Title: Calculating Effective Radiated Power
1And now our Feature Presentation
2Determining the Effect of Antenna System
Components on Effective Radiated Power
- A beginners guide to determining what is an
effective Antenna System
Gene Brewer, KI6LO www.radioroom.org
3Objective Caveats
- The intent of this presentation is to provide a
seed for thought concerning the overall antenna
system performance related to gain or loss of
feedlines and antennas themselves. - To this end, the following issues will NOT be
included to provide brevity to the presentation - Use of external RX amplifiers
- Useful for increasing received signal
- Use of external TX amplifiers
- Artificially increases the antenna systems gain
by increasing the starting input power for
antenna system, effectively increasing the ERP of
a low gain antenna system. - Inclusion or use of DSP processors/equipment
- Helps pull weak stations out of the noise,
however requires operator to gain knowledge of
use to be highly effective - Impedance matching or tuning methods
- For the examples, it is assumed that everything
is matched. - We will overlook losses due to SWR and
mismatches. - That level of detail may be covered in another
presentation.
4Important Point to Remember
Using a high end multimode do-everything
transceiver with a poorly designed lossy antenna
system is comparable to shooting pictures with an
expensive digital camera and printing them on an
old dot matrix black white printer
Sure youll get resultsbut at what cost?
5So where to start planning?
- In order to be able to plan an effective antenna
system, you first need to know how to determine
what is effective and whats not! - And there aint no such thing as a FREE LUNCH
- So youll need to know a little math to do this
and it isnt going to hurt at all!!!!
6What is a Decibel?
- A convenient way for engineers to describe the
input to output ratios of either power or
voltages - named after Alexander Graham Bell
- 3dB half power point proof
http//www.siemon.com/us/white_papers/99-05-17-wha
tis-inadb.asp
7Decibel / Ratio Conversion
- Using the table shown, you can determine the
ratio of voltage and/or power levels for gain or
loss based on dB reference. - Example
- For 3dB loss, multiply power 0.500 (or ½)
- For 3dB gain, multiply power 1/0.5 (or 2)
8Practical Examples of dBs
- As we have shown, power levels double for every
3dB of gain (or halves for every 3dB of loss) - If we consider an antenna system to be a hollow
tube with an input and output - If total system gain is 0dB it is said to have
Unity Gain meaning that it has no gain or loss,
everything that goes in comes out the other end. - If total system gain is negative (dB) it is said
to have loss meaning less than the input comes
out the output. - Example _at_ -3dB Output Input 2
- If total system gain is positive (dB) it is said
to have gain meaning effectively more power
comes out the output than went in the input. - Example _at_ 3dB Output Input 2
9Measuring Antenna Gain ValuesdBi vs. dBd
- Antenna gain values are measured in decibels
referenced to either - An Isotropic Radiator (dBi)
- An isotropic radiator is a theoretical point
source antenna that has unity (gain value 1) in
all directions. This reference antenna is for
calculations only and provides a base reference
of 0 dB to compare against. - A standard ½ ? dipole
- The standard ½ ? dipole has a radiation pattern
resembling a donut with the antenna referenced as
placed through the donut hole. This antenna
provides a standardized gain value of 2.15 dBi to
compare against. - These values are used interchangeable so pay
attention to the reference as used. - 2.15 dBi is considered the same level as 0 dBd
for antenna gain.
10Typical First Time Antenna Install
- It is a common sight for Mr./Ms. FirstTimeHam to
get a 2M or 2M/440 FM transceiver/HT and get on
the air. - Soon they may want to talk beyond the local
repeater and need to install some sort of
external antenna. - Of course that means installing the antenna,
providing some sort of feedline to get RF from
the radio to the antenna. - They may find that the range of coverage isnt
sufficient enough to access desired repeaters or
talk simplex to non-local hams. - It is then that the head scratching starts and
some (hopefully more than few) will actually
start a path of investigation that will lead to
obtaining useful knowledge about ANTENNA SYSTEMS.
11What do we mean by Antenna System?
- The antenna system consists of all those items in
the pathway from the transceiver output to the
actual antenna. - First is the feedline used.
- This is as important as the antenna itself. Maybe
more so depending on situation. - Use of quality feedline will pay for itself many
times over in QSO quality - Second is the physical antenna itself.
- Depending on design and frequency of coverage,
- the gain, polarity, radiation pattern varies.
