ED1ZAC - READ TECH 430

G8MNY > TECH 09.06.25 07:00z 160 Lines 7443 Bytes #168 (0) @ WW BID : 34392_GB7CIP Subj: HF Rx Suckout Trap Path: ED1ZAC<ED1ZAC<LU4ECL<LU9DCE<GB7YEW<GB7CIP Sent: 250609/0650Z @:GB7CIP.#32.GBR.EURO #:34392 [Caterham Surrey GBR] From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Updated Aug 19) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) When doing demo stations with more than 1 HF Tx on different bands (or with a nearby ham), QRM between stations is quite normal, even with the high Q tuned circuit of an ATU. Here is one method to remove most of the problem from the aerial lead. (from a system built up years ago for 2 FT101s by G0SYR & revisited for more modern rigs.) STATION A STATION B \|/ \|/ ³ ÚÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿RF ÚÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄ¿ RFÚÄÄÄÄÄÄÄ¿ ÚÄÄÄ¿ ³ ÀÄ´ATUÃÄ´Rx TRAPÃÄÄÄ´TRANCEIVER³ ³TRANCEIVERÃÄÄÄ´Rx TRAPÃÄ´ATUÃÄÙ ÀÄÄÄÙ ³ B FreqÃÄÄÄ´ ³ ³ ÃÄÄÄ´ A Freq³ ÀÄÄÄÙ ÀÄÄÄÄÄÄÄÙPTTÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÙPTTÀÄÄÄÄÄÄÄÙ It uses switchable "Teed in series tuned traps" (notch) that are only in circuit on Rx. If the transceivers have a transverting loop through ports, then the circuit is quite simple, otherwise a relay operated by the PTT is needed as well. This device also stops the Rx safety lamps (if fitted) or Rx front ends from blowing up. THE TRAP It is only connected in Rx mode, so there is no high voltages to deal with, but good quality components & layout in a sold metal box are needed to give the good Q & deep reject notch on the 50ê line. 50ê coax coax coax TXR o)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ(o ANT Rx<ÄÄÄÄÄÂÄÄÄÄÄÄÄÄ>Relay _³_ ³ _³_ Socket Port o In/Out Port Relay\_ \_ SW ( ( LED L1 (___ O R L1 (___ +12V>Ä´>ÃÄÄÂÄÄÄÄÄ¿ ( ³ Hi/Low ( ³ Hi/Low D1 _³_ ÚÄÄÁÄÄ¿ L2 ( ø/ Band W I T H A L2 ( ø/ Band /_\ ³relay³ (___³ Switch (___³ Switch D3 D2³ ÀÄÄÂÄÄÙ ³_ Rx P O R T ³_ PTT>´<ÃÄÄÄÁÄÄÂÄÄÙ ³/| ³/| o Out/In === C1 === C1 / SW /³ Tune /³ Tune ÚÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄ ÄÄÄÄÄÄÄÄÁÄÄÄÄÄ _³_ D1 LED/1N4001 D2&3 1N4001 C1 2x 350pF Air spaced (MW radio cap) L1 1uH, 12 Turns 1mm Enamelled Copper Wire on 1cm former (oval egotube). L2 10uH, 44 Turns of 0.7mm ECW on 1cm former (oval egotube). Both coils are on the same ÚÄ±±±±±²²²²²²²²²²²Ä¿ former in line, wound in the ³ ±L1±±²²²²L2²²²²² ³ same direction. So more L in ÀÄ±±±±±²²²²²²²²²²²ÄÙ series & less L when L2 shorted. / | \ If you are using a rig accessory socket for ptt relay power, be careful not to short it, Andy G0FTD recommends a series LED as a fuse. If your relay is not very RF isolating to the winding or you experience Tx mode lock up add a capacitor (1nF) across the PTT line. FRONT PANEL ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ ³ Scale calibrating:- ³ 160/80m ___ ³ connect to Rx & mark ³ Band (o) 80Üßú_._úßÜ40 ³ the band ends etc. ³ 40m-10m 20Ü/ / n \ \ ³ by nulling signals. ³ 15Üúú / \ úúÛ160³ ³ 10Ü³ ³ ( ) ³ ß ³ The band switch is ³ Out |_| ³ colour coded, & the ³Filter(o) ³ same colours mark ³ In Notch Tune ³ the ham bands on ³ ³ the dial. ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ IN USE Typical notch depth is 30-40dB, but tuning is critical for the peak. However notching the QRM down by 20dB or so, generally removes all Rx overload QRM. Notch Rx attenuation width, does not extend to the next ham band, so adjacent bands like 5MHz & 10MHz can just be used while notching out the 7MHz band etc. Notch Depth 0dB´ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ-.._ _..-ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 10dB´ \ / 20dB´ | | 30dB´ | 40dB´ ' ÀÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÂÄÄÂÄÄÄÄÄÂÄ 1.8 3.5 5 7 10 14 18 21 28 MHz Note that 2 stations operating locally, have QRM paths other than the aerial! e.g. via mains/12V leads/Mic, poor coax, poor metal case screening etc. The trap does NOT remove any of the other station's Tx harmonics, so you still will have some spot frequencies to avoid. e.g. a 100W of CW on 3.510 MHz will give a strong signal on 7.020 MHz & that can't be notched out! Also the trap does NOT remove any of the other station's broad band Tx noise or spurious, so you have to put up with that, but read on! TX MIXING & ATU BAND FILTER ACTION High levels of coupling between Tx aerials can cause QRM to other HF services as the Tx PA can mix its own signal & with other strong ones! 100W_³ TxA ³_ 0dBc 10W_³ ³ TxB ³_ -10dBc 1W_³ ³ ³ ³_ -20dBc 100mW_³ A-B ³ ³ A+B ³_ -30dBc 10mW_³ ³ ³ ³ ³ ³_ -40dBc 1mW_³ A-2B ³ ³ ³ ³ A+2B ³_ -50dBc 100uW_³ ³ ³ ³ ³ ³ ³ ³_ -60dBc ÀÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÙ So there is still a need to have the aerials separated enough, so that there is next to no power seen by the PA. e.g. the SWR bridge ATU on station A (between ATU & Tx) should not be indicating power from station B (SWR direction). STATION A close aerial B A 100W> \|/ <direct \|/ ÚÄÄÄÄÄÄÄ¿ ÚÄÄÄ¿ ÚÄÄÄ¿ ³ <pick up ³ e.g. ³ TX PA ÃÄÄ´SWRÃÄÄ´ATUÃÄÄÙ ÀÄ< 100W ÀÄÄÄÄÄÄÄÙ ÀÄÄÄÙ ÀÄÄÄÙ <10W B? <100mW B? <100mW B? With a good enough Q between the aerial & the Tx stage in this example 100mW (-20dB of aerial signal) gets to the PA & will produce unwanted products in the PA (acting as a Mixer) say at 10mW each, these then have to go back through the same tuned circuit to reach the aerial @ 100uW each. With valve PA equipment the high Q of the PA tank circuit also helps a lot, but this is not present on a modern solid state broadband HF PA. This is where a manual "T" or "Pi" Hi Q ATUs come in to their own, by providing more band isolation (20dB off resonance & 18dB/O cut off), compared to the simpler 2 component "L" type ATU (Automatic types). oÄ´ÃÄÂÄ´ÃÄo oÄÂÄÄLÄÄÂÄo oÄ´ÃÄÄÂÄÄo oÄÄLÄÄÂÄÄo L === === L === oÄÄÄÄÁÄÄÄÄo oÄÁÄÄÄÄÄÁÄo oÄÄÄÄÄÁÄÄo oÄÄÄÄÄÁÄÄo Loss 0dB´ /\ /\ /\._ _./\ 10dB´ | \._ _./ | _./ ~ ~ \._ 20dB´ _/ ~ ~ \_ -~ ~- 30dB´-~ ~- ÅÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄ T ATU Pi ATU L ATU L ATU Good LF cut Good HF cut some LF cut some HF cut Why don't U send an interesting bul? 73 de John G8MNY @ GB7CIP
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