2400 Mhz Test Aids

["Bill Briles" <w0oqc@xxxxxxx>]

This is in answer to comments provided by KJ6HZ John to the presentation on
the above subject.
The slides to the presentation are contained on N0ZHE Greg's Web Page.
                      http://www.havilandtelco.com/homepages/gregwycoff    
                    
                        
The comments here may help other persons with similar comments.

Thanks for the comments, John.

The slides were prepared for a talk I gave (with N0ZHE Greg support) to the
Boeing Amateur Radio Society (BEARS) meeting on March 7,1998. The slides
do not and were not met to contain equipment details. They are to provide
ideas for experimentation.

Some of the details and answers to John's questions are as follows:     

1. Signal Source
    The oscillator part number on the slide is not correct. The Radio Shack
    part no. should be RSU 11321361. The part no. on the diagram is
    correct.
    I have used clock oscillators from other sources which are a harmonic
    of 2400 Mhz and all have worked fine. The higher the frequency of the
    oscillator, the greater the output. The unit as shown in the diagram is
    a fairly pure 2400 Mhz signal. The tuned circuit is quite selective.
    When I first got the Drake converter, the frequency selectivity was
    not known and I wanted a pure signal to be sure I wouldn't be tuning
    on a birdie.
    A less pure signal will probably work fine with the Drake
    downconverter.
    Clare (VE3NPC) has an article in the Canadian Amateur magazine
    which would work fine and be similar to using a clock oscillator by
     itself. I tried this by soldering a dipole to pins 7 and 8 of the
    oscillator. I could hear the signal just fine on the Drake converter
    and only an S unit below the tuned circuit model. The turned
    circuit for 2400 Mhz was taken from the RSGB Microwave
    Handbook. The clock oscillator idea should work for other
    frequencies. The monopole antenna should work fine.  I was
    testing with a Lance 24 Antenna which is horizontally polarized.

2. Antenna 
   When I first built the Helix antenna, I matched it with a 1/4 wave
   matching section as shown in the ARRL  Antenna Handbook. I connected
   the Drake Converter directly to the antenna feed point. A freak
   lightning storm (for Kansas) in January blew out the input amplifier to
   the Drake converter. I redesigned the matching section to provide
   a short to ground for the low frequency (less than 100 Mhz) lightning
   and static discharge pulses. I also installed a foot of RG8 cable
   between the antenna feed point and Drake converter input to
   act as a pulse filter. The 1/2 wave matching provides a low
   frequency short across the input to the converter. The tap was
   determined experimentally using a signal and should be 1 inch
   from the ground end plus or minus 1/4 inch.
   ( Thanks to W0EKZ Bud for the idea of the 1/2 wave  matching section.)

3.  Protection Circuit
    The protection circuit uses an R.F. sensing and swictching circuit
    design copied from my  Adavanced Receiver Research Pre-amp.
    When R.F is sensed, the relay switchs from the converter output to
    a 50 ohm load and sounds an alarm. The Radio Shack power relay
    was modified to provide low VSWR thru the protection circuit. The relay
    center pole is conected to the front socket by a wire. The wrap around
    increases the VSWR. The relay cover is removed and the relay center
    pole wire is cut at the socket. A hole in the relay cover top is
    drilled for the wire to exit. This makes the relay switch straight
    thru. To lower the inpedance the relay cover is wraped with
    aluminum tape. When completed the VSWR thru the unit is less
    then 1.2. Only 2 watt resistors were used because it is assumed
    the transmitter key will be "let up"  when the alarm is sounded.
    I made a "Live or Die" test with a Drake converter and 50 watts FM
    at 144 Mhz. The converter survuved. I tried a Pirzo buzzer. The R.F.
    would shut off the buzzer with just a beep. The magnetic buzzer
    works fine. 

5. Diagram Rescale
    I am not a Computer type. I will leave that to N0ZHE Greg and N0KTA 
   Joe. They have agree to try to rescale the diagrams to JPEG in the 600
   pic area. I use MGI PhotoSuite and it scales the printer to an 8.5 by
   11 page. 

6. I will revise the slide to correct the part no. error. Greg and Joe will
    work on rescaling the diagrams. I hope this answers John's questions
    and will help others with similar questions. I thank Greg N0ZHE for
    all the help in  building and testing he has done.  Without him the 
    results would not have been possible.
 


    73's  BILL BRILES W0OQC  DERBY KS
    E-Mail    w0oqc@gte.net