I built something like this back in the 70s from Popular Electronics Magazine. It was an Active antenna. Basically, it was just a FET. The Gate was connected to a whip antenna, and the 50 ohms on the source was connected to the radio.

Connecting this amp near the receiver as you show in this video would have the same effect as any internal preamplifier stage. However if you were to mount this at the base of your antenna you would probably see more benefit, as it would be amplifying the signal before losses as well as correcting the impedance mistatch between your antenna and your transmission lines.

I received mine today from Banggood, 30 days to receive it. I took it apart--the chip is the Gainsil GS 8091-TR. 350 MHz CMOS single supply op amp. Non inverting input is biassed at 1/2 Vcc and is capacitor-coupled to the input. The inverting input is tied to the output; the output is direct capacitor-coupled. There should have been a series resistor on the output to ensure stability, but there is none. You can find the data sheet for the IC on the internet.

I would have liked to see you attach it to your Malahit radio hooked directly to the telescopic whip.antenna. That might be useful for a DX outings in the parks, field days etc. 73!

It seems like your only ground connection is through the USB to the computer. A good ferrite choke on the USB cable and a good low noise ground should give better results I think.

Interesting device and video. Certainly raised signal level though perhaps the comparison was slightly skewed by the fact that the AGC was enabled.

The amplifier does seem to improve the ability to understand the transmissions - the noise increases but doesn't seem to increase as much as the transmission. For the price, it might be helpful under certain conditions.

One thing I have found (at least with my copy) of the RSPdx is that there is a certain amount of "bleed-over" between the antenna ports. They are not totally isolated. In other words if you disconnect all but one antenna and switch between ports, you will still receive a signal on the unconnected antenna ports. I wonder if the differences between the two antennas might be greater than what it appears due to the behavior of the RSPdx.

It definitely helped with the SNR especially with the broadcast station where it went from 20 Db to 40 Db. It seemed to help with the SSB signals but those are harder to judge since there is no carrier and you need them to talk continuously in order to even get a SNR reading. Of course it's not going to work with a loop which are by nature low impedance and usually below 50 ohms

I use a couple of metres of wire into a 2N2222 buffer with T-bias. The low component count would suggest this device uses a similar design, unless that SOT23 is some type of amp chip.

For Receiving only I highly recommend the Bonito MA305 with optional longer whip for more gain, good H155 Coax and ground it well and it's one fantastic antenna for it's size, great for DX and low noise, though as always this mostly depends on your location. The performance of the antenna is amazing for it's tiny size but do get the optional longer whip, good coax and ground it well before it enters the house. It only needs to be on a pole around 2-3 meters off the ground. It can be powered via USB power bank rather than noisy mains power supply. I'm able to power the bonito directly from my Malahit DSP 2, original Russian version. Minimises cable mess. The Bonito Megaloop FX is also another excellent antenna and probably a bit better for noisier environments. I have the 10 meter long version and use less amplifier gain, you can set this via jumper inside.

I would be interested how this would compare to an MLA-30 in terms of serving as an amp for a small loop antenna.

I would try a LOG loop on the ground to see if you can change your S/N ratio. You might get a nicer signal, but honestly your noise doesn't seem horrible.

I'm in a high-noise environment (urban area) and have a hard time picking up ordinary 100W signals on HF, even CW. The last SST I participated in, I discovered I was only hearing 500W+ stations at all. I tried a passively-matched Loop-on-Ground RX antenna to try to reduce the noise floor as much as possible, but it's not enough. QRM removers also don't do much, as it's thousands of rf noise sources, not just one I can cancel via phasing. It's bad enough that I've lost interest in playing radio at home. I wonder if something like this with an even longer Loop-on-Ground (or perhaps Loop-near-Ground or non-loop longwire following the property line) would perform better for RX under these conditions.

Wise move asking the audience for their opinion on this subject 😅 Electrical I'm not going to even pretend I know what is going on. Audibly I can notice a slight improvement. Not to sure if its helping to boost certain frequencies of the sound coming out, but listening to the English it was slightly more clearer.

As has been said by a few others, "high impedance" would be a very electrically short antenna, substantially less than 1/10th of a wavelength. Think of a set-top telescopic whip, say a metre long, on the 75 or 49 m broadcast bands for example.

What is the benefits of a Hi-Z antenna over a standard 50 ohm antenna? WHAT I had a lot of trouble with is receiving a low power 900 mhz signal I used 24 volt cellular phone base station receiver booster The frequency range was the higher 900 band or the lower 800 band, as the handheld output is 824 to 849 mhz But it did work for the 898 mhz range pretty well The biggest issue was the heat They got incredibly hot for just being a receiver pre-amp. They got hotter than a 100 watt transmitter on all the time. It would burn your fingers if you touched it. In the winter it was fine but the summer it was just too hot to use.

What is actual current draw? Looks as though device may run 3.7v direct as there didnt appear to be any DC -DC converter. This may indicate output power capability of amplifier. Even moderate levels signals on MW may cause overload.

Excellent, Thanks for the info mate. Would be so simple to adapt it over to bias tee charging for that Cell Or even using a small solar panel To keep it topped up For use at the antenna end. Great Video Mate. 73 de VK3VKe

Makes a difference

Randomly, aren't magnetic loop antennas high impedance? Would this help with a homebrew version of one?

