Bob,
Second quick follow up on the role of the Faraday shield. I reviewed a
second, 20th addition of the handbook today. The second diagram with the
horizontal shield is still, unchanged, in that version.
1. what is the role of the Faraday shield?
2. can the capacitor and diode be removed, and leave only the 50 Ohm
termination resistors?
Thanks - Dan
Bob Alexander wrote:
>Hi Dan,
>The newest ARRL Antenna Book I have is the 18th Edition (1997). I have
>built several of the couplers as shown on page 27-17. I followed the
>drawing in Fig 20 exactly and they work great.
>
>There are some problems with the schematic drawings found in the ARRL book.
>If you look at the schematic in Figure 19 on page 27-17 the shields are
>shown between the primary and secondary windings of both T1 and T2. This is
>incorrect. The shield separates the coupler primary from the secondary so
>it should be drawn, from left to right, below the multi turn winding of T1
>and above the multi turn winding of T2. This can be seen in the pictoral
>drqawing of Fig 20. The turns ratio of T1 and T2 determine the amount of
>coupling and the shield assures no stray coupling.
>
>The drawing in Fig 16 on page 27-14 is incorrect. The shield should divide
>the box vertically.
>
>Look at Figure 12A on page 27-10. Remove both resistors and install RF
>conectors at V1 and V2 and you have a bi-directional coupler. A signal
>applied on the Tx/antenna side will be 30 dB down on the V1/V2 side.
>Likewise, a signal applied on the V1/V2 side will be 30 dB down on the
>Tx/antenna side.
>To clarify: assume all terminations are 50 ohm Z. Apply a 30 dBm signal to
>the Tx port and terminate the antenna and V1 port. The signal level
>measured at the V2 port will be 0 dBm. Move the termination from V1 to V2
>and try measure the signal level at V1. If the device is well built, there
>should be no measureable signal at V1 (no reflected power). Now, move the
>termination from the antenna port to the Tx port and apply a 30 dBm signal
>at the Antenna port. The signal level now measured at V1 should be 0 dBm
>(foward power). If you apply the signal to V1 and V2 and measure at the Tx
>and antenna ports the same results should be obtained. Measurements are
>meaningless without all ports terminated with either a load or source.
>
>Hope this helps explain this type of coupler.
>
>73, Bob, W5AH
>
>P.S. I am not impressed with the RF part of the Ramsey design. B
>
>
>
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