The antenna was bought from a Ukrainian company called Transverters 
Store on eBay. The page is at:

https://www.ebay.co.uk/itm/MiniWhip-Active-Antenna-Assembled-in-Box-HF
-LF-VLF-mini-whip-sdr-RX-portable/222469570201?hash=item33cc383e99:g:Y
ugAAOSwc-tY63MT

The unit is sealed in a plastic pipe and comes with a power splitter. 
Price is <£35 inc postage. It took about 10 days to get here. 

The PCB is 155mm long and the "antenna" part is about 100m of that. 
The amplifier uses a BF998 in the front end, followed by a BCX54.

My big antenna performs very well, but I have to lower it when it is 
windy, and re-erecting it is a tricky and heavy job so I am often off 
the air completely for more than a week at a time. The mini whip is a 
way I can still take part in the LF scene, at least on receive. 

The only tweak I had to make to my station was to slightly improve 
the front end selectivity of my SDR by adding a single tuned circuit 
to compensate for the fact that the antenna is not resonant.

Mike, G3XDV
========== 


> Hi Mike.
> Thank you for that informative report.
> Can I ask:
> 1) What length whip did you use?   Is it enclosed in a plastic sleeve
> or 'open' 2) Which circuit did you build. I believe there are several
> different versions which mainly differ in the design of output
> amplifier (single transistor or MMIC etc)
> 
> Many thanks
> 
> David  G0MRF 
> 
> 
> I have spent a few days experimenting with a mini whip active 
> receiving antenna. As advised I decoupled the feeder by winding it
> around a ferrite core, and ensured the antenna was earthed to a stake
> at the foot of the (20ft) mast. It produced very good results on the
> 136kHz band - about the same as my much larger and higher transmitting
> antenna, which is currently on the ground. 
> 
> However, the performance on 472kHz seemed poor. I was giving WSPR
> reports about 3-5dB below other stations. Eventually I found that the
> 12v PSU (Watson Power-Mite) I used to power the whip had a lot of MF
> noise, and filtering the output failed to completely eliminate it. I
> replaced the PSU with another - also switch mode - and that did the
> trick. I am now giving reports as good as the best stations.
> 
> This is a very effective, yet ridiculously tiny, antenna which anyone
> can use to achieve good results on receive, no matter how small their
> garden is. But beware of PSU noise sabotaging it.
> 
> Not for the first time, I have found Opera and WSPR to be very useful
> tools in determining how well my station is working by being able to
> directly compare transmit and receive performance of other stations.
> Without this facility I might have just accepted the level of
> perfomance I was getting.
> 
> Mike, G3XDV
> ==========