New SOTA Rig

The new Elecraft KX2 arrived last week.  So far it looks like just the thing for SOTA activations.  A battery pack was not ordered for it, so one was constructed from 3 x 18650 2500mAh cells with a protective polyfuse.  A 3 cell protection module is on order from Ebay to complete the battery pack.

An action camera case from Target ($6) is just the right size to house the radio, mic and a few small bits and pieces.

Looking forward to taking it out to the mountains.  Its quite a bit lighter than the FT-817 at 380 grams without batteries.  The display is big and easy to read compared to the squinty 817 screen.  The radio case has a few gaps here and there around connectors and joins, so it will need to be protected from the elements carefully.


So far, the radio performs nicely, the controls are well laid out and fairly intuitive.

The microphone for KX2 is pretty expensive at nearly $100 Aus.  Mine had a something rattling in it so I opened it up to have a look.  The rattling turned out to be a blob of solder.  While apart, I noticed that the braid wire from the cable to the internal connector was very tight and might break away if the curly cord is tugged.   There are some reasonable gaps between the PTT pressel and the shell sides, and it wobbles sideways a bit.  The mic. lets the radio down a bit in my opinion.

As its hard to avoid things getting wet with SOTA, so I wired up another smaller microphone.  This mic is well sealed with a gasket between the shell halves and the PTT switch completely sealed from moisture ingress.  The PTT switch strikes a rubber membrane with the switch is on the other side.  Being a smaller mic., it will pack better as well.    The schematic from this page was followed, although my mic. had a 2k resistor and 0.33 uF cap in parallel.   The level from this mic is much higher than the original, so a 10k resistor was placed in parallel on the cord side of the mic wiring.

20160911_101618 20160911_101823






The audio from the small mic seems OK, although I did add a piece of fabric behind the mic aperture behind the case to reduce popping.

The battery pack was built with 3 x 18650 2500mAh cells.  In this case tagged 18650 cells were used.   I have had good service from Samsung 18650 cells from Ebay.  There are many dodgy cells out there though.

The 3 cell protection pcb for the cells was obtained from Ebay for $4.00 delivered.  The pcb limits the charge and discharge current and voltage to safe levels for the cells.  After the cells were connected in series, double sided rubber tape was put over the exposed cell ends.  The protection pcb was stuck to one end of the pack to the rubber tape and wired up.  Silicone wire connects the power from the pcb to the DC connector.  The silicone wire is very flexible and wont melt.  Some Nitto tape holds the cells together until the heatshrink will cover the pack.  In the mean time the pack is going to get some charge and discharge cycles with the cell voltage monitored to make sure the cells stay in balance.

Note that if you make one yourself, you are doing so at your own risk.  Utmost care has to be taken to ensure no possibilities of a short circuit can occur in the wiring, during assembly and in the completed pack.  A short circuit inside the radio could cause extreme damage to the radio, not to mention a fire risk.  Photos below show the pack before heat shrink applied.







Just to check that the protection PCB was working, I put a dead short on the output and as expected, nothing much happened.  For another test, a potentiometer was put between the battery negative and the junction of the second and third cells.  The slider of the potentiometer was connected to the PCB input for the junction of first and second cells.  This allows a wide voltage simulation of the input to the PCB for testing how it behaves when a cell goes high (above 4.2V) or low (below 3V).

With the pack charging, the pot was slowly rotated from 4.0V to 4.3V while watching the meter on the slider.  As expected, as soon as the voltage went higher than 4.2V, the charging terminated.  Also, when then voltage went below 3V, the charging terminated.

At least I know if the cells go out of balance as the pack will not charge.  The charger used with the pack is a Hyperion RC charger.

