Saturday, October 3, 2009

One way to model a Budipole

This is a summary of how I do my antenna modeling and this post includes an example of a 20m vertical with a rigid counterpoise.

1. Install the modeling tool 4NEC2 which is available at http://home.ict.nl/~arivoors/ . I run XP and Vista and have no problems with the program. I hope you do not either.

2. I have posted an example file at my documents at the following link. Go to the link and download the model file and save it to your pc where you can find it later. Save it as a plain text file.









3. launch 4NEC2 and load the file from step 2. There may be a few parameters you have to set

Settings->CharImp set to 25 ohms

Because, when this antenna resonates is close to 25ohms, this implies that you have a 2:1 balun like the budipole TRSB and it is set to 2:1.




4. Lets run it. Select Calculate->Nec Output data then select a frequency sweep from 13 to 15MHz.









The output should look like this.
Geometry shows a vertical with a loading coil set mid way.
















Sweep shows resonance at 14.05MHz, which is very nice for PSK.














The antenna pattern shows a modest directional pattern, with a lower takeoff angle than can be obtained with a dipole at any reasonable height.















Now lets take a look at the file,



H_feed=2.5 Configuration - feed Height (m) - set this to the height of the versatee

NDipoleArmsR=3 Configuration - Number of Dipole arms on the Red side of the dipole, zero to as many as you want. These things (link), In general you want to get the coil away from the versatee. I think this leads to a better pattern but I cant prove it.

NDipoleArmsB=1 Configuration - Number of Dipole arms on the Black side of the dipole, zero to as many as you want. Same as above

whipTypeR = 1 1 = long whip
whipTypeB = 0 0 = standard whip
Indicate the type of whips you are using, I use a long whip for the vertical, more is better. and a short or normal whip for the counterpoise, the long one places a lot of torque on the versatee.

phiR=90 Configuration - Red Arm Direction (degrees) + is up, - is down, 0 is horizontal
phiB=0 Configuration - Blk Arm Direction
These are angles in degrees, 0 is horizontal, 90 is straight up, so you can see the red (R) arm is up, and the black (B) is horizontal. You can specify what ever angles you want. 0 & 0 makes a horizontal dipole!

coil_TapR=2.392877 Tuning - Red coil tap # turns from the whip end of the coil
coil_TapB=11.10957 Tuning - Black coil tap # turns from the whip end of the coil
OK, these numbers are solved for by the program once you decide what resonant frequency you want. Rounded to the integer, they indicate where to tap the coil. I can not promise the solved solution will be bang on but this is a starting point.

H_cutR_in=0 Tuning - number of inches each whip is pushed in
H_cutB_in=0 Tuning - number of inches each whip is pushed in
This specifies the number of inches each whip is pushed in by. Usually I set 0, but in the budipole examples some times the documents specify a few inches here and there.

H_sectR=6/6 Tuning - number of sections of whip pulled out
H_sectB=6/6 Tuning - number of sections of whip pulled out
These specify the number of extended whip segments.

The items below are fixed and relate to the geometry of the system components.

L_feed=0.05 Fixed - feed wire length (m), fixed to the width of the versatee
H_coil=4.75*0.0254 Fixed - coil length (m), fixed to the physical length of a coil
CoilFactor=1 Fixed - This factor usually set to 1 will scale the inductance of both coils together
DipoleArmLen_in=21.875 Fixed - Length (in) of dipole arm
RedH=28.2uH Fixed - Total Inductance of the red coil
RedTurns=42 Fixed - Total number of turns on the red coil
BlkH=28.2uH*(38/42) Fixed - Total Inductance of the black coil
BlkTurns=38 Fixed - Total number of turns on the black coil
StdWhipLen_in=66.25 Fixed - Length (in) of a fully extended whip
LongWhipLen_in=9.5*12 Fixed - Length (in) of a fully extended long whip
WhipRad=6.719e-4 Fixed - Radius of a whip
K=0 Fixed = controls geometry at feed, usually set to 0, binary input select 0 or 1 only.
OK this parameter is rather nutty, but it controls the geometry details at the versatee, I'm not sure how to explain it, 0 is the right value.

These are the calculated parameters of the model based on your inputs and the fixed values above.

