THE TRANSCEIVER MESSING WITH YOUR MIND… MODULATORS AND DEMODULATORS

The Kaw Valley Amateur Radio Club Newsletter
THE TRANSCEIVER
November 2014
Editor: Doug Dunton
www.kvarc.org
ARRL Affiliated Since 1926
2014 Club Officers
President: Paul Mills
Secretary: Susan Sims
Treasurer: Paul Bayless
MESSING WITH YOUR MIND…
MODULATORS AND DEMODULATORS
What are modulators and demodulators? The average ham operator would tell you that the modulator
is where audio information is applied to the Radio Frequency (RF) wave. And average ham might say
that a demodulator is the detector which extracts the audio information from the RF wave.
Hang with me on this, there really is something in this for the average ham.
But I am going to tell you that modulators and demodulators are the same thing, namely mixers!
(Reference: 2010 ARRL Handbook chapter 10) But of course, you learned that mixers were those devices
used in receivers to transform a signal from one frequency to another. And that is correct. But
modulators and demodulators are also mixers.
Mixers can be described in mathematical terms, and though we often think of them in terms of addition
and subtraction, the process is actually one of multiplication, and we filter out all of the unwanted
products. One thing to note about mixers is that they are non-linear devices, that is, they introduce
distortion. We use this distortion to produce the mixing, but out of control it can create nasty results.
The idea of modulation being mixing is not too hard to grasp, in mixing audio and RF, but it seems a bit
of a stretch to most of us to understand it being a part of the detection process. This is perhaps a bit
easier to understand in a SSB receiver, than most other receivers. SSB receivers use a product detector
(notice the mathematical term product). In signal sideband, you may recall, the carrier and one
sideband are removed, in the receiver we mix the carrier back in in to the product detector. Older SSB
receivers had a BFO (beat frequency oscillator) control to vary this carrier for maximum clarity.
Now, why does any of this make any difference to ‘Leo’ the appliance operator? If you abuse any of
these non-linear mixers, you make a mess.
When you over-modulate that 2-meter FM transceiver, you take up more bandwidth than intended. This
over-modulation interferes with adjacent channels and may create lots of distortion in the receivers of
those listening to you.
When you over-modulate that SSB or AM transmitter, you create splatter all over the RF spectrum. This
makes you not too popular with others, and actually reduces your ability to communicate. This is
because a lot of power is being sent out in places that do not benefit the party listening to you. It can
distort your voice to the point of making it hard to understand.
Hope you all learned something, and are only mildly confused.
73 de AC0HY
Reminders:
Annual 2014 Membership form at KVARC Application
Ham FAQ: For Hams new to the area or are just licensed - Ham FAQ
•
KVARC Club meeting November 7th 7:30pm. This will be at the Topeka Shawnee County Library.
Topeka, KS. Eyeball QSO starts about 7pm
•
Regular test session at December 13 at Topeka Library at 1pm. Pre-register with Paul at
[email protected]
•
Regular test session at November 14th at Carbondale City Hall at 7pm. Pre-register with Paul at
[email protected]
•
Special test session at November 15 at Bartlett & West Bldg at 3pm. This is the test after the
General class. Everyone is welcome to try to upgrade or take a test without the class if you want.
•
Tuesday night ARES net on 145.27 at 830pm
•
Thursday night Carbondale net 800pm on 147.30+ KB0WTH repeater
•
Wednesday night simplex net on 147.440 at 730pm run by KB0WOW –Dan
•
General Class – November 1st, 8th, and 15th Bartlett & West Building. 9am till 5pm. Testing on the
15th.
•
Extra Class – January 3rd, 10th, 17th and 24th. Bartlett & West Building. 9 am till 5pm. Testing on
the 24th.
Other info:
Congratulations to our new hams! We just finished up our Tech class. We had 3 members and all
passed!
Matthew Holevinski
Mark McDaniel
Hal McBee
Boy Scouts:
We have been asked by Washburn University, to participate again for the third year, putting on the
Radio Merit Badge class for their Boy Scout Merit Badge conference. Bill Kuhn noØoo, has been
instrumental for the past 3 -4 years, putting together this class, along with Electronics and Electricity
Merit Badge classes. The last two years, the Radio Merit Badge class has been a full 8 hour day, and it
has been a little tight getting
everything done. Bill has been doing the class in a four hour session,
which requires the scouts to do a lot of prerequisite work prior to the class. He's had about a 20% pass
rate of scouts obtaining their badge, mainly because four hours does not allow time for the scouts to do
a lot of the work in class that they could do prior...
I have always helped Bill at the Washburn Conference, which will be Feb 7th
2015 on Sat. He's in hopes of making this year another 4 hour session, and doing an Electronics or
Electricity class the other 4 hours. In the past we held the class to a max of 15 or 20 scouts, I don't
remember, but we usually had 10-13 scouts. It requires a lot of help from Volunteers, especially if we do
a 4 hour session for Radio.
Bill needs to know who will be able to help this year at Washburn, and he really needs a firm
commitment as soon as possible in order to tell Washburn, a 4 hour or 8 hour class and a max number
of scouts.
Please E-mail him at [email protected] or [email protected] and E-mail me at
[email protected]
You help an assistance would be greatly appreciated. You're representing the KVARC and introducing
Amateur Radio to a lot of young people..
1. Lightning Bolt Quad covers 20/17/15/12/10 meters contact Harold KD0AGX
2. Ed Austin, N0CVQ needs to sale his equipment as he his moving. All equipment was bought new
from AES.
1- UHF 6 element 440-450 MHz, Cushcraft A449 (assembled) $39.00
1 2M 124 WB 4 element Cushcraft 124WB (assembled) $55.00
1- IC718 complete with bencher paddle key $300.00
1- Astron RS35A $80.00
1- Astron RS 20A $60.00
1- Icom AT 180 tuner (new) $200.00
2- Kenwood TM 261 mobiles complete with harness and Mount (5-10-50W)
1- MF 870 HF meter $35.00
1- TM 471A dual band 50 W/50 W UHF use 20A supply $200.00
1- MFJ 873 125-525 MHz $35.00
If interested or for questions , please call Ed 785-214-1774
3. Tower 58' tubler type crankup , will help to remove it. price is $ 650.00 0r we can talk abount it.
N0KPY ph # 785-357-0637
Please send any equipment you have for sale and I will include in next month’s issue
Elmer-ing
Attached is a form for letting me know what you might be interested in having help with. Or If are
available to help someone. Please fill in as appropriate and email back to me or bring to the club
meeting Friday.
I have mentioned this new item to a few people, I would like to suggest adding a get together some
other time of the month as a learning session. I am open to suggestions as to a day and time. I can try to
schedule time at the library or if a different location is available I would take that as a suggestion also.
So what do you think? Let me know by email or at the club meeting.
ARRL Affiliate since 1926
November General Class:
“Need”/”willing to be” an Elmer Info
Call
________________
Name ______________________________
How to contact
Location
Phone _____________________
City
Email
_____________________
Long/Lat____________________
Other _____________________
Grid square__________________
want/need Interests
help
Antennas
CW
Digital
General Info
Radio to buy
APRS
ATV
____________________
level of expertise
Level of expertise (1-5) 1=beginner, 5=expert
Give to Doug(WD0DBS) or email to [email protected]
Willing
to help
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