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When driving the video signal the power supply can experience 50mA+ current swings beyond the idle currents. You can further band-aide things by using a larger cap, perhaps 2200uF. But, this is not a good application for the resistor method; that simple trickery is best suited for static loads or things that tolerate sloppy power.

If you want the best video performance (and who doesn't) then use a suitable Vreg IC. The LM7805 is fine if your supply voltage will be >7VDC. With high input voltages don't forgot to add a heatsink or it might get too hot for safe operation.

And there's no noise at all, even without a capacitor.

Don't omit the caps shown on the LM7805 data sheet. They are a must.

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When driving the video signal the power supply can experience 50mA+ current swings beyond the idle currents. You can further band-aide things by using a larger cap, perhaps 2200uF. But, this is not a good application for the resistor method; that simple trickery is best suited for static loads or things that tolerate sloppy power.

If you want the best video performance (and who doesn't) then use a suitable Vreg IC. The LM7805 is fine if your supply voltage will be >7VDC. With high input voltages don't forgot to add a heatsink or it might get too hot for safe operation.

Don't omit the caps shown on the LM7805 data sheet. They are a must.

Thanks for your response. Every recommendation I've seen has been to use capacitors with the LM7805, but to be honest, I have yet to see a lick of difference (for my application) with or without them. The signal looks the same as the original to me. But it wouldn't be the first time I've missed the obvious (has happened multiple times in this thread already). I'll just keep playing with it to see what I notice. But so far, I see none of the noise that occurred with the resistor. I'm trying to keep everything as small as possible.

So far, the LM7805 hasn't gotten any more than mildly warm (if any heat at all). It was the same when I was using the resistors. The current is too low to produce much heat.

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The LM78xx series Vreg IC's need the recommended caps for stability. Not installing them is just asking for trouble.

I've been involved with plenty of troubleshooting episodes where the caps were missing or improperly installed. My best advice to anyone that builds electronic projects is to obey the data sheet recommendations.

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The LM78xx series Vreg IC's need the recommended caps for stability. Not installing them is just asking for trouble.

I've been involved with plenty of troubleshooting episodes where the caps were missing or improperly installed. My best advice to anyone that builds electronic projects is to obey the data sheet recommendations.

Okay, I'll take your word for it. They shouldn't take up that much space anyway.

Thanks

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Okay, I'll take your word for it. They shouldn't take up that much space anyway.

Thanks

Hi,

I am late with my response, but (sorry Thomas) I have not been checking this forum very frequently lately.

I would like to thank you for your excellent review and post above. Please also note that the optimal voltage to run this thing is around 5V, the resistors which create the input bias are calculated to 5V (correct me if I am wrong Thomas). It will run at lower or higher voltages, however the optimal is around 5V.

So the 7805 is a perfect solution, and please use the capacitors, you can get 2 SMD 1206 size capacitors which will fit perfectly between the pins of the Vreg at the root, so no additional circuit board is needed. If I recall correctly the datasheet calls for a 22uF capacitor at the output and a 0.47uF capacitor at the input. Please use these and you'll be fine (you can add 2 x 22uF, the 0.47 is a reccomanded minimum).

Zoltan.

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So I tested the Video splitter today, this time with properly set up signal line. As per Mr. Rc-Cam's instructions we added a 47uF cap, and 2 resistors. Connected to the 650HQ I've got excellent picture quality on both outputs.

I read this thread twice and didn't see any reference to the resistors values, could you folks share the values and how they are connected?

I am here trying to solve a video problem when I connect the well known GP707 receiver to my jvc miniDV camera, I suspect maybe it is a impedance mismatch.

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The 75 ohm termination resistor should already be installed in your camcorder's video input jack. It would be very unusual to find it missing since it is a industry standard requirement.

What exactly are you trying to fix? For better help, post a video clip of the problem and someone may have a solution.

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http://www.vimeo.com/2941764

You can see in this video the type of problems I have with this receiver directly connect to the JVC.

Must worst problems (missing colours, horizontal scrolled bars, etc) when connected trough a Y cable, still worst with a video amplified splitter similar to the ones described in this thread

If you see the video till the end, you will see a piece of video recorded with this same JVC miniDV camera, BUT with a AWM634 based RX AND a Y video cable divider.

