WELCOME TO RF HELPER!



RF designers generally begin receiver system design by grouping

hardware into functional blocks that can then be analyzed in terms of

gain, noise figure, and third order intercept points (IP3). The latter

is used in computing spur free two tone dynamic range. The parameters of

these functional blocks can then be combined by the RF designer to

determine total system performance.

The goal of RF Helper is to aid the user in this design process by

permitting rapid analysis of an RF design using simple graphic boxes to

represent functions and their parameters. The hierarchical approach of

RF Helper permits the user to first form a simple block diagram and then

expand each box until the desired level of detail is reached. RF Helper

can also be used to load complex RF designs from disk memory in order to

quickly evaluate the results of proposed modifications or parameter


changes.


































1.0 INTRODUCTION

The primary advantage offered by RF Helper is the ability to
determine in a simple graphical way the Rf performance parameters of a
complex system. These parameters include noise figure, sensitivity,
dynamic range, gain and gain ripple. This is accomplished by presenting
the user with an easy to understand screen selection process comprised
of boxes that serve to represent various parts of the RF system. This
simple screen selection process is described in the following paragraphs
along with illustrative examples.

1.1 Screens

RF Helper initially presents the viewer with a white screen with a
small symbol representing an antenna (or RF input) in the upper left
corner connected to a light blue box that reads "SELECT". On the right
side of the screen are a row of brightly colored Selector Boxes that
includes Gain(blue), Coax(green), Divider(violet) and Receiver(red).


+-------------------------------------------------------------------+
| | |
| WHITE SCREEN | GAIN |
| +------------+ SELECTOR BOXES-- | |
| | | | |
| :--| (SELECT) | |-------------|
| | | | |
| +------------+ | COAX |
|


Placing the mouse cursor (hot key selection is also available) on the
Gain, Coax, or Receiver Selector Boxes and depressing the left button
will cause an appropriately colored Title Window to appear. After
entering the requested box name and depressing the "enter" key the upper
left "SELECT" box will be replaced with the selected box having the
entered title. If the selected box was gain then the box would appear as
dark blue and would display the default values of gain and noise
figure(both 0 dB). Connected to the blue gain box would be another light
blue "SELECT" box. If Coax had been selected then the box would have
been green and the default parameters for loss and loss variation would
be displayed. A slightly different process would have occurred had the
violet Divider had been selected. First, there would have been no title
window. In RF Helper the divider is not an RF component but is simply a
way of creating two paths . Therefore, it does not require a title.
Further, it should be noted that use of the divider is restricted to the
first level of boxes where multiple outputs for a single input are
allowed. The Divider box that replaces the "SELECT" box has two outputs.
One of the outputs would be connected to a light blue box that reads
"FIRST" while the other is connected to a similar box that reads
"SECOND". The next selection of a box following the divider will replace
the "FIRST" box. This path will continue until it is stopped typically
by selection of a Receiver box or in a special case when a stop command
is issued (right mouse button with cursor on Divider Selector Box). The
next box selected will then replace the "SECOND" box. If this selection
is the Receiver then a title window would appear followed by a red box
that replaces the "SECOND" box. However, since selection of the receiver
completes the path or thread there would be no new "SELECT" box
generated. Also, since all paths are now complete the select boxes on
the right side of the screen will turn white indicating that the
selection process for this level is complete and no further selections
can be permitted. The red receiver box displays the defalut tangential
sensitivity of the receivers detector and its video bandwidth.
For a relatively simple RF design the process following selection
of boxes is to fill in the parameter list or template associated with
each box and to then display/print results. The parameter list is
displayed and parameters modified anytime the mouse cursor is placed
over a Gain, Coax, or Receive box and the left button is depressed. The
top parameters on each list are shown in white to indicate that they
must be entered to permit results to be properly displayed. In the case
of the Gain box these parameters include gain, noise figure, and IP3
(third order intercept point which is typically 6 to 8 dB above the
device 1 dB compression point). After entering this limited data the
user can accept the other default values (which generally have little
impact on displayed results) by answering "Y" when asked if they are
correct. If the user chooses to answer "N" then he is given the chance
to change all parameters. This includes RF bandwidth used in computing
noise power plus box title. However, in general this second or expanded
set of data are used in computing ripple and other parameters not
displayed but available on the Extended Print Out Option(F9)
The primary and secondary parameters associated with the Gain,
Coax, and Receiver Boxes are as follows:


