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Single-Side-Band Techniques at Microwave Bands, Chapter 9
@ OK1AIY
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3400 MHz (9 cm) Band
This band was officially released for radio-amateur use by 19 July, 2000
Once upon a time , the 9-cm band was included in band list. The first QSO in Czechoslovakia was made by 25 June 1955, in Brno, between OK2KBA and OK2KBR club stations. (Probably also the first in Europe. In the USA, W6IMZ and W6IFE/p made a QSO there over 32.5 km distance in 1947). Equipment designers, J.Janata and B.Pravda have described their work in AR (amateur radio magazine) , 8/1955, and it is presented also in OK2KKW web page.:

One of usable vacuum tubes in the 1950's was 2C40 lighthouse triode (RCA). It was later manufactured by various firms, like EC560 (DDR), 6C5D (USSR). It was used in many VHF transmitters and receivers (Fig.319). An example of a professional preamplifier (Fig.320) in an often mentioned RVG 958 communication system by RAFENA Radeberg (DDR) which was only in 1980's replaced by an updated system.
The frequency band from 2 to 8 Ghz is preferred for communication as there are no weather effects like at higher frequencies. In the earlier times also the circuit technology offered an easier manufacture. In this band also television and other radio links operated: due to this fact the 9-cm and 6-cm bands were not available for radio amateurs. In 1999 there was a rumor of a possible opening, so radio amateurs were urged to make an usable equipment. In that time there were experiments at 145 Ghz, and at 24 Ghz, a third generation of transverters was available. New components were available to update older designs. A sub-harmonic mixer by DB6NT for 24 Ghz offered good features, and could be adopted for the 9-cm band. It was reliable to transmit and receive, required no antenna relay, and using the 2nd harmonic LO gave it a priority in design. Antenna radiator could be connected to the mixer directly or by a connector, and the complete transverter could be mounted in parabolic dish focus. For simplicity no RF filter was used, so the power of about 0.5 mW was split into the sum and difference mixer products. The transverter only needed a 12 VDC power line, and a coaxial cable to IF transceiver. Fig.321 shows the block diagram, and the transverter made by OK1UFL is shown in Figs. 322 and 323. Table 3 presents the bandwidth assignment. Such table was not made by 1999, so the first test QSO from Benecko to Klínovec was made at 3456 MHz. A new improved design followed at 3400 MHz, ready for the coming season of 2000.

Table 3 Frequency assignments of 3400 MHz band:

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Fig. 319 EC560 and 6C5D lighthouse tubes:

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Fig. 320 Preamplifier of RVG 958 receiver (DDR). In operation it was tuned by an electric motor:

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Fig.321 A schematic diagram of the sub-harmonic mixer with antenna radiator for 9-cm band:

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Fig.322 9-cm band sub-harmonic mixer with antenna radiator, component side:

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Fig.323 9cm band sub-harmonic mixer with antenna radiator, PCB side:

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Other transverter designs for 3400 MHz band (9 cm)
The new transverter design used amplifiers in receiver as well as in transmitter. I the magazines we could find designs for 6-cm and 3-cm bands but the design by DC0DA was so simple and well working due to using a sub-harmonic mixer in RX and TX that we liked it best. New transverters can be seen in Figs. 324 and 325. Fig.326 shows an antenna feeder made of a cacao tin can as its size was fitting well, and can be attached to the existing antenna radiator for 6 cm. The carrier arm is movable, allowing to push the corresponding feeder into focal point. It was a right provisional solution and stayed in service for 20 years...
The next experimental QSO was made again during some VHF contest , from Klínovec to Benecko. Improved design brought nice results. We also made a QSO with DB6NT but I have now to apologize to the state institutions for doing so as the band was then not yet authorized for us to use. We even took the transverter to the Field Day 2000 in a hope the band would be made available by that time. But it was only done by July 19th, and we did not know we could have a special permission. Another improvement was the use of a 1.7 m parabolic dish from MT-11 TESLA radio link. It was built in 1962, experts did not like it but it was a welcome boost for tropo or RS operations. To the original „bent pipe“ waveguide radiator we attached radiators for 9 and 6 cm. Using the positioning knob we could adjust the elevation angle by up to +/- 6 degrees and put the right radiator into the focal point. In most cases it was not needed and a QSO was made quite fast with no fine pointing.
In 2001 the setup of Fig. 327 was installed at Benecko. Conditions for tropo have worsened so we failed to be adding more countries to our log. Fig.328 presents a QSO from PA5DD for the first one with the Netherlands. His pages are famous on the Internet. Fig.329 shows a QSL card from OK1UFL for the first QSO OK-SP at 9-cm band. The 9-cm band was allowed for Austrian amateurs much later (Fig.330).

