23cm 500mW Amplifier SXB4089Z

 After calming down over JLPCB's appalling process for dealing with their errors, which is to deny everything and obfuscate to the point I gave up, I populated one of the test boards for the SXB4089Z. My earlier posts here, here and here set out the steps I took to end up with the following:

 

Expected Results

My results did not quite match this. Using the nanoVNA to measure the input and output ports, adjust for the attenuation used and then combining everything into a single file for RFSIM99 to read showed that the output matching was nearly spot on (I will need to change the 1.2pF output capacitor to 1.0pF) but the input matching was all over the place. I repeated the measurements and got the same result.

Actual Results

I am confident that once the input reflections are resolved that it will only take a small tweak to get this working well.

73's

Richard

New part - SMA3109 MMIC

Something different....

I stumble across new parts from time to time that set a price / performance benchmark. So I thought it would be worth alerting readers to these parts. Here is the inaugural post on this subject.

The new benchmark in my shack for general purpose mmics is the SMA3109. It happens to be the cheapest mmic that LCSC stock. I had wanted to use this commercially but the initial lack of S parameters meant I passed it over in favor of another device. That decision might get revisited.

Despite the low price the SMA3109 offers outstanding performance from VHF through to 4GHz. Compare it with other low cost mmics such as the BGM1013 and you will see why I rate it so highly.

When I evaluate a MMIC I consider:

1. stability
2. input and output return loss
3. noise figure at intended frequency
4. gain
5. ease of hand soldering
   

This device is ticking all my boxes but the NF of 4dB rules out demanding low noise applications.

I suspect it is useful outside these ranges but the S parameters kindly supplied by Onsemi technical only cover 100MHz to 4GHz.

Band	Gain	S11	S22
2m	23dB	-28dB	-13dB
70cm	24dB	-24dB	-16dB
23cm	24dB	-38dB	-16dB
13cm	23dB	-15dB	-14dB
9cm	21dB	-11dB	-17dB

The input match on 23cm is outstanding and I will definitely use this device in my 23cm projects where filters are connected to the input. For driving filters I would consider at least a 3-6dB pad to provide a better source termination. Being very stable across the entire frequency range matching if needed is straightforward.

Where linearity is important I would budget to get around 0dBm out of the device.

My hunch is that the feedback within the device makes it useful below 100MHz except for the output becoming a poor match to 50 ohms.

The device appears to be very useful from 2m through to 9cm and represents terrific value for signal outputs up to the Po(1dB) level of +4dBm. Definitely worth a look at US 11cents each!

73's

New Part - VHF Low Noise Amplifier MXDLN02C

So I was browsing for a high speed op amp and I came across this wrongly catalogued part at LCSC.COM. I am now testing it for a commercial project but it could have uses in ham projects.

But there are some caveats that go with a US$0.05 part:

1. The datasheet could be better
2. This is not a strong signal handling part
3. No details exist on how best NF is obtained

The MXDLN02C is meant to be used as a pre-amp for FM broadcast receivers. The datasheet suggests the noise figure is under 1.5dB and gain is above 20dB from 50MHz to 150MHz with good stability. I wrote to Maxscend as part of the commercial project requesting the S parameters in a table format. The response suggests Maxscend will never be one of my preferred suppliers.

So, in Ham spirit because this is a really cheap part, I simply hooked up the input to the nanoVNA and measured S11. Now I don't claim the nanoVNA is the last word in measurement, or that my test board was perfect. But the results I got suggest Maxscend was way off the mark.

From the Datasheet (2.85V) :

From measurement (also 50-150MHz) (3.3V):

I'm not dwelling on the possible reasons why there is such a disparity. What is important that based on my measured S parameters matching networks were easily calculated in RFSiim99. So, a few minutes of tweaking and I had a return loss of -30dB on the input at 6m and about 20dB of gain.

A similar story on the output port.

Summary:

It's ridiculously cheap.

Useful for 6m and 2m in non-demanding front-ends, still has +13dB of gain at 70cm.

This is not a MMIC so matching to 50 ohms, while easy, will be required

Like a MMIC no biasing calculations needed

Stability concerns limit HF applications

I always advocate using what is in your junkbox. But if you had to buy a device for low level amplification at 6m or 2m then this is what I would suggest.

73's

23cm Amplifier SBB2088Z - More Navel Gazing

It occurred to me some time after I had prepared the PCB layout that I had left out the small input "stability" resistor in the transmission line version. Since the minimum resistance needed to ensure stability was 1 ohm I wasn't too concerned. Just putting 1 ohm into the actual circuit wouldn't change much would it?

Well, it turns out it did.I started from scratch and derived a circuit with a 1 ohm resistor and transmission line matching. I found that the capacitors adjacent to the 50 ohm ports were reduced by around 50%. And the transmission lines were around 20% different in length. Now 1 ohm is a really small amount of resistance and these are significant changes.

So I inserted a 1 ohm resistor into the original transmission line version and compared the two.

While there is a small variation in gain, all versions will be substantially the same in practice. Should I be concerned that 1 ohm made such a difference?

I put the difference circuits giving almost the same result as comforting in that the matching will be smooth and relatively insensitive. I look forward to receiving the boards to find out if this is indeed the case.

73's
Richard

23cm Amplifier Musings - SBB2089Z

While I got myself organized to order PCB's for testing the SXB4089 mentioned in the last few posts, I thought it would be worth looking at some of the other devices. The first of these I turned my attention to was the SBB2089Z, a 100mW device.

What I found, if you study the large image below, was that the bare device was acceptable for 6m through 70cm. However, at 23cm the output was not as good a match to 50 ohms as I had hoped (RL= 8dB ).

As expected, matching to 50 ohms at 23cm introduces loss of gain at other frequencies. There was also some slight chance of instability hence the series resistor in the second version to prevent these.

I'm going to get two boards fabricated for testing: one for 6-70cm using just the MMIC, and one for 23cm using transmission lines.


73's
Richard