Roelof,
Thanks for that information. As you will have seen from another post,
my unit is the PA0HNC design sold from the Ukraine. Several other
mini-whips can be found on eBay. My main reason for buying that one
was it needed very little work to get it operational, whereas
several others need construction from a kit or at least putting in a
waterproof enclosure.
The performance certainly does drop off at VLF and does not appear to
be good below about 50kHz despite being advertised as going down to
10kHz. I would have liked one that worked well below 10kHz.
I planned to buy a small transformer-type PSU but I had another
switch-mode one in the shack so that's why I tried it.
Mike, G3XDV
==========
> Hello Mike, David,
>
> Mike, your results don't surprise me, but if at all possible a power
> supply with a transformer is recommended. It does not need to be a
> regulated one.
>
> Since I published this design in 2006, quite a bit of improved
> versions can be found on the Internet. However, a word of warning is
> on order.
>
> Recently I have completed a IMD test set up and I believe that I can
> reliably measure IP2 and IP3 of the mini-whip antenna designs.
>
> The original design using a J310 as input device and a 2N5109 output
> transistor has a gain of -7 dB. IIP2 = +68 dBm and IIP3 = + 40 dBm.
> This is with a supply voltage of 12V at the collector and drain of the
> 2N5109 / J310. Current draw is 49 mA. Power is fed to the antenna via
> my standard interface.
>
> My current design features a BFG591 instead of the 2N5109 as genuine
> 2N5109's are difficult to source and costly. Right now the BFG591 is
> also obsolete, but it's successor the BFU590 performs just the same.
> With the bias optimised for IP2 and 12V at the collector / drain as
> above, gain is -7 dB, IIP2 = +76 dBm and IIP3 = + 40 dBm. I have
> tested three samples and the results are the same.
>
> Tests with test tones of + 6 dBm and 0 dBm gave also the same
> results.
>
> One design found on the Internet is from PA0NHC. The test figures for
> this improved (this is mentioned on the PCB) design are a gain of -8
> dB at 12V and 98 mA. IIP2 = + 49 dBm. IP3 can not be established as
> for 1 dB input step, the third order products change 2 dB instead of 3
> dB as it should. So something is amiss with this design. I have
> omitted the protection diodes at the input, but that did not help.
> Someone in the Ukraine sells a clone of this design and I found the
> same anomaly on two samples.
>
> Last week, Marcel Bos provided a link to a mini-whip design from
> PA3WFM. This design is similar to a circuit Johan Bodin, SM6LKM
> provided in 2005. I have build the PA3WFM design using a MMBFJ310 and
> a BFQ149, but could not find the IMD figures stated in the article.
>
> This circuit does not fathom + 6 dBm test tones. I had to drop the
> level to -3 dBm for sensible test results: 12 V, 44 mA, gain -5 dB,
> IIP2 = + 64 dBm and IIP3 = 36 dBm. This antenna works well as does the
> design from PA0NHC, albeit the latter does not provide reception at
> VLF.
>
> It looks like the original design, developed with the help of Steve
> Ratzlaff, AA7U has outlived the ravages of time!
>
> Best regards and 73,
> Roelof Bakker, pa0rdt
>
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