Jennifer Johnson, KC0IEN Introduction What is amateur radio

1
Coaxial Cable for Amateur Radio Communications

• Jennifer Johnson, KC0IEN

2
Introduction

• What is amateur radio?
• Amateur or ham radio is regulated and licensed
  by the FCC
• Creation was the U.S. would have knowledgeable
  communications personnel in times of need, such
  as natural disasters and other public services
• Also to encourage the spirit of invention and
  goodwill with other countries and other people
• Hams operate on any and all modes of
  communications on a wide variety of frequencies

3
Introduction to project

• Recently, I helped the Cyclone Amateur Radio Club
  (CARC) complete an installation of coax for its
  club station or shack in Friley Hall
• Removed old (20 year old) coax and replacing
  with new and expensive coaxial cable
• Previous runs were probably RG-8 or RG-8 variants
• CARC analyzed what kind of cable to purchase and
  for what purposes

4
Criteria for Coax purchase

• Types of communications to be used
• RTTY, PSK31 (data), SSB, AM, FM, CW (Morse code),
  satellites, etc.
• Power output
• 5 mW to 800 W
• Frequencies to be used
• HF 1.8 MHz to 30 MHz
• VHF 30 300 MHz
• UHF 300 MHz 3 GHz
• Ease of installation
• Coax must be flexible to bend around corners to
  get to roof
• Length of cable required
• Low SWR needed for the 100 ft of coax needed to
  reach antennas from shack

5
Background Information

• Antennas on Friley are HF and VHF beams and
  dipole antennas
• CARC has a 1.2GHz module for a Kenwood TS790
• Installation of 1.2GHz antenna for satellite work
  is planned for a future date
• Picking coax for HF/VHF antennas was easy
• There is an inherent low loss for HF
  frequencies, since the conductor resistance is
  related to skin effect and also because
  dielectric losses rise with frequency.
• Conclusion dont waste money buying low SWR
  cable
• Picking coax for UHF somewhat easy, but more
  expensive
• Attenuation is the sum of the conductor
  properties times the square root of the frequency
  plus the dielectric properties times the
  frequency.
• As the signal frequency is increased, the
  attenuation component contributed by dielectric
  will increase faster than the attenuation
  component contributed by conductors.
• It is for this reason that it is important to use
  the highest quality of dielectric materials
  available to optimize performance at high
  frequencies.
• Conclusion Buy the best quality cable you can
  LMR series is a good choice

6
Coax Comparison
7
Final Decision on Purchase

• UHF operations are very important to the club
  members
• CARC owns two UHF repeaters at 443.375 MHz and
  442.375 MHz
• Club members have expressed interest in doing
  satellite, EME (Earth Moon Earth bounce), other
  types of communications.
• CARC bought LMR400 and LMR600 coax (thanks GSB!)
• Because both has very low loss and is highly
  flexible
• LMR400 for five runs for HF/VHF operations
• LMR600 for one run for the 1.2GHz operations
• Isnt this a little overkill?
• Yes, but only just a little because.
• Club members dont have the time or opportunity
  to replace coax often
• Members come and go often so it makes it harder
  to organize to make repairs and revisions to coax
  lines
• Also have to set up times and dates with DOR
• CARC has diverse and changing group of members
  that may wish to explore more on UHF frequencies
  at a future date

8
LMR600 Attenuation
9
LMR400 Attenuation
10
Belden 8214 Attenuation
11
Comparison of Coaxial Cable Specifications
Specifications for LMR600
Specifications for LMR400
12
Purpose of Experiment/Investigation

• To analyze several different types of coaxial
  cable
• Justify the purchase of expensive coaxial cable
  versus other types of inexpensive cable
• During these tests I analyzed these coaxial
  cables
• LMR600
• LMR400
• Belden 8214 (RG8/U)
• unknown
• RG-58
• Belden 8267 (RG-213/U)

13
Testing Procedures LMR600, LMR400, RG8/U, and
unknown

• LMR600 and LMR400 are brand new off the spool
  that is in the shack
• The RG8/U (Belden 8214) was a used piece that was
  used by the CARC for various types of RF
  communications
• Unknown piece is an used piece of RG/8 that has
  N-type Male connectors on it
• I purchased 6 connectors to use for these tests
• Two are for the LMR600
• Four are to be used for the LMR400 and Belden
  8214
• Why N-type connectors?
• They have low loss at high frequencies when
  compared to UHF or BNC connectors.
• Most of the radios in the shack use N-type or UHF
  connectors. It would be more realistic and
  practical for me to test the coax using commonly
  used connectors for ham radio gear
• The network analyzer and most of the equipment in
  the lab uses SMA and the lab already has N-type
  to SMA connectors
• I didnt want to purchase UHF to SMA connectors
  as they are expensive
• Using UHF connectors would be impractical as no
  good amateur radio operator would stand for the
  amount of loss that would result from using UHF
  connectors at frequencies above 1 GHz

14
Testing Procedures LMR600, LMR400, RG8/U, and
unknown
N-male to SMA male (similar to adapter in lab)
N-female Crimp connector for LMR600
N-female Crimp connector for LMR400 and RG8/U
15
Testing Procedures LMR600, LMR400, RG8/U, and
unknown
N-male to SMA-male
N-female to N-female
16
Testing LMR600,LMR400, RG8/U, and unknown

• Used oscilloscope and network analyzer
• Problems
• Coax lengths were too long (approx 60)
• Connectors were not crimped properly
• Problems with RG/8U did not test
• Bad adapters

17
LMR600 without load
18
LMR600 shorted
19
LMR600 with 50 ohm load
20
LMR400 without load
21
LMR400 shorted
22
LMR400 with 50 ohm load
23
Unknown without load
24
Unknown shorted
25
Unknown short (return)
26
Unknown with 50 ohm load
27
Why VSWR for Amateur Radio?