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18 Responses to New SOTA Rig

  1. VK2TWR says:

    Hi Glen
    you will be very happy with your Elecraft Rig i got my KX3 last year and wouldn’t be without it
    look forward to working you with it soon
    73 Rod

  2. VK2TWR says:

    Hi Again Glen
    i have a the 50 amp surplus to requirement here if your interested it only made it out once
    until i started using my 857 let me know if you are interested

  3. Andrew VK1AD says:

    Compact rig, looking forward to reading your reports on its performance.

  4. vk3cat says:

    Glen, guessing the mic is the same as the KX3? If so, then it could be wise to be careful on how you treat the mic cord. Both Gerard and I have had the same problem with a manufacturing fault on the cord. I have fixed mine twice now. I think the way I stored the mic with the cord folded made the problem worse? Looking foward to seeing in the flesh. Tony

  5. Paul Taylor says:

    Look forward to an activator’s review in the future. I suspect your homebrew projects (HF1?) might start gathering dust in light of the new kid on the block! (Mine have done whenever I bought a new radio in the past!). 73 Paul vk3hn.

  6. vk5hcfCol says:

    Hi Glen,
    I am interested in your construction of a four cell 18650 battery pack for my KX3. (particularly using charging protection circuitry and voltage regulating devices).
    Any chance of a separate article on this please?

    • vk3yy says:

      Hi Col,
      I dont have a KX3, so not sure of the battery space available on the radio. 3 cell should be OK for the KX3 as my KX2 is happy with 3 cell and Elecraft’s pack is a 3 cell. Will write up the protected 3 cell pack when the module arrives. Am currently using an unprotected pack in the KX2 with a polyfuse. Cheers, Glenn.

      • vk5hcf says:

        Hi Glen.
        Thank you for the quick response.
        I do not intend to make up a battery pack for internal use but rather as an external supply.
        I currently use a small car battery.
        I want to build a four cell pack to be able to run the KX3 at the full 15 watts for DX use. (If I ever get around to making a multi band antenna. (sigh)
        I will watch your site with interest.
        Many thanks for some excellent write ups and information.
        Col. VK5HCF

      • vk3yy says:

        No worries Col and OK on the reasons for 4 cell. It might be better to use LiFePO4 cells instead of 18650s for external use. The LiFePO4 battery in 4 cell puts out about 13.2V nominal, a fully charged 4 cell LiPo gets to 16.8V, which is too high for the KX2 and KX3. I use a 4200mAh LiFePO4 4 cell pack from Hobbyking for external battery.

      • vk5hcf says:

        Hello again,
        I do not want to pay for a 4 cell LiFePO4 battery as I feel that they are still a bit expensive. I am pretty sure that I can make up a pack using an 18650 4 cell holder for a lot less money and also as an experiment.

  7. vk5bje says:

    HI Glen,
    Good luck with the KX2. Like some of your other readers I will be most interested to hear your story about it and read your review. I am sorry I missed the post when you first published it. It is disappointing that Elecraft haven’t done something to fix the microphone weakness.
    John D

  8. vk3cat says:

    Glenn, did you purchase the paddle too? As for LiOn batteries, I was considering just using them in individual cell format and charging them in a combo charger that can do LiOn, and NiMh cells. The advantage of this whilst travelling being able to use a single charger for multiple purposes. Shame about the mic. Mine is a heap of crap. Am looking also at the KX2 as it would be a better package for travelling weight wise than the KX3. Not sure if I would bother taking a HH away again. Never used it last year and yet to do so this year. Cheers Tony CAT

    • vk3yy says:

      Hi Tony, I didn’t purchase the paddle and will use the Palm or HB paddle for the moment. I had similar thoughts about individual 18650 cells in a holder but the holder wont fit. As you say, you can use a multicharger for AAs or other batts as well as the 18650s while travelling. Also the nipple type 18650s can be short circuit protected, so good for air travel. I have done this with the ‘817 in the past using an 18650 cell holder. Following your travel blog with interest! Cheers, Glenn.

  9. Pingback: Thoughts on Elecraft KX2 Transceiver for SOTA | VK3YY

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