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I have modified a number of Alpha 76CA amplifiers as well.
Here is a picture of two Kilovac HC-1 relays, mounted with silicone rubber strips, on a new bracket. The relays operate
silently during QSK. Many thanks to Stormy N7WX for the nice picture of his beautiful amplifier.
| QSK conversion for Alpha 76CA using Kilovac HC-1. |
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| The relays are mounted with silicone rubber strips. They operate silently during QSK. |
View Video of QSO with PA0GO
During early 2007, I had an interesting QSO with Gerrit, PA0GO, an old timer on 20 meters. Gerrit has
been very active with homebrew equipment for over sixty years. Gerrit has donated his station to the Openlucht
Museum in Arnhem, Netherlands. The Museum has made a video recording of a couple hours of Gerrit telling about amateur radio.
Part of this recording was my QSO with Gerrit, which you may view via either the broadband link, or dial-up
link below. Many thanks to Henk, VK2GWK, for providing these links.
Broad Band Link to PA0GO Video
Dial Up Link to PA0GO Video
ADJUSTING THE ORION II ALC FOR 100 WATTS PEP
OUTPUT AND OPTIMIZING THE SPEECH PROCESSOR PROFORMANCE
The IF Converter Board is located directly under the speaker in the O2.
Below is a photo which clearly shows the ALC Set pot. It is to the right of three
others, including the meter calibration pot.
Besure you have an accurate PEP and average power wattmeter, and a 50 ohm dummy load attached
to your Orion II. Select the PWR button on the O2, and use the multifunction encoder to show 100 watts on the
O2 screen. Key the O2, and then set the ALC Set pot to produce an output of about 110 watts maximum.
Your radio should then be able to output 100 watts PEP easily into a 50 ohm dummy load.
Ignore the ALC lamp. It is not a good indicator of adequate audio drive level. The
lamp should be lit continuously, and your Speech Processor on and set to number 7.
Adjust your microphone gain, and your hardware microphone gain, to indicate an average power
of about 45% of the Maximum PEP output.
Without adequate microphone gain, the RF compressor will not produce a significant increase in
the average power output.
After you have adjusted your O2, according to the above, get some on the air quality checks.
You should receive excellent reports, as the processor does not distort the audio in any way at these levels. When changing
the maximum PEP output of the O2, recheck the audio drive level to maintain appropropriate average power.
| Ten Tec Orion II IF Converter Board |
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DRIVING A LINEAR AMPLIFIER
WITH A HIGH INPUT SWR
A
question which arises frequently from operators utilizing modern, solid state transceivers, is what to do when their radio
sees a high input SWR while driving their amplifier. This problem often arises when a new amplifier is installed in
the station, and the operator is puzzled by the issue suddenly appearing.
This problem
often causes power output foldback from the high SWR, as the transceiver protection circuit does what it is designed to do.
Most solid state transceivers start to foldback the power output when working into loads with a SWR of between 1.5 and 2 to
1. Some operators have merely engaged the built in antenna tuner to solve the problem, while others may have installed an
outboard tuner between the transceiver and the linear amplifier. In certain cases the phase shift introduced by the
tuner can actually cause the amplifier to oscillate, and in general, this may actually introduce increased IMD.
Collins
Radio, when they introduced their famous 30S1 many years ago, provided a specific length of coax to go between their S line
driving transmitter, or KWM2 transceiver and the amplifier. You will find the details of their design in the 30S1 instruction
manual.
Collins indicated
that this special length of coax acted as a kind of transformer, and provided an even multiple of 180 degrees of phase shift
to provide for the lowest amplifier output distortion.
Experience
tells us that although changing the length of the interconnecting cable does not actually change the actual amplifier input
SWR, it does change the apparent SWR which the driving transceiver SWR bridge sees, and effects the performance of the foldback
circuitry.