An SDR doesn't need an amp as much as some sort of band pass filter to block the signals from out of band strong local stations.

nice and Very cheap but would this work on a discone antenna???

Curious what the six pin chip was, since it appeared to be the only active device in the signal path.

This should be good for sampling from transceivers that don't have SDR capabilities. I think also for dummy load signal sampling.

Have You tried this on long wave? Or the "beacon band" between lw and mw.. Your wire would be way too short there, thus very high impedance so in these frequencies that amp should do wonders.. also that high input impedance presents another quality that may present a problem of it's own at least dx-wise; It's very hard, almost impossible, to choke out the common mode type noise coming from the house (chokes can bring some few hundred ohm impdance which doesn't do much against specd 1Mohm input impedance..). So i would recommend at least putting the amp outside and farther from the house and trying to choke out the 50ohm feedline.. Basically following the same guidelines as with miniwhip.. Also on lower frequencies You shouldn't even need a wire..any shape metal object would work as a "capacitive probe" and surface area defines the voltage level received.. too large and you'd get distortion and im products on upper bands..too small and your reception is weak.. hard to judge by the looks of the guts, but i'd be weary of too large signals because of the im distortion.. I've been toying around with high impedance receive antennas and they can be very dx capable if implemented properly!

I wonder how a 49:1 un-un would compare? It would have the advantage of being able to transmit through it too.

The 50 ohm Sma Connector Impedance is Not seen as Any Impedance at the Long Wavelengths usage...The Input Sma Connector simply looks like a Moderate size Solder Blob signal Connection.....Works perfectly, No issues !!

So no shielding... on an antenna feed? That can't be good.

What is the ohm reading of the Hi-Z antenna?

You can't really apples to apples compare the setup between Antenna A and B as you have it setup. For starters running a long wire onto the 50ohm Antenna A input without some sort of matching is going to significantly reduce the performance of what the RSPdx is capable of. Secondly (not knowing exactly what the high Z amp does inside) It will probably help lower the noise floor on Antenna B if you give the high Z amp a short counterpoise wire on the ground side. A better comparison could be if you connect Antenna A via a Nooelec 9:1 UnUn Balun, which will level the playing field. Or even better is use a SDRPlay RSPDuo, which has a High Z input built in. In any way, love your vids thanks.

Hi Matt, the issue here is that an 11m wire is not necessarily a high impedance above a few MHz. It is a 1/4 wave, close to the ground, on 40m. I would expect it to have much more effect on MF/LF than HF. Perhaps repeat with a shorter wire, say 2-3m? Also noted the no longer used QO!00 antenna in the garden.

I would want to test it at 500 Khz and below.

It's really a functional battery powered Lo noise Unity Gain Hi-Z (1 Mohm) Input to 50 ohm Out impedance Converter....The Slight S/N Improvement Demo in the Video is Typical 10 db Hi Z antenna to 50 ohm receiver Impedance Mismatch loss Correction gain....

What Mini-Whip does

Dear Matt, thanks for the test, interesting little box with surprisingly good results. You created a good test setup but then showed a not so ideal test ... when testing signal/noise don't do that with the strongest signals on the band, do it with the weakest, it will get you a better differentiation between the two. The 3 empty solder pads in the input and output section of the PCB seem to have been for an optional BAV99 dual switching diode, limiting every voltage peak exceeding 0.7V ... its sometimes good to have, keeps the amp protected, but at higher RF levels it can cause intermodulation ... so I wonder why they decided to leave it out? It seems to be ideal for portable operation to avoid any mismatches that will also cause you to pick up unnecessary computer/USB noise from a poorly terminated coax. For that price including the tiny lipo battery that is really a great deal.

For many decades now we have receive antenna jacks on radios and no one ever cared about the impedance. For a more repeatable test: Take any signal generator (Si5351 module is fine), attach a piece of wire of wire to the output and measure the SNR of the signal on both inputs.

When looking on LW a lot of intermodulation artefacts are seen when the amplifier is active. This is not a good sign!

Maybe it would be productive to run an S21 test on a VNA

Try it with a massive undersize antenna and solid grounding on the shield. Ideally on something tower-ish out in the yard. It should ideally cover a very wide span without any tuning. For DIY projects: BUF802 looks interesting indeed, like should cover the full span of sdrplay in ONE* antenna! * Yeah right, could be interesting to see how it actually works! Probably forgetting something important.

I am at a complete loss to know why any manufacturer would use an SMA socket as a means of connecting a wire antenna to a device. I see that you had to resort to using an SMA to SMA male adaptor and an SMA PCB mounting socket in order to connect your wire antenna to the device. This must have added over £4.50 to the price of the device and entailed soldering, which a small number of people aren't equipped to do?

Is the voiceover read by an AI? There's something super uncanny about it.

It is a strange decision to use a standard 50 ohm SMA connector for a Hi-Z interface. Connecting antenna with high input impedance to 50 ohm connector creates an impedance mismatch. I would have expected just standard screw terminals for a ladder line which would be more suitable for a Hi-Z interface.

You'd get betterr results fixing your antenna so it isn't mismatched. Heard of baluns? They are utterly silent! You can't change impedance with an amplifier.

Its worth a tenner, wouldn't give a score for it

the HI-Z input with an SMA is incorrect. I suspect this is a POS

Sorry, thought you were British. That would be ZED, no ZEE please@