Digital TV antena booster - Page 1
Forum section: electronics / rf-microwave

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 01:08:57 pm
content: Hello guys, I searched for a simple tv signal booster and I found a circuit, it was written this circuit is for 3-900 MHz amplifier with 20 db gain, after two weeks of trial Finally I failed because after installing device between antenna and tv there is no signal, my circuit is here please take a look at it and help me what is wrong please.Parts:R1 = 120 Ohm (brown, red, brown)R2 = 1,5 KOhm (brown, green, red)R3 = 270 Ohm (red, violet, brown)R4 = 82 KOhm (gray, red, orange)C1,C5 = 100pF (ceramic)C2,C3 = 1nF (ceramic)C4 = 2,2pF (ceramic)D1,D2 = 1N4148 diodeTransistor = BFR90, BFR91, BFW92Misc = PCB, 6pins, solder, 9V battery clipL1,2:diameter : 5mmwire thickness : 0,5mmturns : 8Input 4 and groundOutput 1 and groundPositive pole 3Negative pole 2Thanks and sorry for my English.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 01:23:34 pm
content: What is happening with pin 6, how is it connected to the device?What is pin 1 supposed to do?Do you have a picture of the completed device?

author: Delta
author_rank: Super Contributor
timestamp: September 20, 2016, 02:02:22 pm
content: With black magic RF, especially up at those frequencies, board layout is just as important as circuit design. If you've just slapped it together as you would an audio (for example) circuit, there is next to no chance it will work.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 02:43:00 pm
content: Quote from: PA0PBZ on September 20, 2016, 01:23:34 pmSorry my badOutput is 1 and 6Input is 4 and 5

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 02:46:21 pm
content: Quote from: Delta on September 20, 2016, 02:02:22 pmAny suggestion?

author: Chalcogenide
author_rank: Regular Contributor
timestamp: September 20, 2016, 02:57:22 pm
content: Try AC coupling the input. If the antenna has a power feed to reach the amplifier on the roof, you will just short it to ground through the protection diodes.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 05:07:43 pm
content: Quote from: farzadlatifeh on September 20, 2016, 02:46:21 pmDo you have a multimeter? If yes, can you measure the supply voltage and the voltage on the base, collector and emitter of the transistor, all relative to ground (pin 2)?

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 05:21:21 pm
content: Quote from: Chalcogenide on September 20, 2016, 02:57:22 pmThere is no power feed. I did not really get about AC coupling.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 05:49:03 pm
content: Quote from: PA0PBZ on September 20, 2016, 05:07:43 pmHere Multisim simiulation dataAnd mine: Collector 3.12- 2.96 Base 0.85 Emitter 0It seems there is no problem with my workIt's about circuit

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 06:07:33 pm
content: Quote from: farzadlatifeh on September 20, 2016, 05:49:03 pmYour DC measurements look ok, I get the same when I simulate in LTSpice.When I do an AC measurement it amplifies the signal correctly, so maybe there is an error on the PCB?Can you post pictures of top and bottom of the device you built?(Edit: Why the strange component values in the simulation?)

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 20, 2016, 06:52:17 pm
content: Did you use a PC board layoutEXACTLYlike the one in your photo?VHF circuits are VERY VERY sensitive to physical configuration.The slightest, seeming insignificant difference can kill it dead.Did you adjust the spacing of the coils to achieve the proper inductance?Do you even know what the inductance values for L1 and L2 are supposed to be?It seems rather unlikely that you will get this to work without better information.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 08:38:09 pm
content: Quote from: PA0PBZ on September 20, 2016, 06:07:33 pmHere PCB photoesWhat values you mean? Capacitors? I measured their true value by multimeter and I just put them in simulator to find any problemCould you send me print screen of your simulation with ACThanks

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 08:43:38 pm
content: Quote from: Richard Crowley on September 20, 2016, 06:52:17 pmYes exactly I dont know about L1 and L2 true values and I just try to make a typical inductance, you can see my PCB in previous post I have just posted.

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 08:48:20 pm
content: Your input and output coax shields should be connected to the PCB ground plane.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 08:57:19 pm
content: Quote from: voltz on September 20, 2016, 08:48:20 pmI tried and I failed, there is absolutely no signal, this is the problem.in any case there should have been signal with noise or something I guess but there is nothing totally.

