Antenna data, and design note for this horizontal loop antenna resonating on 80 Meters by K0ZE
The information in this article has come from many amateur sources, the most notable was from WA6TEY (sk 1985) Ray Frost, who was a pioneer of VHF Quad designs and one of the best Southern California Transmitter Hunters of the 1980’s. Ray built hundreds two meter quads in single and paired configurations as well as his famous mobile radio direction finding quad. At Ray’s request I have used his information and expanded upon his basic designs.
Dimensions for the inverted V antenna from 160 to 2 meters by N6JSX
This modification has been found on the net. Please use at your own risk.
WARNING: Improperly performed modifications can severely damage your adio. I have performed these modifications successfully, but I offer no guarantee or warranty for them. Proceed at your own risk.
1) Small philips-head screwdriver
3) Magnifying glass
4) Low-wattage (15 watt) soldering iron
5) Long-nosed pliers
Enables out-of-band transmit for 1.6 MHz to 54 MHz.
This does not enable extended VHF transmit This does not enable AM or FM broadcast band ransmit. Your memories will be cleared after this modification, ince you need to reset the CPU.
1) Open the top of the radio by removing the 3 top screws and 2 side screws. Look at the radio from the with the front panel facing you. crews.
2) Gently pull up the speaker and set is aside without damaging the speaker or the wires that attach it to the rig.
3) Note the silver rectangular box near the middle of the PCB marked something like “9 MHz SSB Filter”.
4) Move your eyes up from this filter toward the back of the radio.
Just before you get to the “D 108” marking, you will see two tiny diodes, two blank spaces, and one additional diode. They look
something like this:
[XX] [XX] [ ] [ ] [XX]
Remove this diode ^^^^
5) The second diode from the left needs to be removed. I did this by crushing it with long-nosed pliers. You can also heat it with a
low-wattage soldering iron and pull it up with tweezers. Be sure not to damage the other diodes or the PCB. Be sure that you don’t
apply too much heat, since the heat can damage the PCB and the other diodes.
6) Re-assemble the radio. Reset the CPU by pressing and holding down the UP and DOWN buttons on the front panel and pressing POWER.
Improved VHF recieve mod:
154-200 MHz RANGE
To open up the 154-200 range,cut the yellow wire on the plug labled “j-4” on the right side of the radio on the bottom,the book points to this connector.
I did this and it opened up the rx between 154-200 mhz.
(It was printed in CQ VHF a couple of months ago.)
For those who like to scan VHF Hi-band, there is a mod that restores sensitivity, but at the cost of reduced sensitivity below 120 MHz.
This allows the filter to switch at the corner frequency (apparently around 129 MHz) as you tune.
PROCEED AT YOUR OWN RISK
There are no guarantees you won’t trash your radio.
Remove the radio top and bottom covers according to the manual.Remove the speaker. Now with the radio facing you and right side up, you’ll see a single connector with discrete wires at the rear of the control board. The fourth wire from your left should be a yellow wire (caution, the 5th and 6th wires on the other end of the connector are yellow too, don’t get confused).
Disconnect this wire from the connector. This will enable the 2 meter band-pass filter to work outside the 2 meter band, and will restore sensitivity between about 130 MHz and about 165 MHz (above and below that range, sensitivity still stinks, especially above 165 MHz). Before this mod, a low pass filter with a corner frequency around 129 MHz was in the circuit all the time except when you were actually tuning inside the 2 meter band, and that killed high band sensitivity completely. Before removing the yellow wire, sensitivity at 155 MHz was 30 uV for an S1 indication,after the yellow wire is removed, sensitivity increases so that only 0.5 uV is required for a S1 reading. At 165 MHz after the mod,sensitivity is 3 uV for an S1 reading, before the mod, a very large signal was required for an indication.
Disconnecting the yellow wire has the unfortunate side effect of reducing sensitivity between 60 and 129 MHz since the radio never switches from the 2m bandpass filter to the low pass filter. Signals below 60 MHz don’t go through either filter and are unaffected by the mod.