H_armR=(NDipoleArmsR*DipoleArmLen_in*0.0254)+1*0.0254 Calculated - arm below Red coil, Calculated length of the dipole arms specified, each arm is 21.8inches
H_armB=(NDipoleArmsB*DipoleArmLen_in*0.0254)+1*0.0254 Calculated - arm below Black coil, Calculated length of the dipole arms specified, each arm is 21.8inches
L_coilR=CoilFactor*RedH*coil_TapR/RedTurns Calculated - Red Coil Inductance
L_coilB=CoilFactor*BlkH*coil_TapB/BlkTurns Calculated - Blk Coil Inductance
H_whipR=((StdWhipLen_in*(1-whipTypeR)+LongWhipLen_in*(whipTypeR))*H_sectR-H_cutR_in)*0.0254 Calculated - Red whip length
H_whipB=((StdWhipLen_in*(1-whipTypeB)+LongWhipLen_in*(whipTypeB))*H_sectB-H_cutB_in)*0.0254 Calculated - Blk whip length

So, you should be able to adjust the number of accessory arms, the whip types, the angles of the arms etc.

The trick is getting it to solve for the tap positions. You do this with the following solver in 4NEC2.


Above is the solution for 14MHz resonance. How about 7.07MHz?


The model predicts red Coil 42 from the whip end, i.e. the entire coil, and the black 31.6 turns from the whip.

I'll have to give this a try outside and see how close it is to reality I expect some adjustmnts to the model will be needed. Only through doing enough if these I'm learning through trial and error how the model needs to be set for things like the wire diameter whcich has a profound effect on the predictions.

73
Adrien

Wednesday, September 30, 2009

Amateur Radio

This post is just to take a snapshot of where my Amateur Radio hobby has progress to.

I've been licensed for about 2 years now, with the call sign VE3IAC. My radio station is here in Ottawa and although I'm in the suburbs I have space to put up a 30ft tall 40m to 6m multi-band vertical and a 120ft 80m to 6m offset center fed dipole.

The rigs here in the shack span from a 2008 all solid state rig to a 1970's hybrid rig w/ a tube based final.

The Yaesu 2000D is a very competent 200W base rig, it is very fun to play with and has more settings than you can shake a stick at. This rig usually stays at home, although I have taken it out to ARRL Field Day this past summer. At Field Day I operate a digital station running PSK31 which is a digital mode similar to RTTY. I have found a great bunch of guys here in the Ottawa region called the 3730 group. We enjoy a nightly net at 9:00PM Eastern and checkins come from VE1 VE2, VE3 land, and a hand full of US stations.

The ICOM-7000 is a 100W portable rig that I use when I operate portable which I try to do as often as I can. I have a portable antenna called a Buddipole which is a simple component antenna system that uses a combination of whips, and loading coils. Vertical and dipole configurations can be made for 40m to 6m.

On the older side of things, is a pleasent Kenwood TS850S. This rig belonged to my Dad Alcide, VE1JNA. Dad was pleased with his radio and when he became a silent key I made sure I was able to keep the rig back on the air for him by getting my ticket and continuing the hobby. Thanks Dad.

All of these rigs are 100% solid state and each have their strong points.

On the older side, I recently picked up a 1970's Yaesu FT-101E at a local flea market. Sold as-is with some work needed, I was pleased to have it on the air in a few days. I remain convinced it needs an alignment. This is a semi solid state 100W rig with a tube driver and a pair of 6JS6C's finals. This is very different rig to run and some how seems more like a radio than the more recent rigs. It needs more attention to operate and it simply seems right to see the tube glow and hear them crinkle under the load of transmitting.



Above is an image of the contacts I have made over the past few years. These are from either the house, the cottage, or portable operation from the Ottawa Valley Region.

The sunspots are very very low over the past few years and my most remarkable DX contacts were two to New Zealand on 40m near midnight local time.

Thanks for stopping by.

Vern, I hope you were able to find this and enjoyed seeing where this hobby has taken me.

Adrien

Sunday, September 13, 2009

A New Old FT-101E

Well there simply must be at least 1 boat anchor in every shack, and being somewhat new to the hobby I had the pleasure of needing to `go out and get one`.

The Yaesu FT101 series radios were met with quick adoption by the Ham community when these radios were introduced in the early 70`s. Since I have no experience with a tube based radio I quickly set my determination on getting one of these rigs. I was interested in seeing what I could learn both in terms of operating a tube rig.

I was able to pick up at a local flea market, a FT-101E which was in need of a little work.


First Impressions

Simply stated `Very solid`, this little rig weighs in as heavy as the FT2000D, largely due to the built in transformer which supports providing the 230W of input power to the finals as well as the remainder of the radio. It is safe to say that these radios are hand crafted, which is simply great for the operator who wants to get his `hands on`, and potentially also shocked, but lets hope that does not happen.


