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-
- An Absorption RF Wattmeter, (up to 10 Watts into 50 Ohms).
- ----------------------------------------------------------
-
- Technical Specifications:-
- --------------------------
-
- RF Power Range................ Up to 10 Watts.
- Useful Power Range............ Up to 11 Watts, the readings will continue
- up to approximately 15+ Watts.
- Calibrated Spot Frequencies... 21MHz, 51MHz, 70MHz, 145MHz and 435MHz.
- Useful Frequency Range........ 1MHz to 520MHz.
- Coaxial Load Resistance....... 50 Ohms.
- Load Resistance Rating........ 15 Watts (Continuous).
- VSWR.......................... Better than 1.3:1.
- Settling Time................. Approximately 1 Second.
- Accuracy...................... Better than + or - 3dB of full scale.
- Temperature Stability......... Better than + or - 10% of full scale.
- Overlaod Point................ 11 Watts.
- Overload Condition............ Power Reading changes colour and reads
- up to approximately 15+ Watts.
- Maximum Overload Time......... 2 Minutes, (allow 5 Minutes to cool down).
-
- ----------------------------------------------------------------------------
-
- Overview:-
- ----------
-
- This tool will measure RF Power, generated by Transmitters, from 21MHz to
- 435MHz. It is the most expensive single project to date. The basic
- accuracy was checked against an old Marconi Absorption Wattmeter type
- TF1152A/1 and also a Bird Thruline Wattmeter Model Number 43 with a
- Termaline Coaxial Resistor Model Number 8080.
-
- Note that the ranges on the software are similar to that of the
- Bird Element Ranges that come with the Thruline Wattmeter. Compared with
- professional RF Power Meters this is VERY cheap and if you are an RF
- engineer, VERY useful. The A-D Converter from ~TestGear2.lha~, ~Project6~
- is required for this project.
-
- ----------------------------------------------------------------------------
-
- Parts List:-
- ------------
-
- A) For the Sampling Head:-
- --------------------------
-
- 1) Circuit Box 50 Ohm.......... Farnell part number 309-801.
- 2) Coaxial Adaptor............. Maplin part number DV35Q.
- 3) R1.......................... Coaxial 50 Ohm Resistor, ~DUMMY LOAD~.
- Maplin part number ZA10L.
- 4) VR1......................... 50 KilOhms preset variable. Maplin part
- number WR43W.
- 5) SK1......................... 3.5mm mono switched Jack Socket. Farnell
- part number 152-201.
- 6) R1.......................... 33 KilOhms, 1/8 Watt.
- 7) C3.......................... 4.7pF, 100 Volts or more.
- 8) C2.......................... 10nF or 0.01uF, 100 Volts or more.
- 9) C1.......................... 1000pF, 1nF or 0.001uF, 100 Volts or more.
- 10) D1,D2....................... 1N4148 silicon diode.
- 11) Hardware, wire, sleeving etc.. etc.. as rqeuired.
-
- B) For the A-D Converter connecting cable:-
- -------------------------------------------
-
- 12) 3.5mm Audio Jack Plug.
- 13) Length of Audio Coaxial Cable.
- 14) RCA/PHONO Plug.
-
- C) Optional Extras:-
- --------------------
-
- 15) N Type Adaptor.............. Maplin part number FJ82D.
- 16) PL259 Adaptor............... Maplin part number YW05F.
- 17) TNC Adaptor................. Maplin part number FE83E.
- 18) Any other RF Cables/Adaptors as required.
-
- Note:- All items without a reference can be sourced from any supplier
- and the tolerances for these items are + or - 10%.
-
- ----------------------------------------------------------------------------
-
- Construction of the Sampling Head:-
- -----------------------------------
-
- 1) Strip down the ~Circuit Box~ as per the label.
- 2) Drill one hole 1/4", (6mm), diameter at the centre of the full face
- of the main body of the ~Circuit Box~. Deburr as required.
- 3) Fit the 3.5mm audio jack socket into this hole.
- 4) Connect the link between the BNC socket and the BNC plug in the
- ~Circuit Box~.
- 5) Wire up the remaining components as per the ~Hardware~ drawing.
- 6) Keep the leads of D1, D2 and C3 as short as possible. These components
- are self supporting.
- 7) Take note that one terminal of the jack socket is used only as a
- component solder tag and it is on the same side as the jack socket's
- Earth/Common tag.
- 8) The preset variable resistor is also self supporting.
- 9) CHECK an RECHECK your construction work thoroughly.
- 10) Do NOT refit the outer casing yet.
- 11) The unit is now ready for calibrating.
- 12) A 9 Volt PP3 battery WILL be required to calibrate, see below.
-
- ----------------------------------------------------------------------------
-
- Construction of the connecting cable:-
- --------------------------------------
-
- 1) Strip the sleeving off of both ends of the audio coaxial cable,
- approximately 3/8" (10mm) long.