Now here’s how to get the low pass filter back when tuning below 129 MHz. On the bottom board, right behind the MENU button,
there are 5 SMD transistors. These transistors apparently switch the VCOs for the various band segments. The one in the middle of the 5 apparently switches the 60-129 MHz VCO. The single pin (one side of the SMD transistor has 2 pins the other only 1) switches to 5 volts when this VCO is active, and is low otherwise. This is exactly what we need to feed the yellow wire. There’s a board trace coming from this pin over to a feedthru hole near J8. Connect the yellow wire you disconnected earlier here.
The filter should now toggle between low pass and 2m bandpass as you tune below and above 129 MHz, and you should have good sensitivity both above and below this frequency (at least up through 165 MHz).
Remember, CAUTION WARNING This is tiny SMD stuff. If you trash your radio, you’re on your own.
As far as FM Broadcast intermod in the Aircraft band, I noticed the IF is a little overdriven into compression, so I turn the preamp off(greeen to no light—preamp switch), and noticed no difference in sensitivity, intermod in aircraft band disappeared.Running the preamp in the Aircraft 118-129 does not really help sensitivity, even though the S-meter shows higher signal levels (jumps around alot due to saturating IF when signals are not there!!! )
the noise floor actually, degrades, thus I leave the switch (no preamp-black instead of green). Leaving it on green is just driving the IF into saturation, with worst dynamic range.
Now connecting it to the VCO switch bank, the radio performs to my satifaction, hearing the weather at 162, forestry at 171, TV audio near 200Mhz and remembering to turn the preamp off in 118-129 aircraft region, no 2 meter images any more in 82-83Mhz area from 2 meters.
I can listen to FM broadcast in the 88-108Mhz area.
Q:Does this mod affect HF or 6m?
A:The mod affects only frequencies above 60 MHz. If you just cut or remove the yellow wire, the 2m bandpass filter is used all the time. After the mod you can listen to the airport on 134 MHz but 128.4 is still drowned in intermod from the FM BC band.
Proceed at your own risk
The receiver sensitivity above 120MHz (except the band between 144-148MHz) is very poor and also the transmitted FM deviation for NARROW FM is too small; therefore I did some tests and came to the following two modifications.
To carry out these modifications it is necessary to use the IC706 service manual, which can be bought at any ICOM dealer.
1. When choosing NARROW at FM, then during transmitting the max. deviation is reduced from 4.8kHz to 2.4kHz. It is still desirable to choose NARROW at FM because the receive performance is better then.
After changing resistor R272 from 1K to 8K2. (at the bottom side of the MAIN UNIT), then the max. deviation during transmitting goes from 4.8kHz to 4.3kHz when choosing NARROW at FM.
The modulation at AM is also changed now, but this can be corrected with potmeter R271.
2. To improve the receiver sensitivity between 120 – 144MHz and between 148 – 200MHz the following modifications can be carried out.
At the PA UNIT, change the 60 – 200MHz bandpass:
1) Remove C53(20p), C152(20p), C153(12p) and C154(20p).
2) Short-circuit L49(82nH) by soldering an interconnection at the place of the removed C153.
3) The inductance of L16, L17, L18 and L19 must be reduced somewhat.
This can be done by separating the windings somewhat with a small screwdriver.
Now the sensitivity is good up to about 175MHz. Also the sensitivity in the airband is much better now.
For receiving above 175MHz the low-pass filters at the ANT2 input have to be changed (components around L16, L17, L18, L19. I would not recommend that, because the spurious suppression during 2M transmitting becomes worse then!
To expand the band on the VHF portion.
(I have not tried this mod.I received this infomation via e-mail)
Caution: This is quite involved. If you are not too good you might be advised to get someone who has the experience to handle this mod!
1. Remove the main board from the unit. Keep the cutout hole away from you. This I consider the top of the board.
2. Remove the shield from the top of the board. There are 30-40 solder
points from the shield to the board.
3. Under the board on the top of the board, remove R-353 and Q-38. They are located to the left of the IC-36 chip on the top of the board under the shield.
4. On the underside of the board, Locate IC-32. There are two IC chips. IC-32 will be just down and to the right of the shield.
5. Using a pointer, point at the left upper pin, and go toward the top of the board. You will find a trace that stops. It comes out from under IC-31, and stops. It should be the sixth trace up from the top of the Chip.
