Making the K3S internal Transverter more External Transverter proof

Having suffered with the K144XV internal transverter's lack of useful output adjustment range, I finally decided to do something about it. The issue is that with the power control fully clockwise the 144 MHz output power is 9W. With the power control fully anticlockwise the output is 1W. This is the only band you cannot turn the output down to 0W!.  If you set the the IF level to -10dbm, fully anticlockwise is still 1W, as is every other setting of the knob.

The issue was raised with Elecraft over 3 years ago, but they said there was no software solution. They did point out that there is a drive pot in the module that could be adjusted to make the maximum level suit my transverter. After blowing up the pin diodes in my DB6NT transverters on more than one occasion, it was time to investigate.

Reference to the circuit of the K144XV revealed the pot was labelled R87

After removing the K3S top cover and the Transverter top cover, R87 was physically located between L3 and L4. It is shown in the following picture:-

Next a small hole was drilled to allow a trimming tool to adjust VR4 with the lid still on the transverter, as shown below:-

I set VR4 to give 1.2W with the drive level set in the menus to 0dBm. The adjustment range is similar, but now there is no risk of overdriving and destroying the transverter.

Another advantage of the new configuration is that the positive  voltage on transmit present on the XV connector centre pin is retained for transverter switching. Previously with an external attenuator the DC component was dissipated and an external Bias-T was needed to switch the Transverter.

Upgrading the K3S for 475kHz

Having had the initial try of the K3S on 475kHz here It was time to properly implement the low frequency bands on the K3S. The first step was to convert both KBPF3 to KBPF3A (one on the main RX one on the SUBRX). It is a simple process requiring the removal of 2 inductors from the board and adding 3 capacitors in parallel with existing capacitors. To make it look neater I actually replaced the existing capacitors. While the KRX3 was open I also added the electrolytic capacitor specified across the 9V rail. The whole process took 30 minutes

While the box was open I also added the K3EXREF 10MHz lock board and the K144XV (with K144RFLK)

I hooked up the RX antenna port to the PA0RDT active antenna in the loft and was pleased to see some DX:-

Timestamp	Call	MHz	SNR	Drift	Grid	Pwr			km	az
2016-03-28 00:04	G0MRF	0.475770	-13	0	IO91tk	5			151	300
2016-03-28 00:00	DK7FC	0.475682	-20	0	JN49ik	1			827	295
2016-03-27 23:50	DH5RAE	0.475755	-28	0	JN68qv	0.5			1161	294
2016-03-27 23:16	PA3ABK/2	0.475785	-24	0	JO21it	0.5			481	277
2016-03-27 23:14	F1AFJ	0.475703	-27	0	JN06ht	1			625	341
2016-03-27 22:26	DJ0ABR	0.475665	-30	0	JN68nt	0.2			1148	294

Seperate Receive and transmit paths for the Elecraft K3 Internal K144XV Transverter

When using the Internal K144XV  2m transverter in my Elecraft K3, it has a single BNC connector on the back panel for receive and transmit signals. Having obtained an HA8ET 2m mast head preamp I needed to separate the two signal paths to avoid putting RF up the back of the preamp.

Elecraft in the past have said it is possible to connect a separate RX antenna to transverter but nothing has ever been documented! The only clues have been the comment  in the K144XV manual about not removing links P2 and P3 inside the transverter. Time to investigate!

I took the cover off the K3 and the K144XV transverter and found that if the link between pins 1 and 2 of P3 was removed the receiver went deaf.  Pin 3 was ground.  I connected a coax cable with centre conductor to pin 2 and the braid to pin 3 the GB3VHF beacon could be heard on my collinear. The radio still produced the normal 9W out of the BNC connector on the back panel.
I did not want to solder to the header so I found a 3 pin female header (previously used for arduino shields) and soldered a piece of RG174 with a BNC socket on the other end, which hung out of the back of the lid panel. I did look at tidying up the cabling by using the AUX RX BNC connector but this would mean taking the K3 apart and removing the sub receiver every time I wanted to change between internal and external 2m antenna switching.
For reference P2 link allows the Receive IF output to be diverted from going to the KXV3A module. P8 link enables the DC voltage on transmit on the centre pin of the Transmit port.


I have written up the "Seperate  Receive and transmit paths for the Elecraft K3  Internal K144XV Transverter" modifications with pictures at http://g4fre.com/kx144_split.htm