k1drw wrote:
Hello:
I am looking words of advice on conducting an informal exercise to
evaluate performance of 75m mobile systems. I have done much reading
of rec.radio.amateur.antenna threads and have learned much from Cecil,
Reg, Keith, Roy, et al. The msg threads addressing how measurements
were taken during past shootouts have been very helpful but equipment
used in those events seem to be beyond my capabilities.

I am part of an ARES/RACES HF Mobile team. We are in the early stages
of assembling our team and have conducted a couple of field
exercises. I believe I adequately understand many of the issues
related to operating 75m mobile and have concluded (from assessing our
mobile configurations) that our systems are VERY compromised. As we
conduct our EmComm field exercises we take the opportunity to
experiment and make system adjustments that clearly improve
performance. Primarily we are using 100w mobile hf rigs with 75m
Hamsticks or Hustler resonators. We understand that the vehicle, the
antenna, the ground, etc comprise the "System". One important note
is that we are not focused on achieving DX communications. Our field
of operations is primarily Groundwave within a tri-county area in
Eastern Pa (many 600-700 ft ridges and valleys, heavily forrested),
perhaps 100 miles max. We do use and experiment with NVIS (using
restricted space configurations: tilted whip, Hamstick dipoles, etc)
however, this query is relative to Groundwave.

I would like to add an occassional field exercise expressly for the
purpose of measuring the performance of our systems (for improvement
and detecting problems). We currently have no equipment for this
purpose. One device I see advertised and would like some feedback on,
is the MFJ-802 Field Strength Meter.

- Would the MFJ-802 be an adequate measuring device for our use ? Any
caveats ?
- What test FIELD environment should we try to arrange (e.g. large
empty parking lot, or a rural open field) ?
- When testing each vehicle, what space should separate it from other
vehicles waiting to be tested ?
- Should the vehicle sit stationery, or be moving in a circle ?

Any suggestions offerred to assist with this effort will be sincerely
appreciated.

regards,
Dennis, K1DRW


If the option is available to you, consider choosing a meter with an
external antenna connected through a coax connector. By placing a
calibrated attenuator between the antenna and the meter, you can readily
obtain resolution and repeatability approaching 1 dB. When coupled with
a DMM, as Richard Clark suggested, you will have very effective
instrumentation.

If you rely instead only on the meter dial, most likely calibrated in
volts, your measurements will be affected by circuit and meter
nonlinearities and the need to convert voltage readings into dB.

Good luck,

Chuck
NT3G



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