Optimizing Your Stations Performance

Transcription

1 Optimizing Your Stations Performance A few hints / techniques, recommendations for getting the most RF out to the Antenna from your HF, VHF / UHF station. Tonights Presenters: Doug Theriault NO1D John Laing - K7PRS

2 Target Audience New to ham radio, building station perhaps for first time Wondering whether signal could be improved. How do I measure performance of station, what tools or components? Few thoughts, perhaps a better understanding of how to optimize RF getting to the antenna with less loss. Suggestions from two OLD Hams wanting to share their experience. Briefly touching many topics, these can be expanded upon as a separate future presentation if there is interest. YARC has a Very Strong Elmer Group willing to assist you in building out a top notch station or debugging problems.

3 Agenda Station Components Basic block diagrams Power Supply and RF Grounding Antenna and SWR Transmission Lines Quality of Connections Measuring and Measurement Tools Understanding Loss Basic concept of Decibels

4 Station Components Power Supply Mains based, 110v to 12v, Linear/Switched Ground System Transceiver HF, VHF, UHF or beyond New or Old Perhaps Home Brew! Antenna Rubber Ducks, Verticals, Dipoles, Yagi s, loops and more Feed Line / Transmission Line Coaxial cables, Open Feed Lines Connectors, PL-259, N, SMA and others Coaxial Switches

5 Station Block Diagrams

6 Basic Measuring Tools SWR / Watt Meter Antenna Analyzer Volt / Amp and Ohm Meter RF Loads, Reference and or Dummy Load Short pieces of Coax cables with quality connectors/adapters All measuring tools have an accuracy factor and a +/- 5% to 10% not uncommon for consumer grade tools. Commercial / Professional gear can still be 1%

7 Volt Meter / Amp Meter

8 Watt Meter / SWR Meter Cross Needle meters fast measurements RF Power Forward vs. RF Power Reflected Wide range from QRP ranges to 2KW HF vs VHF/UHF

9 Antenna Analyzer Useful tool to measure SWR over range of frequencies Some have nice Plotting capabilities Portable so you can measure right at an antenna Can read Impedance in Ohms as well as SWR Utilizes low power RF signal so not used for Watt measurements! ie: Do not connect to your Tx!

10 RF Loads Precision 50 ohm loads With or Without Metering Can operate over very wide frequency range Dummy loads are very useful to test without an Antenna

11 Equipment Age Considerations Electronic Components age Performance of components can degrade over time Old Coax, weathered Coax cuts in coax, breaks, water intrusion Poor Connections tarnish / oxidization soldering or crimp quality Capacitors are big culprit Semi-conductors typically do not degrade, they Fail and stop working. Tubes however can degrade with age Solder or Crimp connections can break down due to stress, heat Be forewarned buying old gear, esp rigs 20+yrs or older Old gear is great, you just might need to upgrade components before putting it on the air Old Microphones, elements can impact your audio quality

12 The Transmitter / Receiver

13 Power Supplies Linear vs. Switched Make sure capacity is greater than your load Use proper gauge wire Not all ports created equal Voltage/Current sagging can cause rig to cut out, reboot... or worse Make good connections; power poles for instance

14 Grounding Lightning protection Electrical Safety RF Ground Especially important for certain types of antenna ¼ λ Verticals, end fed long wires, unbalanced Helps eliminate common mode currents, RFI, noise from ground loops

15 Antennas Many Many Types Basic Forms Dipoles Verticals Loops Yagi Have Gain factor in db Generally larger and higher performs better

16 High Frequency - HF Height above ground for Dipoles varies w/ frequency; higher is better Dipole Element Lengths cut elements accurately Pattern and performance can be impacted by placement to nearby metal objects Low dipoles can help optimize signals within 600 mi. Verticals can lower the take off angle of RF on lower frequencies, 160m/80m for instance for greater distance

17 VHF/UHF Rubber Duck antenna, not very efficient Hand-held antenna pattern sensitive to placement Line of Sight comms. Polarization, Horiz vs. Vertical Mobile Antenna Placement can have big impact

18 Coaxial Cable Most common feed line Easy to use Not affected by nearby materials Has higher loss than open-wire line at most frequencies Air-insulated hard line has lowest loss Cheap versions of coax have braid that has been reduced to the point that any bend can cause a gap in the braid. This results in RF leaking and loss Technician License Course

19 Open-Wire Line Lighter and less expensive than coax Has lower loss than coax at most frequencies More difficult to use since it is affected by nearby materials Requires impedance matching equipment to use with most transceivers

20 Coaxial Transmission Lines

21 Coaxial Cable Loss Many types of Coax Not all created equal Impedance, 50 vs 75 vs xx That which works at HF may not work well at VHF/UHF Loss means less RF power makes it to the Antenna Loss is directly proportional to coax length. Minimize excessive lengths

22 Hard-line Coax For very long runs of coax Used at repeater sites and very large antenna installations Lower loss factor

23 Low Loss Coax Yikes!

24 Double Shielded RG-214/U Reduces RF leakage Reduces Noise from getting into cable Less susceptible to shield braid opening up during bending of cable

25 Practical Feed Lines Coaxial cables Larger diameter cables have lower loss Loss is measured in db/foot Loss increases with frequency Keep water out! Protect the jacket from cuts and cracks and ultraviolet exposure. Some cable is UV-rated