Fig.324 9-cm transverter, 2nd generation, by OK1AIY, 2000:

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Fig.325 9-cm transverter, 2nd generation, OK1UFL:

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Fig. 326 9-cm and 6-cm antenna radiators on a movable arm in the focus of a 75 cm dish:

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Fig.327 170-cm laminated dish for 3,6 and 9-cm bands, on a tripod in Benecko, winter 2001:

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Fig. 328 A QSL card for the first OK-PA QSO at 9 cm:

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Fig.329 A QSL card for the first OK-SP QSO:

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Fig.330 A QSL card for the first OK-OE QSO at 9 cm. The reverse side shows the date of 1/9 2015, output power 22W, 3-meter dish:

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More designs of 9-cm band transverters and beacons
During the last 20 years the designers have made many functioning types of equipment, also beacons , for the successful work at 9-cm band. Like in other microwave bands the effort was great, so let us remind us of some of the designs. Like always, Milan OK1JHM was one of the first: Figs.331 and 332 show his transverter. It is the third in his setup for 23-cm thru 3-cm bands, with one parabolic dish and a combined feeder ( PE-AR 7/2015, third envelope picture.) Another well-designed transverter for 9-cm band is by Mirek, OK1DGI. His perfect design is shown in Figs. 333 and 334, the complete systém is to be mounted on a pole, of OK1KKD radio club.
During the mentioned era we could procure surplus (or brand new) professional power amplifiers capable of units or tens of Watts of power. Various types required 12VDC, 18 VDC, 28 VDC (some also -12VDC). They were controlled by a positive voltage, 3...12V, or by grounding the control pin. The output has an isolator, and the „monitor“ output allows the user to indicate the output power. They require an input power of 1 mW (0dBm), some even less. Some amplifiers operate in A class, other in B class, so a corresponding cooler is needed. Such amplifier in a transverter also uses Petr, OK2STV, see Fig.335. Similar amplifiers also operate in beacons. Fig.336 shows a 9-cm beacon built by Petr OK2ULQ for OK0ER beacon. A similar exciter is used in OK0EL beacon (Figs. 338, 339). As this one was made first, it has no power amplifier. In these beacons an output filter must be used. Professional power amplifiers use isolators as filters which prevent stray signals from getting into the PA (e.g. From VHF FM radio transmitters). The stray signals can get mixed and reradiated (at microwatt level), and cause interference to many other communication systems.

Fig.331 Transverter by OK1JHM, 1st generation, 9-cm band (3400 MHz):

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Fig.332 The same transverter by OK1JHM, bottom view on the block:

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Fig.333 9-cm band transverter by OK1DGI, component side view:

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Fig.334 9-cm band transverter by OK1DGI, filter-side view:

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Fig.335 9-cm band tranverter by Petr, OK2STV: Amplifier from Stealth Co., SM34-37-43L:

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Fig.336 OK0ER, new beacon in 9-cm band, by Petr OK2ULQ:

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Fig.337 OK0EA beacon in 9-cm band, with the power amplifier and a power supply, top view:

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Fig.338 Exciter for OK0EA and OK0EL beacons on a DF6VB board:

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Fig. 339 An inside view of OK0EA and OK0EL beacons on a modified DF6VB board:

