[TowerTalk] steppIR Gain--test method
garyschafer at comcast.net
Wed Mar 16 14:36:17 EST 2005
Not even a step attenuater in the circuit. On top of that using the log
scale on a 141T spectrum analyzer! Lucky to get within a couple of db
with that setup alone.
I am not saying their gain figures are right or wrong. Just a poor way
> Here is how the testing is described on the SteppIR site...
> (http://www.steppir.com/, click the Field Test button)
> "We started by placing a reference dipole at one end of an antenna
> range and a receiving dipole at the other, with both antennas being of
> an equal height of 48'. From the reference dipole station a 100 watt
> CW signal was transmitted via an Icom 706 transceiver to the receiving
> dipole, with the signal strength characteristics being recorded by an
> HP 141-T spectrum analyzer. This was done for each frequency to be
> tested. SWR measurement was accomplished with a Bird model 4391 RF
> Power Analyst. The reference dipole was then replaced with the SteppIR
> Yagi test antenna. The two antennas were on level terrain, separated
> by a distance of 705 feet. A CW signal was transmitted from our
> SteppIR Yagi, beamed directly at the receiving dipole, with the HP
> 141-T acting as the "receiver". The differential between the recorded
> gain of the reference dipole and that of the SteppIR Yagi (in the
> exact same conditions) determined our actual forward gain at a given
> frequency. We also performed front to rear tests. Front to rear is the
> response from the back of the antenna at it's least favorable point.
> Front to back, on the other hand, is simply the response of the
> antenna at exactly 180 degrees. In many cases this is not the worst
> case response from the back of the antenna. We feel that specifying
> front to rear measurement is much more useful to our customers. Also,
> keep in mind that front to back varies with the angle of arrival of
> the particular offending signal."
> Similar to the technique used by N0AX and K7LXC for the triband beam
> comparisons detailed in their book "HF Tribander Performance, Test
> Methods & Results, 2nd Edition".
> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Tom Rauch
> Sent: Wednesday, March 16, 2005 11:08 AM
> To: jimjarvis at ieee.org; towertalk at contesting.com
> Subject: Re: [TowerTalk] steppIR Gain--test method
>>If I recall correctly, Mike and Jim have their own range, with the
>>unit under test on one tower, and an HP spectrum analyser connected
>>a dipole on another tower, many wavelengths distant. Tower heights
>>were on the order of 60'. A calibrated attenuator was used with the
> Well, the many wavelengths distant is already a problem.
> Measurements would be much more accurate just out of the near field. I
> don't know why anyone would measure an antenna in the null of the
> pattern, and when a horizontal HF antenna is at 60ft and the path is
> long there is a null along the horizon! Bad measurement protocol.
> Measurements would also be more accurate with a directional antenna at
> the receiver also, and a good meter instead of a spectrum analyzer.
> Measurements like this are always a problem. Look at the silly claims
> of the RAIbeam and that little two element hex quad thingy. It's
> commonplace that measurements made in test ranges that aren't really
> test ranges are a few dB off.
>>Theoretically, the steppIR could be a bit better than a canonical
>>yagi...in practice, it's hard to tell, because the differences are
>>small to matter.
> Bingo....and probably too small to measure accurately also.
> 73 Tom
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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