6. Using a Xacto knife, (or something similar) Cut the trace the bend halfway between IC-31 and the solder point.
7. Make a jumper wire, and jump the connection, from Pin 11 of IC-32 to the newly isolated trace.
8. Reassemble the radio.
Transmit from 200 Hz to 200 MHZ continuous!!!
ICOM does not warranty these mods.
The mirror-image J-Pole is very easy to construct and requires only two T-Fittings plus a length of copper pipe.
To visualize the antenna, one must only picture a 3 half-wavelength vertical and a 2 quarter-wavelength vertical positioned a few inches away from and centered on the the tall vertical.
Construction of the mirror-image J-Pole is accomplished by starting with two T-Connectors separated by the distance shown for the band of choice. For two meters the space between the two vertical pipes should be 2 inches.
Two vertical pipes will point upwards and two vertical pipes will point downward from each T-Connector.
The tall vertical pipes are affixed to one T-Fitting and the short vertical pipes are affixed to the other T-Fitting. The tall vertical pipes are of the length shown as the Overall Length on the plans for the Copper Cactus. For 2-meters this distance is 58 inches to the centerline of the T-Fitting or an overall antenna length of 116 inches.
The short vertical pipes form the tuning stubs and are the length shown as the Stub Length on the plans for the Copper Cactus. For 2-meters this distance is 19-1/3 inches to the centerline of the T-Fitting or an overall stub-length of 38-3/4 inches. The nice thing about the mirrored-J is that mistakes in measurements up to 2 inches on the long vertical and 1/2 inch on the tuning stub, will not affect the performance or SWR of the antenna.
The mirrored-J is mounted on the end of 1-1/2 inch PVC pipe about 5 or 6 feet long. The PVC pipe is mounted horizontally from your tower or roof gable. The tall vertical pipe of the antenna is slid through a comperable size hole drilled into the side of the PVC at the end. A PVC T-Fitting may be sawn in half and used as a saddle to mount the antenna to vertical masts.
The antenna itself sits vertically. The coax is connected as per the instructions on the Copper Cactus plans to the upper vertical and tuning stub. On this particular antenna, the center conductor of the coax should go to the tall vertical and not to the tuning stub as in normal J-Pole construction. As always, keep the center conductor of the coax as short as possible, lengthening only the shield if necessary, using copper wire.
For Safety, the shield of the coax should be grounded to earth ground before entering your shack.
Article posted by KGØZP
How To Read Propagation Numbers
The A index [ LOW is GOOD ]
- 1 to 6 is BEST
- 7 to 9 is OK
- 11 or more is BAD
Represents the overall geomagnetic condition of the ionosphere (“Ap” if averaged from the Kp-Index) (an average of the eight 3-hour K-Indices) (‘A’ referring to amplitude) over a given 24 hour period, ranging (linearly) typically from 1-100 but theoretically up to 400.
A lower A-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Ap-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
SFI index [ HIGH is GOOD ]
- 70 NOT GOOD
- 80 GOOD
- 90 BETTER
- 100+ BEST
The measure of total radio emissions from the sun at 10.7cm (2800 MHz), on a scale of 60 (no sunspots) to 300, generally corresponding to the sunspot level, but being too low in energy to cause ionization, not related to the ionization level of the Ionosphere.
Higher Solar Flux generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; Solar Flux rarely affects the 30, 40, 60, 80, & 160 Meter Bands.
K index [ LOW is GOOD ]
- 0 or 1 is BEST
- 2 is OK
- 3 or more is BAD
- 5 is VERY VERY BAD
The overall geomagnetic condition of the ionosphere (“Kp” if averaged over the planet) over the past 3 hours, measured by 13 magnetometers between 46 & 63 degrees of latitude, and ranging quasi-logarithmically from 0-9. Designed to detect solar particle radiation by its magnetic effect. A higher K-index generally means worse HF conditions.
A lower K-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Kp-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
Copyright VR2/KQ6XA and ARRL OES
Two 4CX1000A’s in grounded-screen push-pull – an amplifier that did not work.
Describing this amplifier may seem a really silly thing to do, as it never worked well. However, someone else might learn from our mistakes, or even perhaps someone can tell us why it did not work.