First Steps

The seller provided me with a set of crystals 3 6JS6C spare finals, with 2 already installed in the Radio and 1 12BY7A Driver. I installed the crystals and the 1 driver tube, plugged it in to AC source and hoped for the best. I was also supplied with a complete hard copy of the service manual which is very complete and has all the information I will likely need.

From here on in, I have structured this post into three sections. Things what work, Things that do not and repairs I have done.

Things that work

The rig powered up, fine, and most things looked O.K. on first glance. Lots of audio, and some signals could be had on LSB. Heaters did light up as expected. All lamps worked as expected, and the cooling fan for the finals ran nicely.

  • 80M/40M/20M/15M/11M/10M Rx
  • Preselector
  • WWV 10MHz Rx
  • 100 and 25kHz markers
  • Bias Adjust; Bias current responds smoothly with adjustment of bias control variable resistor VR1. Bias was set to 60mA as required.


Things that still do not appear to work as expected

The vernier slips as the main tuning dial is rotated.
Meter function switch contacts are poor.


Items worked on

  • Fixed: Low sensitivity on bands that work. Don't ask me why but I tested PL4, the lamp that is in series with the signal path in from the antenna connector. It was not open, but resistance was north of 100 ohms. The replacement part form the local hardware store also PN 1815 was about 5 ohms. Sensitivity is much better with the replacement part.
  • Fixed: USB is "as dead as a doornail". LSB worked fine but USB was not operational. I tracked the lack of any signal reception to the Q3 on the modulator unit. There was a repair attempted and this was part of the hint. I noticed that the transistor was not the part called for in the schematic. The design part 2SC372Y was replaced by a 2SC383. Q3, Q5 abd Q6 are all the same device, is responsible for the generation of USB, LSB and CW/AM carrier inputs. I moved the Q6 part too the position of the Q3 and this fixed the USB mode problem. I replaced Q6 with a silicon part 2N3904. Now all modes work, LSB. USB, Tune, CW and AM.
  • Alignment: Bias. Set Bias to 60mA as required. There is some play in the meter function switch which makes getting a reading a bit awkward.
  • Alignment: ALC level. ALC level was low, at about 0.3, Adjusted Level control to set ALC level to 0..5 as required in the alignment procedure.

Sunday, August 23, 2009

Field Operation, IC 7000 and Buddipole at Champlain Lookout

It occurred to me while reading through the Buddipole information for the Triple ratio Switch Balun (TRSB) that I should be able to make a 20m vertical with a rigid loaded counterpoise.

This antenna configuration would
  • have a lower take-off angle as compared to the flattop dipole
  • would be directional to a degree
  • would be easily rotatable as compared to a wire counterpoise
  • would not need a standoff stake for a wire based counterpoise
  • would operate very similar to a setup w/ a longer wire counterpoise
Modeling

I started with some simple modeling in 4NEC2.


The vertical arm is constructed with 3 dipole arms, 1 red coil, and 1 standard whip. Using more than 1 dipole arm helps make the antenna longer and more effective. The loaded counterpoise is built with a single dipole arm, a black coil and a standard whip.


The antenna is brought to resonance at the frequency 14.1MHz which is what I wanted with the following parameters and settings

Vertical
  • Whip fully extended
  • Red coil taped 9 turns from the whip end
  • 3 standard dipole arms
Counterpoise
  • Tilted down at 30degree angle
  • Whip fully extended
  • Black coil taped 12 turns from the whip end
  • 1 standard dipole arms
In 4NEC2 I first assumed the red coil had an inductance of 28.2uH for all 42 turns. This is the value I have used in the past. However with this value, resonance was predicted at only 12MHz. Testing the antenna in the backyard confirmed that the antenna does resonate at 14.1MHz. I temporally centred the model at 14.1MHz by scaling the full coil inductance to 69% of the 28.2uH.


The predicted antenna pattern is as expected for a vertical w/ 1 counterpoise.

Putting it all to use.

Nearby to the city of Ottawa, is a federal park with some breathtaking lookouts. For a Ham operator this looks like very nice spots for an antenna, high up over the surrounding land.



The setup was simple and compact, 2 50AH Gelcells, IC7000, Laptop and the Buddipole



The above 2 pictures show the "picnic table shack" and the vertical. The counterpoise made with the standard whip, coil and arm is raised above the ground and this allows the antenna to be "pointed" and also there is no pesky wire counterpoise to string out.

