n6gn

For $US50 DX Engineering shipped me a pair of filters and two short cables to allow inserting them in-line. But before actually trying them out, I had to at least take one apart to see what they were. Essentially these are back-back HALO HFJ11-1G46ERL Ethernet filters, RJ45 connectors with built-in current and voltage baluns

As you can see there is no DC connection between shields and there is the balance/symmetry of the transformer isolating shield and pair currents from appearing on the output lines. DXEngineering's page doesn't indicate what the test conditions were for their measurement showing > 20 dB CMRR across the HF bands. In use, the attenuation obtained will depend upon source and load impedances which aren't specified but were perhaps 50 ohms for their measurement. I'd expect typical long lines of CAT5 to show considerably higher impedance at some frequencies and so net reduction of CM current may not be nearly so great as their plot would indicate, at least not everywhere.

They indeed will not allow POE since one of the two baluns is flux-coupled and is essentially a HPF with no DC response.

From Martin's, G8JNJ's, schematic of the BB grounding it looks like these filters could potentially improve the noise floor for KiwiSDRs. If I'm reading it correctly, the CAT5 shield is connected to BB and enclosure grounds directly. Thus any CM current injected onto the CAT5 shield or lines and given a return path out the SMA isn't suppressed. As I've written before, I measured about 70 dB attenuation for this path - an isolated 0 dBm 50 ohm source placed across the SMA/LAN-end grounds resulted in about -70 dBm signal detected by the Kiwi. This implies to me that many of us may have our noise floors raised with spurious signals getting in by this mechanism. Since the ultimate floor of the Kiwi itself is about -157 dBm/1-Hz there's a lot sensitivity to see this kind of interference.

But the LAN cable is not the only way for CM currents to be injected, the PS and even GPS cable are other possibilities as well. And I haven't even tried the filters out here and so it's too soon to judge, just thought I'd pass along these details since I was thinking about it.

If you want to roll your own filter, Mouser sells them in singles for US$12.50 so DX Engineering is giving them to us mounted on a board in a little molded housing along with a cable for the price you'd have to pay for 4 connectors alone. However, if you're willing to make several yourself, at quantity of 25 they drop to US$8.57/per and getting the finished product from DXEngineering isn't such a good deal. I wonder if we'd see any improvement in a KiwiSDR if the RJ45 connector were replaced with one of these.

Attached is a pdf that describes my current efforts to design and build an antenna switch for the KiwiSDR and the reason behind them. I'm posting it in case it may be of interest or useful to KiwiSDR owners, not because I'm interested in manufacturing or providing one - I'm not.
This is subject to revision...

Glenn n6gn

Attached is a pdf that describes my current efforts to design and build an antenna switch for the KiwiSDR and the reason behind them. I'm posting it in case it may be of interest or useful to KiwiSDR owners, not because I'm interested in manufacturing or providing one - I'm not.
This is subject to revision...

Glenn n6gn

Here's a photograph in case you just want to see it but don't want to download the pdf

Not sure if I got all the parameters in but
http://n6gn.no-ip.org:8074/?mute&sp&iq&f=25000:0,20&ext=iq,off
seems to let one examine the phase of the Kiwi w/ Bodnar against US NIST.

I sometimes run a common GPDSDO derived external 66.660 MHz clock to correct and synch frequency.

But for time I have no solution that gets multiple kiwiSDRs exactly synchronized.

N6GN/K, N6GN/K2 & N6GN/K3 from Fort Collins, Colorado running 5-21 receivers on 1-3 different antennas, using AI6VN scripts.

Yes, there's a chance. On my list of interesting projects is a fast-switching block converter. Essentially this would be a transverter (up/down converter) to an IF above the highest frequency of interest, perhaps 3+ GHz. This uses an LO synthesizer of reasonable performance, (e.g. Harris chip set) speed, phase noise etc paired with isolation stages to drive two mixers with BPF filtering. Picture a, say, 3.0 GHz transceiver that converts 10-32 MHz from a Kiwi or other SDR up/down.
That 3.0 GHz IF is then used with another pair of mixers and the same chipset as the fixed LO synthesizer but this time that LO is stepped in [20 MHz] steps from [3.5 - 6.5 GHz] . This is paired with another similar mixer and converts the original 3.5 GHz IF back *down* to 0-3 GHz. Because LOs are identical and use the same reference, phase noise contributions largely cancel and the result is an all-band receiver using the Kiwi as the last 'IF'/detector/demodulator moving anything the base HF KiwiSDR can do at HF to 0-3 GHz. With stitching it becomes a wide band spectrum analyzer as well.

Synthesizers that can do this are pretty inexpensive as are mixers and gain/isolation stages. Other than BPF & LPF filtering, done between planes in the PC board there isn't much to it. Since all LOs can have high PLL bandwidth, close in spurs and phase noise can be that of the base clock which is perhaps coherent with and also providing the 66.660 MHz Kiwi external clock.

A nice side effect of all this is that it can transmit at low power, as well as receive. Low noise pre-amplification and PA stages can be added as desired (or not).

I think it would make a nice open source hardware/software addition to the KiwiSDR and even Apache/Red Pitaya ... style SDR transceivers. With only 20 kHz of information bandwidth, the Kiwi might not offer every sort of mode that *could* be desired at VHF-microwave, it's not going to receive WiFi or WBFM, but it would still be good for a lot of interesting uses.

It's not a small project but a prototype could probably be running in only a few months...

Glenn n6gn

How about a spectrum instead, there's information in that display that is hard to see in the waterfall.

Thanks to all for ideas and suggestions. I expect to have a little more detail once we actually visit the remote site again (-2F/-19C here this morning!). In the past, the Kiwi has always restarted, so I don't suspect the power supply. On all my Kiwis I am using simple LM2596 buck converters to get from 12VDC to 5V. These have ample peak current capability such that startup has mever been a problem. In addition, once or twice in the past when on-site, the Kiwi was seen to have the "double beat" LED pattern indicating no DHCP after power was interrupted. I should have taken the "one error is a pattern" adage more seriously.

We don't know for certain but it looks from this end like the problem is one of a bridge/adaptor not coming up before the Kiwi needed it. This problem could also plague other Kiwi users, particularly anyone who might be using a WiFi adaptor as a means of eliminating all antenna feedline (and associated common mode noise currents!) by placing all the radio hardware right at the antenna. Separately I've created a very light active dipole/Kiwi/Wifi module that is light enough to be lifted by helium balloon. Such a device becomes a sort of portable e-field probe for measuring both signal and noise as a function of height and distance from residential/commercial noise sources. Perhaps more on this in another post.

I was able to scan the 169.254/16 address space using nmap (it takes a while even with only ICMP/ping probing!) but discovered only the Ubiquiti answering. A visit to the hilltop will answer the question of whether the Kiwi is actually powered and without DHCP-provided address or whether it is a power supply issue after all. This is a first test in very cold weather so anything is possible. It certainly would have been nice to have a remote power/restart control on the Kiwi. We presently have APRS delivering panel/battery/load status, separate from the microwave link, but no way to actually restart the Kiwi remotely.

Again, thanks all, I'll try to report anything else I discover that might be useful to others.

Glenn n6gn
Fort Collins, CO