A friend Paul G8WYI and I were are a radio junk sale when we were offered a pair what appeared to be new Eimac 4CX1000A tubes. Paul bought them, and I set about designing a 2 m amplifier to use them. The first thing that became apparent was that the correct Eimac SK-800 series bases, with the screen decoupling capacitor, were very expensive. However, a design published in the 1991 ARRL handbook, A Legal-Limit 2-Metre Tetrode Amplifier, pages 31-57 to 31-72, using a single 4CX1000A had avoided the need for such a base. The authors, K1JX and W1VD, had used a SK-800 series base with a damaged screen decoupling capacitor and grounded the screen for both RF and DC. They claimed that this avoided the need for the decoupling capacitor in the base and instead meant a cathode decoupling capacitor was needed. However, they argued that any reactance in this cathode decoupling capacitor would not make the amplifier unstable, but would act as negative feedback, and increase drive power.
We did not have any base, but I decided making one was not too difficult, having access to a good mechanical workshop at university. A picture of the SK-800 base appeared in an Eimac publication, so making one seemed easy. In fact, making a base was a lot of work, and with hindsight is not something I would try again, but I did make a pair of bases that grounded the screens.
The data sheet for the 4CX1000A gives the following as typical operating conditions.
Anode voltage 3000 V
Screen voltage 325 V
Grid voltage -60 V
Cathode voltage 0 V (cathode grounded for DC+RF)
Output power 1630 W
Zero signal anode current 250 mA
We proposed to run like this
Anode voltage 2675 V
Screen voltage 0 V (screen grounded for DC+RF)
Cathode voltage -325 V
Grid voltage -385 V
Note that voltage differences between our proposed design and the recommended ones are the same. We have 385-325=60 V between grid and cathode, 2675+325 = 3000 between anode and cathode etc. We aimed to return the negative of the HT supply to the cathode and not the ground. Hence a 3000 V HT supply was needed, but the +V would be at +2675 V wrt ground and the -V at -325 V wrt ground.
With the DC sorted out, the next step was to design the RF deck. Having had a lot of success with a well known twin 4X250B amplifier , I decided to base the twin 4CX1000A on this. The grids had two lengths of 6.3 mm (1/4″) pipe, inductively coupled to the input with a loop and a series capacitor. The anode line was in the shape of the letter U. with the tubes at each end of the U and the DC fed into the middle via an RF choke.
The amplifier was switched on and the DC operating conditions seemed okay. The zero signal anode current was close to the 500 mA expected (2 x 250 mA). It could be adjusted to be exactly 250 mA each tube, by taking the grid voltage very negative on one tube at a time to cut it off. It was clear the DC conditions were fine. It was also clear that the amplifier was stable no matter how we neutralised it – something necessary to get 100% right on the W1SL design, otherwise it took off and took the HV fuses with it. Our twin 4CX1000A amplifier was remarkably stable. So far so good !
Application of RF.
When RF was applied, the amplifier did a job of amplifying. In fact, with less than a Watt of drive, several hundred watts came out. However, it was soon apparent was that the amplifier started to draw grid current very early – by a couple of hundred Watts out, the amplifier was drawing grid current. By the time the output was up to 700 W, our grid current meters were at full scale ( 1 mA). I think we eventually ran up to about 800 W out, when the grids were taking a couple of mA each. Clearly the amplifier was non-linear and we were likely to destroy the grids of the tubes if we pushed it any harder.
The grid dissipation rating of the 4CX1000A is 0 W !!!
Despite a lot of effort, a lot of asking around, the amplifier still amplifies, but has never been used in a QSO, as we know it would be non-linear. Why it draws grid current so early is not known to us. We have thought the problem was one of incorrect loading, but have tried various methods of coupling the RF out from the amplifier with no success. No matter what we try, the positive grid current problem will not go away. If you have any comments on this, we would like to hear from you. by email at firstname.lastname@example.org G8WRB is now making a conventional cathode driven YC156/3CX5000A7 amplifier and hopes he has less problems than this design that was unusual to say the least.
I wanted to make my own cable to program my Kenwood TH-G71A ham radio with a PC, but the owner’s manual simply did not show the pinout needed for the connector plugs. I searched the web but was not able to find this information but I did discover that several other radios used an RS-232-to-logic (0-3.3V) level-shifter and a Full-duplex serial connection (separate RXD / TXD), and found schematics for such interfaces for other radios. I also found a device called the “MAK interface” which claimed to work with the TH-G71A, and the web site listed an interface cable.