Thanks for your help

(Sorry Ginger for the highjack)

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(1) What video buffer/amp are you using? Do you have a vendor link to it?

(2) With the camcorder turned off, use your ohmmeter and measure the JVC's video input. What do you read? Should be 70-80 ohms.

(3) Does this setup work fine on other recorders and monitors. Is it specifically just the JVC that has the video tears?

(4) Is the Video Tx the one that is specifically designed to pair up with the video Rx? Mixing brands is not always a good idea for a variety of reasons.

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(1) unbraded chinese product, with specs equal to the one dpcav sell

(2) nope, 147kOhm, I suspect we have here a cap...

(3) all perfect, even with Y cable, the problem is only with GP707 and brighter images or image portion, as the sky

(4) No, Awm633 based TXs, they work well with AWM634 and AWM635 Rxs

I bought the GP707 because the seller show the exact channel/frequencies of airwave modules, and since a friend of mine has one (which he use with Airwaves modules Tx based without problems), I bought it.

Thanks for your help.

Edited by jalves

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(1) unbranded Chinese product, with specs equal to the one dpcav sell

Does it have a variable gain pot on it? Can you post a link to the device?

2) nope, 147kOhm...

Ok, that is something that will cause issues. Do you have an o-scope?

I bought the GP707 because the seller show the exact channel/frequencies of airwave modules, and since a friend of mine has one (which he use with Airwaves modules Tx based without problems), I bought it.

FWIW, mixing and matching brands is not always a grand idea. Besides the usual things that can vary, like pre-emphasis techniques and audio sub-carriers, rarely are the video levels the same (they need to be Tx/Rx matched). But since you have good luck with this pair on your other video playback devices, we can assume that things are close. But I doubt the video levels are ideal (heck, those are often mis-adjusted even when the same brand is used). Goofy video levels can cause unusual compatibility problems.

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Does it have a variable gain pot on it? Can you post a link to the device?

Ok, that is something that will cause issues. Do you have an o-scope?

FWIW, mixing and matching brands is not always a grand idea. Besides the usual things that can vary, like pre-emphasis techniques and audio sub-carriers, rarely are the video levels the same (they need to be Tx/Rx matched). But since you have good luck with this pair on your other video playback devices, we can assume that things are close. But I doubt the video levels are ideal (heck, those are often mis-adjusted even when the same brand is used). Goofy video levels can cause unusual compatibility problems.

Yes it has a pot, but turning it gives us from a blurred image (or none at all) till the image clean with some colour problems (the result image is better than using Y cable, but still...)

As o-scope only have the soundcard of my pc, can we use it?

As usual, you're right.

You write this advices all over the place, but... I was stubborn, and animated by the success of my friend with the gp-707 and by the good reviews this GP707 received , bought it.

To clear up a misconception, this gp-707 receiver show the same problems when i record the video signal using the jvc miniDV, the same if I use a panasonic miniDV , thus I think the problem is the GP707, BUT the gp707 provides a clear image in a TV set.

Remember now that my Fatshark goggles show the same type of problems when they are receiving the video signal from the GP707. The resultant image has the same artefacts when a FAST futaba Tx is the area and mess up the 2,4GHz video link.

In resume, the GP707 only provide a good image when the signal go to a television through a scart.

Thanks again for your time.

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This really sounds like your TX doesn't match the 707.

For the record, I have 2 identically looking sets with "707"-type receivers that actually come from different manufacturers (many use the same design), and indeed while the frequencies are the same I can not mix the 2 sets. One works with Airwave and the other doesn't.

If you want to be safe, always use TX/RX from the same line/brand.

Edited by Kilrah

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A sound card o-scope won't be of much help.

It's time to experiment. Take a 150 to 220 ohm resistor and put it on the video input of the JVC camcorder; One end to the signal, one end to ground. Then plug the video buffer into it. The Rx will go into the video buffer Vid-In.

Use the video buffer's variable gain to restore the lost brightness. Do you see any improvement at all? If the 150-220 ohm helps, then try a 470 ohm and see if it works well (must re-adjust video amp). If 470 makes it worse, then try 100 ohms (+ re-adjust video amp). It is a long shot, but maybe you will find some success doing this.