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 09:06:03 pm
content: You could try and disconnect the output coax and use it as a test probe. Begin at input pin and work your way through to the output and see where the signal fails. I suspect a broken track.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 09:12:19 pm
content: Quote from: voltz on September 20, 2016, 09:06:03 pmI am not proWould you mind telling me how to do that? Is it possible with multimeter? It's only thing I have and I have no oscilloscopeEdit. I think I get what you mean, you want me to get output from other places to find the problem! NiceThanks

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 09:19:47 pm
content: No worries. Its quite simple really. Disconnect your output coax.. Then use the center conductor only like a probe.Place the coax center wire (probe) at the input pin on the PCB. You should get a signal (not amplified) to your TV. Hopefully you can see a picture even if scrambled.Then proceed along the circuit, base of transistor, collector of transistor etc.. All the way to the output pin.Your TV should get a better signal from the collector onwards.. Any sudden loss of signal may show a break in the PCB.Hope that helps!

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 09:22:54 pm
content: we replied togetherYes, output from other places to find the fault.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 09:27:03 pm
content: Quote from: voltz on September 20, 2016, 09:22:54 pmThanks broI'm gonna test itHope to find a way

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 09:36:12 pm
content: Another point, those resistors with long leads, they should all be flat to the PCB not standing up. The correct practice in RF is to keep component leads as short as possible. I would re-solder those flat down. ( the leads act like small inductors, this can upset the circuit at high frequencies).

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 09:40:26 pm
content: The resistors should not stand upright on the pcb, put them flat onto the pcb so that the legs are as short as possible. Connect the coax shields to the ground track. If you are going to use the output coax to probe around the pcb put a 1nF capacitor in series with the inner conductor of the coax and use the other end of the capacitor to probe around, because you do not want to short any DC to ground.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 09:46:35 pm
content: Quote from: voltz on September 20, 2016, 09:36:12 pmOK I will make resistors leads flat down to PCB but it's my second PCB, the first one had short leads but still did not work

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 09:47:45 pm
content: Fair point regarding the 1nf blocking cap. I had assumed this circuit was driven from a 9v battery and therefor floating with no possible DC path. However thinking about it, its probably driven from a PSU of some kind which may create a DC path if shorted. Thanks.

author: farzadlatifeh
author_rank: Contributor
timestamp: September 20, 2016, 09:49:25 pm
content: Quote from: PA0PBZ on September 20, 2016, 09:40:26 pmThanksOK I am going to flat down all resistors and use a 1nF capacitor in case of probingHope to find a way

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 09:54:42 pm
content: Quote from: farzadlatifeh on September 20, 2016, 09:49:25 pmJust don't give up yet, we will find a way to make it work

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 09:57:26 pm
content: Quote from: voltz on September 20, 2016, 09:47:45 pmIt's not about a battery, you just don't know what is connected to the other end of the output coax. If there is a DC path (inductor) across it will short any DC.

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 10:02:56 pm
content: Yes it is, the o/p Shield is not connected, and center is to a TV tuner input. There's no DC path if the circuit is isolated. Battery or PSU makes a difference if the PSU is not isolated from earth.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 20, 2016, 10:09:34 pm
content: Quote from: voltz on September 20, 2016, 10:02:56 pmIt should be connected

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 10:11:18 pm
content: I agree! see earlier post

author: farzadlatifeh
author_rank: Contributor
timestamp: September 21, 2016, 07:00:09 am
content: Quote from: PA0PBZ on September 20, 2016, 09:54:42 pmThanks man

author: farzadlatifeh
author_rank: Contributor
timestamp: September 21, 2016, 07:02:11 am
content: Quote from: voltz on September 20, 2016, 10:02:56 pmThanks bro

author: farzadlatifeh
author_rank: Contributor
timestamp: September 21, 2016, 10:29:01 am
content: Thanks to all of you, it works finallyNow I know how precise is this work.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 21, 2016, 11:21:10 am
content: Quote from: farzadlatifeh on September 21, 2016, 10:29:01 amSo, tell us what you did to make it work

author: farzadlatifeh
author_rank: Contributor
timestamp: September 21, 2016, 12:01:39 pm
content: Quote from: PA0PBZ on September 21, 2016, 11:21:10 amJust made resistor legs as short as possible, connect COAX as you mentioned carefully, change the inductor and made its legs as short as possible. The TV signal is around 600 MHz that means a little divergence would make it dead (Now I know).

author: voltz
author_rank: Frequent Contributor
timestamp: September 21, 2016, 01:32:30 pm
content: Great