R8 HF Vertical

(http://www.lairdtech.com/)

Recently I picked up a second hand Cushcraft R8 vertical.

I had the folliwing goals in mind

1. Vertical
2. Multiband
3. No radials
4. Low take off angle
5. WARC bands included
6. Possibility of field day operation
   

• Vertical

Given the layout of the my house's lot, a second antenna would be easier to install if it were a vertical. Also my existing antenna is a 80M to 6M Windom Buxcomm model 802136 and I am intersted in having a vertical to compare. I'll likely never setup a beam so this second antenna will be it.

• Multiband

Multiband is tablestakes, because I need to able to get as much out of an antenna as I can. The R8 is one among very few 8-banders covering from 40 to 6m, WARC included.

• No radials

I like the idea of no radials, mainly because of the ease of installation and flexibility of installation lacation. R8 uses 7 49in stainless radial rods at the base of the antenna.

• Gain and Low take off angle

DX, DX, DX, Low take off angle is important for DX work. With its low radiation angle R-8 vertical should have distinct advantages compared to my windom. The 360 degree coverage should be nice as well.

• Power Handling

The R8 supports 1500W which is plenty for my FT2000D which is a 200W rig.

• WARC bands included

I enjoy digital operation and I often find that the WARC bands have activity, but the Windom antenna does not tune up on 30m for example.

• Possibility of field day operation

The R8 could be used in field day operations but due to its weight it is not easy to get it down without help. Once installed, I think its up there for the long run.

Considerations

• Guying
  

I did guy the antenna down to three points.

• Grounding

I have grounded the mast to a single 8ft ground rod with a run 10ft run of #6 ground wire.

Specifications

Model R8
Gain, dBi 3
Height, m. 8.7
Horizontal rad, deg 360
Power Rating, Watts CW 1500
Vertical Radiation Angle, deg. 16
Band / Bandwidth (kHz) 10m >1500
Band / Bandwidth (kHz) 12m >100
Band / Bandwidth (kHz) 15m >450
Band / Bandwidth (kHz) 17m >100
Band / Bandwidth (kHz) 20m >350
Band / Bandwidth (kHz) 30m >50
Band / Bandwidth (kHz) 40m >150
Band / Bandwidth (kHz) 6m >1500
VSWR at resonance (typical) 1.3:1
Weight, kg. 10.5
Wind Survival kph. 120

The Cleanup

Since the antenna was second hand I had quite a time cleaning up the antenna and setting all the element lengths to the specification.

• I cleaned up external surfaces with a combination of steel wool and lots of work. With this I was able to restore the antenna to showroom look, shine and all.

• The short 6" terminal tuning stubs rods were oxidized such that it was impossible to remove these from the longer stub tubes. I did confirm that all stubs were all stuck in place at the right lengths.
  

• I opened the R8 matching network box and confirmed that there were no mechanical failures of the components inside. A mechanical inspection was complete.
  

• I completely assembled the antenna indoors to see the antenna fit together and confirmed nothing was mechanically broken or missing.

Installation Preparation

• I decided to install the vertical on the corner of my backyard shed. A 2 in pipe was installed up through the roof of the shed.
  
• I decided to guy the antenna from the initial start
• I placed a 1:1 choke at (near) the antenna.
  
• Grounding, 8ft copper clad steel rod at base of mast
  
• Feed line, was 100ft RG/8
  
• Lightning arresor, was placed at the house

Operation

• All bands tune up and better than 1.5:1 on all but the high end of 40m.
  
• Have not tried to see how it tunes on 6m.

Safety Code 6

As a licensed amateur radio operator in Canada this is my personal interpretation of Safety Code 6. I am presenting this here for any like minded amateur radio operator who is interested in this topic.

Regulations

The Radiocommunications and Broadcasting Regulatory Branch of Industry Canada states in "CPC-2-0-03 Radiocommunication and Broadcasting Antenna Systems" (link) that Health Canada has established safety guidelines for exposure to radio frequency fields, in its "Safety Code 6" (link) publication.

"Safety Code 6" states that current studies in Canada and other countries indicate that there is no evidence that a person will experience adverse health effects from exposure to radio frequency fields, provided that the installation complies with Safety Code 6.

It is my responsibility that my amateur radio station comply with Safety Code 6 at all times.

Safety Code 6

Safety Code 6 recommends general procedures for ensuring that exposure of the general public in the vicinity of RF devices is not greater than the levels specified in this Code. A safety factor of approximately 20 to 50 was incorporated with reference to the scientific-consensus threshold for adverse health effects.