• SWR is probably considered the gold standard in
  measuring line loss for most ham operators.
• Why?
• SWR/Wattmeters are easy to use and relatively
  inexpensive.
• Hams do not usually have regular access to
  network analyzers, oscilloscopes and other
  specialty equipment
• A large majority of hams, regardless of their
  nerdy nature, do not have the funds to purchase
  such expensive pieces of equipment.
• Why is SWR important to hams?
• As part of the amateur radio service, hams are
  expected to serve as volunteers in cases of
  disaster or other times of need.
• During these times, amateur radio operators can
  anticipate having to operate on emergency power.
  
• Usually this involves battery and solar power.
  Obviously, it is very important to conserve as
  much power as possible.
• Other considerations
• Many older pieces of ham radios do not have built
  in protection for high SWR. If you dont know
  what youre doing, you can definitely damage
  radio and other equipment
• New radios have built-in protection that will
  automatically scale back transmitter power if the
  radio detects a high SWR.
• This has surely saved a number of radios from the
  workbench, including several of my own.

28
LMR600 Network Analyzer Return and Insertion
loss
29
LMR600 Network Analyzer VSWR Plot
30
LMR400 Network Analyzer Return and Insertion
Loss
31
LMR400 Network Analyzer VSWR Plot
32
Unknown Cable Network Analyzer VSWR Plot
33
Unknown Cable Network Analyzer VSWR Plot
34
Conclusions on Network Analyzer Testing

• LMR600 really does live up to reputation
• Adding in adapters and connectors causes a lot of
  loss
• N-type connectors can be painful
• The right tools make for easy and lasting work
  (crimpers)
• I wish I could have tested with different
  connectors with the right equipment to do a
  better, more thorough analysis

35
Testing Procedures Ham radio style

• This portion of the testing process involved
  doing some real world testing that hams would do
  in the field
• Case in point
• When we were removing the old coax lines from
  Friley to make way for the new runs, we noticed
  some of the cables had deep gashes and cuts
• Some cuts were cut clear to the center conductor
• When testing our equipment and antennas before
  doing the new coax installation, we found that
  our SWR readings were extremely high
• Of course, at the time we were unaware of the
  cuts in the coax and thought there may be a
  problem with the antennas
• Since we have installed our new coax some of the
  SWR issues have gone away, however some issues
  still remain. Investigating the antennas will be
  the next step

36
Testing Procedures RG58 and RG8/U

• Using basic tools that hams use, test to see if I
  can get reasonable results for VSWR
• Test SWR using dummy load, SWR meter, and
  transceiver (1.8MHz 440MHz)
• Use PL259 (UHF) connectors
• Use working RG-58 cable from radio to SWR meter
• What happens when there are cuts in coax?
• Is VSWR worse at higher frequencies?

37
What kinds of equipment do Hams use for testing?
MFJ VHF/UHF SWR Analyzer (144 440 MHz)
MFJ HF SWR Analyzer (1.75 MHz to 33 MHz)
38
More SWR Meters (cheaper ones)
144/440 MHz SWR Analyzer
39
Testing Equipment
Variable Power Supply 2-20V 3A max
Dummy Load
Yaesu 817 Low-power HF/VHF/UHF transceiver (5W
max)
40
Testing RG58 and RG213

• First I tested VSWR at low frequencies (HF) since
  dummy load was not tuning above 10 MHz

41
Field applications

• Going back to the case for the damaged coax in
  Friley what happens when coax is damaged?
• How much damage can be managed before VSWR gets
  very high?
• Can I tell a difference in VSWR vs. frequency?
• To test this, I used my mobile radio setup in my
  car to see

42
Mobile Radio Setup
43
Test Results

• Equipment used
• RG-213 cable I made and tested earlier
• MFJ VHF/UHF VSWR analyzer
• Kenwood D700A (mobile transceiver)
• Diamond SG7500A antenna
• Made strategic cuts to coax to test VSWR
• Surprisingly, VSWR at 146.58 MHz never changed

44
When good coax goes bad
45
Test Results
46
Conclusions Network analyzer vs. amateur radio
equipment

• Amateur radio testing equipment can be accurate
  and easy to use
• Small SWR meters are a quick and easy way for
  testing VSWR when youre on the run
• For specialized applications or specific testing
  requirements, network analyzer is the way to go
• Ive gotten better at soldering coax
• Since Im a ham and engineer, given the
  opportunity I would prefer to have both types of
  equipment at my disposal ?

47
Questions?

• More info on ham radio on campus is available
  from CARC
• wwww.stuorg.iastate.edu/radioclub