MW Breakthrough

[gazzzman]

Hi Everyone, I am new here, and new to the world of SDR!
I have just bought a RSP2 but I have some issues :O
firstly. I live 1Km away from a few small broadcast TXs
one at 2.2KW 2 at 400W spaced along the MW.
where I am, I don't really suffer problems with things like my ICF2001 or my Degen 1103
however, with the RSP2 I am suffering serious IMD
on ALL bands
now, as my main areas of interest are FM and MW broadcast bands, I am looking for suggestions!
the broadcast filter only reduces IMD on the 49M band (another area of interest)
and obviously makes MW and FM broadcast bands pretty useless
at the moment I am just using a discone (I am awaiting a Ukranian Mini Whip)
anyone have any ideas where I could start?
Gazzzman

[Paul]

Hi there
This is unlikely to be of much help in receiving the MW and FM broadcasts that appear to be your main interest. However, perhaps my own observations as another newcomer may help clarify things a little.
FYI: I own an RSP2 and live in a rural area with no really nearby AM broadcast stations.
I am happy with my "Ukrainian mini-whip", which performs very satisfactorily on Port A in the VLF/MF bands (despite this Port being rated from 1.5Mhz and up).
However, even using the inbuilt MW/FM filter, there is still widespread AM breakthrough in the MF range.
Received wisdom indicates that the addition of external filters is one of the best solutions.
You may find that under certain conditions this antenna will also perform very well at higher frequencies (in my case from the 40 Meter band upward).
To be honest, the RSP with the setup that I have,receives excellent AM broadcasts in the HF broadcast bands.
Port B is "like it says on the tin," and is not suitable for MF/VLF.
I would think that the Hi-Z Port would be an attractive option for you to use with the mini-whip if it's not otherwise engaged.
However, this port lacks the inbuilt MW/FM filters of course.
I hope that you may find these observations of some use, although there are many others out there with FAR deeper knowledge than me and who always appear ready to advise....
Best of luck!

[Roger]

I suggest you join the Facebook SDRPlay and SDRUno groups. There has been a lot of discussion and technical solutions recently about what to do if you live near AM transmitters. You can use the search function in the groups to get all the historical posts.

https://www.facebook.com/groups/sdrplay/

https://www.facebook.com/groups/sdruno/

[g1hbe]

Hi Gazzman.
First of all, welcome to our happy band. The RSP's are fine receivers, but they need a certain amount of care to get the best out of them. First of all, the two SMA inputs are really not suitable if you have big signals in your area. They have a lot more internal gain and are noisier on MW than the Hi-z input. I use the Hi-z input for my LF/MF and low-HF listening and don't find too many problems (but see later).
Your problem seems to be strong local MW signals causing problems within MW itself. So obviously the MW rejector is no good in this situation. I wonder if your mini-whip is just clobbering your front end? I know they can deliver quite a lot of RF. Have you tried reducing the gain? Remember - by default, the gain slider is a 'gain reduction' control, so minimum gain is at the top. I changed mine to a straight 'gain' slider to save confusion!

I too live a couple of miles from a MW TX site which has a couple of low KW stations and one 100-w. To the north of me is the big Moorside Edge site with three truly massive stations which put huge signals in here, but I don't get any major problems. I use a Wellbrook 1530 active loop antenna which I can turn to null down the big signals if they cause any bother.
My main beef is big MW sigs aliasing into the LF/VLF bands (below 300 KHz mostly) and the only answer was to build a couple of filters, one for getting rid of everything above 500 KHz and another getting rid >100KHz for when I'm poking around at the bottom end. With these in place the RSP2 becomes a very capable LF receiver.
Do you use the mini-whip on your other radios? If not, they will be picking up much lower-level sigs than you get from the mini-whip.
I'll stop going on now, but just a few suggestions:

1. Try the Hi-z input. You can find a diagram of how to wire it here: https://www.sdrplay.com/wp-content/uplo ... uidev2.pdf
2. Remember the gain pot works backwards.
3. Are you sure the intermod is not happening in the mini-whip itself?

Good luck. Please keep us informed. The SDRPlay team regularly visit and they like to hear about problems and solutions.

[gazzzman]

Hi everyone
thanks for the welcome
well... sadly I avoid Face book like the plague (too many people want to argue there it seems to me)
though you have given me a great Idea (to look in Google groups) so thanks a lot for that!

as yet the Ukranian mini whip has not arrived and I am simply using a discone
I tried using a "short" longwire in the Hi Z input, but I really couldn't receive "anything" because of the loud buzzing noises all the way up to at least 300MHz
so I removed that!
an interesting question is, if there is a likelihood I am having issues because of a long USB lead (10 M)
I thought it a good idea to locate the RX well away from all the PC stuff so I kept the RX by the aerials and used a long USB lead... I suppose RF could be getting in on that?
the miniwhip will be a later voyage of discovery!
a while ago I had a SDR4+ from CCW and a different miniwhip. that was no use for FM DX obviously but on AM it didn't have this problem, instead, it was as deaf as a post :O
so it looks like I am going to have to have a fairly radical rethink?
probably having to find something like a preselector for HF and a notch filter for FM?
in passing, I take it the "broadcast band filter" is not usable as two separate filters?
if I could use "just" the MW filter, at least I could use FM! but I suspect there is only a dual filter?
also.. I take it there is only an IF gain adjustment and no RF adjustment (sorry, I understand TRF and Superhet but not really SDR yet)
it isn't a defect in the SDR I suspect, just that I live in a challenging enviroment?
may well be some sort of loop might be a better proposition for the AM BCB?
it seems I am just looking for more headroom than I have
even with the gain reduction fully up, I am experiencing IMD
I have never heard a single station completely clear of hum or hiss LOL
even my "local" FM station I have to have the gain so low that there is significant hiss...
OH well,thanks for all your help thus far...
it seems like another simple idea is going to get complicated LOL
Peace and Love
Gazzzman