Operation

There was 070 PSK contest going on and there was plenty to listen to. A big plus of this location is the excellent s1 noise level. Many US stations were on the air as expected but notable and very easily copied stations were from Uruguay, Brazil, Argentina, and a good selection of European stations including, Spain, France, England, and some Russian stations.

QSOs

Thanks to all who helped make this an interesting afternoon. I had some difficulties with the 7000 running a bit hot due to the hot sun. Also, at times there were a few stations who were answering my calls at the same time and I did my best to unravel these situations.



  • Start Station Name Country QTH Distance (km)
  • 21:34 IK4JQS Maurizio Italy Molinella 6,515.32
  • 21:23 PD5DP Henk Netherlands Wolvega 5,681.14
  • 21:16 W6DEI Peter USA Berkeley CA 3,893.00
  • 21:05 K0WIU Bill USA Yankton, Sd 1,912.58
  • 20:49 HA6ZB Gyuri Hungary Aldebro 6,836.85
  • 19:53 N4MGA Don USA Rex, GA 1,512.57
  • 19:40 N0EPW Simon USA 1,360.02

Thanks to IK4JQS and HA6ZB for the 6000km QSOs. and thanks for stopping by.

Adrien

Monday, March 9, 2009

R8 HF Vertical

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

Recentl
y 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.

Sunday, March 1, 2009

RSQ and PSK

A recent look into my own signal quality on PSK made me take a search on the net for information on PSK signal quality.

I came upon this web site (link) which is a site concerned with

"
This site is devoted to promoting RSQ as an improved signal reporting system for narrow band digital modes and to demonstrating its application to the popular PSK31 mode."

To this end, they recommend and point out that Regions 1 and 3 have adopted the following

Readability
(% of text)
R5 95%+ Perfectly readable
R4 80% Practically no difficulty, occasional missed characters
R3 40% Considerable difficulty, many missed characters
R2 20% Occasional words distinguishable
R1 0% Undecipherable

Strength
S9 Very strong trace
S7 Strong trace
S5 Moderate trace
S3 Weak trace
S1 Barely perceptible trace

Quality
Q9 Clean signal, no visible sidebar pairs
Q7 One barely visible pair
Q5 One easily visible pair
Q3 Multiple visible pairs
Q1 Splatter over much of the spectrum

Seems very reasonable to me and will become part of my operating practices.

PSK Splatter solved

While operating PSK on 20m this morning I received a report that I was splattering across the band. With this in mind I though I should look into this.

I was not operating outside my normal situation.

FT2000D
30W - 80W depending on the QSO
Signallink USB
HP PC
only have 1 antenna, the Windom

Let the experiment begin.

Not knowing how bad the problem was, I went up to 18.1MHz to find a quiet place to poke around.

The only station I saw on the band was a fellow operator here in Ottawa, VE3OIJ. We transmitted back and forth a bit and found nothing remarkable. Leading me to think nothing is seriously broken.

I wanted to see my own signal, so I used the IC7000 to receive the tx output of the FT2000D

Rig
TRX - FT2000D
Freq - 18.1MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz

SignalLink
Tx - 3/10

Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB

Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??

At 6dB/S-unit, if my fundamental was received at his station at S9, then this "splatter" would be received at -S2, i.e. 2 S-units below, S0, these cannot possibly be the splatter my fellow operator saw.


VE3OIJ was able to see these terms, but we are less than 10km apart. It may make sense to follow these terms a bit more. The plot below shows my signal from 1W to 150W into my dummy load. In all cases the relative size of the "splatter" remained fixed. This tells me that these terms are not being generated by the radio's linearity ans regardless of my transmit power would not be a problem to any one but an operator in my city.


How to get gid of these? Don't know.

Next step was to try back on frequency, in case it was RF feedback into the shack that only happens on 20m.

Rig
TRX - FT2000D
Freq - 14.070MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz

SignalLink
Tx - 3/10

Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB

Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??


Identical results.

Below is a typical waterfall on 20m, "strong" signals are 30dB above the noise floor. If anyone else had terms like the ones above in their transmit signals there is no way I would ever see or be concerned with them.



Summary

I cannot improve the relative power in these terms by adjusting my TX power, as they go dB for dB with my fundamental signal.

Only someone in my local area will see these signals as significant, and the operator who indicated I was splattering did not leave his call so I can not tell. I should has asked, but I did not, a short QSO may have been a better idea.

For now I'll assume every thing is ok and go back to having fun.

Update:

Here is another plot of my tx signal.


