EH L+L AND NO COAX
THE TRANSCEIVER
THE TEST SITE
THE RECEIVER
THE ANTENNAS
TEST NO. 1
TEST NO. 2
TEST NO. 3
TEST NO. 4
BACK TO HOBBY
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An EH Antenna without Coaxial Feeder Cable
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A test that shows that the EH L+L Antenna works well without a coaxial cable and without a Ground Plane
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On Ted Hart's Yahoo EH Antenna Forum I once mentioned that I had tested the EH L+L Antenna mounted directly on a CB Portable Transceiver and talked to a CB Operator located some 22 km away from my QTH. First I called him up with the 73 cm glassfiber whip on the portable transceiver. I told him that I wanted to check out another antenna, but I did not say what kind of antenna I was going to use. The receiving station recorded my S-meter reading on the glassfiber whip. Then I changed to the EH L+L Antenna. This time the radio was better on both sides and the S-Meter reading at the remote station was recorded once again. This time I got a report which was 2 S-Meter units higher than with the 73 cm whip. Perhaps we're not talking absolute dB:s here, but the S-Meter showed a much stronger signal. That is the point.
When I mentioned this on the EH Antenna Forum, I got bombarded with comments about useless S-meter readings and my body might be a part of the antenna radiation, and the two S-units could not be possible etc. Well, we don't know exactly how many dB higher the EH L+L Antenna signal was. But the fact is that the signal when using the EH L+L Antenna was stronger, not weaker, that is the main interesting observation. Which I was keen to prove - that the EH L+L Antenna works even without a coax cable.
After this on-air test I wanted to compare different antennas under different working conditions. Therefore I set up a measurement site in the garden and did some radiation tests.
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The Test Transceiver:
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The Antennas Under Test were connected directly to the portable Maycom AH-27 CB transceiver set to channel 30, or 27.305 MHz. The power source was a 12 Volt, 600 mAh Nicad Battery which had been fully charged prior to the test. This Nicad Battery is slid onto the transceiver body without connecting wires. On top of the transceiver there is a TNC connector. It is possible to switch the power between 1 W (LO) and 4 W (HI). The RF output power was checked on the Stabilock 4040 after the test and was recorded as 1.01 Watts on LO and 4.03 Watts on HI.
The picture of the Maycom CB Portable shows it with the 24 cm Helical "Rubber Duck" mounted on the TNC socket. The Battery casing is plastic. The small vice is used to keep the transmitter in a stable, vertical position.
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The AH-27 mounted in a small vice
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The Site:
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The transmitter was placed about 125 cm above the ground on a wooden table. It was placed in a small vice to keep it from toppling over by the weight of the different antennas during the test.
The distance to the receiver, the Radiometer AFM3 was measured to 9.5 meters, slightly under one wavelength. The receiving equipment was placed on a wooden table on top of two cartons. The height over the ground was about 1 meter. The receiving antenna was a 73 cm long glass fiber whip. The same whip was used on the transmitter side in the tests. There was no attempt made to calibrate the receiver on the site; all measurements were made with the antenna in the same location and with the same settings. Only the difference in ERP was recorded. The AFM3 has a level meter calibrated in dB. The dB readings are absolute and correct. I had checked this by connecting the AFM3 to a calibrated Signal Generator.
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Device Under Test placed 9.5 metres
from the AFM-3 receiver
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The Receiver:
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The receiver used for the level recordings is a Radiometer AFM3. This instrument can be used to measure AM and FM modulation. It has a 40 dB input attenuator (10 + 10 + 20 dB) and the input impedance is 50 Ohm.
When the level meter is set to position "Manual", the AFM3 can be used as a level meter. The instrument is scale is calibrated in dB. As we are interested only to see the difference between the different antennas under test, a calibration as such is not neccesary.
Important is not to alter any potentiometer settings. Only the input attenuator was altered from time to time to keep the deflection within the panel meter scale and to ensure an optimum meter reading. All input attenuator settings and the meter readings were taken note of.
The Antennas used for the test were:
- The Helical antenna is 24 cm long from top to bottom. It has a loading coil in the middle. The antenna is made of a copper coated steel spring. The upper part is factory tuned to 27 MHz.
- The glass fiber whip is about 73 cm long. It has a loading coil at the bottom end. The antenna is a flexible copper stranded wire covered by plexiglass and resin.
- The EH L+L Antenna consists of 2 copper foil cylinders, each 15 cm long, separated 3.2 cm (the tube diameter). The pipe carries the matching network coils and the trimmers. Its overall length is 45 cm.
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AFM-3 used as a receiver
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The Tests:
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There were three different tests made with the three different antennas. An additional test with the EH L+L Antenna held in the hand (Test No. 4) was also made.
