[K3] Installing the PR6 pre-amp

[K6LMP]

Over the weekend, I installed the KXV3A transverter and Receive Only antenna interface, and also the PR6 6-meter pre-amp. Installation went smoothly for both, but I found myself doing a lot of head-scratching about the proper way to hook up my antenna. Finally figured it out, with assistance from Wayne at Elecraft, who has confirmed the following is correct.

My problem was trying to determine where to connect the antenna feed line so that I could use my 6-meter 3-element quad antenna for both receive and transmit functions.  An inspection of the circuit diagrams of the KXV3A and PR6 made it clear that these components are not intended to carry transmit signals, even though they have a "receive antenna out" port.

To save equivalent puzzlement for others, here's how it works.

1. Configure the PR6 to be switched on when the K3 is set to six meter band using DIGOUT 1, as explained in the PR6 manual, and connect the PR6 to the RX Antenna In and RX Antenna Out BNC connectors on the KXV3A; connect the power cord to the 12VDC switchable power port (RCA jack) on the back of the K3, and connecting the DB-9 connector to the ACC jack on the back of the K3.
2. Connect your 6 meter antenna to ANT 1 (or, optionally, to ANT 2 if you have the optional second antenna port installed with the KAT3 internal antenna tuner).
3. Don't connect any cables to the "bypass" connectors on the "back" side of the PR6. (They have other uses, but not for normal transmit/receive through a single antenna.)
4. When operating on 6 meters, if you wish to engage the PR6 preamp, tap the RX ANT button (right next to the POWER switch).  This causes the receive antenna signal to be routed from the ANT 1 jack through the  KXV3A Receive Only circuitry, then through the PR6, back through the "input" side of the KXV3A, and from there back to the front end of the receiver circuitry.  
5. When you transmit, the K3 automatically routes the signal directly to the ANT 1 jack, bypassing the KXV3A and PR6.

Notes:

1. If you're working a strong station and want to dis-engage the PR6, simply tap the RX ANT button and you'll remove the PR6 from the antenna path.
2. Since the KXV3A "returns" the receive signal to the front end of the receiver, you can receive on 6 meters using just the PR6 or with the PR6 AND the internal pre-amp both engaged.  From what I have read, you don't normally need or want to engage the internal K3 pre-amp while using the PR6, but some K3 owners have reported that they can dig out really, really weak signals using both pre-amps. (see, for example, N5GE's report at http://www.mail-archive.com/elecraft@.../msg86350.html)

Thanks to Wayne for guiding me through the K3 block circuit diagram and other help in working this out.

BTW, the 6 meter antenna is a three element quad, fed through an Elecraft BL2 balun at 1:1 ratio, horizontally polarized  This is a lovely 6 meter antenna. It collapses into a small bundle for portable/rover use, mounts on a six foot boom, and has a natural impedance of 50 ohms. It has several dB more gain than a 6 meter Yagi of equivalent size, is easier to make, has lower material  and easier to transport than a Yagi.  

Lew K6LMP
 
Lew Phelps K6LMP
Pasadena, CA DM04wd
Elecraft K3 Serial #3805
Yaesu FT-7800 (2m and 70 cm, 50 watts FM)
K6LMP (at) me.com




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