Update #2

I was in a QSO with a Spanish station and received a 575 report, so again I thought something must be wrong. A plot of my transmit signal is below.

This time I recognized that the "regrowth" was at N times 120Hz, pointing me to a power problem. Also, I though I'd take a look at my CW output as a means to remove the PSK hardware and software from the equation. Below is my CW plot, this was for 10W output.


In my shack I power my table from two power bars. One regular power bar for all the ordinary stuff, PC, lamp, monitors, and a filtered power bar for the FT2000D, DMU2000, and the Kenwood PS-53 for the IC-7000 and / or TS-850. Both power bars are powered from the same wall outlet which has a dedicated 15A circuit for the sta

I can see in the plot above, that the same N*120Hz side tones are present, the first pair are only 35dB down.

Below is a plot of the same CW transmission when the FT2000D + DMU2000 and Kenwood PS-53 supply are on the same power bar as the rest of the shack. (avoiding the MFJ power

I can see in the plot below, that only the first 120Hz side tones are present, but now are 60dB down, a 25dB improvement. The MFJ-1164B power bar will need some further investigation.


In the meantime, returning to PSK mode, below shows a much improved transmit signal.

Rig
TRX - FT2000D
Freq - 18.10MHZ
Tx Power - 130W (by the FT2000D meter, just for testing)

Excellent.



Now I think I have a very good idea of how clean the PSK signal should be from my radio and will keep an eye.

Summary:

1) If you have an extra radio and Signallink you can run 2 copies of DM780 and see your own transmit signal. Grounding the second rig's antenna input will enable enough signal in to be detected.

2) Your AC supply should be suspected if you have N*120Hz sidebands

3) Read an understand how volume controls should be set for your software and PSK interface hardware

4) Looking at your CW output can help isolate the problem

5) a good transmit signal will have better than 25dB IMD, better than 25dB SNR and 60 to 70dB spurious free range.

All for now.

Thursday, February 26, 2009

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%
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.


Tuesday, February 24, 2009

Buddipole 4NEC2 Model Files

I have found a way to post my 4NEC2 Buddipole modeling files on line using Google Documents.

Eventually I will log many of my design files here for anyone to use.

4NEC2 is available at http://home.ict.nl/~arivoors/

Below is a list of the files I have created.

FILE AC_Vbud_40M_09_V01
40m Vertical, (longwhip, 4 dipole arms, red coil)
FILE AC_Vbud_40M_08_V01 40m Vertical, (longwhip, red coil, 4 dipole arms)

Detailed Files:

FILE AC_Vbud_40M_09_V01

Description, LongWhip with RedCoil and 4 Dipole Arms on VersaTee w/ TRSB set to 25ohms (2:1) and 1 8.6m Counterpoise.

This is a new configuration
a) attempting to generate a lower takeoff angle and more gain
b) 40m PSK31 frequency (7.07MHz)
c) Red coil was moved to below the arms and whip
d) Suggested by Ray (K7RFW)

1 fully extended Long Whip
4 22" Dipole Arms
1 RedCoil tapped turns from Bottom
1 Versatee
1 TRSB,(2:1) 25 ohms
1 8.6 (m) Counterpoise



Takeoff angle 30 degrees
Gain 0.0 dBi
SWR 1.6 into 25 ohms

Conclusion:
Moving the red coil to below the dipole arms, resulted in a modest loss of antenna gain from 0.6dBi to 0dBi, the take off angle remained the same at about 30degrees. The inductance needed to maintain the antenna at resonance (7.07MHz) was reduced from 15uH (18 turns form the bottom) to 10uH (25 turns from the bottom). Best case SWR was increased from 1.1 to 1.6 as the impedance of the antenna decreased from 22.5ohms to 15.6ohms.

Overall, I would take from this, that is it better to not have the coil placed adjacent to the feed point.

-------------------------------------------------------------------------------------

FILE AC_Vbud_40M_08_V01

Description, LongWhip with RedCoil and 4 Dipole Arms on Versatee w/ TRSB set to 25ohms (2:1) and 1 8.6m Counterpoise.

This is a new configuration
a) attempting to generate a lower takeoff angle and more gain
b) 40m PSK31 frequency (7.07MHz)

1 fully extended Long Whip
1 RedCoil tapped 18 turns from Bottom
4 22" Dipole Arms
1 Versatee
1 TRSB,(2:1) 25 ohms
1 8.6 (m) Counterpoise



Takeoff angle 30 degrees
Gain 0.63 dBi
SWR 1.11 into 25 ohms


-------------------------------------------------------------------------------------