[Elecraft] Minimalist Mobile with the Elecraft KX3

[Wayne Burdick]

If you're serious about using the KX3 (or other rigs) mobile, read the excellent treatment of the subject by Matt, W6NIA:

   http://www.elecraft.com/manual/Rev-B1-1.6-KX3-Mobile-Owners.pdf

But if you just dabble in mobile occasionally, like me, or you're on a budget, you might want to try the minimalist approach presented here. You'll be a few dB shy of an optimal signal, but it'll be a good time nonetheless, and it'll set you back just a couple of hours and around $100.

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N6KR's MINIMAL-MOBILE SYSTEM


RIG

While you can use just about anything for mobile operation, I'm focusing on the KX3 here. At less than two pounds, the KX3 has the advantage that when you get to your destination, you can take it hiking, even use it pedestrian mobile. If you need more than 12 W while using it in the car (or at home, or for travel), you can add an amp like the KXPA100.


MIC

I used the Elecraft MH3, which is well-suited to this application. It's small, has a great sound, and plenty of output to maximize S/N ratio. I found myself using the UP/DN buttons a lot rather than the VFO knob.


RIG LOCATION AND MOUNTING

Much has been written about Ram Mounts and the like that work with the KX3. To keep things simple, I just placed the rig directly above the steering wheel, wedged between the dashboard and windshield. Next time I go out I'll add a bit of velcro (or something), since it did slide around a bit and could become a projectile in a worst-case scenario. But a simple friction fit was fine for the maiden voyage. I also found that this location worked well ergonomically. Since the rig is so small, it didn't obscure any part of my view of the road. Having it above the steering wheel also placed the mic jack to the left, allowing me to easily use the mic with my left hand. The metal tab on the MH3 fit into a left-side console vent, so I could hang the mic when I wasn't using it. 


SPEAKER SYSTEM

The KX3's internal speaker is not intended for use in noisy environments, and you can't legally wear headphones while driving (in most places). Yet I really wanted speakers, and I wanted stereo. Just about every vehicle has an FM stereo, including my Honda CRV, so I used an FM modulator (Monster Mobile RadioPlay 300, $25 at Amazon). You just pick a clear FM channel (107.9 MHz in my case), tune your car stereo to it, power the modulator from the 12V accessory jack, and insert it's 3.5-mm plug into the KX3's headphone jack. Instant stereo with lots of audio power, with reasonably low noise. One nice thing about doing it this way is that the car stereo's volume and tone controls can be used, and they're always within easy reach.


ELECTRICAL SYSTEM (12 V AND GROUND)

Matt (W6NIA) went to great lengths to Do the Right Thing in terms of grounding, using short battery cable runs, etc. I didn't have much time for this exercise, and after all it's supposed to be Minimalist, so I didn't attempt to ground by any means other than what was provided by the antenna coax and the 12 V system. (Purists are surely cringing as they read this--my apologies.) Keeping with the spirit of the project, I picked up a 2-to-1 12-V car accessory adapter at Radio Shack, into which I plugged the rig and FM modulator. Worked like a charm, with very little engine noise heard. I touched things up a bit using the KX3's noise blanker and noise reduction. Had there been significant engine noise, I would have tried setting MENU:RX SHFT to 8.0.


BANDS

I like 40 and 17 meters for mobile operation. 17 m is not a contest band; a more relaxed, less competitive spirit pervades, and it's great for both DXing and single-hop rag-chews. You can also do pretty well on this band with a physically short antenna, since a full-height vertical would be only 234/18.1 = 13 feet. 40 m is excellent for regional QSOs and nets by day, and DX by night. The combination of the two covers the bases pretty well. If I had to pick three more bands, they'd be 20, 15, and 10 meters.


ANTENNA

I spent some time perusing the reviews of HF mobile antennas on eHam.net. Strong opinions are the rule. Since my goal was something easy to install and remove, not to mention inexpensive, I limited my scope to under-$100 fixed-band whips that were in stock at HRO (Ham Radio Outlet, www.hamradio.com). I ended up with two Hustler whips that are surprisingly well made for the price: the RM-40 ($25) and RM-17 ($20). I perched one of them at a time on the company's short mast, the MO-4 ($20). This gave my antenna a total length of about 56", counting the mag mount. While this antenna won't beat a Texas Mega Coil With BBQ Attachment, it seems to do the job.


ANTENNA TUNER

An antenna tuner is a huge help while operating mobile with a short whip. (I used the KXAT3 -- the KX3's internal ATU. The KXPA100 amp has a similar built-in ATU option.) Bypass the ATU while doing initial adjustments of antenna length to find the lowest SWR. Then put the ATU back in-line and do an ANT TUNE every 20 kHz or so in the band. This will almost always give you and SWR of < 1.5:1 across an entire band, even if the whip itself is very narrow banded. In fact the KXAT3 was able to tune the 17-meter whip to reasonably low SWR on 40-10 meters. I was able to copy lots of signals on all of these bands, but transit efficiency would be pretty poor on any band other than the one the coil was intended for.


ANTENNA MOUNT

I bought an MFJ Max-Strength Hi-Flux Magnet Mount (5" diameter, $16). In hindsight it seemed insufficient to handle the antenna's wind load when configured for 40 meters. It was fine on 17 m--I took the freeway for that portion of the journey. But when I stopped to set up for 40 m, I took surface streets, just in case. The guy at HRO was right: I should have opted for the 3-magnet mount. None of the in-stock trunk/hatch mounts worked with my vehicle.


OPERATING NOTES

I learned a few important lessons about how to operate the radio mobile:

- Set MENU:VFO CTS to 128 instead of 256. Easier to tune the VFO on rough roads. You might also want to push the VFO knob tighter against the felt washer to add friction. The KX3 comes with an Allen wrench for this purpose (see page 24 of the owner's manual).

- Program your band scanning ranges ahead of time (manual page 17). Scanning allows you to monitor the bands safely while driving. When a signal pops up, just tap PTT, then use the mic UP/DN buttons to tune it in. 

- SET MENU:VFO CRS to 0.5 in SSB mode. This is the best coarse tuning rate for casual scanning or VFO tuning, since most stations quantize to 0.5 kHz increments when selecting a VFO frequency.

- The KX3's "AFX" (audio effects) and dual watch work great with the car's stereo speakers. See AFX and DUAL RX menu entries.


RESULTS

My initial test was brief -- just the half-hour drive from HRO back to my home QTH. But I had a Q5 QSO with a VE7 on 17 m, followed by a net check-in on 40 meters where the net control in Oregon had no trouble hearing me. This was with 10 watts. 100 W would have made it easier, but wouldn't have been maximally minimal.


73,
Wayne
N6KR