26 The effect that feedline selection can make on station performance can be quickly appreciated by reviewing the chart below: It is important to note that the choice of feedline also has an impact on your station s receive performance. Without a preamp at the antenna, the line loss is the equivalent of adding an attenuator equal to the feedline loss in the receive path. Assume 100 watts input to 100 feet of the following coaxial cables; Pout (Power out in Watts) Pout@ Pout@ 50 MHz 144 MHz Pout@ 432 MHz Pout@ 902 MHz Pout@ 1296 MHz RG W 24 W 9W 2W <1 W RG W 53 W 30 W 16 W <1 W LMR W 71 W 54 W 41 W 31 W 1 5/8 in Hardline 97 W 94 W 89 W 83 W 81 W

27 Coaxial Connectors UHF SO-239/PL-259 BNC N SMA F (cable TV)

28 Connectors

29 Adapters Minimize if possible

30 Installing Coaxial Connectors Soldering is the traditional way Use rosin-core solder and avoid cold solder joints See The Art of Soldering on the ARRL website Crimp connectors are becoming widely used by hams Obtain and learn to use proper crimping tools

31 Waterproofing Connectors MUST be waterproofed for use outdoors Type N are waterproof but still usually protected anyway Use good-quality electrical tape first, then a layer of self-vulcanizing tape, then another covering of electrical tape Air-core coaxial cable requires special connectors and techniques to waterproof

32 Connections - Trust but Verify

33 Too Much Heat!

34 Crimped Connectors work If you use right tools

35 Measuring Techniques Measure individual components to avoid interaction and confusing results Transmit Power Tx into Watt Meter into Dummy Load Coax Feed-Line(s) Tx or Analyzer to Feedline and into Watt Meter/Load. Antenna Analyzer to measure SWR against frequencies plan on using Take Notes, record losses, add them up Measure with connectors and all cables you plan on using in your final configuration

36 Transmit RF Power Verify your rig is producing RF output it should Watt Meter to measure Eliminate Feed line and Antenna SWR Good time to validate power supply is not sagging during Tx

37 Calculate Feed-Line Losses Measure w/o antenna, just RF Load and Coax Use your Transmitter or Antenna Analyzer With Tx, use Watt Meter; Loss % = (1 - (Pout / Pin)) * 100 With Analyzer, measuring SWR or coax loss in db Measure across multiple frequencies you intend to use Measure all interconnect cables

38 Antenna SWR Measurement Ideally want to measure at connector of antenna where feed line goes into If you measure with feed line, make sure its integer multiple half wavelength at frequency being measured. Velocity factor in Coax must be considered when calculating length of half wavelength.

39 Tx Power What s Acceptable? Minimize where you can Loss means less RF radiates at Antenna Also can generate Heat which is wasted energy High SWR, Loss, can damage your finals on some rigs. There will always some loss in your system. But with good antenna, you can also add some gain W VSWR % Reflected Wasted Watts At Antenna db Loss 1: : : : : : : : : : : : : : : : Err:502

40 Identify Areas of Possible Loss (1 or 2 db) Old Coaxial cable Coaxial lengths longer than required Poor coaxial connections (solder or crimping) Coaxial switches can lead to loss. Use only good switches Minor issues can add up to station db loss. Just take a step back and look at your station

41 What a difference a decibel can make! Many Hams will say Oh well, it s only a decibel (db) or 2 - or 3. That is not very significant so who cares! Well, true it is a very small number, but it amounts to one half (1/2) of the power to your station. Every db is important! You spend a lot of money to create power to your Station, so you don t want to lose it to leaks and loss.

42 New Ham: What s the difference between a 3element Yagi and a dipole antenna? Elmer: About 6 db. In the Technician License Course you learn two rules of thumb about decibels that get you through the exam and provide a rudimentary understanding of their use: 1)A doubling or halving of power equals a change of approximately 3 db. 2)A 10X change of power equals a change of 10 db. 3 db equates to about a 2:1 power ratio 10 db (aka 1 bel, or 1 10) equates to a 10:1 power ratio 20 db (aka 2 bel, or 1x10x10) equates to a 100:1 power ratio 30 db (aka 3 bel, or 1x10x10x10) equates to a 1000:1 power ratio and so on

43 How to calculate Decibels (db) A ratio expressed as an power of 10 to make large numbers easier to work with. db = 10 log (power ratio) db = 20 log (voltage ratio) Positive values in db indicate ratios > 1 and negative values of db are for ratios < 1. Antenna gain is discussed in terms of db Technician License Course

44 Loss in db is directly proportional to coaxial length. Be sure to cut the coax to the proper length. Don t leave excess coax just to save the coax for a later project. It will cost you in signal loss. Standing Wave Ratio (SWR) and coax line loss, i.e. mismatch load Since reflected power makes two (2) complete trips through the line (coax) each with attenuation it receives twice as much loss as that portion of the power that makes only 1 trip down the line.

45 Closing Thoughts If there is interest, we can setup demonstration perhaps in breakout session in future meeting: Connector installations Verifying your coax cables Many of topics touched on tonight can be greatly expanded upon; let club know what you want to see in future talks Elmer group does great job at getting your station up and running; as a New Ham you should gain knowledge to maintain / debug for peak performance.

46 UHF: Mt. Union, PL IRLP: 7100