If you want to be safe, always use TX/RX from the same line/brand.

I agree. The funny thing is that even the same brands are sometimes not compatible with their various offerings. So, there are times that you have to stick with the matched pair they provide in their gift box set.

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Folks,

This is the inners of the video splitter I am using.

I am almost convinced that this is a total crud.

The video level (again a Vpp measured with a sound Oscope) from its output is lower that the video level of the signal at its input.

Is this normal for a active video splitter??

post-3901-1233436881_thumb.jpg

post-3901-1233436896_thumb.jpg

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It is normal for that class of video buffer. They usually do a trick where the video input is not terminated, so that the supplied video is not attenuated like is should be. Then they use simple emitter-follower transistor buffers for the outputs, which have a gain of 1X, but with the input level at 2X normal levels, and the small value series terminators on its outputs, there is net effective video signal gain on the output.

A good clue is to measure it's video input with an ohmmeter. If you see a high resistance then it is unterminated. So, it would have the same issues your unterminated camcorder input sees. If this is the case, then you have probably just moved the video receiver's problem from "here" to "there." So, you should try adding a pseudo terminator to the input of the buffer, perhaps try the values mentioned earlier for the camcorder. Or better yet, try the resistor trick without the buffer installed to see if there is hope of an improvement. Eliminating the buffer will reduce the number of unknowns during the troubleshooting.

A sound card scope is good for audio frequencies (low KHz). Although the video's vertical syncs are low frequency, the horiz syncs are probably too fast, plus the active video region is several MHz wide. So, the typical soundcard scope will not work well at all with video. But if it works good enough for troubleshooting the basics, then that is grand. Be cautious though and don't trust much of what you see.

Keep in mind that video is 1.0Vpk-pk for full whites, as measured from the bottom of the syncs to the top of the video region. A good scope is needed to do that. A sound scope doesn't stand a chance.

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Is this capture any good?

OT

Thomas,

I am looking for a "real" scope, New ($300 maximum) or used (cheaper), but I am lost regarding what I should look, do you give me a hand here?

What specs should I look given my $$limitations?

Thanks in advance

OT

post-3901-1233483966_thumb.jpg

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Hi,

I meant to send this early this morning, but then I had to run to work.

The chip is a Max4217 video buffer/amplifier. The voltage is between 3.3 and 11.5 as it is required by the Max chip, there is nothing else which would be voltage sensitive on the splitter. Since there is barely any power consumtion on this, this will run as old as possible, barely any heat dissipation.

The splitter has a 75 ohm resistor termination at the input - some installations may not require this.

Some issues were reported on some situations, but the splitter works very well in most cases. The issues reported were incompatibility with some cameras, because some would require biased AC input signal to work properly even if the MAX chip does not require this.

The only way to see if this works o not in your particular installations is to try it out.

The splitter will require an external power source. The original design was to complement the SGTX type transmitters, so it will take the 5V coming from the transmitter, but since there is barely any power consumption, a simple LM2940 5V regulator can do the trick.

Sorry for the late answer, I did not have time lately to check this forum.

Kilrah, thanks for the support... :)

Attached is the design of the splitter, so this will give you a clear view on what's inside.

Zoltan

New Generation Hobbies.

To dispell any myths here all video applications must be terminated into a 75 ohm load, while sometimes the video consumer device provides this(most cases), there are those other cases where the Video input is HiZ. Without termination most video sources will produce a 2x signal. On the flipside a double terminated line will only be developing .5 Vpp in which case the image will be dark at best and most likely the display will not be able to syncronize at all. Also do not tee tap video cables, the unterminated leg of the tee will reflect the 3.58MHz color carrier at wildly unpredictable phase angles leading to green faced people and blue grass. also it should be noted that the terminator is at the end of the line, meaning at the jack of the recorder or monitor's input.

Edited by AJ_Scott

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Is this capture any good?

OT

Thomas,

I am looking for a "real" scope, New ($300 maximum) or used (cheaper), but I am lost regarding what I should look, do you give me a hand here?

What specs should I look given my $$limitations?