Primary Default Secondary Default

Gain Box gain 0 dB ripple 0 dB
noise figure 0 dB temperature drift 0 dB
IP3 99 dBm vswr in 2:1
vswr out 2:1
bandwidth 10000 Mhz
box name ?
Coax Box loss 0 dB
ripple 0 dB
bandwidth
box name

Receiver Box gain 0 dB single tone dr 50 dB
noise figure 0 dB vswr in 2:1
IP3 99 dBm ripple 0 dB
Tang.Sens. -60dBm/mHz temperature drift 0 dB
RF Bandwidth 10000 mHz threshold snr 14 dB
Video BW 10 mHz box name ?

2.0 Controls/Selections

2.1 Corrections/Data Entry


In the process of selecting boxes it is not unusual to make a
mistake and wish to back up. RF Helper provides such capability via the
small box labeled "BACK/DONE" that is located beneath the four selector
boxes. Placing the mouse cursor in this blue area and depressing the
left button (or Ctrl-PgUp) will cause the last box entered to be
removed. The one exception is when selection has been completed and all
selector boxes are white. In this case depressing the left mouse button
first causes the selector boxes to return to normal colors and then
allows removal or new box selections to be made. If the right mouse
button had been depressed then the red Results Display Window would
appear. In this display receiver results such as sensitivity are shown
in yellow. When multiple receivers are present the last entry and sums
are shown both for the first receiver and then again as the starting
point for the next receiver path.
At any point in the design process the user can elect to save the
results to disk using F2. Multiple saves are recommended for larger RF
designs.
It is also possible to insert or remove gain and coax boxes from an
RF design. The Alt-I key combination starts the process that inserts
either a gain or coax box at the mouse or hot key selected box location.
However, at present RF Helper limits box inserts to non-Recevier boxes.
The Alt-R key combination allows removal of a coax or gain box.
There are two methods of entering data into RF Helper. The first,
as described above, is to enter data into the parameter list that
appears when the left mouse button is depressed with the cursor within
the selected box outline. The second method is to depress the right
mouse button jumping the program to the next higher level. A new clean
white screen or sheet is then shown with the box title and level
displayed at the top of the screen. New boxes can now be selected and
data now entered through either the parameter lists or by again jumping
to a higher level. The use of multiple levels permits RF Helper to
analyze very complex systems that are represented as large blocks on the
first level with more and more detail provided as the levels increase.
It should be noted that since a higher level represents a single box on
the lower level there can be no Divider boxes on other than the first
level. Similarly, there can be no Receivers in any higher level box
unless the lower level box was also a Receiver box. Eventually data must
be entered into a higher level box and the results then brought back to
the first level to complete the analysis. When a higher level data entry
is deemed complete the user must simply display results by depressing
the right button when within the "BACK/DONE" outline. After the results
of that level is displayed the screen returns to the previous lower
level. The starting box is now filled with the new computed results from
the higher level entries. Also, the bottom of the box is marked with two
white asterisks to indicated that it's data came from a higher level
source and that this box can be expanded. At anytime an RF Helper box
can be opened for observation by depressing either the left button to
observe the data present on the parameter list window or, if the two
asterisks are displayed, by depressing the right button to see the boxes
that generated these parameter values. Parameter values can be modified
at the lower or upper levels by opening the parameter list window of any
box and making changes. However, changes made in the upper levels will
only impact the lower level parameter list window values when the user
returns to the first level. It should be noted that print outs will be
based on old data unless the user returns to the first level prior to
printing. Parameter changes can always be made at the lower level by
opening the parameter list table. However, in the case of boxes with
asteriks this change is temporary and any time a level change is made the
data returns to orginal values. This ability to make temporary changes can
be a valuable analysis tool.

2.2 Hot keys/Mouse Selection

The following are the hot keys used by RF Helper. An identical
table is provided within help(F1).

