Very informative explanations Cecil. Just wanted to add that the acronym
"RIT" is mostly self explanatory. It means (R)eceiver (I)ncremental
(T)uning and it does exactly as you explain it. It tunes the receiver (and
the receiver ONLY) in small increments. A lot of transceivers, such as the
"Orion's" also have "XIT" which means it tunes the transmitter (and the
transmitter ONLY) in small increments and leave the receiver frequency as it
is displayed by the frequency readout.
I use the RIT a lot when being a net control as I NEVER change my TX
frequency to accommodate off frequency check-ins. A net is held usually on
a particular frequency plus or minus QRM etc. It's funny to hear a check-in
say "you are off frequency" if you moved slightly for whatever reason. My
usual reply (with tongue in cheek off course) is "the net control is ALWAYS
on frequency hi.. hi..".
Great job Cecil. 73, Tony VE3DWI.
----- Original Message -----
From: <chacuff@cableone.net>
To: "Will Jones" <wjones@bellsouth.net>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Friday, August 30, 2013 11:46 AM
Subject: Re: [TenTec] Explanations of the Different Types of Filtering on
Radios
Ok, here goes with an analogy...
I’ve been up in the Smokey Mountains many times and they have some of
these beautiful short tunnels through rocky hillsides for the roads to
pass.
Lets say you were standing in the middle of the road at one end of one of
these short, straight tunnels looking through to the other side. At the
other end of the tunnel you see a very nice looking young lady just to the
left of center and a really ugly old lady just to the right. Of course
the desirable view at this point is the nice looking young lady but it’s
really difficult to get a good look because of the really ugly lady...so.
Say you had a knob that would allow you to move the end of the tunnel left
or right just enough to block out the view of the really ugly lady leaving
only the view of the very nice looking young lady...there you have IF
Shift....also called PBT by other manufacturers.
Now re-center the knob where you have both ladies in view. Hold up the
index finger of your right hand out at arms length. Close one eye and
place that finger over the really ugly lady blocking the view of her and
leaving only the view of the nice looking younger lady...there you have
the Notch Filter. It may not cover the whole view of the ugly lady but it
does enough to allow a better view of the nice looking young lady.
The others are a bit more difficult to explain...
RIT is really not a filter at all...just another way to tune the frequency
of the receiver a small amount without changing your transmitter
frequency. Say you are having a short SSB QSO after calling CQ with a
fellow who doesn’t seem to be tuned properly to your frequency and he
sounds like he has been snorting helium so you need to tune your VFO to
make him sound more natural. If you tune your main VFO you are not only
tuning your receiver but also your transmitter...which will result in a
change in how you sound in his receiver. Well on the next over he may
retune his VFO to make you sound normal in his speaker and it’s an endless
chase up and down the band. (this can be caused by radio alignment issues)
Better choice would be to engage RIT and just move your receiver until he
sounds natural to you which will not change your transmit frequency only
your receiver frequency leaving you sounding the same in his receiver and
less likely causing him to retune...ending the chase.
DSP Noise reduction...well this being a software feature is implemented
differently in every manufacturers radios and sometimes even between
models in the same manufacturers radios.
The goal of all is to reduce random noise as much as possible while
identifying the desirable young lady...um...signal and bringing it out of
the noise. All this is done using math inside the computer. Some work
better than others. The Icom system works well at reducing background
noise without adding too much digital artifact noise as long as you don’t
over use it. Seems some think if a little is good then a lot is
better...it’s a balance. Turning the knob full clockwise will result in
digital noise and not help at all. The DSP system on my Orion II is
different and I’m not sure exactly how to explain it..except the way
Ten-Tec does that advancing to a higher number increases the length of
time sampling is done before the digital filter is built. Which results
in a better built filter in software but it takes longer to get there. Of
course the desirable signal needs to be there for the duration of the
sample or it probably will have a hard time doing it’s job. None of them
are magic...and most work well some times and not so well others...it’s
just another tool.
Noise Blankers. Most are designed to work on repetitive noise pulses like
old auto ignition system noise or electric fence pulses. Some works well
on power line noise some not so much. I’m surprised sometimes at how well
some work and how poorly others don’t...and it doesn’t seem to matter how
much the radio cost. Some of the older cheap radios noise blankers do
wonders on power line noise and a high dollar radio won’t touch it...go
figure. Won’t do much on atmospheric static crashes because they don’t
happen on a timed repetitive timeline which noise blankers are designed to
sense.
Well that’s about all I got...my apologies to any of the ladies out there
with my analogy...it was the first vision that popped into my head this
morning when envisioning an answer to the question. No harm intended...
I’m sure others will have more insightful answers and between the group of
us we should answer your questions.
Best of the Labor Day weekend....
Cecil Acuff
Gulfport MS
K5DL
From: Will Jones
Sent: August 30, 2013 9:33 AM
To: tentec@contesting.com
Subject: [TenTec] Explanations of the Different Types of Filtering on
Radios
There are a few of us who meet together every Wed. morning at a local
restaurant to talk about ham radio and stuff.
Some are new hams. One asked this week a question which I think would be
an interesting study in comments.
He asked, "I have an I.F. shift on my radio and I have read about what it
does but don't really understand "what" it does. Also how does it compare
to the other features I see on radios such as PBT, notch filters, RIT, DSP
noise reduction and noise blankers. Without having a radio with these
features on them it is hard to explain just what your signal will sound
like when these devices are used.
So can anyone give us some ideas how to explain these different types and
why we would want one and not another and why radios don't have them all
on one radio.
Bill, N4LB in TN
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