- required supports can vary from modest to
elaborate, inexpensive to extremely costly. - to increase the gain of the antenna (and in most
cases the directivity) usually requires
increasing the size of the physical antenna. - Third is the support/mast and rotational device,
if required. - The mast or support the antenna resides on is
inconsequential to the antenna system performance
providing it places the antenna at the correctly
required height above ground and securely retains
it there and does not deter from the maximum
possible system performance. - Guy lines should not effect achieving the
designed antenna radiation pattern or
performance. - The rotational device should match the antenna
weight and windload requirements but it too is
inconsequential. - Lastly is all the miscellaneous hardware such as
connectors, antenna switches, etc. - These can add loss to the overall system
performance.
12(No Transcript)
13Basic Antenna System
ANTENNA Provides launch point for RF
propagation. Directional antennas place the
majority of the RF from the TX into a single area
of the antenna or lobe, thereby increasing the
effective radiated power levels. Conversely, the
received RF signal is stronger in the direction
of the designed radiation pattern. Design of the
antenna also effects the polarity of the TX/RX
signals. Antennas can provide gain or loss,
depending on design and implementation.
TRANSCEIVER - Provides RF output and obtains
information from received RF signal at specified
frequency and mode. Can provide RX gain using RX
amplifier or DSP processing. TX power level is
used as reference for determining gain or loss of
overall antenna system.
COAXIAL Cable / Feedline Provides physical
conduit for RF between antenna and transceiver.
Better coaxial cable possess less attenuation to
RF, both TX and RX, but usually at a higher price
(per foot). Feedline can only provide unity (0dB)
or greater loss, no gain.
Reference
Unity or Loss Only
Gain, Unity or Loss
Basic Antenna System ERP TX Power Level
(Total Feedline Loss Antenna Gain or Loss)
(Total Feedline Losses include feedline,
connectors, antenna switches, etc losses)
14What is meant by ERP?
- FCC definition
- Effective Radiated Power (e.r.p) (in a given
direction) is the product of the power supplied
to the antenna and its gain relative to a
half-wave dipole in a given direction. - Any feedline losses must be taken into account to
determine the power supplied to the antenna
based on the power at the RF connector of the
radio. - Conversion from dBi to dBd may be required to
compare target antenna to a half-wave dipole - Several factors are required to determine actual
ERP values. - Transmitter power output
- Transmission line losses
- Antenna type and position
15Do I really need to know my ERP?
- Well in most situations, the acceptable answer
can be NO, however. - Part 97 of the FCC Rules assign responsibility to
the amateur operator of determining that
transmitted power exposure levels are safe for
general public as well as the amateur themselves. - Part 97.13(c) describes the requirement for
determining exposure levels for ham frequencies - It can be very helpful to know your antenna
radiation pattern and ERP levels to maintain an
effective, safe perhaps legal ham station.
16Common Coaxial Feedlines
17Common Coaxial Feedlines Losses
Typically the larger the coaxial cable diameter,
the lower the loss at higher frequencies. Notice
that RG-8 and 9913 are the same diameter (0.405)
but 9913 is much better above 6M (50Mhz). This is
due to the dielectric and other internal
properties.
Upper HF Bands VHF 20 17 15 1210
6
222
18Common Amateur RF Connectors
- UHF
- Invented in the 1930s by E. Clark Quackenbush of
Amphenol. It was designed for use in the radio
broadcast industry. The plug version is commonly
referred to as the PL-259 connector and uses a
threaded coupling interface which cause a
non-constant impedance. Limited to frequencies of
up to about 300 MHz, the UHF connector is the
cheapest of typical ham use RF connectors. It is
relatively easy to install on coaxial cable. - Type-N
- Invented by and named for Paul Neill of Bell
Labs, the Type-N was first connector capable of
true microwave performance with operation up to
11 GHz in the common 50 ohm impedance design. It
too has a threaded coupling interfaces but the
impedance is constant at 50 ohms. There are also
75 ohm versions available, but they will not mate
with the more common 50 ohm version. The design
is inherently weather-resistant. Type-N
connectors are more expensive than UHF and harder
to install on coaxial cable.
19Common Amateur RF Connectors
- BNC
- One of the most popular of the coaxial connectors
developed in the late 1940s. BNC stands for
Bayonet-Neill-Concelman. Bayonet describes the
interface coupling mechanism, while Neill and
Concelman were the inventors of the N and C
connectors. BNC connectors are available in both
50 and 75 ohm versions, both versions will mate
together. The 50 ohm designs operate up to a
frequency of 4 GHz. Commonly seen on older HTs. - SMA
- The SMA (Sub-Miniature-A) connector was developed
in the 1960s, originally for use with .141
semi-rigid cable (RG-402). SMA connectors have
threaded coupling interfaces in 50 ohm impedance
designs. Certain precision versions of the SMA
connector can operate up to a frequency limit of
26.5 GHz. The maximum usable frequency of cabled
SMA connectors is limited by the type of coaxial
cable which the connector can terminate. SMA
connectors are used in applications where higher
frequencies, miniaturization and size reduction
are key considerations. The SMA has also been
chosen for a wide variety of microwave system
designs. Microwave uses for SMA connectors
include transitions from coax to waveguide and
transitions to microstrip printed circuit board
traces. Newer generations of HTs use SMA for
antenna connections.