With these clues, and after studing the signals coming out of the radio (and lots of debug time …), I finally figured out the plug connections at the radio end.
I was able to use basically the same interface schematic that was claimed to work for the Kenwood PG-4S cable (which is used for the TM-G707 / TM-V7 radios instead of the Kenwood TH-G71).
Refer to http://home.attbi.com/~kc7zru/pg4s.html for the schematic for the PG-4S interface:
The DB-9 connector to the PC is the same, but the connector on radio side is different. (Instead of the 6-pin mini-DIN connector, use the 2.5mm and 3.5mm phono plugs for the TH-G71)
Refer to Drawing at the URL above (Tate Belden’s site), right hand side, starting at the top:
1. Ignore the tie between pins 4 and 5 of the mini-DIN connector. (There is no such tie on the TH-G71 Cable)
2. The interface’s “TXD” goes to Ring of 2.5mm plug. (cathode of the diode on the interface)
3. The interface’s “RxD” goes to the Shield of 3.5mm plug. (collector of NPN on interface)
4. GND goes to shield of the 2.5mm plug.
5. The tips of both plugs are No-connect.
Note: If you have an interface that already works on another radio such as the Kenwood TM-G707 / TM-V7, then you may not need to make these changes!
1. Change R1 from 150ohm to 1K ohm (this is the resistor feeding the zener diode). I found that 150ohms loaded the line too much and the resulting voltage was too low to power the interface from the Serial port. If you have problems, be sure that the cathode of the Zener is at about 4.9V. I found that the interface worked down to about 3.2V when I just powered this from a variable power supply instead of through the PC serial port (after removing R1 and the zener and just applying voltage at C1)
2. add a 150K ohm resistor between the Radio TXD to gnd. I did this just to keep the voltage down on the TxD pin because the radio seems to be 3.3V I/O pin (not 5V)
Update: Dec 2001: The Kenwood manual for the newer TH-F6 radio shows the pinout for the Plugs (page 46). Through Dec 17, 2001, this web page showed the Ring and Shield of the 3.5mm plug both shorted together, but I have updated the plug pinout to match the Kenwood documentation, and I confirmed that it does work as shown, without the connection to the ring.
I was able to find a 90-degree “elbow” shaped, 2.5mm stereo plug at Radio Shack (p/n 274-298).
Using the interface / software
1. For TH-G71: Menu 15, TC ON
Transceiver Control must be enabled, or else you will get a communication timeout error when trying to communicate with the radio after connecting the cable up to your PC. “TC ON” enables the plugs on the side to work as data lines instead of as external mic/speaker.
Press the “F” button, and then Band, turn the main tuning
knob to Menu 15 Transceiver Control and turn it ON for
Programming. You will need to use a free com port (Com 1 or 2) on the PC.
Note: For the TH-F6 radio, the Kenwood manual states: Access Menu No. 9 and select “PC”
2. Kenwood Programming software
Download the PC Programming s/w from Kenwood FTP site ftp://ftp.kenwood.net or web page http://www.kenwood.net/amateur -> downloads -> software -> THG71A
You should see the files mg71200.exe and readme.txt .
Install the software and Run mcp-g71.exe. go to file menu, and be sure your com port is set correctly, then turn on radio, and plug in, and do “Radio-> Read”. Try it a few times — I found that it sometimes said something like “Communication timeout” the first time I tried after connecting up the interface.
Debugging problems with the interface
1. Be sure you have done everything listed under “Use”. If you are really stuck, you can try these checks:
2. Verify power + side:
1. With the interface connected to the pc, connect a meter to node 1 (cathode of the Zener) and ground.
2. In the MCP program, do radio->read (you should see “reading data from radio”) As it is “trying” to read the radio, quickly check the voltage.
3. The voltage should be about 4-5 Volts. This is needed to power the interface from the serial port. Note: The voltage at the RTS and CTS pins of the DB-9 connector will NEGATIVE when the Com port is inactive (when you are not trying to read or write to the radio with the software). But the voltage will go POSITIVE (about 9V on my PC) when the Com port is active.