[g1hbe]

Gazzman. Sounds like you have major local noise problems which can really complicate matters. I am in the same boat but much less severe. Trying any type of wire antenna (even well away from the house and fed with coax) just produces noise. The Wellbrook loop mounted at gutter height at the end of the house is brilliant - the noise is gone and MW down to VLF is clear. I feed the loop with coax and use a balun at the house end to feed into the RSP. The low-pass filter fits in the coax just before the balun.
Trouble is, every situation is different and the solutions are too. Look out for any switch-mode PSU's or wall-warts and get rid. I once had a nice Icom RX that blatted its own AM reception with the supplied SMPS. That was ditched pretty quick and replaced with a small linear supply.
BTW I used to feel the same way about Facebook, but if you just join the group you want and stay away from the great unwashed everything is fine. I enjoy the SDRPlay group very much. Where are you based if you don't mind me asking?

[Paul]

Just a VERY DIFFIDENT addition...
As an aside from AM breakthrough:
I think it very likely that you already know about LED lamp-bulbs, but I did not and was quite happy with what I was receiving, then turned the desk-lamp on and was his with a wall of noise - that's hoe I found out,
You might profit from a look at this:
https://www.youtube.com/watch?v=EDRPzoNoFhc&t=524s
A "proper" loop it is not, but makes an incredibly good 3Mhz upward antenna (with amplification - at least for me) - works indoors and may provide a "yardstick" to experiment with and indoors....
The first one that I made (very recently) was with a child's hula-hoop, the second a more ambitious, but interestingly it did work in the FM broadcast band and even into the vhf airband and beyond (to some extent).
MK 2 is a little better.
I do hope you achieve success.

[gazzzman]

Hi everyone!
thanks for all your kind replies!
well... I seem to be in a bit of a pickle LOL
I am blind in all practical senses, not total, just bad enough.
that means home automation with LED lights galore!
plenty of SMPS's too I have several PCs on full time, and literally dozens and dozens of SMPS's Oh!
and the aforementioned local AM transmitters!
all in all, I see I have my work cut out for me!
VHF should be easy enough if I sort a LPF and there is sufficient isolation between the inputs, but MW I think is going to require a loop!
and, as my house is like a shoebox (full of electronic noise) I see the poor loop is going to have it's work cut out for it!
and, it's all beginning to look complex and expensive :O
well... I will have to go loop hunting I think!
I think getting the RSP2 put in a aluminium box (or even copper) with the filters in a separate compartment might be needed..
though surprisingly the ICF 2001 and 7600D, and my Degen all seem "reasonable" on AM (they do have the advantage of directionallity using their ferrite rods) there is no hope of DX using them however, and the front ends can't handle a short longwire...
looks like this isn't going to be a quick fix!
but hey! rome wasn't built in a day!
oh and g1hbe I am located on the "Sunny" wirral LOL
thanks everyone...
off loop hunting LOL
Gazzzman

[g1hbe]

Great to see a positive outlook, Gazzman. Yes, the ferrite rod antennas in your portables are basically loops, so they do reject noise to a certain extent. but they are very small loops so as you say they don't pick up very weak sigs like a big loop does.
Like Paul, I have built loops using plastic hula-hoops with the amplifier (usually the PA1M design) housed in a plastic conduit box at the base. These work pretty well but not quite as good as the Wellbrook - but the price of the Wellbrook these days is a bit stiff!
And as you point out, even loops cannot cope very well with indoor use because of all the noise.
A thought has just popped into my head re the imaging - how about a passive tuned loop? This type has to be tuned to the frequency of interest and rejects other frequencies, so reducing spurious responses. You'd still have the 'indoor noise' problem though, and the wide spectrum display would become compromised.
I suppose being partially sighted doesn't help, so it looks like a major struggle you've got on your hands. Good luck.

Andy.

[gazzzman]

Hi Andy! (and everyone else)
more interesting ideas, thanks
I have just been a eBaying and spent my savings on a used Wellbrook Communications LFL1010
here's hoping
the plan is, to rotate it so the null is pointing at the local TX (yes, apparently the mast can be seen from my house LOL)
and hope that will reduce the LF issues (and some of the noise) screening and earthing seem to be key?
I will probably use the discone with a high pass filter so the FM band and above will be accessible probably looking to source a HPF that gives cutoff at about 5MHz
this is unlikely to be the most sensitive arrangement, but I "think" it will be workable.
why oh why are people being herded into smaller and smaller houses, in more and more densely populated areas?
I have enough issues with WIFI LOL
(there is a "Local" 100w BT WiFi link, and, due to population density I can detect 30+ local wifi networks :O
I wish I lived out the way more lol
anyhow... thanks for all the help guys (no Gals spotted)
oh did I mention there are a lot of Sky customers locally using ethernet over mains adapters too?
I will let you all know how the LFL1010 works out there is no coupler with it, but I imagine that is just the usual choke capacitor arrangement
I suppose, a little background might be useful here..
I am (was?) a qualified elecrtonics engineer, until I stopped soldering because I was repeatedly burning my nose with the iron LOL
these days, I work in IT with a HUGE screen and, prepare for a future where my sight gets even worse (hence my interest in home automation)
back in the day I would have built my own loop using a 6SN7GT or something (I still believe valves are superior front end devices, especially at MF)
but these days home construction gets delegated to my long suffering friends
I do fix their PCs (and try to convert them to Linux) in return mind
again, thanks everyone!
Gazzzman