20RF Connector Insertion Loss
- The name UHF was applied to the UHF connector
when first developed as 100Mhz was considered UHF
region. - With the design over 70 years old, there has been
much debate over the use of UHF connectors at VHF
and higher. - Due to the design, the impedance is NOT constant
at 50O and limited to 300Mhz - I refer you to the two study reports in the chart
below. - Type-N, BNC and SMA all have a constant 50O
impedance and very high max frequency coverage
21Antenna System GainRules of Thumb
- All components from the transmitter RF output up
to, and including, the antenna either provide
gain or loss to the transmitted RF signal. - The algebraic sum of these values provide a
system gain (or loss) to the transmitter RF
output. - Feedline losses should be low as possible within
budget - 2dB or less preferable
- Antenna Gain should be has high as required for
intended use - For local FM repeater use, lower gain antenna
could be employed. - If max distance is driving requirement, use
highest gain possible - Quality In Quality Out
- Using known good quality components will provide
better results
22Joe E. Ham
- Joe is a Technician class amateur...
- He is just starting out and runs a modest 2M FM
station - a typical dual-band (VHF/UHF) FM transceiver
- Cushcraft AR-2 Ringo 2M vertical
- AR-2 has 3 dB gain spec over a isotropic antenna.
- 100 foot of RG-58 coaxial feedline using PL-259
UHF connectors - At 2M, RG-58 has appx 4.5dB of loss per 100 and
UHF connectors have minor loss (well use 0.5dB
for two ends combined) at VHF frequencies. - Recently Bill, Joes brother, who lives 100 miles
away behind some hills, got his Technician
license and they would like to QSO through a
remote repeater located 80 miles from Joe and 25
miles from Bill. - Bill has no problem getting into the repeater
from his QTH. - The repeater can be heard at Joes QTH but it is
scratchy and Joes has problems maintaining a QSO
through it. - This may indicate 2 problems higher ERP and
more RX gain needed - Joe is curious about his transmitted signal and
what it will take to talk to Bill using 2M?
23Calculating Joes current ERP
- Using the following values for Joes setup, let
us help him determine his ERP - 50W RF transmitter output
- From the previous slide, we can see that the
feedline Joes is using possesses appx 5 dB loss
at 2M frequencies. - Since the power levels effectively double for
every 3dB of gain (or half for every 3dB of loss) - a quick calculations reveals a possible area to
improve in Joes station - For 50W output into 100 of RG-58 coax / two
PL-259 connectors (total 5dB feedline loss) , the
effective power input to the antenna itself is - PowerANT 50W 0.316 15.8 W
24Calculating Joes current ERP
- So Joe has appx 16W feeding into his AR-2
antenna. - As previously shown, the AR-2 is speced at 3dBi
and 3dB gain 2 times effective increase so - ERP 15.8W 2 31.6W
- A net antenna system loss of 36.8 (Not too
good!) - So we have determined that Joes ERP of 31.6W is
too little to hit the remote repeater solidly - This doesnt directly address the scratchy
receive. - How much more ERP is needed?
25Whats Joes next step?
- Joe needs to determine at what level his ERP must
be in order to successfully contact the remote
repeater and QSO his brother. - This can be done by various methods
- Trial and error locally or mobiling
- Finding a local ham who has a proper setup and
calculating their ERP for a reference - Calculating required remote repeater receiver
levels needed for solid signal - This is beyond most amateurs means and isnt
covered here.
26Improving Joes ERP
- There are several ways to improve Joes ERP
- The most effective way would be to change the
coaxial cable for a type more compatible with VHF
frequencies (e.g. less loss) - Additionally it would be very beneficial to
change the antenna for a higher gain, perhaps
directional beam type. - The current antenna might possibly work if raised
to a much higher height above ground and fed with
low loss feedline? - To improve Joes signal, his monetary budget and
immediate needs have to be balanced to achieve
the desired results.