- Test with 1 Watt RF output power
- Test with 4 Watt RF output power
- Test with 1 Watt RF output power and holding one hand on the transceiver (but still fixed in the small vice and standing on the wooden table).
- Test with 4 Watt RF output power with the EH L+L Antenna plus holding one hand on the transceiver (but still fixed in the small vice and standing on the wooden table).
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Test No. 1, test with 1 Watt RF output power
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Antenna under Test
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Attenuator (dB)
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Meter Reading (dB)
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Substitution
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Difference
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Signal (dBuV)
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f = 27.305 MHz
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(AFM-3)
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AFM-3
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(Stabilock 4040)
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Helical 24 cm
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10 + 10
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-7.5
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+72.6
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0
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Fiberglas whip, 73 cm
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10 + 10
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-3.0
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+77.1
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+4.5
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EH L+L Antenna 2 x 15 cm
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10 + 20
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-6.0
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+84.2
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+11.6
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The Helical "rubber duck", which comes with the transceiver as a standard accessory was considered to be the "reference" level. It has been well known for many years, that the glass-fiber whip performs about 2 dB better than the 24 cm long (or short) helical antenna. It is interesting to note that the 45 cm long EH L+L Antenna outperforms both the helical and the fiberglass antenna!
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Test No. 2, test with 4 Watt RF output power
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Antenna under Test
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Attenuator (dB)
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Meter Reading (dB)
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Substitution
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Difference
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Signal (dBuV)
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f = 27.305 MHz
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(AFM-3)
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AFM-3
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(Stabilock 4040)
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Helical 24 cm
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10 + 10
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-2.0
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+77.9
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0
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Fiberglas whip, 73 cm
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10 + 20
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-8.7
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+81.7
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+3.8
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EH L+L Antenna 2 x 15 cm
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10 + 10 + 20
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-11.0
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+89.5
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+11.6
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Again, the Helical "rubber duck", was considered to be the "reference" level. The 73 cm fiberglass whip again performs better than the 24 cm long helical antenna. The increase in dB is rather identical with the first test with one Watt RF power. It is interesting to note that the 45 cm long EH L+L Antenna again outperforms both the helical and the fiberglass antenna at almost the same rate!
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Test No. 3, test with 1 Watt RF output power and placing one hand on the transceiver:
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Antenna under Test
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Attenuator (dB)
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Meter Reading (dB)
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Substitution
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Difference
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Signal (dBuV)
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[Test 3 - Test 1]
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f = 27.305 MHz
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(AFM-3)
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AFM-3
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(Stabilock 4040)
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Helical 24 cm
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10 + 20
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-7.0
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+83.2
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+10.6
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Fiberglas whip, 73 cm
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10 + 20
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-4.2
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+85.9
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+8.8
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EH L+L Antenna 2 x 15 cm
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10 + 10 + 20
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-10.0
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+90.1
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+5.9
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The Helical "rubber duck", was once again considered to be the "reference" level. I compared these readings with the Test No. 1 Substitution Signal (dB�V) readings, just to show the difference compared with the transmitter sitting on an insulated table. Thus the figures shown in the "Difference" column are the difference between the Signal Generator levels from Test No. 3 and Test No. 1, not the difference within the table in Test No. 3.
We can see that the 24 cm Helical antenna profits most from holding the transceiver in the hand. Interesting is that the 73 cm glassfiber whip does not profit that much from holding the transceiver in the hand.
The most interesting observation is that the 45 cm long (overall), 2 x 15 cm (effective length) EH L+L Antenna, which manages rather well on its own, without a feeder cable, without a ground plane shows the least additional gain when held in the hand. That means that it already performs well even without a ground plane.
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Holding the 2x15 cm
EH L+L used in the tests
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Test No. 4, EH test with 4 Watt RF output power and placing one hand on the transceiver
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Antenna under Test
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Attenuator (dB)
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Meter Reading (dB)
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Substitution
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Difference
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Signal (dBuV)
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f = 27.305 MHz
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(AFM-3)
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AFM-3
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(Stabilock 4040)
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EH L+L Antenna 2 x 15 cm
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10 + 10 + 20
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-5.0
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+95.2
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+5.7
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The figures shown in the "Difference" column in the Test No. 4 is the difference between the Signal Generator levels from Test No. 4 and Test No. 2. Again we see that the 45 cm long EH L+L Antenna gains 5.7 dB when set to HI output power and placing a hand around the cabinet. The increase is much like the increase recorded with 1 Watt RF.
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Conclusion:
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This test clearly gave proof to that the EH L+L Antenna can radiate power even without a coaxial line. It also clearly shows, that it works much better than the other two test antennas. Therefore I am tempted to say that I have proved that my signal over 22 km (the test I did with a 73 cm whip and the EH L+L) must have been stronger on the EH than with any of the other antennas in the test.
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Document created on 17th April 2003. Text reviewed and edited on 15th October 2013.
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