Field Strength Limits (Source Safety Code 6)

Within the 3 to 30MHz bands, a person shall not be exposed to electromagnetic radiation in a frequency band listed in Column 1 of Table 5, if the field strength exceeds the value given in Column 2 or 3 of Table 5, when averaged spatially and over time. The spatial averaging is carried out over an area equivalent to the vertical cross-section of the human body (projected area). A time-averaging period of 0.1 h (6 min) should be employed for frequencies up to 15 000 MHz.

src: Safety Code 6

Canada's National Amateur Radio Society (link)

States that while Industry Canada expects radio amateurs to meet the requirements of Safety Code 6, generally most amateur installations will never exceed the recommended exposure limits. There are many reasons for this including the fact that most amateur installations are operated at relatively low power levels (typically 100 watts), are not on a 100% continuous duty cycle and the amount of transmission time is often limited."

Interpretation

From Table 5

From 1 to 10MHz, Electric field strength is limited to 280/f (V/m) and Magnetic field strength to 2.19/f (A/m).

From 10 to 30MHz, Electric field strength is limited to 28 (V/m) and Magnetic field strength to 2.19/f (A/m).

For each band from 80m to 10m the table below captures the E and H field limits according to the safety code 6 definitions.

I assume 200W output from my rig, which is worst case. 100ft of feed line is assumed with 1.3dB/100ft at 30MHz. To get the losses at other frequencies I scaled the loss by the frequency of each band. I assumed a 3dBi antenna gain which is correct for the Cushcraft R8 Vertical. Effective radiated power is 380W to 290W.

Power density is calculated assuming a worst case 3m distance to the antenna.

For PSK modulation I assumed a 50% time averaging over 6 minutes which is consistent with PSK operation, as I listen 50% of the time, and a typical transmission is much less than 6 minutes. On the other hand I assume duty cycle of 100% when I am transmitting. This factor would be less than 100% for SSB and CW for instance.

Operating Mode	Duty Factor
Morse code (CW)	40%
SSB phone	20%
FM	100%
RTTY/Digital	100%
AM	100%

source: http://n5xu.ece.utexas.edu/rfsafety/power.shtml

I then calculated the resulting averaged E and H field strengths.

Simply taking the ratio of the resulting field strengths and the limits results in a safety margin over and above Safety Code 6.

A copy of this file is available at Google Docs at link.

Limits
Band	(m)	80	40	30	20	17	15	12	10
Freq	(MHz)	4	8	10	15	18	20	25	30
E Field Limit	(V/m)	75	37	28	28	28	28	28	28
H Field Limit	(A/m)	0.58	0.29	0.22	0.15	0.12	0.11	0.09	0.07
Transmitter and Antenna
Output Power	(W)	200	200	200	200	200	200	200	200
Feed line	(ft)	100	100	100	100	100	100	100	100
Feed line Loss	(dB)	0.2	0.3	0.4	0.7	0.8	0.9	1.1	1.3
Antenna Gain	(dBi)	3	3	3	3	3	3	3	3
Effective Radiated Power	(W)	384	370	361	344	335	327	311	296
Density
Distance to Antenna	(m)	3	3	3	3	3	3	3	3
Power Density	(W/m^2)	3.40	3.27	3.19	3.04	2.96	2.89	2.75	2.62
Averaging (PSK-31)
Time averaging		50%	50%	50%	50%	50%	50%	50%	50%
Modulation		100%	100%	100%	100%	100%	100%	100%	100%
Resulting Fields
E Field from antenna	(V/m)	25	25	25	24	24	23	23	22
H Field from antenna	(A/m)	0.07	0.07	0.07	0.06	0.06	0.06	0.06	0.06
Safety Factor
E Field		2.9	1.5	1.1	1.2	1.2	1.2	1.2	1.3
H Field		8.7	4.4	3.4	2.3	2.0	1.8	1.5	1.2
Feedline	dB/100ft	1.3
	MHz	30

Conclusion:

I would state that a Cushcraft R8 vertical at 3m, being fed with a with Rig power of 200W in PSK mode and 100ft of feed line will pass safety code 6.

There are details concerning the Safety Code 6 in the near field which I have not reconciled.

I believe the calculation above to be correct, however all should realize you are accountable for your own calculation, should you attempt to do one for your own station.