27Joes Analysis for ImprovementComparison 1
- Joe contacted Steve, a local ham who was known to
use the remote repeater frequently. - Joe examined the Steves station and found he was
running the same radio but had a much better
antenna system. - He had a 2M yagi that was speced at 13.2 dBd
gain - He also was using 75ft of 9913-F7 coax which had
a much lower loss at VHF (-1.8dB vs. -3.8dB) - Joe contacted Bill from Steves QTH and it was a
very enjoyable QSO, full quieting and noise free. - Steves ERP was calculated at
- Steves ERP 50W (-1.35dB -0.5dB 15.35dBi)
50W (13.5dB) ? 1110W - 75ft 9913-F7 Loss of 1.35dB
- Two PL-259 connectors Loss 0.5 dB (appx)
- 13.2dBd antenna gain 15.35dBi antenna gain (We
are using dBi since that is what we used to
figure Joes original ERP) - Steves effective transmitted signal is 35 times
stronger than Joes current effective signal,
using the same radio model. Hint Its the
antenna system!!!! - 31.6W 35 ? 1110W
28Joes Analysis for ImprovementComparison 2
- Joe contacted Tom, another local ham friend who
also was setup on 2M. - Tom had never tried to get into the remote
repeater. - Joe tried contacting Bill from Toms QTH.
- He found that they could QSO but it wasnt as
solid signal as from Steves QTH. - However it was much better than from Joes QTH.
- Joe calculated Toms ERP to get another reference
point. - Tom was using
- Dual Band HT with a 50W amplifier
- a 2M vertical that was speced at 7 dBi gain
- 50 of RG-8/X coax
- From the table shows 3.6dB per 100 VHF
- His ERP was calculated at
- Toms ERP 50W ((-3.6dB/2) (-0.5dB) 7dBi)
? 154W
29Joes Course of Action
- From the comparisons Joe made, we can see that
the upgraded antenna system must possess an ERP
of 200W or greater to achieve the desired
results. - Joe has decided to install a similar setup as
Steves with the following - It might have a bit less gain after all he only
need at least 200W ERP - This is a budget constraint to be considered
(total system gain vs. total cost) - He would like to limit the project budget to a
maximum of 400. - New antenna system should include but not limited
to - A directional antenna (yagi or quad) of
sufficient gain (9dB or greater) - A rotational system (e.g. rotor) to turn the beam
- A light duty tower/roof-tower/telescoping mast to
support the rotor and antenna - 9913-F7/compatible coaxial cable to reach antenna
from radio in the shack - Rotor cable to also reach rotor from controller
in the shack - With a directional antenna (beam) with higher
gain than a vertical, the RX signal at Joes end
should be much cleaner with little or no
scratchiness (e.g. full or near full quieting) - Joe will need to recalculate the new systems ERP
before acquisition of parts - Once new system components are identified, test
design before purchasing. - Avoid wasting money and hassle of returning, etc.
30Summary
- When thinking about antenna systems, dont forget
to bring all variables into the process. - Cheap coaxial cable and connectors can ruin a
good antenna system design. - Dont reinvent the wheel
- Visit others stations - See what they have
learned - Check out product reviews online at EHAM.NET or
QRZ.COM - Investigate antenna modeling software
- Can help optimize antenna radiation pattern and
gain height - Limited version of EZNEC3 comes with ARRL Antenna
Book - The transceiver/radio is only a part of the
system - Many times we caught up in a transceivers ooohs
and aaahs and over look the other important parts
of the system. - Invest in read some Antenna Books from ARRL or
others - They are well worth the money you wont be sorry
31 32References
- Websites
- Amphenol RF connector data- http//www.amphenolrf.
com - Siemon dB whitepaper - http//www.siemon.com/us/wh
ite_papers/99-05-17-whatis-inadb.asp - ARRL Part 97 reference http//www.arrl.org
- Belden Cable Co coaxial specifications
http//www.belden.com - Davis RF - BURY-FLEXTM specifications
http//www.davisrf.com/ham1/coax.htmburyflex - Cambridge Products RF Application Guide -
http//www.cambridgeproducts.com - Cushcraft AR-2 Specs http//www.cushcraft.com/co
mm/support/pdf/RINGOS20AR2206201020ARX4502022
0B202B.PDF - Antennex.Com (Antenna Information mecca
subscription required however) -
http//www.antennex.com - Books
- ARRL Handbooks various years 1976 - 2005
- ARRL Antenna Handbook 20th Edition
- ARRL Antenna Modeling Course EC-004
- Software
- W7ELs EZ-NEC 3.0
- W4RNL (L.B. Cebik) Antenna Model Library
(available from Antennex.Com)