VHFDesign 2m QRO EME LNA

Discussion in 'Amateur Radio Equipment Reviews' started by W2WDX, Jul 5, 2018.

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  1. W2WDX

    W2WDX Ham Member QRZ Page

    Hi all,

    While in the process of build a totally new station I set out to try and find a better 2M LNA. Now while I haven't operated any EME, I do like to be able to pull out weak-signal SSB DX via tropo when it happens. So a good LNA really helps when you can't put up multiple stacked big Yagi's. For my humble 2m array I use a 10el dual polarity Yagi and a pair of stacked 2m loops. So having some pre-amplification up on the two masts is crucial for me.

    The other problem is finding an LNA that can handle the amount of power I can run, in my case 1kW (when needed). Add to that the crucial noise figure and linearity I prefer. I have used everything from the crummy Mirage products, Advanced, and many others. Some worked OK, but most were lacking in some category. Either they amplified but were noisy, or weren't as noisy but had poor linearity. Some just couldn't handle the power.

    Being the eBay maven I am (I say that with great shame), I came across a bunch of guys in Ukraine who are building what seemed to be very we designed products for VHF and higher applications. They seem to be a group of engineers working on various projects simultaneously to advance the art. However when they come up with something good they build a few and make them available for purchase.

    First let me say I know some of you are going to comment, "This should be like this ..." or "People always give false specs ..." yadda yadda ... Well ... I fortunately have a few friends with gear I could never afford myself who work in the microwave, so I have tested these products to verify the specification. So don't comment if you are one of those doubty types. Buy one yourself and do the tests. Otherwise ... don't waste everybody's time with baseless opinions.

    VHF Design 2m QRO/EME LNA

    VHFlna1.JPG VHFlna2.JPG
    Sorry about the fuzzy images, no tripod and low light!!
    It was packaged for travel very well, with a nice heavy box, plenty of carefully fitted bubble wrap and each piece housed in it own heavy zip-loc bag. Travel time from Ukraine to New York was about two weeks. On first glance out of the box this LNA is constructed very well. A nicely machined housing (not waterproof unfortunately), good quality PCB and superb soldering. Even the "N" connectors have the plastic protective covers.

    Three factors really determine the quality of a LNA. (1) It's linearity, measured as Third Order Intercept Point (OIP3), (2) The noise figure in dB, (3) and the maximum input level. Another important consideration is the output bandwidth. There is a plethora of cheap amplifiers boards , kits and projects out there claiming low NF and other specs. Most are based on older GaasFET components like the PG-103. These broadband amplifiers will certainly increase gain and do so with a relatively low NF, however in my experience they are very susceptible to saturation, IM issues and a host of other shortcomings.

    This LNA uses an ATF-531P8 E-pHEMT device. These devices exhibit excellent linearity, high gain and very low NF at 2m. They also should be more reliable than even the low power ATF-54143 (SAV-541+). Here's a PDF of the device: ATF-531P8

    My friend and I put the LNA through its paces on his Agilent test equipment. For the NF figure we used a recently NIST calibrated Agilent N8973A and came up with an average figure of .3dB. Next we tested for OIP3 (sorry forgot the model number of the test apparatus) which came out to 37dBm. Gain was about 23dB (slightly lower than specified). We also measured the bandwidth at about (-3dB) 14.6MHz. We also tested each and pushed the input until we saw any change in a given spec, and we found the input maximum on average was about 26dBm, more than I thought possible. So the figures stated on the label are conservative and the true specifications are slightly better than advertised, in this case. I have two of these and used both for the averages. I have no way of determining piece-to-piece variations and have only these two examples (purchased at different times BTW) as my only comparative basis between pieces.

    My only concern about these are the relays; however, looking at the specs for these OSRAM relays as long as I keep SWR to minimums they should do fine. These LNA's do not have "RF sense" nor do they use coaxial DC injection, but instead rely on voltage on and off to achieve switching via a control cable (which I prefer since I used DC blocked coaxial lightning/surge protection devices anyway). I normally use a sequencer for my transceiver PTT, amplifier and LNA using a homebrew setup which I am currently updating. For this I am using another VHF Design product; a little sequencer board. Again very small and well built and all SMD. A far cry from my terminal boards, timers and relays sequencer. I'll let you know how that works in future installments.

    At least on the bench these little 2m pre-amps seem to smoke anything I have tested or used previously. I am currently building up a NEMA enclosure for this (and other remote stuff like antenna polarity switching) and promise I will revisit this review to give my impressions of this LNA in actual use.

    John, W2WDX
     

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    Last edited: Jul 5, 2018
  2. W2WDX

    W2WDX Ham Member QRZ Page

    Update: Just so you know they have been building (and have available) a PG-103 GaasFET version of this LNA, which has higher NF and OIP3 figures. The one using the ATF-531P8 device is designated with the "EME" labeling. Not just simply "QRO". So that's "QRO EME".
     
  3. W2WDX

    W2WDX Ham Member QRZ Page

    I have this preamp up right now, for now on an AR-2 Ringo just to test my sequencer. The preamp seems to perform very well, increasing signal while not adding any extra noise. Very preliminary test, and I will know more when I get the yagi going.
     

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