[Elecraft] KX1 lab tests with Maldol whip, various grounds

[Wayne Burdick]

I've been playing with "peripatetic QRP" (i.e., operating while walking around)
using the KX1 with a lightweight whip and running from an internal 9 V battery
pack (6 lithium cells). I still haven't made any QSOs, but I wanted to quantify
the effects of two different antennas and several different grounds. So I did a
few transmit-mode lab tests on 20 meters. As a receiver, I used an HP 8553B
spectrum analyzer connected to a 20 m dipole that was about 50' from the KX1 and
its whip. Ideally the dipole would be farther away, but even close-in tests can
be useful. 

I hope this information isn't a 100% dupe of what everyone on the HF Pack list
already knows :)  Those who were thinking about trying hand-held operation and
didn't know what to expect will find the results interesting, and I'd encourage
you to try it.

The two antennas were:

  1. Maldol whip with 20-m loading coil (AH-C14)
  2. Maldol whip with 10-m loading coil (AH-C28), matched on 20 m using internal ATU

The overall length of the Maldol portable whip is 48", and it weighs 2.5 oz. I
wouldn't connect an antenna any heavier than this to the KX1's BNC jack.

The grounds tested included:

  1. No ground wire at all, not even holding the rig
  2. No ground wire, but holding the rig (with one hand)
  3 & 4. 7' wire, with and without holding the rig
  5 & 6. 16' wire, with and without holding the rig

I repeated all tests with a K2 as the transmitter (running from internal
battery) to confirm results. I'll spare you the full details, but here are my
basic findings.

Antenna tests: Using the 10-m coil (matched with the internal ATU) on 20 meters
resulted in a 2 to 4 dB loss in signal strength vs. the 20-m coil. I had
expected a larger differential. Conclusion: using a monoband loaded whip
directly connected to an internal ATU can provide useful, somewhat compromised
multi-band performance. 

Ground tests: With either antenna, the signal strength with the various grounds
was as follows (normalized to the first case):

  1. 16' wire (rig held or not):     0 dB
  2. 7' wire, holding the rig       -8 dB
  3. no wire, holding the rig       -8 dB
  4. 7' wire, not holding the rig  -11 dB
  5. no wire, not holding the rig  -24 dB

It's clear from the above how important a 1/4-wave trailing ground wire is.
Lacking a 1/4-wave wire, even a wire about 1/8th wavelength long is better than
nothing. Surprisingly, just holding the rig produces results a bit better than
that of the 1/8th-wave wire, at least on 20 meters where a six-foot guy couples
to ground pretty well. I'm guessing that a 12' or so wire would be only a few dB
down from the 16' wire, and might be more convenient when hiking.

In any case, I'll be out walking again tomorrow, armed with my 3-dB-better
resonator and 16' trailing ground wire. My signal should be a few S-units
stronger than before, hopefully good enough to make an HFP-CW QSO.

The trick will be keeping cars from running over my "tail."

73,
Wayne
N6KR

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