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HR3A Design
Creators of microwave equipment often welcome a chance to use some part of a former „professional product“, or use a complete equipment with modifications. Sometimes a chance happens, and allows to design a functional systém with less money. Such chance happened with AIRSPAN AS4000 from UK which has served till 1990s in various regional data networks.
The B Plus TV a.s. Company in Klimkovice has modified such equipment from an infinished project for use by radio amateurs. Fig.340 shows a design concept of a microwave radio link. Manufacture of ten transverters was made by Milan, OK2MMO. Testing of the prototype and beta-versions was done by Olda, OK2ER, and Jarda, OK2VLT. (Olda OK2ER even temporarily abandoned his SW activities to which he returned by his Magnetic Loop Antennas). A kit of HR3A was introduced to the market with a complete list of modifications by B Plus TV company.
A non-commercial promotion of HR3A transverter in radio-amateur community has been undertaken by OK1VM with OK1EM who took part in activation process for SHF enthusiasts (Fig.341) . The redesigned equipment had a flat antenna on its front panel, and was a compact unit suitable for mounting on a pole. (Fig.342). Its sensitivity and stability was excellent. Its ouput power, 100 mW, was not too much from the actual point of view, but it allowed to make nice QSOs. A good improvement was locating the HR3A into a parabolic dish, best in an offset version (Figs. 343,344). A correct focal position must be set by trial and error as shown in Fig.345, by OK1VM and OK1EM. A ten- dB antenna gain in the empty 3.4 Ghz band was a welcome boost. This simple boost to the output power and noise figure was first tested by OK2MMO and OK2ER. Olda OK2ER has successfully used this type of transverter during his temporary SHF contest activity,( Figs. 346,347,348).

Fig. 340 A complete transceiver on one board:

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Fig. 341 Practice testing outdoors, OK1EM, OK1VM, Cínovec 2009:

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Fig.342 A view on HR3A from the pole mount side:

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Fig.343 Mounting of HR3A in a parabolic dish:

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Fig.344 HR3A holder allowing to set a correct position, by OK1VM :

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Fig.346 Olda OK2ER during a UHF/SHF contest:

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Fig.347 Testing a HR3A mounted on a caravan roof:

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More on HR3A and the first EME QSO at 9 cm
Any redesign of a professional equipment for radio-amateur use is always a hard work. Whoever enters the process should be admired. The basic idea is to reuse a device which was discarded, and the successful were Milan, OK2MMO, and Jarda, OK1VLT, Figs. 348, 349. Similar links redesigned for 9-cm band were operated in the past. Over time they were replaced with others with a higher data rates, and they became a surplus in a short time. Updated systems were more difficult to redesign as the components were smaller and PCB design more demanding. Among radio hams the newer PCBs were called „ a crude sand paper“, and of all discarded parts, the most valued was the aluminum case with cooling fins...
The idea to design and manufacture the complete transverter at home by one's own hands was generally abandoned, and many ended up with an order to DB6NT.. then the thing can only be assembled. This is usually the best procedure not only for „tropo“ systems, but for EME designs where there are many components not available on the market, and must be manufactured at home. The EME operations at 9 cm started by Franta, OK1CA, when there was a lack of experience.

Franta, OK1CA, writes about it:
When the 3.4 Ghz band was awarded to the amateur service in OK, I started thinking about EME. By then only few stations were active, and mostly those from the U.S. Operated at 3456 MHz which was not allowed to use in OK. In 2002 I arranged the first tests with W5LUA as cross-band : I transmitted at 3400 MHz and listened at 3456 MHz, W5LUA in reverse order. I used a TRX by DB6NT, 3400 /145 MHz with an external OCXO, and modified it so it could receive at 3456 MHz with an IF of 201 MHz. To transmit I used TRX FT-736R, to receive, AR 3000 Rx at 201 MHz. My final RF amplifier had 15 W output power, the LNA was with ATF36077, the antenna was a 3-meter dish with a linear feed. The first QSO happened by 13 June 2002, I listened to W5LUA 559, I received 549. This was the first EME QSO in OK at 3.4 Ghz, and the terrestrial distance of 8580 km was the world record at this band. In the following years the EME operation frequency moved to 3400 MHz worldwide, and circular polarization was adopted.
Individual parts of the equipment are shows in Figs. 350...353.

