Display and VOX mods pg7
Contents
1. Notice they are soldered together and run to a trace to a surface mount resistor Carefully cut the trace next to the 2 pins Now locate 2 rows of pins to the top of the chip The bottom row last pin on the right has 5 volts DC on it Solder a 10K resistor to that pin and to the pins 28 and 29 Now reassemble the radio and your done The radio will now tune 26 MHZ thru 30 MHZ REMOVE THIS BOARD AND TRAY 1 of 2 7 28 2007 8 11 AM Frequency mod pg3 aa ant LOTITI ia ATADOS El CUT TRACE AFTER 2 PINS 2 of 2 http www gsl net kf2tz fregmod html 7 28 2007 8 11 AM LSBmod pg5 http www gsl net kf2tz lsbmod html LOWER SIDEBAND MOD THIS MOD WILL GIVE YOU LSB AND CW Remove top and bottom covers Locate L12 that s an adjustable metal can inductor located rite behind PC board PC 132AA To the LEFT of L12 is a 12 picofarad disc capacitor Change this to a 47 picofarad capacitor Readjust L12 to a known source on LSB Reassemble the radio and your done NOTE The capacitor I have shown on my diagram is not the one you need to change Change the capacitor to the left of L12 I will update the picture soon BACK OF RADIO AS fi var La E PB 130AA CHANGE THISIGAPACITOR TO A47 PICOBARAD FRONT OF RADIO 1 of 1 7 28 2007 8 12 AM Microphonemod pg4 http www gsl net kf2tz micmod html MICROPHONE ENHANCEMENT Remove top cover of radio Locate C3 near the front right of the radio To the right of th2. the RF sections were indeed almost identical I reasoned that the 2510 being an allmode radio with AM included may use the common CB radio design practice of having a wider compromise IF crystal filter to improve the RX audio response on AM The center frequency of both filters is 10 695 MHz so assuming that the carrier oscillator signal is placed on the slope of the filter a check of the carrier oscillator alignment frequency for USB should tell us the approximate bandwidth of the filter Sure enough the USB carrier oscillator frequency is different in the two radios Shown below is a chart of the carrier oscillator frequencies for both rigs with a LSB value extrapolated for the HTX100 As can be seen from the graph the HTX filter is indeed significantly narrower than the 2510 filter Visit this site to view graph e HTX 100 Service Manual available here e 4558 opamp history discussed about half way down in this thread e What exactly is an Op Amp o HTML web page format o pdf document format Intro o The term op amp was originally used to describe a chain of high performance dc amplifiers that was used as a basis for the analog type computers of long ago The very high gain op amp IC s our days uses external feedback networks to control responses The op amp without any external devices 1s called open loop mode refering actually to the so called ideal operational amplifier with infinite open loop gain input resistance band
3. the web like a cap across the Mic Att stage on how to cure or mitigate this muffled audio response spurred me on to write this web page in order to point out EXACTLY what is taking place inside the HTX 100 to cause muffled transmit audio AND what a proper cure involves It also appeared during testing that the microphone was extremely sensitive verily this was born out during testing and the A half of opamp IC3 was found to be operating very near open loop gain Block Diagram Below is a block diagram with the circuitry under scrutiny shown in red In particular the Microphone Attenuator Q24 driven by ALC Control Q25 and the Mic Amplifier using one half of IC3 are the subjects of this webpage Part of the ALC Automatic Level Control circuitry shown in blue as well as other circuitry are shown as they surround and interface with circuity around in near or share an opamp in IC3 with the Mic amp et al The Mic Amplifier using the A half Opamp in IC3 delivers an amplified audio signal to the Gilbert cell active component Balanced Mixer IC2 Barrie Gilbert on the invention of The Gilbert Cell The output of IC2 is routed through FT2 FL205 THIS is the filter that makes this radio FT2 FL205 is the sharp filter that defines the receive characteristis of the HTX100 as well as the ultimate transmit bandwidth assuming subsequent RF stages are operated linearly and not into clipping Shortcomings in the se
