Active Miniwhip antenna (e-field probe) performance on higher frequencies

[radar_hunter]

I'd like to hear people's experience on mini-whip antennas on the higher HF and low VHF frequencies, above 20 MHz.

My personal experience is that mini-whips work well from VLF to about 20 MHz (lower range requires common-mode choke or isolation transformer), but above that their performance quickly degrades.

Comparison between a mini-whip and a full-size vertical CB antenna is like night and day as one may expect, but I have noticed that even my FM/TV antenna system seems to work better on those frequencies.

Does anyone know what exactly causes this performance degradation?


I think all my mini-whip antennas are based on PA0NHC design, but at least one of them has "modernized" design which uses different transistors (BF998 and BCX54). Those transistors are rated for much lower frequencies than those of the original design that should work in the GHz range. But even the BCX54 has rated transition frequency of 180 MHz.

PA0NHC measured the original circuit and it had a nearly flat response up to 150 MHz without the input choke.
I tried bypassing the input choke and got a slight improvement, perhaps. But nothing spectacular.

I measured the circuit using NanoVNA before and after the modification and the difference above 20 MHz was massive. On the other hand, my measurement setup may not have been very good.


If I could find simulation models for those transistors I could try to simulate the "modernized" amplifier design. Or I could buy another miniwhip with different design and see if it works better, but who knows what design is actually used by eBay sellers. Buying components and building one from scratch would at least guarantee that the parts and design are what I want.

 

[Dirk_SDR]

I can compare 3 Mini Whip versions: PA0RDT, PA0NHC and PA3FWM.
My DIY PA3FWM version performs best, followed by PA0NHC.
I think you cannot compare these broadband antennas with tuned CB or TV verticals.
They are made for VLF up to HF (PCB design, transistors, input choke, Bias-T PCB & chokes ...), but I can also listen up to FM with my PA0FWM.
Of course there could be improvements for higher frequencies like the Boni-Whip up to 300 MHz shows:

Boni-Whip - Bonito Hamradio

Active Wideband Antenna 20kHz - 300MHz Wide frequency range 20 kHz - 300 MHz Small dimensions Ideal

www.bonito.net

... or the GigActiv GA3005 even up to 3 GHz:

GigActiv GA3005 – Extreme Wideband Aktivantenne - Bonito Hamradio

GigActiv GA3005 - Eine Aktivantenne für alles Die rauscharme und sehr hochwertig verarbeitete GIGACT

www.bonito.net

 

[radar_hunter]

I can compare 3 Mini Whip versions: PA0RDT, PA0NHC and PA3FWM.
My DIY PA3FWM version performs best, followed by PA0NHC.
I think you cannot compare these broadband antennas with tuned CB or TV verticals.
They are made for VLF up to HF (PCB design, transistors, input choke, Bias-T PCB & chokes ...), but I can also listen up to FM with my PA0FWM.
Of course there could be improvements for higher frequencies like the Boni-Whip up to 300 MHz shows:

Boni-Whip - Bonito Hamradio

Active Wideband Antenna 20kHz - 300MHz Wide frequency range 20 kHz - 300 MHz Small dimensions Ideal

www.bonito.net

... or the GigActiv GA3005 even up to 3 GHz:

GigActiv GA3005 – Extreme Wideband Aktivantenne - Bonito Hamradio

GigActiv GA3005 - Eine Aktivantenne für alles Die rauscharme und sehr hochwertig verarbeitete GIGACT

www.bonito.net

A full-size CB antenna will perform better near 30 MHz than a miniwhip of course.

TV antenna, not sure about this. My TV antenna setup has yagis for UHF and VHF and a folded dipole for radio (FM). And it feels like it receives the 30 MHz range better than the miniwhip. It's higher up on the roof which may explain something.

It's possible that the miniwhip amplifier does not perform well above 20 MHz, either due to design, or implementation. But PA0NHC measured his circuit and it had a fairly flat response up to 100 MHz and beyond.

I'm not sure if the "modernized" design works that well, but I measured measured my miniwhips, and after bypassing the input choke, the response looked decent in the low VHF range.

The power injector had a decent response too, no significant attenuation as far as I remember.

I was thinking if there is something related to propagation, or other things, that makes the miniwhip less useful on these frequencies.

I think I tried once to receive the local airport radio and it worked. But I think it even came through when the amplifier was powered off.


I could try to simulate the miniwhip amplifier but that would require good simulation models of the transistors. Generic models won't work well.
I could also try constructing a miniwhip exactly according to PA0NHC or PA0RDT design, no "modernized" stuff. Or even design my own circuit.
Or, buy a different cheap one and hope that it works better.

Still curious to hear people's experience with miniwhips above 20 MHz.