ED1ZAC - READ tech 26

G8MNY > TECH 13.03.24 09:45z 156 Lines 6968 Bytes #164 (0) @ WW BID : 3185_GB7CIP Read: GUEST Subj: 2M 65W PA with 2x M6774H Path: ED1ZAC<ED1ZAC<GB7CIP Sent: 240313/0930Z @:GB7CIP.#32.GBR.EURO #:3185 [Caterham Surrey GBR] $:3185_GB From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Updated Mar 23) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) My local club had a source of these Class C VHF PA blocks. The specification for them is a max of 500mW drive for 33W out on 12.5V, but the H type is 150-175MHz! So there usefulness on 2m was unknown, although some 2m kit was reported to use them. ÚÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ¿ Heatsink ³ ³ ³ ³ I tested one on a heatsink with just coax is ground³o³ M 6 7 7 4 H ³o³ connected & it produced 33W, so all looked good. ³ ³ ³ ³ ÀÄÁÂÄÂÄÄÄÄÄÂÄÄÄÂÁÄÙ DC1 powers the 1st low current stage, ³ ³ ³ ³ DC2 @ 8A Max for full output. in DC1 DC2 out A 1.5W handheld can do more drive than that, so I used 2 of them to make a 2m PA with a good power level out of junk bits. ÚÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ¿ A PCB (double sided) was cut ÞÛÝ ÞÛÝ to fit over the heat plate & ÞßÝ M 6 7 7 4 H ÞßÝ under the screws & connection ÞÛÝ ÞÛÝ wires, to provide connection ÞÛÝÂÄÂÄÄÄÄÄÂÄÄÄÂÞÛÝ pads, through links were put ÞÛÝÛ ÛÞÛÛÛÝÛÞÛÝÛÞÛÝ in to. An old 900MHz phone PA ÞÛÝß ßÞÛÛÛÝßÞÛÝßÞÛÝ casting was used as heatsink ÞÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÝ & case. 2 PA MATCHING PRINCIPLE Assuming the PA blocks are identical in power level, gains, & signal phases (time delay). Then there are a couple of ways to connect them, I have used the simplest using just coax. To match the 2 PA blocks to the 50ohm input & output, 4x 1/4 wave 75ohm coaxes are needed to make the connections. Each 75ohm 1/4 wave transforms the 50ohm to approx 100ohm & 2 of these paralleled up give 50ohm again. 50RÚÄÄÄÄÄ¿50R ÉÍÍÍÍÍÍÍÍÍÍÍÍµBLOCKÆÍÍÍÍÍÍÍÍÍÍÍÍ» º ¬ Wave 75R ÀÄÄÄÄÄÙ ¬ Wave 75R º 50R InÄ¶ ÇÄ50R Out º ¬ Wave 75R ÚÄÄÄÄÄ¿ ¬ Wave 75R º ÈÍÍÍÍÍÍÍÍÍÍÍÍµBLOCKÆÍÍÍÍÍÍÍÍÍÍÍÍ¼ 50RÀÄÄÄÄÄÙ50R I measured the velocity factor of a good length of the 75ohm coax (0.6 - 0.90 the speed of light depending on the type of coax) with an open circuit teed on a signal generator & scope/(Detector) & adjusted the frequency to give a null which was 22MHz for my length. This meant I needed 22/145 times this length to get the same @ 2m (46cm for my white foam filled coax). PA SCHEMATIC ÚÄÄÄÄÄÄ¿ ³RF PTTÃÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ Sense³ ³ ÚÄÄÄÄÄ¿ ³ ÀÄÄÄÄÄÂÙÚÄÄÁÄÄ¿ ÉÍÍÍÍÍµBLOCKÆÍÍÍÍÍ» ÚÄÄÁÄÄÄ¿ RIGÍÍÍÍÍÍÍÍÏÍµDRIVE³ º 75R ÀÄÄÄÄÄÙ 75R º ³OUTPUTÃ(o AERIAL 50ohm ³RELAYÃÄ¶ ÇÄ´RELAY ³ SO239 Coax ÀÄÄÒÄÄÙ º 75R ÚÄÄÄÄÄ¿ 75R º ÀÄÄÒÄÄÄÙ º ÈÍÍÍÍÍµBLOCKÆÍÍÍÍÍ¼ º º ÀÄÄÄÄÄÙ º ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ¼ 50ohm Rx coax CIRCUITS ÚÄÄÄÄ>To Handheld Rig 2x 1N4148 ÚÄ100RÄ¿ ³ ÚÄ´>ÃÄÄÂÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄ´<ÃÄÁÄÄÄÄÂÄÄÄÄo\oÄÄÄÁÂÄÄo-oÄÄ< +12V ³ === ³/e ===30n //TX 1K ON ³ 13A Car lighter * ÃÄ´<ÃÄÄÁÄÄÄ´PNP _³_ LED _³_ ³ ÚÄ< 0V 4pF³ 1n ³\ \_/=ON 12V _³_ === ÃÄÄÄÄÄÄÂÄÄÂÄ470RÂÄÄÄÄÄ¿ ³ LED to PA 1W>ÄÄÁ>Drive ÚÄÄÄÁÄÄ¿ ³u1³ ³ ÚÄÄÁÄÄ¿ _³_ Blocks Rig Relay ³Output³ === ³ +³ ³Drive³ Common ³Relay ³ ³ _³_ === ³Relay³5V ÀÄÄÄÂÄÄÙ12V³ /_\ 10u³ ÀÄÄÂÄÄÙ ÃÄÄÄÄÄÄÁÄÄÁÄÄÄÄÄÁÄÄÄÄÄÙ _³_ 1N4148 A tiny amount of drive RF current is fed through the 4pF to voltage doubler to turn on the PNP (* I tried different values, & this worked with my PNP & relay load @ 100mW low drive power). The 2 changeover relays are both plastic encapsulated ones, the drive one is a smaller 5V DIL type, they are both held in place with a local earth tag soldered to the coil connection & the coaxes ground there too. The RF detector & relay drive PNP transistor are mounted UGLY fashion around the drive relay. To stop the output relay operating when RF power is present, I delayed the driver relay by about 1/100 second, with the 470 & 10uF. I checked the drive relay operated on low RF power 100mW & low voltage of 11V OK, even with the series Tx LED! The diode across the relays stop back EMF from damaging the PNP, the u1 cap across the output relay coil reduced VHF RF pickup on the wiring when 65W is on the contacts! For each PA block ÚÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ¿ ³ ³ ³ ³ Power filtering capacitors are ³o³ M 6 7 7 4 H ³o³ applied to each module keeping the ³ ³ ³ ³ leads short for good VHF practice. ÀÄÁÂÄÂÄÄÄÄÄÄÄÄÄÂÄÄÄÂÁÄÙ75ohm Coax A ferrite bead (FB) is used to feed DC1. ððððÙ ³ _FB ³ Àðððððððððððð _³_ ÃÄÄÄÂÄÄÄÂÄÁÄ¿ _³_ The 1N4001 is only there in case ³ ~ ³ _³_ +ÃÄÄÄÄÄÄÄ+12V of power rail reversal & 2 of them u1=== === /_\ === should be able to blow the 13A fuse. ³6n8³ ³ ³1000uF ÁÄÄÄÁÄÄÄÁÄÄÄÁ¿ 1N4001 _³_ LAYOUT Fitting in all the coax ÚÄÄÄÄÄÄÄÄÄÄÄ¿ is the main problem with ³ [±±±±±] Ã¿SO this design, as my finned ³ ³_____³[]ÃÙ239 blackened dye cast box was ³ PNP O/PÃ Tx LED is only 18 x 13 x 3cm. ³[] =ð³]Fuse ³Drive Ã On LED Heat conductive paste is ³ [±±±±±] ØÍÍÍÍÍÍÍÍÍÍÍ12V Lead put under the modules & ³ ³_____³ ] On Sw the temperature remains ³ ØÍÍÍÍÍÍÍÍÍto Rig quite cool for short overs. ÀÄÄÄÄÄÄÄÄÄÄÄÙ (Fan might be needed for heavy use) RESULT With 13.8V & just over 1W drive output was a good 68W, 13A drawn & with 200mW about 50W needing only 10A. Harmonics from these modules are quite low, I measured them at >-30dBc (near the limit of my testgear @ VHF), but I did add a RF pi low pass filter @ the aerial socket. Tx relayÄÄÄÄÄÂÄ()))ÄÂÄÄÄÄo)SO239 The 23pF caps are 2 Tx grade ceramic ³23pF=== L ===23pF³ the L is 2 turns, dia & wire gauge ÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÙ select for 1:1 SWR match on test. If the modules are misterminated of course anything can happen & as with many PAs loads of sprogies might result! Through/Rx loss was 0.5dB with 1m of driver coax & BNC in circuit. A switched Mutek well filtered preamp was fitted in the Rx path, so the PA not powered up the drive power was available, this overcomes any Rx insensivity as well as proving good out of band Rx protection. See my tech buls. "RF Modules List", "Scope RF Trick", "Coax Traps", "Non relay instant RF Switching", "DC/RF Sensing PA Switching", & "2m Cavity Filter". Why don't U send an interesting bul? 73 De John, G8MNY @ GB7CIP
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