An inverted-L can be "broadband" in the sense a moderate-sized version can cover much of the HF spectrum. It is likely to also suffice at low frequencies since atmospheric noise swaps even relatively small antennas down there.
I would have to perhaps research it further, but IIRC, even an inverted-L at like 22' vertical by 22' horizontal or so actually shows decent lobes across a considerable swath of HF spectrum. Efficiency drops considerably at lower frequencies, but most receivers have plenty enough gain to offset the differences.
The 9:1 unun should suffice. Oftentimes it is often more about improving common-mode isolation than improved impedance matching for HF receiving antennas; withing reason of course. Considering it is an unun, you might want to experiment with an 1:1 galvanic isolation choke behind it if not already present. Also if just using a ground rod or similar, opting for a few on-ground radials might further improve efficiency.
VLF noise is a common issue even with a clean power supply and good galvanic isolation of the antenna. Unless you are perhaps in the middle of nowhere on a large rural plot, expect plenty of low-frequency noise these days.
That said I am in a neighborhood and often note plenty of NDBs plus even an occasional longwave broadcast, but reception of those tends to fair *much* better with my Airspy HF+D and 31' vertical. The HF+D has rather impressive dynamic range, selectivity, image rejection, etc. for a sub-$200 receiver.
Pending controversy over US government shortwave broadcasts aside, on a technical note, I can probably up amplification on my 148' LoG if Radio Marti discontinues on 6030. Right now it is my worst offender for overload here even with my 148' LoG well into negative gain numbers. o.0
My online SDRs are slightly down on the SNR charts for now. Awhile back I replaced my cheap preamp with the following:
https://www.sv1afn.com/en/product-category-5/high-linearity-pre-amp-(lna)-for-hf-receivers-30-khz-30-mhz.htmlIt is much cleaner overall, especially from an electrical noise standpoint, but it can sometimes overload a little when Radio Marti 6030 is on the air, even with currently (IIRC) 10dB attention on the input side. That attenuation tends to drop my SNR measurements by a few dB. Anyway.
Next I need to toss the current inexpensive active RF splitter for hopefully a little further signal cleanup. It appears somewhat electrically noisy at lower-HF and below. A passive splitter on a mix 73 binoc core for feeding my online SDRs should likely suffice for my purposes.
Speaking of preamps, I have a couple of inexpensive W7IUV-style preamps from AliExpress needing further evaluation. Not exactly a high-end preamp design compared to more modern designs, but the rather simple circuit is still quite popular. Naturally they have the usual cheap counterfeit 2N5109 transistors considering the low price point, but I have a few vintage (IIRC) RCA 2N5109 transistors available for swapping.
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