Antenna splitter to use an external receiver
With the KXV3 transverter interface, the antenna feed can be looped via an external filter or pre-amplifier. I have connected an external antenna splitter to mine, the RX OUT feeds the input of the antenna splitter, one port of the splitter connects to the RX antenna in, the other to an external receiver. I use a Perseus SDR receiver to both work with CW Skimmer and also for use as an outboard receiver. The splitter can be switched in and out of operation by the K3 front panel button "RX ANT".
Of course, the splitter can be used for other purposes and is not restricted to being used with a K3. The circuit and measured performance of the splitter are shown below, it is designed for use between 500 KHz and 55 MHz.
The above image is insertion loss between the input and either RX 1 or RX 2, with the other RX port terminated in 50 Ohms
The above image shows isolation between RX 1 and RX 2 with the input termined in 50 Ohms
I previously used 8 turns for T1 and T2, there is an improvement in performance at higher frequencies when using 4 turns, around 0.5 dB less insertion loss at 55 MHz and 4 dB better isolation.
Here are a couple of modifications that can be done to a K2 in order to operate it as a stand alone transmitter, and also interface it to a VHF (or UHF) transverter.
The image at the top of the page shows my Drake R4A hooked up to my K2. The R4A is being used as an outboard receiver with a buffer amplifier fitted internally within the K2, together with an external mute unit. Here is a link to the full article in Adobe Acrobat format (400 KB file size).
I used to run a Microwave Modules MMT144/28 transverter with my K2. If you would like details of the interface, attenuator and interconnections, download this Adobe Acrobat file (92 KB).
The K1 is a quite useful transceiver for portable and QRP operation. It does have one or two limitations, one being a tendency for VFO drift and the other being the limited tuning range of the internal ATU. I have a couple of mods that overcome the drift and increase the tuning range of the ATU. My VFO needed up to 3 hours to settle down, although the amount of drift was close to specification it was annoying. This mod adds a Cumbria Designs X-Lock to the K1.
The ATU mod adds a couple of additional capacitors, and removable jumpers, to the KAT1 in order to provide additional capacitance on the lower bands. The links can enable the additional capacitors to be inserted or removed depending on the antenna configuration and are usually inserted when I use the 80/40 band board and removed when I use the 40/30/20/15 board.
None of the above modifications are official Elecraft modifications and are done at your own risk.