n6gn

In a kiwi itself rather than my router, after trying it with FORWARD, I ran:
iptables -I INPUT -s 47.88.219.24/24 -j DROP
iptables -I INPUT -s 184.22.160.13/24 -j DROP
since I'm trying to stop packets from two different offenders at the kiwi rather than from being forwarded by the router. This I followed with:

iptables-save

so that it will (I hope) get restored upon reboot. Examining the results I get:

root@kiwisdr:~# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
DROP all -- 184-22-160-0.24.nat.tls1a-cgn02.myaisfibre.com/24 anywhere
DROP all -- 47.88.219.0/24 anywhere

Chain FORWARD (policy ACCEPT)
target prot opt source destination
DROP all -- 184-22-160-0.24.nat.tls1a-cgn02.myaisfibre.com/24 anywhere
DROP all -- 47.88.219.0/24 anywhere

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

I'm not familiar enough with iptables yet to know if this will be sufficient, perhaps only the INPUT rule is needed. Maybe someone who knows can suggest whether this is correct or whether there's a better way.

W1EUJ,
I have been working on exactly this for some time. I started with a variety of broadband approaches several years ago. A prototype was published by W6SFH in QST a couple of years ago. I've visited both short dipoles and loops as well as various FET/BJT approaches such as several iterations on the Trask design.
My target has been to get to or very close to the "quiet rural" ITU noise floor with an antenna (system) that can cover the range of the kiwi. It turns out that with small antennas the limiting point is the same as that of the kiwi - upper HF. Although 'radiation resistance' and the associated signal&noise levels are dropping with increasing wavelength, the noise floor at these long wavelengths is rising faster so that allows a very small antenna to work well from LF-midHF. The problem is that to get to the ITU limit above ~14 MHz (or so) one needs to get rather close to KTB. This is not presently possible with available devices. For a dipole, the device that can provide the input Z (low capacity, high R) to avoid mismatch loss can not simultaneously handle the broadband onslaught of highlevel signals and very low noise floor. I have been able to achieve this with an OpAmp design but only VLF up to midHF.

Lately I've been working on a hybrid passive/active approach just as you suggest. But to make this system work with a passive over an [octave] requires some complexity. The Q of a single dipole (around 7) is too high to avoid mismatch loss (see paper by Fano) that raises the effective noise floor. But there are techniques that can do this. For example, a biconical or modified-biconical can be built from wire and give only ~2 dB mismatch loss from 14-30 MHz (and above). It also appears to be possible to couple an active dipole with a passive one to get partial-hybrid, though not over an octave. With a suitable diplexer at, say, 12 MHz, one can combine the best of the active antenna performance with that of the passive and get to a suitably low noise floor.

Presently I'm trying to understand the effects of ground/earth proximity and polarization better. I have kiwis outfitted with both active antennas and multiple V/H passive dipoles (with LNA) available should you like to investigate. The active dipoles are on N6GN/K3 and N6GN/K2 (a remote site) while orthogonal 21 MHz dipoles are at N6GN/K. All three have antenna switches so you can play around, though be cautioned that I'm always messing with things so there's no guarantee what you'll find. I try to keep the Antenna labels current but don't always succeed.
Write me if interested in any particular part of this.

Glenn n6gn

Martin,
The mechanism I have observed is in addition to these, looks something like this:

without perfect balance (infinite CM impedance) at the far end of the (shielded) LAN or PS cable there is *still* ingress at the ADC.

The splash image on http://n6gn.no-ip.org:8073/ has a schematic of a MW band stop that surpresses MW BCB by about 20 dB and allows for one additional notch elsewhere. This may protect a Kiwi from OV while still allowing only slightly reduced access to stations in MW and good access elsewhere. It can be fabricated from inexpensive SMD components.

While " /sys/class/gpio/gpioNN/value" did allow toggling the lines, it seems that it is toggling more than one. I haven't studied the class to understand it and there may be a way around this, however, Gwyn G3ZIL, kindly pointed me to another way that seems to do exactly what I want even more directly. It is:

rsh root@[kiwi IP address] "/root/extensions/ant_switch/frontend/ant-switch-frontend N;" 2>/dev/null

where N is the Antenna N selection desired and 2>/dev/null throws away the return text from the BB resulting from the remote shell call. I expect using this method requires compiling the ant_switch extension into the Kiwi but that is well documented and only takes a few minutes.

This seems to work precisely as hoped and allows setting the GPIO lines of the ant_extension one-at-a-time. I measured 600 ms/setting across my local network.

If someone simply wants a few control lines to use to programatically control an external device on a kiwi - whether an antenna switch or something else - this seems to be a quick, easy and effective way to do it remotely.

I've only tested from a remote computer running Ubuntu Linux but perhaps someone more familiar with Windows can provide an equivalent method for that OS.

See https://github.com/OH1KK/KiwiSDR-antenna-switch-extension/blob/master/docs/antenna-schedules-using-crontab.txt
for automating this with crontab from the kiwi itself.