4. 0 HZ 0 dB ToS iz O JB 2500 Hz Modeled frequency response 57 4d8 SII f 521 TSI f 522 Gila E Ad Start 5042 401 points Stop 10kHz 291 kHz OC F1 4dE e Circuit value changes to improve high frequency response and modeling of new circuit values as shown below Reference Old New Designator Value Value R96 urre 180K ROS 100 330 Cie 560pF 82pF Measured Gain at peak 45 3 dB A 184 Measured frequency response 6 dB 140 Hz 3 dB 250 Hz Peak 1250 Hz 6 dB 10 KHz 10 dB N A Modeled frequency response 146 6648 511 fe Sal i 7512 i Sea D 20Log E 36 6548 Start 5042 401 points Stop 10kHz f 10kHz C dA EGOE d 0 2 e On air testing In circuit test of new values in situ voice quality observation by other operators Indications are that the effort expended resulted in improvements good reports are now had Parts location changing the components The area in blue below contains the Microphone Amplifier and Mic Attenuator ALC circuit components The area in blue is shown in more detail in an excerpt further below EST iF ii E 3 Ln i d pri E EM A ii lar 3 all i AI SO 1 sll pm i KI a ji zi Y Mad f is ri J 7 u Main PCB Top View The components outlined in red are the components changed out to improve microphone amplifier frequency response To gain access to the rear of the HTX100 Main Bo
5. Display and VOX mods pg7 http www gsl net kf2tz vox html microphone CHANGE DISPLAY COLOR Remove top cover of the radio Locate the 2 white wires running into the display light housing Remove the light and remove the green cover on the light Put the light back into the housing you can wedge the wires in between the 3 electrolytic capacitors to hold the light in place Reassemble the radio and now your radio will have a light brown display like the big rigs b zer ADD VOX The VOX circuit can be obtained from RASON org You can wire the TX RX switch on the front of the radio to 12 volts to turn the VOX on and off Microphone wiring 1 of 2 7 28 2007 8 14 AM Display and VOX mods pg7 http www gsl net kf2tz vox html microphone Pin 1 Microphone input Pin 2 Push to talk Pin 3 Scan down Pin 4 Scan up Pin 5 8 Volts Pin 6 Audio out Pin 7 Microphone Ground Pin 8 Ground NOTE Connect these pins to ground for function to work BACK NUNU726 altavista com 2 of 2 7 28 2007 8 14 AM Radio Shack HTX 100 Microphone Amplifier analysis and improvement METER SEE TRANSCEIVER EOI ITZEI AN AIK Equipment Radio Shack HTX 100 10 Meter SSB CW Transceiver Catalog Number 19 1101 On air reports of muffled audio coupled with off air confirmation of same led to a technical investigation of the transmit audio response characteristics of this radio A cursory review of a few of the hacks on
6. ad marked 8 volts Solder the center leg of the pot to the part of the trace closest to the front of the radio Turn the radio on hook up your voltmeter positive lead on the leg soldered to the cut trace and negative to ground Adjust the pot for the same volt reading you wrote down earlier This puts the radio back on frequency Reassemble the radio and your RIT will now tune 1 1 2 KHZ to each side and track the frequency on transmit 8 VOLT I S in DC L e ME pla ee ba eai a da ez perre o a ay eez gn ed PF ek A E O y a 1 bedi r L i ia E Pd macara Se E ak Perrie el S Eee PF Bak He gt poz Dumme a i B Si Pa E an 2 A ZI i II ia E b d rates ths ern 1 of 2 7 28 2007 8 13 AM RITmod pg6 http www gsl net kf2tz ritmod html BACK 2 of 2 7 28 2007 8 13 AM