Fig. 348 Milan OK2MMO, testing HR3A transverter with the new OK0EI beacon at 3.4 GHz:

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Fig.349 Jarda OK2VLT, mounting antenna system on Praděd:

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Fig.350 9-cm band transverter by OK1CA for EME, with the antenna radiator:

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Fig.351 Block diagram of OK1CA transverter for EME, transmitting at 3400 MHz and receiving at 3456 MHz:

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Fig.352 One of EME antennas at OK1CA for 9-cm band:

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Fig.353 Franta OK1CA, with EME antenna, 10-meter dish :

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Fig.354 OK1 CA in his ham-shack:

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EME activity at 9 cm, Equipment at OK1KKD
The transverter for EME at OK1CA, shown in Fig.350 in PE-AR 4/2020, is by size comparable with designs for „terrestrial operations“. Installed in an aluminum enclosure which is weatherproof, and functions also as a cooler for the PA stage.
Next Fig. 355 shows the equipment by Zdeněk, OK1DFC. Its design is clever, one side is mounted on hinges and allows to flip it out. It makes maintenance , testing or modification easy, and there is still a lot of room for hands and needed tools . It can be operated in an „open“ state, the side can be closed when needed. The hinge design is not new, it was used in complex systems like by OK2JI, and also in the transverter for 70, 23 and 13 cm bands from 1980, also described on our website. Following pictures show individual parts of the EME systém at OK1KKD and careful designs of Mirek, OK1DGL, is seen in every detail (Fig.356). The transmitter and receiver are the last phase, though. All starts and ends with a suitable antenna: here we have a 4.5 meter dia.dish, with a massive mount. Originally it was used at the ČHMU, Czech meterology station, at 1500 MHz approx, and sat on the roof of the Institute in Prague-Libuš. Kladno radio club members organized its transfer by themselves.

Mirek, OK1DGL, wrote about it:
To use the antenna on the lot of Petr, OK1FAQ, its support had to be extended to make sure there were no obstacles for operation and the horizon was clean. (Fig.357). One of the Kladno team was a former employee of Poldi metal works, so he knew a lot about heavy machinery. Also electrical modifications were needed. Original drive equipment was broken, so a new drive systém had to be manufactured. DC motors with permanent magnets are used, with electromagnetic brakes, and need 28 V/90A DC. This explains the battery of high-power FETs on the copper plate in the new drive control box, Fig.358.

A lot of work was needed for the full team, to fasten antenna into a heavy base, and to avoid any damage or destruction by a strong wind. (Fig.359). Even with the mesh paraboloid design, a strong wind pushes it like it were full metal. Thanks to a detailed documentation with pictures, a reader can see what is hidden under ground, Figs 360...362. The system is complete with a shack house shown in Fig.363. The operations room will be shown next. The OK1KKD team plans to add another dish for frequency bands above 3400 MHz. Its size will be smaller but it will have a fine drive, with a zero sliding in the gears. And another shack house will be next to it...

Fig.355 Transverter for EME operation at 9 cm:

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Fig.356 Phasing device for two PAs, for EME at 3400 MHz, by OK1DGI:

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Fig.357 Base for this large dish must be massive:

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Fig.358 Drive for dish positioning: power supply is in a separate location :

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Fig.359 Antenna mount for 4.5 meter dish required a clever design:

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Fig.360 Frame for antenna base:

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Fig.361 Base frame on bottom of the dug cavity :

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Fig.362 Base frame filled with concrete panels:

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Fig.363 EME operation center of OK1KKD at Petr's place, OK1FAQ, Malé Přítočno near Kladno:

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EME Operation in 9-cm band, equipment b OK1KKD and OK1KIR
In the last issue of PE-AR 05/2020 there are some pictures of the massive antenna base of OK1KKD. Its size can be seen in comparison to the builder, Petr, OK1FAQ, see Fig. 365. Fig.366 shows a neatly equipped ham-shack in the house. All that was needed to obtain successful results for TROPO and EME work.
The full view of the 9-cm feed with the transverter in a weatherproof case located in dish focus can be seen in Fig.367. Switching bands is done by swapping transverters. This is done by using the platform with a protective railing, Fig. 368. The dish is parked to facilitate access and transverter swapping. With smaller parabolic dishes located low above ground this action is easy, but with high-above-ground antennas one needs to use a ladder from which is easy to fall deep down. This happened not only once, and even with a tragic ending.
Such ladder can be seen in the picture of OK1KIR antenna systém presented in one past issues of PE-AR 06/2017, p.40. Here in Figs. 370,371, we can look directly into antenna focus to see OK1KIR transverter for 9-cm band. In the weatherproof case there are two coupled 45W amplifiers by Toshiba. Two 3-dB couplers were built, the output one can be seen in Fig.370. In the focus there is also the „septum“ radiator for the circular polarization, well seen in Fig.371. The LNA with the protection relay is located in a PVC box (Fig.372). The relay disconnects LNA input from antenna during transmission and is activated by a sequencer to switch after a delay. PA is cooled through openings in the case: this is why the PA is mounted slant inside to avoid rain water to enter under any elevation angle possible during EME. (Fig.372).