So
how do we reduce the driving power required to reach full amplifier output, achieve the full potential solid state transceiver
output without foldback, and provide for the lowest distortion? Here's how to do it:
The
solution length of the cable chosen to be inserted between the transceiver and the amp will be dependant upon three variables;
the output circuit of the transceiver, the input circuit of the amp, and the particular primary transmission parameters of
the interconnecting coaxial cable. To solve for the ideal length, start with a length of high quality RG 8 type cable
of approximately 23 feet! Yes, I know that is considerably longer than the cable you are using now. When you are
finished you can coil the cable neatly, as this will not effect performance.
Install
a PL 259 on one cable end, and trim back the other end as if preparing it for a connector also. This end you can insert
carefully into the SO 239 input connector on your amp, being careful not let the braid wires short to the center conductor.
You can hold the braid wires in place with a clothespin onto the connector body. After you plug the PL 259 connector
into your transceiver, drive your amp at low power, with the transceiver internal TUNER OFF, thru the new cable,
and check the SWR using the internal radio SWR bridge on the offending band or the highest frequency offending band.
Chances are you will already see a reduction in SWR. Note this reading, and now prune the cable back by about 6 inches,
and take another reading. Continue this process pruning shorter lengths until the SWR meter in the transceiver
indicates as close to 1:1 as possible. Now you can install the second PL 259 onto the solution length cable.
Why
does this work as it does?
In cases involving RF signals, some time will pass during the 'round trip of the
reflected energy and the phase of the reflection will also depend upon this length of time. Imagine that a resistor in a black
box is at the end of a length of cable. From the outside world this length of cable will give the reflection from the resistor
a phase shift since the signal must make a round trip through the length. If a 100 ohm resistor has an SWR of 2, a cable long
enough to invert the signal after the round trip will make it look like a 25 ohm resistor, also with an SWR of 2 but with
inversion (a cable with a multiple of 1/4 wavelength would do the trick). Since the impedance looking into this black box
is a function of the SWR and the cable length, it can be seen that intentionally mismatched lines can be used to transform
one impedance into another. Notice that the 1/4 wave cable inverts the impedance and preserves the SWR. This impedance inversion
may be used to match two impedances at a particular frequency by connecting them with a 1/4 wave cable with an impedance equal
to the geometric mean of the two impedances. (The geometric mean is the square-root of their product.) A 50 ohm, 1/4 wave
cable will match a 25 ohm source to a 100 ohm load : sqrt(25 x 100) = 50. Of course, it is not always easy to find the desired
impedance cable!
Multiples of 1/2 wavelength will give enough delay that the reflection is not inverted
and the impedance will be the same as the load. Such cables may be used to transfer the load impedance to a remote location
without changing its value (at one frequency).
Other cable lengths will transform an impedance which differs from the cable's impedance
with a reactive component. If the load is a lower impedance than the cable, a length below 1/4 wave will have an inductive
component and above 1/4 (but below 1/2) wave a capacitive component. If the load is a higher impedance than the cable, the
reverse is true. Above 1/2 wavelength, the reactance will alternately look capacitive and inductive in 1/4 wave multiples.
This reactance will combine with the load's reactance and offers the possibility of resonating the reactive component of the
load. Therefore, a cable with the "right" length and impedance can match a source and load with different resistance and reactance
values. Obviously, these calculations can become quite involved and most engineers resort to a Smith chart, a computer program
or perhaps the most common method, trial and error with a SWR meter or return loss bridge!
Our trial and error experiments with an external or internal transceiver SWR meter, suggest
that the solution length is usually between 20 and 22 feet. Therefore, considering for example that on 20 meters where
this length is greater than a 1/4 wavelength, your input SWR is too high and your amplifier is presenting a load
impedance of less than 50 ohms, this solution length will have a capacitive component. This would be true for 15 meters
as well.
It is also possible that
the longer length of coax acts as a "stub" and strips shield currents from the interconnecting cable which are fooling the
internal SWR bridge, and therefore it eliminates power foldback. In this case, a line isolator installed between the
driver and the amplifier may also be of major benefit in eliminating the power foldback.