7. alysis The following schematic was entered to determine the AC characteristics of the HTX 100 s microphone transmit audio amplifier frequency response SO Aa en DY eat lah acacia alt a Bes aeb mL ha AEE NEA TATEA De iL eee Ue beeen ir ie ship de Sea A EA AEA AAA ar EA Se ER ie ar A RO ane EA eye BA TE EE A E EEE EK UR E AEE EE AEE E DE BE o NC a ITS EE OI ER IO E Ok GR E E OI Ou E E E E TE OTERO E OTE OTO A d aA a GE HEE Eu E E ee a GE NE AE GE a A ATE AA A EAE a a E A ak E RE er see a ia eo ME eg A Ak E a E A a ge ER PD Re d ERARA d bd SISA SIIS Zr Mu Bate E SA e Ea I ye EEE BRETT 1nF IEA 4nF GE en er 1nF A ee REIMR geie cc Ro 04JR gt ObLgain 80cB The following schematic was entered to determine the AC characteristics of the proposed improvements to the HTX 100 s microphone transmit audio amplifier note that two resistor values and one capacitor value were changed per a chart to be found further down below deaz eGela eka E E EEE AAE aA Ea a aea aak idea Gereka ERO ea da aaa Ek da EN RA EA AK ON o ei Me EAEE AAA ANEA O SN e e Als EEE ANE EEE EN E Ea EGE O E Ol Ep _ 220nF BR Mi OE 41 1 A 1 1 De 2 ZO l EEK SZ Mag E ug da ae a a pene oa po li se an E ETE E ZEZ E E y 0 Hee n ER ae d EEE 2 2 er EE RATAS EA A RE RER co Dlgain 50dB Analysis of existing circuit Measured Gain at peak 56 dB A 630 Measured frequency response 6 dB TOS HZ Peak 53
8. ard and change these components the PLL Assembly located under the Main Board will have to be temporarily removed this is an easy task involving four screws and three connectors two multi wire connectors and one coax connection After the PLL Assembly is removed the rear of the Main Board is easily accessed to allow desoldering and removal of the orginal components and installation of the new components Link summary e Open loop gain practically the gain is so high that the output will be driven to Vee or Vee for any appreciable difference between the inverting and non inverting inputs e Negative feedback or closed loop gain feedback is used to stabilize or set the gain to a useful fixed value that is relatively independent of the opamp s open loop and device fabrication and process yield dependent gain figure e The Gilbert cell mixer e Barrie Gilbert on the invention of The Gilbert Cell e HTX 100 Filter comparison with an HR2510 radio Over the years I have talked to several people who have owned both the HR2510 and the HTX100 The comment inevitably comes up that the HTX100 has a better receiver that the HR2510 But how can this be Everyone knows that the 2510 and the HTX have virtually identical RF sections When I finally managed to acquire an HTX100 last year I decided to investigate to try and prove or disprove this notion once and for all Examination of the schematics for both radios showed that
9. e 4558 family of opamps from such manufacturers as Raytheon and Fairchild as an RC4558 which is described as a Dual High Gain Operational Amplifier The RC4558 integrated circuit is a dual high gain operational amplifier internally compensated and constructed on a single silicon IC using an advanced epitaxial process Combining the features of the 741 with the close parameter matching and tracking of a dual device on a monolithic chip results in unique performance characteristics Excellent channel separation allows the use of this dual device in dense single 741 operational amplifier applications Note that the NJM4558 in the S package has two Vcc pins pin and pin 9 In the annotated HTX 100 schematic fragment above R104 along with R105 provides bias sets that opamp s DC voltage operating point via pin 4 by applying a DC voltage to the non inverting input of the A half of opamp IC3 and furthermore this connection is shown to be through IC3 to the 8V supply IM4S58s NJM4558 RC4558 Opamp Open loop frequency response Compare the open loop gain in the chart at around 2 to 3 KHz around 60 dB to the gain of an NJM4558 in the actual Microphone Amplifier circuit as measured further below It appears the 4558 n th s app was running very near open loop save for the negative feedback contributed by the 560 pF capacitor Avo dB 65 021 4 10 100 1K 10K 100K 1M ON F Hz Microphone Amplifier AC Circuit an
