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Old 22nd Oct 2018, 8:47 pm   #21
G0HZU_JMR
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

It's going to be fairly noisy at the output anyway because of the 30dB gain but yes, it might not be obvious if it is hooting up at a GHz or more.

However, the board must be fairly stable most of the time or they wouldn't be selling them and it does look like someone has tried to add lots of vias but with this type of device I'm not sure if it's enough to preserve unconditional stability, especially with a 1.5mm thick PCB.

I recall about 25+ years ago Avantek brought out a series of low noise, high gain MMICs in SOT-86 and I think they were marketed as 'Magic Modamps' and they used an extra gain stage to produce high gain, high bandwidth performance like this. On paper they almost looked too good to be true as they claimed unconditional stability for these parts as well as low noise and high/flat gain over a huge bandwidth.

These MMICs used the familiar darlington stage but they also had an extra (high gain!) grounded emitter stage driving the darlington. I think the problem with these old MMICs was that both stages had to share the common ground pins of the SOT-86 package and this meant that the design was a bit marginal unless the device was grounded almost perfectly when mounted on a PCB. I suspect that the device on your PCB will be doing something similar internally. It's unlikely to contain two darlington stages in series as that would probably be even worse in terms of stability if both stages shared the common ground pins of the SOT-86 package.

The best thing to do is play with it and seen what it does and if it behaves itself. It's amazing how the sellers can buy the bits and the PCB and build it and then ship it to the UK for just 4!
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Old 22nd Oct 2018, 11:32 pm   #22
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Arrow Re: 0.1-2000 MHz Wide Band Amplifier ~4

Bazz4CQJ: Quite likely. As you know, quite some time ago I set about designing a wide-band R.F. millivoltmeter (2 MHz - 100 MHz) - which, incidentally, is still on the 'back burner'. At one stage during development, I had substantial attenuation at about 80 MHz that I couldn't account for, nor detect the reason why - until I went searching with my 1 GHz spectrum analyzer. I found substantial oscillation at approx. 730 MHz, over a bandwidth of about 100 kHz! That was cured by increasing capacitive decoupling plus a few judiciously-placed ferrite beads.

Al.
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Old 23rd Oct 2018, 3:10 am   #23
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Quote:
Originally Posted by Skywave View Post
Bazz4CQJ: As you know, quite some time ago I set about designing a wide-band R.F. millivoltmeter (2 MHz - 100 MHz) - which, incidentally, is still on the 'back burner'. Al.
Yes indeed; the question about how Marconi and Booton et al got probes working at sub-millivolt levels, yet various published designs, when tried, got nowhere near that
B
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Old 23rd Oct 2018, 5:27 pm   #24
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

One thing to note is that there appears to be at least three almost identical revisions of this PCB artwork for sale. At first glance the PCB layout looks the same on all of them but the difference between them is the amount of ground vias near the MMIC and also around the supply decoupling caps. On close examination, the version in the picture Bazz posted up in the first post appears to have the best via pattern of all of them. However, it still might not be fully adequate. But it's a lot better than the others. There is also a board for sale that has a similar MMIC on it but with an obviously different PCB shape and design and this one looks even worse than the others in terms of the MMIC grounding.

So it's worth looking for the version with the most vias around the MMIC as this is probably the latest attempt at keeping this MMIC stable when used in real world applications.
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Old 23rd Oct 2018, 5:36 pm   #25
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

I also did some digging on our old parts database at work to look for examples of the old 'Magic Modamps' and I found two of them. The one closest to the spec of the ebay MMIC is the Avantek INA-02170. This is a really old part (nearly 30 years old?) but the datasheet plot for gain and noise figure vs frequency shown on the ebay auction looks like the Avantek plot of this old INA-02170. So my guess is that the MMIC used in this board is closely related to the plastic package version of the INA-02170 and this would be the INA-02186.

Ebay seems to have loads of new INA-02186 MMICs for sale and some of them have the same 'N02' logo stamped on them so maybe these are Chinese clones of this old Avantek/HP part. I think the original INA-02170 was quite expensive partly because it is in the posh '70' package and it probably cost about 25 about 30 years ago.
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Old 23rd Oct 2018, 5:53 pm   #26
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

HP bought out Avantek many years ago and it became part of their microwave semiconductor operation.

When HP split up, the microwave semiconductors folk went with Agilent.

Agilent promptly sold them off, intended to be floated off on the stock market, but a dominant share was bought by a financial consortium. The name was changed to Avago.

A year or so ago, backed by the resources of the consortium, Avago bought out Broadcom semiconductors. This looked a bit like a minnow tackling a shark, but think more of the size of the financiers, not Avago. So they now set to amalgamating all this, and decided the Broadcom name was nicer. So the name changed again!

And a year or so ago, the new broadcom decided to drop all the microwave amplifiers and diodes. So they're all obsolete now. Rather a shame as it was one of the most comprehensive and coherent ranges in the industry. Many of us are still trying to design our way round the now-vanished parts. Some of them have been difficult to find alternatives for.

So that's where Avantek went.

David
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Old 23rd Oct 2018, 6:02 pm   #27
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Yes, it's all a bit of a shame that it ended in this way. I managed to find some early Avantek INA-02186 info and I've posted it up below. The gain vs NF vs frequency shows that it isn't quite the same as the ebay device but it is very similar. It looks like they were called MagIC MMICs rather than Magic Modamps.
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Old 23rd Oct 2018, 6:15 pm   #28
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Another question someone might be able to answer; I wondered what was the primary use for which these boards were made? OK, so some (excess production?) have obviously come on the market for Joe Public to buy, but I'm guessing that there must have been a commercial driver for these to have gone in to production, but what is there that needs 0.1 to 2400MHz?

