What got me thinking was an incident that happened during a RTTY contest last
year. Someone called (several times!) on my 20m run frequency to tell me that
I was splattering real bad. I run FSK with an IC-756 PRO III. Concerned, I
reduced power and turned up the load control on the amplifier thinking it might
be IMD. Guy called back still complaining.
To make a long story short, I was very concerned and "spoke" with a couple of
hams that I had QSOs with and they told me that they saw nothing unusual with
my signal. Now, on 20m, I (for whatever reason) am very loud into the upper
midwest when I'm running full power. After thinking about it, the complainers
receiver was likely overloaded. I have probably 5,000 RTTY contest QSOs with
this setup with no other complaints, so I assume nothing is fundamentally wrong.
I know that with amateur radio, no one is going to declare a single objective
standard, not least because getting hams to agree on anything is like herdiung
cats. Or getting one of them to pick up a lunch tab.
But it would still be nice to know what to measure and what is generally
accepted as "good".
Al
AB2ZY
________________________________________
From: Jeff Blaine [keepwalking188@yahoo.com]
Sent: Wednesday, January 09, 2013 12:56 PM
To: aflowers@frontiernet.net; Al Kozakiewicz; rtty@contesting.com
Subject: Re: [RTTY] RTTY Now trashy signals
Al,
You have a great point. And I think it's worse because you are assuming
that once some "standard" is established, then guys will be able to measure
it the same way, and as we can see in the PSK case, it's not at all a safe
assumption.
In fact, one of the reasons I hate to run PSK is the amount of busy-body
signal police on the band. I got tired of guys calling me out for having a
wide signal when the actual issue was their improper receive setup. I have
the KK7 PSK IMD meter here on the shelf and could send those guys shots
of -28 db readings. At the same time, they would swear I was 5 db only.
We have the same issue here with RTTY. If you are going to critique
someone's signal, you had better make sure that your setup is IMD product
generation free. And that is not a simple task considering things in the
environment beyond the antenna are potential contributors in the case of
strong signals.
My guess is most FSK installations are fine. And most AFSK installations
are fine. And that the cases where guys have trouble is at it's root either
AF feeds with some clipping due to improperly set AF levels. Or that they
have their antennas close to their gear and are not properly controlling the
RFI.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: aflowers@frontiernet.net
Sent: Wednesday, January 09, 2013 11:03 AM
To: Al Kozakiewicz ; rtty@contesting.com
Subject: Re: [RTTY] RTTY Now trashy signals
>Don't underestimate the importance of the words "in the sense that"!
Fair enough, Al! I've had my coffee now...
Here's a very simple way that might get at the crux of the issue. Let's say
that signal number #3 was your signal (yes, this was recorded off the air
this weekend, and no, I'm not going to identify him or her publicly):
http://www.frontiernet.net/~aflowers/rtty_examples/
Would knowing that was was being heard up and down the East (and probably
West) coast bother your conscience enough to look for ways to change
something? Does anyone want to say 'no'?
We all (well, most of the big contesters) managed to modify our early model
MPs to reduce the nasty CW key clicks without some objective standard from
on high. The problem was identified and people came up with solutions
pretty quickly. Hams have historically been able to make many changes for
the better without big brother drawing a line in the sand.
Andy K0SM/2
________________________________
From: Al Kozakiewicz <akozak@hourglass.com>
To: "aflowers@frontiernet.net" <aflowers@frontiernet.net>;
"rtty@contesting.com" <rtty@contesting.com>
Sent: Wednesday, January 9, 2013 11:08 AM
Subject: RE: [RTTY] RTTY Now trashy signals
Don't underestimate the importance of the words "in the sense that"!
While we are all ultimately responsible for operating to a set of acceptable
standards, the FSK operator has no choice to make in the matter short of
ceasing operation if their transmitter is performing poorly*. The AFSK
operator, on the other hand, makes all kinds of choices in software,
soundcard, interface, computer output levels, transmitter gain, compression,
ALC, etc. etc. All have a direct impact on signal quality.
I too would be interested in knowing both how to define and measure the
quality of FSK transmissions and how products perform with respect to those
metrics.
*-Anyone can plot quality (however you'd like to define that term) of
transmitted signals along a line from bad to good. What I'd like to know is
where you draw a line distinguishing acceptable from unacceptable? If width
is king, queen and everything in between with respect to RTTY signals, how
many db down do the modulation byproducts have to be how far from the
mark/space frequency? And who gets to decide that?
Al
AB2ZY
________________________________________
From: RTTY [rtty-bounces@contesting.com] On Behalf Of
aflowers@frontiernet.net [aflowers@frontiernet.net]
Sent: Wednesday, January 09, 2013 10:28 AM
To: rtty@contesting.com
Subject: Re: [RTTY] RTTY Now trashy signals
Al,
I respectfully disagree in small detail (and please forgive me if I
misunderstood). I think everyone owns equal responsibility for his or her
signal *regardless of the process creating it*. We make the decision to
either trust that the manufacturer has implemented the feature properly and
we choose use it, or we choose to do it by other means. Contesters are
always making decisions like this. Really capable people will measure the
things that matter to them, if they can, and the magazines try to publish
product reviews to help us out. In the final analysis we make a good choice
or we make a bad choice based on available information, but either way we
make the choice and we are responsible for the signal we put out. Sometimes
getting a new radio may be the only viable option, and that is expensive,
and yes, we will be upset at the manufacturer for giving us a raw deal.
I think your main point is that "the transmitter made me do it" isn't a
justification for keeping on doing it. Spot on, in my opinion.
I think that begs a really important question though: is there any
meaningful difference among the FSK signals generated by different radios'
internal FSK generators. Forget whether it's done by switching the LO
frequency, by magical DSP fairies, or by black and white mice spinning the
mark and space wheels next to the flux capacitor: *among the internal FSK
generators in the K3, IC-7800, FT-1000MP, and IC-706, or any radio made in
the last 15 years, is there any meaningful difference when it comes to the
RF coming out?*
If so, what are the differences? Anyone have pictures of radios side by
side when keyed in their "FSK" mode?
Andy K0SM/2
----------------------------------------------------------------------
Which was basically my point. Discounting analog FSK implementations from
30 years ago, there is nothing you, Joe Ham, can do should it be proved
that, yes indeed, your 2 year old DSP transceiver is splattering when
modulated using FSK. There are no user accessible adjustments and with the
few DSP designs I've looked at there are no internal hardware adjustments
either so you can probably safely attribute the problem in that case to bad
design. Which has no cure except to buy a different model radio.
A ham running AFSK owns a lot more responsibility for the cleanliness of his
signal than one running FSK in the sense that AFSK performance is more
dependent on user configuration.
Al
AB2ZY
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