Condition RTS/CTS Voltage
Com port idle, not reading/writing radio about -6 to -12V
Com port active, reading/writing radio about +6 to +12V
4. If you don’t have good power here, something is wrong. (This is why I increased R1 resistance from the original schematic – as the original lower value loaded my serial port down too much due to the diode at node 1).
You can power the interface externally: Remove the rts/cts connections from the PC and just power node 1 with a battery or external power supply. This was the main problem I had getting my interface working (besides trying to figure out the pinouts of kenwood jacks).
3. Verify power negative (-) side:
1. With the interface connected to the pc, connect a meter to node 7 (negative terminal of the Cap C2)
2. In the MCP program, do radio->read (you should see “reading data from radio” As it is “trying” to read the radio, quickly check the voltage.
3. The voltage should be negative (more negative than about -5 or -6V) This is needed to generate a negative voltage back to the PC RxD.
4. If this power is good in the previous steps, but the interface still does not work, recheck the interface to make sure everything is wired up correctly including all ground connections, and the pinouts the serial port DB connector. Check all part values and that the polarity of caps is correct, and that NPN and PNP transistor are wired up the correct way.
5. If that does not find any problems, I would then test the interface to be sure it does the correct level-shifting and “inversion” of the levels from the PC (RS-232) to lower-voltage for the Radio. This can be a bit tricky and you need some power supplies and clips to do this, with the interface disconnected from the PC and the Radio. Basically, you want to verify the following:
1. With TXD (out from the radio) = 0V, the RxD to PC should be about 5V
2. With TXD (out from the radio) = 3-5V, the RxD to PC should be between -5V to -12V.
3. With TXD (out from the PC) between -5V to -12V, the RxD to the Radio should be “floating” (Q2 off) (and the weak pullup in radio pulls the node to a logic “high” value)
4. With TXD (out of the PC) > 5V or so, the RxD to Radio should be 0V (Q2 is “on”).
But the catch is that the interface generates the -12V (or so) by the switching on TXD. So you need to fake it out to be sure you have this voltage (which should be there in step 3c) because you don’t have the interface connected to the PC anymore. Otherwise, you won’t get the negative voltage in step 5B.
Programming the TH-G71
See this page for information used to program and control the TH-G71 through a serial port. Serial Port command protocol is provided. This is useful if you are interested in how Kenwood’s MCP memory control program works, or if you are interested in programming the radio using a PC.
Chris Koza email@example.com
Home-made antennas can greatly improve the performance of AM and FM radios, short-wave receivers, and scanners. If you are a talk-radio fan then experiment with the AM band antennas and you will be able to hear shows from all over the country with surprising clarity. Short-wave receivers are always coping with weak signals and they must have a good antenna to perform adequately. Scanners can pick up local police and two-way radio with the little telescoping antenna provided but with good antennas a scanner becomes an amazing ear on the world nearby. No pre-amp, filter or other receiver refinement offers anywhere near the level of performance improvemen t that a well-designed antenna offers. The results can be quite satisfying, leaving no doubt that the project was well worth the effort.
This PDF file contains several SWL antennas
There are many kinds of satellite antennas that will get you on the birds (some better than others) and allow you to have lots of fun. If you are new to amateur satellites, though, all the options may be confusing, or worse, a disincentive to try the birds. It’s really not that bad. I offer below some facts and some opinions about the state of the art today and I hope it helps you try some new things and have some fun. I have arranged the information in a progressive outline, allowing you to visualize a step-by-step methodology, gain some experience, and make incremental improvements each time you try something new.
Hearing the Birds:
Often, the first challenge is just to hear the satellites. The easiest thing to try first is an HT with 70 cm capability and a “gain” antenna. HT antennas 500-900 mm long (often collapsible) were very effective for UO-14 and SO-35, but are a little weak for AO-27 and SO-50. If you have a mobile dual-band FM radio, try a ¼ wavelength 2 m antenna on 70 cm. These antennas are 3/4 wavelength at 70 cm and offer considerable gain above 30 degrees elevation (deaf below that).