I'm just waiting for some SMD resistors to arrive, and I'll report back on the tests suggested.

B
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Old 23rd Oct 2018, 6:34 pm   #29
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

I suspect that the headline specs of these old MagIC MMICs sell themselves.

I think these ebay boards are aimed at the hobby market and many people will be attracted to a device that offers high wideband gain and low noise and so I suspect that whoever is designing these PCBs has managed to get access to lots of cheap versions of this old MMIC. So the lure of low noise and high gain and wide/flat bandwidth will attract users of SDRs or scanners or people who need a wideband distribution amp for a TV network within a house. But 30dB gain is a lot of gain so these high gain amplifier boards could cause more problems with overload than they cure wrt sensitivity...

I hope I'm not breaking the forum ebay rules but have a look at the images below and compare them to the PCB image in the first post. They all look similar but the via patterns around the MMIC are not as good as the PCB shown by Bazz in the first post on this thread. It looks like there are three versions so it might be worth trying to avoid the ones that look like the images below? The green PCB looks the same as Bazz's board but if you look closely at the via patterns it isn't the same. At first, I wondered if this was a jpg compression issue but it isn't. The via pattern is different in several places on the board even though the PCB silk screen has the same version number. So this image is of an earlier version of this PCB. Most of the other images show the same via patterns as Bazz's board so I guess you have to hope the sellers are now all stocking the later version of this green board and they aren't holding lots of stock of the older version?
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Old 23rd Oct 2018, 9:02 pm   #30
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

I've just looked at the actual listing for the supplier I used and the photograph there is of the version with fewer via connects. That is to say, the boards I received are the preferred ones, but different to the ones in his picture. So, anyone buying these from any supplier may be subject to pot luck, unless they are now only shipping the revised boards.

Both (green) boards are designated Rev 1A.1. The only other distinction is that the board with most vias has one "straight edge" corner (top right), the board with fewer vias has 4 rounded corners.

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Old 23rd Oct 2018, 11:15 pm   #31
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Quote:
Originally Posted by Bazz4CQJ View Post
but what is there that needs 0.1 to 2400MHz?
Low noise preamp for a spectrum analyser (they normally have an input noise fig of a bit over 20dB)

preamp for an Icom R9000 stuck up the mast on a discone.

Lots of uses for small amps at various frequencies. One design which covers 1-2400 MHz will do the lot. If you did a narrowband design, you'd have to do a lot of different designs.

1-2400 MHz is really the spread of applicability. The little beastie may be a worthwhile thing in an application even if that application uses only a tiny fraction of its capability. I use MMIC amplifiers spec'd for 10-6000MHz on the front end of a receiver tuned to a spot frequency of 1030MHz. A 1020 to 1040MHz amp would be fine, but nobody makes such a limited MMIC and the price would be bad if they did.

David
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Old 25th Oct 2018, 1:33 am   #32
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

So, making use of my extensive collection of 1950's signal generators and my 20MHz scope , I think I can fairly safely say that these two 4 amps work very happily at that frequency, with ~30dB gain. I'm guessing that if they work at all, then they may well work as per spec, or at least to 150MHz, where my interests die off? I'll see what I can devise to do more tests.

Ironically, the SMA to BNC adapters that I bought with them, well, .

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Old 25th Oct 2018, 10:18 am   #33
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

The cheap BNC/SMA adapters where the connectors are mounted directly on each other are terrible. Have thrown all mine away. The ones with the 4" of RG316 are fine plus also it gives a bit of strain relief.

Can't complain at the cheap SMA stuff really. 20 on aliexpress is about 200 on RS.
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Old 25th Oct 2018, 6:56 pm   #34
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Yes, I'm sure you're right on all those issues. I've used SMA connectors in the past at work, but these boards are the first ones that have made it in to my play room, so I'm on a little learning curve. I think I should get these amps safely boxed up asap before anything 'unplanned' happens to them.

Just one other comment I noted about them, the gain is very dependent of the DC voltage; shoots up between 7 and 8 volts and then flattens out somewhat.

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Old 25th Oct 2018, 8:07 pm   #35
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Arrow Re: 0.1-2000 MHz Wide Band Amplifier ~4

Gain dependent on supply voltage: I've met that with modules similar to the one discussed here. But there are two advantages. One, by adjusting the Vcc you can change the gain to meet a specific need (ideally using a 3-pin regulator); two, if the gain is excessive when used 'as is', the addition of an R C network for decoupling can help improve stability.
But there are other factors that may be relevant in the above: dynamic range, linearity and, possibly, constancy of input & output impedances. So, as is always the case with things like this, a good deal of experimenting & measurement first is called for, prior to automatically employing the device in a given application.

Al.
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Old 25th Oct 2018, 10:41 pm   #36
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Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

Yes, Al. There have been quite a few comments about the risk of instability with these units, and so it's useful to look at "Tip #4" that was in the info from the seller (see post #1). It says that best S/N and stability is in the range 8-10V. Not that he's actually saying that it may be 'less stable' if you push it over 10V, but we can all draw our own inferences, and if you don't need max gain at 2000MHz, 10V (or less) may well be enough.

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