This
solution is simple to achieve, and inexpensive as well. Just a little patience is required when trimming the cable.
In the event that your transceiver does not directly read SWR, you may install a SWR bridge coupler onto the output connector
of your transceiver to obtain the solution length of cable.
If your linear amplifier input circuits are tunable, you can finish up with adjusting the input coils for the
absolute lowest input SWR on each band. You will be pleased to see that after following this solution, your transceiver
will be able to operate at an even lower level of drive to produce full amplifier output.
Modifying the Inrad Mark V Roofing Filter
Board
I have noticed over the years that I may have some IMD issues with moderately strong close in
signals despite my installation of the new roofing filter.
Pretty interesting, notice the rather dramatic improvement in close spacing IMDR and BDR
when the Inrad mod is removed. I suspect that this will be true for all spacings within the bandwidth of the filter.
Now, I also suspect that the filter bandwidth is actually wider than the advertised spec of 4 Khz, more like something between
5 and 6 Khz.
I conjecture that there is too much gain in the 1st IF. I believe this because after installation
of the roofing filter, it is necessary to reduce the IF gain in the transceiver menu to return the S meter readings to be
equal to those before installation. When you reduce the gain in the menu it is in the third IF, not in the first.
Therefore, since I believe that most of the IMD originates in the second IF mixer, reducing the gain in the menu does nothing
to reduce IMD created by too much gain in the first.
In discussing this issue with Inrad, I was informed that the prototype board filters
had greater loss by about 3.5 dB than actual production boards, and the amplifier design results in 3.5 dB net gain rather
than exactly balancing the filter insertion losses. Inrad didn't think this was a big deal since it was only 3.5 dB,
but I look at this issue somewhat differently.
As I wrote to Inrad:
"It does make sense to me that the higher gain in the 1st IF would lead to
lower IMD numbers,
if the IMD is generated mostly in the 2nd IF (mixer).
This seems most reasonable since for 3rd order IMD the rule is 3
dB for
every 1 dB of tone power increase. Thus, 3.5 dB more power per tone would
increase the IM power by 10.5
dB. This exactly corresponds with W8JI's
experience with the module and is most interesting."
So I conjecture that this gain would result in considerably lower IMDR and BDR numbers, like
those corresponding with the W8JI table.
So, how do we get the narrow roofing filter benefits without reducing the dynamic range so greatly?
We reduce the gain of the on board Inrad two stage amplifier.
Here's how to do it:
In order to keep the proper input impedance for loading the filter, two resistors must be
changed. R5, the 12 ohm resistor should go to 15 ohms. R6, the 220 ohm resistor should go to 150 ohms. This
will lower the gain by about 3.5 dB.
You can find the schematic of the roofing filter module on
the Inrad website for more details.
You should be able to return the IF gain menu setting to
the factory setting after making the changes on the filter board. Obviously, in the ideal situation, you would be able
to adjust the gain for the particular insertion losses of your filter. No two filters will be exactly alike, and this
is a close approximation of the average production filter.
Now, I do not understand why the ARRL and RSGB labs didn't
find the same results, except, perhaps they received the early prototype production units for their testing.
Now increasing the IF gain setting in the menu will slightly
increase the noise floor again back to the factory condition. You will loose the improvement there, but it only a dB
or two. Personally, I think my new BHI DSP module, the ANEM, of which I wrote about in the March QST, will easily take
care of that issue.
This is a simple change, and can be made easily. Your
radio should be less susceptible to intermod generated from strong close in signals, particularly from garbage being thrown
around the band from very strong close by signals.
Operators with large antennas in great locations should benefit
from this small change. When the signals are of lower strength, this change will not do anything for the receiver.
BUT, the new sun spot cycle probably has begun, and we will see more and more days when every signal will be S9 and the band
will be wall to wall. It should really help then.
