I don’t know how effective this might be: maybe a sheet of earthed reflective material (foil-backed insulation, chicken wire, or similar) behind your emonBase as seen from the garage direction?
Let’s wait for Bill.
The first thing that got my attention was the ~10-15dB drop in RSS just after 1 December.
So while it may indeed be the Christmas decorations doing the dirty deed, that might be just
part of the story. There’ shouldn’t be a problem with an RSSI of ~-70dBm, but that combined with
the Christmas lights may be a problem.
There is a low-cost way to do that.
e.g. one of these (or similar):
https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B011HVUEME/ref=sr_1_3?crid=98815UXAU0DK&keywords=rtl-sdr+v3&qid=1576361553&sprefix=rtl-sdr%2Caps%2C201&sr=8-3
Software defined radio. Price is 30 USD. Available on Amazon.
Software cost is zero. https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/
e.g. http://www.hdsdr.de/
That would enable you to check the RF spectrum from 24MHz to 1.7GHz.
Could you post a picture of that antenna?
Know what you mean there. These are in my front yard:
And that’s the benefit of having an expert look at things 
I hadn’t even noticed that. So maybe my hypothesis is wrong or more complicated. Still, it makes me even more keen to investigate the source.
The antenna is one of these https://www.amazon.co.uk/gp/product/B07DNLBHH6/ I looked at it this morning and it still seems to be positioned in the same place.
It’s available on Amazon in the US but not here in the UK. The US site will ship to me but I think it will be easier and cheaper to order from Aliexpress. Thanks for the link, though, I’ll order one. Again it’s obvious what the solution is when you already know
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Ah, HDSDR is Windows. I run Linux so I’ll need to look at something else. The first few are:
- Linrad
- GQRX
- CubicSDR
- ShinySDR
Do you or anybody else have any experience with them to know what they’re good for? Are there specific features in a package that would be good to have?
There’s GNUradio and rtl-sdr packages in the openSUSE repositories as well as various other hits for SDR, so again it’s a question of [not] knowing what I’m looking for. I see there are various web pages about using SDR for interference analysis on linux systems but any known-good resources would be very helpful.
Of those, I’m only familiar with gqrx but it can do what you need.
Also look out for rtl_433 which is capable of decoding many devices on 433 (and 868) MHz. I use it together with a bit of python to feed my emonPi with data from some CurrentCost power monitors and a weather station.
This should do the job:
(Not bad for 10 quid)
https://www.amazon.co.uk/Andoer®-Portable-Digital-RTL2832U-Receiver-Blue/dp/B013Q94CT6/ref=sr_1_9?keywords=rtl-sdr&qid=1576501810&sr=8-9
I’ve not run any of the Linux variants.
Any of the avaiable apps will be able show you the RF spectrum at/near 433 MHz,
so the choice ends up being a personal one.
The display will be similar to this:
What you’re looking for is signals at/near 433 MHz. e.g.:
(this example shows the HF spectrum at 7.162 MHz)
In particular, this part:
will show you what signals it’s receiving, their frequencies, bandwidths and relative strengths.
What I was hoping for was a picture of it as installed.
It’s actually fairly easy to “detune” one (read that as decreased performance)
if it’s not located and mounted correctly.
rtl_433 is aimed at decoding data from various personal weather stations and the like.
While it’s something he might want to look into later, ATM his need is for a simple spectral
display to detect any signals that may be interfering with his OEM system.
I’ve already ordered the RTL-SDR kit. 
How would you use the Andoer unit, since it seems to have an omnidirectional antenna? My main question would be about software support for it though since it only mentions Windows. It looks vaguely interesting as a toy since I run TVH with a TBS 6805 quad tuner.
Here you go
The view is looking west. North is to the right and south, where the base station is, is to the left.
Like any of the other SDRs.
The antenna isn’t hardwired. Viz.:
Many of the of the low end SDRs are based on the RTL2832U chipset and
R820T / R820T2 tuner which is the chipset/tuner combo supported by much of the available software.
The same can be said WRT almost all of the USB dongle type SDRs.
There are some exceptions, but they don’t carry a 20 dollar price tag.
Airspy (169 USD) and SDRPlay (99 USD) are two examples that come to mind.
The RTL-SDR.com V3 receiver is one of the better low-end units.
OK, that helps. Quite a bit.
Three things.
- mount it further away from the wall if you can. I realize that may not be practical/possible.
- move it away from the wire bundle it’s adjacent to.
That’s a definite detuner / radiation pattern modifier. - bring the feedline straight out from the elements, i.e. perpendicular to them,
for a distance equal to, or greater than, the length of one element.
I could fashion a stand-off out of something or other I’m sure. How long should it be?
That’s the mains supply to the house, FWIW. I could move it out onto the ply to the left of the picture. Again, how far?
Ah, OK. That’s definitely doable.
Many thanks, Dave
Rule-of-thumb is one-quarter wavelength (or more) separation distance.
(roughly the length of one element) One-half wavelength or more is better
but if that’s not possible, quarter-wave separation is better than nothing.
So mount your dipole as high and as far away from the wall and mains cables as practical.
OK, the mains cables take a right angle above the picture and run above the antenna, towards the south/left. I suppose I should stay half-wave below that.
Correct.
Only one of the dipole elements radiates energy. Ideally you want that one on top.
So you can try flipping it end for end. It may or may not make much, or any, difference,
but it’s easy to do.