HOT KEY CONTROL
FUNCTION KEYS SELECTOR KEYS BOX LIST KEYS BOX EXPANSION
F1=HELP KEYS BOX KEYS BOX KEYS BOX
F2=LOAD FILES ALT-G GAIN ALT-1 1 ALT-F1 1
F3=SAVE FILES ALT-X COAX ALT-2 2 ALT-F2 2
F4=NEW RUN(CLEAR) ALT-D DIVIDE ALT-3 3 ALT-F3 3
F5=NOT USED ALT-R RECEIVER ALT-4 4 ALT-F4 4
F6=NOT USED ALT-F FORM FEED ALT-5 5 ALT-F5 5
F7=SOUND ON/OFF CTRL-PGUP BACK ALT-6 6 ALT-F6 6
F8= COMPONENTS CTRL-END DONE ALT-7 7 ALT-F7 7
F9= ALL RESULTS CTRL-D STOP ALT-8 8 ALT-F8 8
F10= DISPLAY ,Q QUIT ALT-9 9 ALT-F9 9
(ALT-R TO REMOVE BOX) ALT-A 10 ALT-F10 10
(ALT-I TO INSERT BOX) ALT-B 11 CTRL-F1 11
MOUSE CONTROL ALT-C 12 CTRL-F2 12
Right Side Box Selection = Left Button(Gain,Coax,Divider,Receiver)
BACK = Left Button - Removes last box
DONE = Right Button- Stops Selections & shows results
Gain/Coax/Receiver Boxes = Left Button - Shows Parameter List
= Right Button- Expands Block to Next Level

2.2.1 Function Keys

The key definitions listed above can be observed within RF Helper
by depessing F1; the help key. In addition, the help files include a
simple mouse controlled example.
The F2 and F3 function keys serve to load and save 'RFH' files
respectively. The F2 key also generates a listing of the 'RFH' files in
the root directory. It should be noted that file name can contain
directory path information allowing separate storage of files.
The F4 key produces a window asking if the user really wants to
clear screen and start over.
RF Helper begins with most beeps and other computer sounds removed.
The F7 key turns on sound generation and modifies the sound status
indicator at the bottom of the screen.
Three different print outs are provided by RF Helper. One is a
direct copy of the displayed information and is called up by the F10
key. It should be noted that the Alt-5 key combination determines
whether or not a form feed (needed for laserjets) is generated at the
end of the print out. Another is an extended print out (F9) that
includes ripple, single tone dynamic range and other parameters not
displayed. The third print out (F8) provides a listing of
components/functions and the major parameter values associated with
each.
The function keys are also used in combination with the Alt keys as
a means of expanding specific boxes. For example, Alt-F1 combination is
equivalent to depressing the right mouse button while the cursor is
located in the first box or the box in the upper left corner. The result
is that the box is expanded or moved to the next higher level.

2.2.2 Key Combinations

Alt plus letter key combinations are used to choose various
selector boxes (ie,. Alt-G for a Gain box). This selection is
equalivalent to placing the mouse cursor on one of the 4 selector boxes
located on the right side of the screen and depressing the left mouse
button. It results in the generation of both an appropriately colored
box plus a window requesting a box title.
Two special Alt plus letter key combinations are Alt-R for removing
boxes and Alt-I for inserting boxes. Neither of these combinations have
a mouse counterpart. Use of either results in the generations of
instructions at the bottom of the screen.
Alt plus number combinations are used to open and list the
parameters of a selected box. The numbers to be used correspond to the
box location on the screen with Alt-1 indicating the upper left box and
Alt-C (C for 12) indicating the lower right box. These key combinations
have the same result as placing the mouse cursor on the desired box and
depressing the left button.
The user can leave RF Helper and return to DOS by depressing either
the 'Q' key or ESC key. In either case a window will appear asking if
you really want to leave the program.

2.3 Equations

RF Helper makes use of a number of well established equations in
combination with a few engineering "rules of thumb". To illustrate,
detection sensitivity is computed using equations based on Lucas
(Tangential Sensitivity of a Detector Video System With
Preamplification-proc IEEE, August 1966) using equivalent noise figure
and summed gain of everything in front of the detector. In these
equations the TSS(DET) is as follows:

TSS(DET)=TSS(1mHz)+5*log(video bandwidth in mHz)

RF Helper allows TSS to be entered for any selected video bandwidth. This
permits data entry in the 2 mHz , 10 mHz, and other video bandwidths used
in defining detection components.

