with a scope that the keying waveform had been
significantly improved.  No problem sliding up to within a kHz of his
nearly full-scale signal and making contacts.

If the IMD and BDR measurements mean something, why have I been able
to do what I've described here?  Working anything within 5 kHz of a 50
or 60 dB over S9 signal should have been very difficult.  Do our
measurements really predict how our equipment will behave under actual
band conditions?

73,
Brad, KV5V