Fig.364 OK7FA – OK1FAQ in a contest:

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Fig. 365 Petr, OK1FAQ, a short relief from a hard work:

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Fig.366 Operator's place in the house:

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Fig.367 9-cm band transverter from the workshop of Mirek, OK1DGI, and Petr, OK1FAQ, in an enclosure at parabolic dish focus:

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Fig.368 Platform for an access to transverter:

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Fig.369 New house for OK1KKD EME operations. The new antenna to be assembled:

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Fig.370 OK1KIR: before fans we can see a coupler for two 45W amplifiers :

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Fig.371 EME: OK1KIR, a view on the radiator in parabolic dish focus:

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Fig.372 A view on the PA stage at OK1KIR. In the PVC box we can see the low-noise amplifier with the protection relay switch:

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EME at 9 cm – a peek into Poland
he described microwave technology has been pursued by a number of stations in the Czech Republic as well as at our Polish neighbors in SP6. What is needed is the equipment as well as a suitable outdoor location where the demanding designs can be realized, and also skill and patience. Fig. 373 presents the equipment of Staszek, SP6GWB, in a cramped „construction unit“ on Černa Gora, from which he runs nice QSOs by tropo on all bands from 2m through 76 Ghz. In his home QTH at Klodzko he is building his EME equipment: Fig. 374 shows a power amplifier utilizing two coupled 100W amplifiers for 9-cm band, in Fig.375 we can see his transverter on a mount.
Quite a gargantuan operation workshop we saw of the club station „Klodzka grupa EME“, or the EME group of Klodzko (a district in Poland). There was a report about them in PE-AR devoted to the radio-amateur meeting (Zieleniec 15-17 August 2014). Their development coninues, see their website :

Fig.376 shows the parabolic antenna of 6.5 meter dia., and Andrzej SP6JLW can be seen mounting the transverter in focus using the platform (this platform has no railing, thus requires him to be very careful). The power section of the transverter for 9-cm band can be seen in Fig. 377. Two coupled power amplifiers deliver some 100 W, using an exciter with some tens of milliwatts of power.
Block diagram of the above is shown in Fig.378. A side view shows more components, the box in Fig.379 in a circle is the oscillator using DF9LN design, made by OK1UFL. It is quite stable and can meet the demands of EME operation. Fig.380 shows the antenna feeder. A complete transverter in a weatherproof case at antenna focus is shown in Fig.381. The 9-cm band is quite practical as we observed after our first experiments : there was a mention about it in PE-AR 12/2019. Also professional users are highly interested. Let us hope that our government officials would push for at least a partial saving of this band for radio-amateur activities, and prevent it from falling into another WiFi one.

Fig. 373 9-cm band operation workshop of SP6GWB on Černa Gora, J080JG. Transverter on the left, power supply 3 x 5V, 40 A on the right:

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Fig.374 Coupling two power amplifiers at 9-cm band for EME:

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Fig.375 9-cm transverter by SP6GWB for EME, 2nd generation, with two Toshiba PA blocks:

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Fig.376 SP6GWB on a platform mounting the 9-cm band transverter:

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Fig.377 A view into the power section of the 9-cm transverter:

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Fig.378 Block diagram of EME transverter for 9-cm band, design by SP6OPN: 1. Septum radiator, 2. Kathrein coupler, 3. 3-dB hybrid coupler, 4. 90 W PA by DF1SR (BLF6G38-100) 5. Toshiba PA, 6. LNA by DG0VE, 7. LNA, 8. Transverter by DJ6EP., 9. Merrimac R attenuator, 50 W resistors:

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Fig. 379 A side view of the transverter, oscillator DF9LN by OK1UFL in a circle:

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Fig.380 Septum radiator for 9-cm band, a detailed view inside:

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Fig.381 Septum radiator installed in the focus :

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This paper was also published in print in Practical Eectronics magazine, with permissione (PE/AR Magazine – Practical Electronic and Amateur Radio, Czech amateur magazine, in Czech).


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