Thanks in advance

OT

Finding a good Techtronics or B&K 100 Mhz dual trace analog scope is fairly easy on the Ebay auction site. Be sure to insist on an answer to operability, as you may not have the time or skill required to repair a malfunction unit without already having a running oscilloscope. My last scope cost me 150.00, and i had to repair it, which for me was not an issue as I had another scope in the past of the same family and was already familiar with its geriatric failures(bad caps in the power supplies)

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Is this capture any good?

I can see a single PAL video field, but honestly it is not a trustworthy image.

Forget the scope troubleshooting for now. What are the results of the resistor experiments? If you don't see any hope of improvement with them then moving forward will probably be a lost cause.

To dispell any myths here all video applications must be terminated into a 75 ohm load

If only it was so easy. There are some pieces of consumer/hobby video equipment that cheat and do not employ industry standard 75 ohms. Their design accounts for their goofy termination techniques and simply sticking 75 ohms on them causes other issues.

Fortunately, the incorrect terminations are fine for some installations, but occasionally we are not so lucky. One reason is because some video sources require a proper termination (or something close) to fully derive their video signal. I see this more often now that some video designs are eliminating the legacy A/C video coupling and are using other methods. Long story short, that is why we are playing with various resistors in this troubleshooting episode. It's just an attempt to cheat a cheat.

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If only it was so easy. There are some pieces of consumer/hobby video equipment that cheat and do not employ industry standard 75 ohms. Their design accounts for their goofy termination techniques and simply sticking 75 ohms on them causes other issues.

Since I only have here a set of 75Ohm resistor (the other ones are a to high resistance) I try to terminate all the items in my video chain with them.

All my gear (video receiver/ FPV goggles/Jvc miniDV) has infinite Resistance in the video input/output.

1st experiment:

I Solder a 75Ohm resistor between signal and ground in the Video receiver output. attached the cable and add the Y splitter, got aprox. 75 Ohm in both outputs, then connect the goggles and in the other output fall to aprox. 50Ohm. Then connect the JVC, the problems became a slightly worst, the goggles show good image as usual.

2nd experiment:

Add 75Ohm in the three devices, the JVC image become crude, with colour problems and banding, goggles good as usual, maybe a slightly grain in image.

One more data, the JVC connected directly to the video receiver output show no problem at all.

Tomorrow I will buy the resistors to complete the tests suggested by you Thomas

Again,

Thanks

OT

Will I be "burned" with this type of O-scope ?

OT

Edited by jalves

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One more data, the JVC connected directly to the video receiver output show no problem at all.

I am confused. I thought the problem was that your JVC did not work when directly connected to the receiver. Perhaps your 75 ohm termination is still installed on the JVC's input in this experiment?

1st experiment:

I Solder a 75Ohm resistor between signal and ground in the Video receiver output. attached the cable and add the Y splitter, got aprox. 75 Ohm in both outputs, then connect the goggles and in the other output fall to aprox. 50Ohm.

This is a double terminated condition. Double terminations will usually cause issues.

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I am confused. I thought the problem was that your JVC did not work when directly connected to the receiver. Perhaps your 75 ohm termination is still installed on the JVC's input in this experiment?

You are right, I forgot to report that I didn't use the GP707 for this test, my fault, sorry.

This test was conducted with a FatShark/Airwave 634 Rx

With this Rx, the only problem of the jvc when in Y is in the upper area of the screen, where the osd puts the info, I think the osd mess with the sincronism.

I will redo the test with the gp707.

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My recommendations are based on what you have reported about the GP707 Rx when used with the camcorder. But now I am lost as to what you are trying to fix. Please keep in mind that these little experiments are very particular to what you tell me, so any deviation to the plan will just add lots of confusion.

It is important to break down the problem into its simplest form, rather than complicate it with Y'ing various devices together, adding buffers/amps, or testing with the OSD installed. Issues from doing that are another ball of wax to discuss.

So, I'll start at the beginning and recap what I know: I understand that you are using a video camera and Tx combination that does not work with your camcorder when the GP707 is used (some minor video tearing due to video content). Additional problems (lack of color, contrast, etc.) are seen on the recorded image when you 'Y' the camcorder with your glasses (note: a common issue with simple Y'd video cables). But this Rx works fine with your glasses or video monitor, even while Y'd with the camcorder. Furthermore, the camcorder works fine with the AWM634 Rx. You have found that the camcorder's video input is Hi-Z. Is this correct information?

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