See what you think.
73,
Mike
W2AJI
Fixing Audio Distortion with the Mark V and MD 200
Microphone
Over the years my Mark V has suffered
on and off with RF distorting my audio. Certain positions of my yagi could occasionally result in audio distortion during
transmissions. I normally use my MD 200 microphone to drive some outboard compressor/limiter with a downward expander to control
noise. As you know, this microphone was developed to work with the Mark V specifically. I have previously needed to use ferrite
snap-ons to control the problem. The problem is especially pronounced when running higher power with an amplifier.
Recently,
I realized that the RF was entering the audio chain via the MD 200 microphone. I started to examine the microphone carefully,
and here is what I discovered:
1. The element housing is floating, and not connected to chassis ground. It seems to
act as an antenna, and picks up RF.
2. The powder coating on the housing does not permit continuity between the upper and
lower portions of the housing.
3. The vibration damping mounting bracket is not grounded to the base either.
4. No chassis
ground is carried in the cables to the microphone board, which is grounded to the floating housing.
5. The base of the
microphone and its switching board are indeed chassis grounded.
Here's how you fix the problem:
1. At the point
of attachment of the mounting bracket to the housing, remove a small amount of the housing powder coating around the holes
which are used by the gold plated retaining pivot screws. This will permit the mated upper and lower housing halves to be
electrically connected. ONLY REMOVE the coating from the small area around the screws, from the surfaces where the upper and
lower housings meet. When the housings are reassembled, these contact points will not be visible
2.
Remove the coating from the mounting bracket, at the very bottom, ONLY FROM the surface that mounts onto the post which extends
from the microphone base. The post is at chassis ground already, and this change will ground the mounting bracket also.
3.
Next, the MD 200 can accept a second cartridge, there is a switch in the base to select either the stock variable pressure
element, or the optional cartridge which you can install. This means there are two extra wires in the microphone housing cable,
which are not being used if you DID NOT INSTALL THE ADDITIONAL CARTRIDGE. Remove the top housing and examine the microphone
board. You will see the two small pads, next to the microphone element connector, which is white. One pad is marked, GRD 2,
this is the unused microphone ground for the optional cartridge. Solder a small gage wire to this pad, it will connect to
the internal wiring, which is connected to the base. The other end of the small wire can be connected to the board ground,
which can be obtained at the near by pad with the mounting screw which attaches the board to the housing. Providing this link
will ground both the board to the housing, and the housing to the base, once the other
end of the cable is grounded. Reassemble
the housing.
4.
Remove the base cover, you will see the small slide switch which selects the microphone cartridge. In front of this is a row
of pads which appears to be the termination of the cable conductors. The 4th pad from the right is the 2nd cartridge microphone
ground, you can confirm this fact now, by using your VOM to see that the cartridge housing is common now to this pad (make
sure that the upper housing is plugged into the base of course). Tack solder another short wire to this pad, and solder the
other end to the board ground, also at the point that the board is retained by the screw at the lower left hand corner. This
board is already at chassis ground, so completing the wiring to the housing, makes everything common. Reassemble the base
cover, and install the cartridge mounting bracket, and the cartridge housing into the bracket.
I made some measurements
and found that the housing screens are common to the housing itself, so grounding the housing grounds the large screens.
In
my case, the RF distortion was eliminated completely, and the audio quality was greatly improved. It is surprising that Yaesu
produced a microphone without grounded shielding for the element, with as large a screen area as this microphone has. Obviously,
take care not to damage your microphone either electrically or mechanically during this modification,
which does require
moderate experience to complete. This modification is done at your own risk, and no liability is assumed by the author for
errors or damage. Check your work carefully, it should work well for you.
I will eventually take some pictures of the
mods on the two boards and place them on my website. If you have any questions, please let me know.
73 and Happy DXing,
Mike
W2AJI
HAS SUNSPOT CYCLE 24 ALREADY BEGUN?