10. e chip and n front of the chip is a disc capacitor marked 561J this is a 560 picofarad cap Remove this capacitor Now reassemble the radio Now your mic will have an added punch that will work great for dx ing and better under all conditions OR REMOVE THIS Already removed MK 1 of 1 7 28 2007 8 12 AM htx 100 MIC WIRING http www gsl net kf2tz micr html Microphone wiring Pin 1 Microphone input Pin 2 Push to talk Pin 3 Scan down Pin 4 Scan up Pin 5 8 Volts Pin 6 Audio out Pin 7 Microphone Ground Pin 8 Ground NOTE Connect these pins to ground for function to work 1 of 2 7 28 2007 8 15 AM htx 100 MIC WIRING http www gsl net kf2tz micr html BACK NUNUT726 altavista com 2 of 2 7 28 2007 8 15 AM RITmod pg6 http www gsl net kf2tz ritmod html OPEN THERIT THIS MOD WILL ALLOW THE RIT TO WORK ON TRANSMIT AS WELL AS RECEIVE AT THE SAME TIME Remove top cover of the radio Locate 2 white wires comeing from the display light houseing going down to the circuit board Locate the solder pad marked 8 Volts Now look to the right and you will see a white plastic wire plug in socket Next to the socket you will find a 1 inch trace with solder points on each end that runs front to back direction of the radio Hook up a DC voltmeter to this trace and write down the reading Now turn the radio off and cut the trace in half Obtain a 10K potentiometer and solder one leg to the solder p
11. lected component values of the Microphone Amplifier IC3 however serve to severely limit the highs above 1500 Hz as will be shown further below GOA IWITCHIHC as EZ 35 Py ic ce aL cont atie D ures mar CONT PROCESSOR pere rr pm f Electronic Schematic Diagram The following schematic fragment was excerpted from a scanned copy of the HTX 100 Service Manual found on the web here In the following schematic fragment the following color conventions were chosen to highlight key functions in the transmit microphone and ALC audio circuitry Red Audio Mic circuit input Blue Opamp Output and feedback network Green ALC circuit Note that the majority of the resistors appearing in that badly drawn and confusing schematic are for bias that is they merely set the DC operating point of the two opamps that are resident in the NJM4558S 9 pin in line package Note also that only one of the two opamps inside the NJM4558S package device is used as an audio amplifier the other opamp is used as a simple comparator level shifter in the transmit keying circuit E AREGO gr pe 024 25C3242AE soro 27 3 GO Ede Eu 3 e g gt d e uP TX ory y d IN ei Bu ei er ae ka eg ude 3 A MIC PSs e E Audio Input CW 031 zi 25094540 TTV NJM4558 RC4558 Opamp Below is the pinout of the NJM4558 IC Note that this device is a member of th
12. width and a zero output resistance E However in practice no op amp can meet these ideal characteristics And as you will see a little later on there is no such thing as an ideal op amp Since the LM741 NE741 uA741 Op Amps are the most popular one this tutorial is direct associated with this particular type Nowadays the 741 is a frequency compensated device Let s go back in time a bit and see how this device was developed The term operational amplifier goes all the way back to about 1943 where this name was mentioned in a paper written by John R Ragazzinni with the title Analysis of Problems in Dynamics and also covered the work of technical aid George A Philbrick The paper which was defined to the work of the U S National Defense Research Council was published by the IRE in May 1947 and is considered a classic in electronics e The very first series of modular solid state op amps were introduced by Burr Brown Research Corporation and G A Philbrick Researches Inc in 1962 The op amp has been a workhorse of linear systems ever since Frequency mod pg3 http www qsl net kf2tz freqmod html FREQUENCY MODIFICATION Remove bottom and top covers Remove the PLL board and tray that is held in by 2 screws on each side of the radio After you remove the board you will see a 4 sided surface mount chip IC 1208 that has 64 pins Look to the right of the chip and locate the 4th and 5th pins from the top right of the chip pins 28 and 29
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