If you want to hear a little better, try a small 70 cm beam. I have plans here for a little 3-element Handi-Tenna. The very popular Arrow Antenna is a convenient and very effective portable antenna. Cushcraft makes a 3+3 dual-band beam with a built-in duplexer, suitable for both portable or fixed station use. All of these antennas are “linearly polarized.” For a great discussion on linear v. circular polarization, see The Amateur Satellite Handbook, by Martin Davidorff, K2UBC (available from both ARRL and AMSAT). Small quads, quagi’s, and helix’s are also workable at 70 cm, but a little more awkward to handle.
Working The “Easy Sats”:
Of course, “easy” is a relative term. See the AMSAT web site for some general introductory articles. The next step for a home station might be to try a simple, omnidirectional circularly polarized antenna. The most common of these is the M2 eggbeater. You can also build a popular version of this antenna, but I have found them to be ineffective at low elevation passes (most passes are below 45 degrees 90 percent of the time). An improved version of this classic design, the Eggbeater II, will give pretty fair results from horizon to horizon, especially if combined with a preamp. The basic Eggbeater II design is fixed right-hand circularly polarized (RHCP), leaving it susceptible to the “fades” common in satellite downlinks (you will not hear 100 % of the pass), but is still an effective, simple antenna–and MUCH better than the “classic” eggbeater. Other antennas in this class are the turnstile, the quadrifilar helix array (QHA), and the Lindenblad.
The next step up is to buy or build a higher gain antenna and rotate it to match the satellite’s position (azimuth). Gain in the 6-7 dBi range, corresponding to a 60 degree beamwidth, is about the maximum that can be utilized without needing elevation control. Unfortunately, there are no commercially available circularly polarized antennas available in this size/gain range. If you don’t mind building somethng from scratch, I recommend the TPM II antenna as a perfect solution for working all the LEO’s. The TPM II antenna does not require an elevation rotor or even accurate pointing (you can do it manually with no trouble). A crafty and inexpensive automatic azimuth rotor system can be easily constructed using WB4APR’s design. I built my TPM II with coaxial relays to switch the circular polarity, allowing me to optimize both downlink and uplink. I can hear and work ALL the LEOs from horizon to horizon using this simple to build antenna and a manual TV-type rotator: I have literally thousands of contacts and have Worked All Continents, WAS, and VUCC with this antenna..
Working AO-10 (not heard since March 2002):
You can work AO-10 with any of the antennas described above when it is near perigee (less than 10,000 km or so with an omni antenna). To work it further out, though, requires considerably more gain. A typical “OSCAR class” station uses 100 Watts on 70 cm for the uplink into a 40 element antenna (20 x 20) and a 22 element (11 x 11) downlink antenna (with mast-mounted preamp). Both antennas are circularly polarized and usually switchable. The most common models here in the US are KLM, Hy-Gain, and M2, but many people also use large linear antennas (or arrays of linear antennas). These antennas require both azimuth and elevation control, most often from a Yaesu or Kenpro rotator. The narrow beamwidth of these antennas also requires precise pointing, making computer control of the rotator almost mandatory: popular devices include FODTrack, Kansas City Tracker, Uni-Trac, and others. This setup is the standard of excellence in satellite antennas today.
Working AO-40 (not heard since December 2003):
AO-40 operation is pretty attractive: a high-altitude orbit that repeats every 4 days, lots of DX, and lots of interesting and educational technical challenges. Mode U/S was the most popular combination, but L/S was favored by many of the operators. Smaller UHF ground station antennas than those used for AO-10 can be used: many use 70 cm uplink antennas in the 10 dBi range. Most any Yagi-Uda beam in the 4-6 element range will work. For L-band, 23 cm, antennas in the 20 dBi range are required if you only have a 10 W rig. Many L-band ops use amplifiers with 40 or more Watts (for BIG! signals). Many operators are taking a wait-and-see approach to AO-40, but if you want to put something up now, you will probably want to consider a small parabolic dish for S-band, 13 cm, as a starter system. For about $200 you can get a 3′ BBQ dish and a low noise MMDS downconverter modified for 2 m. The microwave bands lend themselves to experimentation, so expect to see lots of new and interesting antenna designs published. Almost all of the future satellites have some plans for mode U/S or L/S.
Article by K5OE originally available a http://members.aol.com/k5oe/new_ant_intro.htm