- 2) Place the body of the Jack Plug onto the coaxial cable.
- 3) Connect the inner conductor of one end of the coaxial cable to the
- inner solder tag of the Jack Plug.
- 4) Connect the braid to the to outer solder tag of the Jack Plug.
- 5) Screw the body of the Jack Plug on to the Jack Plug itself.
- 6) Do ~2~ to ~5~ on the opposite end except change the words ~Jack Plug~
- with ~PHONO/RCA Plug~.
-
- ----------------------------------------------------------------------------
-
- Calibrating the RF Wattmeter:-
- ------------------------------
-
- 1) Switch OFF tha AMIGA and read the ~Warning~ file.
- 2) Connect the A-D Converter from ~TestGear2.lha~, ~Project6~ to the
- parallel port.
- 3) Connect the Audio Coaxial Cable from the ~Circuit Box~ to the A-D
- Converter.
- 4) Connect the 9 Volt, PP3, EVEREADY (ULTRA PLUS) Red Body type 6F22
- battery from TP1 to TP2. Positive (+) terminal to TP1, Negative (-)
- terminal to TP2.
- 5) Switch ON the AMIGA.
- 6) Start up the ~Parallel_Test~ software from ~Project6~.
- 7) Adjust VR1 in the ~Circuit Box~ to give 48, (flashing 49) in the
- window.
- 8) Switch OFF the AMIGA and disconnect all of the hardware.
- 9) Now refit the outer casing of the ~Circuit Box~.
- 10) Fit the Coaxial Adaptor, (Item 2 in the Parts List), to the BNC
- Socket of the ~Circuit Box~.
- 11) Finally fit the Coaxial Resistor, the DUMMY LOAD, (Item 3 in the Parts
- List) to the Coaxial Adaptor, (Item 2 in the Parts List).
- 12) You now have a fully working RF Wattmeter, (RF Power Meter).
-
- ----------------------------------------------------------------------------
-
- Important Information:-
- -----------------------
-
- Due to the limitations of cost, method of sampling, component tolerences
- and construction techniques, etc. etc. this device will NOT be able to
- perform as well as the VERY expensive ~BIRD THRULINE~ or the ~MARCONI~
- RF Power Meters. On the ~SPOT~ frequencies however (which are all in the
- AMATEUR bands) the unit should be reasonably accurate, either side of this
- errors may occur so be aware of this when taking any measurments.
-
- Also when the readings go greater than 11 Watts the colour changes to let
- you know that you are in OVERLOAD condition. Do NOT stay in this condition
- for more than 2 Minutes, allow time for the ~DUMMY LOAD~ to cool down.
-
- Lastly RF (Radio Frequency) is a strange beast and all kinds of errors
- can occur due to poor Transmission Lines, Coaxial Connectors/Adaptors,
- poor Connections and loose Mechanical Assemblies etc. etc. so be very
- aware of this when taking any measurements.
-
- ----------------------------------------------------------------------------
-
- Using the RF Wattmeter:-
- ------------------------
-
- WARNING!!!
- ----------
-
- RF Voltages CAN cause burns to the skin so be VERY CAREFUL.
- -----------------------------------------------------------
-
- 1) Switch OFF the AMIGA and read the ~Warning~ file.
- 2) Connect the A-D Converter to the parallel port.
- 3) Connect the Audio Coaxial Cable from the RF Wattmeter to the A-D
- Converter.
- 4) Attach the RF Wattmeter to a Transmitter under test using any
- neccessary Coaxial Cables/Adaptors as required.
- 5) Switch ON the AMIGA.
- 6) Start up the ~RF_Wattmeter~ software.
- 7) Choose the required range and read the power output.
- 8) When finished switch OFF the AMIGA and disconnect all of the hardware.
-
- ----------------------------------------------------------------------------
-
- Acknowledgements:-
- ------------------
-
- First of all many thanks to my wife Tricia who allows me to spend many hours
- on my computers.
-
- Also to David Benn and Herbert Breuer for the ACE/AIDE combination supplied
- on an AMIGA FORMAT floppy disk which made it easy to compile this program.
-
- Also to Laurence J Greatorex for giving these a shakedown on his A1200 with
- a Turbo LC '030 accelerator board and 32MB of fast ram, also to Bob Eva for
- testing on his A1200 setup, with a total of 10MB of memory, and to all the
- other people that have given any of these projects a rigorous testing.
- And finally to anyone else who I may have neglected or forgotten.
-
- ----------------------------------------------------------------------------
-
- Mr Barry Walker,
- 70 King George Road,
- Loughborough,
- Leicestershire,
- LE11 2PA,
- England.
-
- Email to:-
-
- 106161.3245@compuserve.com
- or
- wisecracker@tesco.net
-
- BYE.....
-
- ----------------------------------------------------------------------------
-