The Lucas equations used for computing sensitivity are:

For n >= 2
____________________________________________
SENS=SNRoKTBvF[1+ 1+(/4SNRo)+(2n-1)/+(2TSS(DET)/KTBvFG)^2 ]

where: n=Brf/Bv, SNRo=14 dB(default), =8 dB

The gain value used in this equation and others is simply the sum
of all front end gains and losses (Gtot = G1+G2+...) while the
equivalent noise figure(F) is that computed from the standard equation:
F=F1+(F2-1)/G1. However, the equavalent RF bandwidth computations used
are not quite so apparent or rigorious. In most designs the smallest RF
bandwidth is that of the receiver and this is the RF bandwidth used for
sensitivity calculations. However, in other caases the bandwidth may
vary or even be less than that of the receiver. The difficulty lies in
then determining sensitivity for those cases where the RF bandwidth
changes in various parts of a subsymtem. RF Helper addresses this
problem by first computing total noise power base on summing noise power
in watts and then using the following approximation to compute equavalent
RF bandwidth:

BW=GAINtot*KTF/NOISEPWR.

Variations on the above sensitivity equation by Lucas are also used
by RF Helper for those cases where n is less than 2. It should be noted
that that there has long been disagreement in industry whether
conversion of Lucas from tangential or 8 dB to a more reasonable
threshold value of say 14 dB should be 3 dB, 6 dB, or in between.
RFHELPER uses the worse case 6 dB as the default case but provides
equations for each. The 3 db equation is that of above with 3 dB
subtracted prior to display. The 3 dB equation is used when the program
is started with a space then '1' as follows: RFHELPER 1. Similarly, the
inbetween equations are used when the program is started as follows:
RFHELPER 2. The inbetween equations used by RF Helper are based on a
paper provided by M.C.Hoover Jr. dated 5/6/89. The equation used for
n=>2 is as follows:

_________________________________________
SENS=SNRoKTBvF [1+ 1+(2n-1)/SNRo+(TSS(DET)/KTBvFG)^2/ SNRo]

where: n=Brf/Bv, SNRo=14 dB(default), =8 dB

A special purpose worse case sensitivity has also been provided in
the extended printout of F9. This sensitivity has been computed by
subtracting the frequency ripple and temperature drift from the total
gain used in computing sensitivity with the selected equations. It is
acknowledged that temperature drift is generally not symetrical around
the mean temperature as assumed in RF Helper. Future versions of RF
Helper may address this difference.

The two tone dynamic range (TTDR) presented in the both the screen
display and the display printout (F10) is computed using the following
equation:

TTDR = 2/3 [ IP3-Gs-SENS ]

The single tone dynamic range (STDR), while not displayed, is the
difference between the maximum RF or antenna input, based on not
exceeding any of the 1 dB compression points of any of the boxes and the
computed sensitivity. The 1 dB compression point has been estimated at 6
dB less than the IP3 rather than requiring more user input data. The
STDR cannot exceed the STDR provided data for a given receiver. The
resulting STDR is part of the extended printout (F9). Similarly, ripple
is computed based on engineering rules of thumb and is not displayed.
Ripple is based on the RSS of both indicated box ripple and VSWR induced
ripple. The equations used for ripple are as follows:

Ripple(VSWR)= ABS(20*log(1-((o-1)/(+1))*((i-1)/(i+1))))
_______________________
Ripple(total)= (ri)^2+(r2)^2+...

Temperature gain drift is based on a simple sum of box data rather
than RSS.

3.0 Registering

3.1 Future Plans

In return for registering we will provide you with any and all
future updates. Envisioned updates include addressing multiple receiver
types, coax selection by type, graphic or box type print outs, and a
sensitivity print out. In the latter case each gain and noise figure
will be varied to determine its impact on performance parameters.
Consideration is also being given to allowing each box to store 5 values
for each parameter for purposes of providing a crude frequency
capability. However, it should be recognized by any and all users that
the number of RF designers that would be interested in this or any other
similar program are few. Therefore, if you find this program interesting
and of some use please support it by sending the small registration fee
of $20.00 to:

Willmore Video
401 EDIN GARTH
SEVERNA PARK MD. 21146

If you know someone who might find this program useful feel to give them
a copy of RF Helper along with this RFHELP.DOC.

3.2 Disclaimer!

The author rejects all responsibility for any direct or indirect
damages resulting from use of RF Helper.