Sunspots are planet sized magnets created by the sun's inner magnetic dynamo. They share the common feature of
all magnets in the cosmos of having polarity, that is a north and south magnetic pole. Studies of the sun tell us about
the expected sunspot polarity in each region of the sun's surface during specific cycles. During the 11 year sunspot
cycle, we can describe the polarity as either normal or backwards, depending upon a sunspot's north and south pole orientation.
Sunspot cycles over a period of one or two years actually share the sun, in a mixed up combination of forwards and
backwards polarity, until the newer cycle takes over entirely. Currently, in Cycle 23, sunspots in the Northern
Sun Hemisphere have South to North polarity. As the new cycle begins, new spots will appear with North to South polarity
in the Northern Sun Hemisphere, and South to North polarity in the Southern Hemisphere. This new orientation will indeed
apply to Cycle 24.
This past July 31st, a very small sunspot was born at about 65 degrees west, 13 degrees south. It emerged
up from the sun's interior, floated around for about three hours, and suddenly vanished. This sort of sunspot activity
is not unknown. In fact, this particular sunspot was so short lived that astronomers who number sunspots did not even
think it worthy of a sunspot number. But it had one remarkable quality, it was BACKWARD in polarity!
David Hathaway, a solar physicist at the Marshall Space Flight Center, Huntsville, Alabama, says, "We've been waiting
for this, a backwards sunspot is a sign that the next cycle is beginning."
Besides being very short lived, this backward sunspot also popped up at an unusual location for new cycle sunspots.
It appeared at 13 degrees south latitude, whereas new cycle spots normally appear at 30 degrees north or south latitude.
These two facts will keep NASA from declaring a definite beginning for the coexistence of Cycle 24 with Cycle 23, but they
will be keeping a watchful eye for other new BACKWARD sunspots.
If Cycle 24 has begun, don't expect any great storms immediately, according to Hathaway.
But I personally will keep an eye on propagation improvements as perhaps Cycle 24 begins to overtake Cycle 23.
73
and Happy DXing,
Mike
W2AJI
EVERYONE KNOWS FATHER MORAN
I thought I would share an email which I sent to Brooke Allen, who had recently
written a wonderful article about perhaps the greatest DX legend of amateur radio, Fr. Marshall D. Moran. Moran, 9N1MM, has
been a silent key now for some fifteen years, but is well remembered by his many radio friends around the globe.
Hello Brooke:
I particularly enjoyed your
article about Moran, as he called himself on the
air. Everyone knew he was Father Moran, but when asked, he would
just say
"my name is Moran".
While you may remember him from the pile-ups on 15 or 20 meters, I remember
hearing
his "BREAK" while chatting with local stations on 15 meters, way
back in the sixties.
"Standby breaking station,"
said I. I then finished my last thought, and
said, "breaker go ahead please".
Then I heard, "This is 9N1 Mickey
Mouse", said the voice. "This is Moran
in Katmandu".
I was really stunned, here he was, the best known
DX station in the entire
world, breaking into my QSO. I swallowed hard, and said, "hello Father, how
are you today?"
Moran said, "Mike, (God he knew my name from reading the
mail), have you got the newspaper there with the scores from the
weekend
football?"
"Sure Father, let me see where it is".
"Tell me how Notre Dame made out on Saturday please".
Well,
that was the beginning of many contacts with Father Moran. I often
read the scores to him, and he always broke in
when he heard my signals. My
callsign for 45 years was WB2AJI, and I was operating from West Orange, New
Jersey
in the sixties.
To avoid creating pile ups, I always mumbled his callsign. His signal
wasn't very strong as
I remember, and I could almost keep a contact with him
a secret for a while, until the anxious tuner uppers would finally
bury
Moran's little signal.
Thanks for putting a smile on my face tonight as I read your article. I
remain
an active DXer to this day, but those contacts with Father Moran were
really special.
73,
Mike Schatzberg
W2AJI
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