Where can you buy MuRata 80 kHz filters?

FM receiver discussion
User avatar
John Faulkner, Skegness
Posts: 5380
Joined: 19 Sep 2014 15:55
Location: Skegness, Lincolnshire. JO03dd
Contact:

Re: Where can you buy MuRata 80 kHz filters?

Post by John Faulkner, Skegness » 02 Feb 2015 13:56

Depending on where you mount your 9.2 you should still find some of your deepest nulls will be at 90 degrees to the forward beam. So if you beam south-east you should have minimum pickup of Tacolneston.

Damien Read
Posts: 76
Joined: 17 Nov 2014 20:20

Re: Where can you buy MuRata 80 kHz filters?

Post by Damien Read » 02 Feb 2015 17:12

I have to echo other members view, don't waste your money and time in regards fitting filters, you can much more vfm with a dongle .

My RTL dongle overloads with my fm8 beam, but it's well reported that the dongles have poor front ends. I haven't had a chance to see how it performs using my TGN PREAMPLIFIER, as that got rid of the overload and made my Elad SW2 as sensitive a XDR.

I don't have it installed at the moment, but l know John runs a Preamplifier on his Elad, perhaps if you ask him nicely, he will answer the question of what happens when you run a Preamplifier into a dongle.

Damien

daveB
Posts: 1246
Joined: 07 Oct 2014 16:49

Re: Where can you buy MuRata 80 kHz filters?

Post by daveB » 02 Feb 2015 17:44

I can answer the pre-amp question in front of a dongle - total wipeout! In my location with one local giving 70+dB on the Sony I had to fit an expensive double-notch filter in order to be able to use the dongle. With my FM5 aerial pointing east the Wrotham stations come out at 55dB and I needed attenuation. It was only when I installed the 5ele K6STI yagi with better f/b ratio that I could effectively use the dongle for DXing - even then I needed up to 10d attenuation in good trop conditions. I still had a lot of good success with it - and I've now upgrade to a better SDR receiver.

Rgds

David
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

satnipper
Posts: 1062
Joined: 03 Oct 2014 12:58
Location: Western Europe

Re: Where can you buy MuRata 80 kHz filters?

Post by satnipper » 02 Feb 2015 21:55

If a pre-amp is getting rid of overload then it is doing so by acting as a pre-selector. The dongle front-end is wide open with no effective hardware bandpass filtering at all; It's designed for wide-band TV signals after all. To try and lessen the overload you would adjust the gain within the SDR application. If that doesn't work then you need more than a ten dollar dongle. However I would not have thought a Norfolk village would have such RF issues.

Regards

Stuart

Damien Read
Posts: 76
Joined: 17 Nov 2014 20:20

Re: Where can you buy MuRata 80 kHz filters?

Post by Damien Read » 03 Feb 2015 00:33

I guess l will have to try it out. The TGN PREAMPLIFIER that l have, is designed to handle strong signals before the amplifier, you can also vary the gain, this was how l resolved the overload on my Elad using my beam.
I am taking a wild guess, but isn't lthe Preamplifier is acting as a front end? It's worth mentioning that the TGN only covers 88-108 Mhz,so it's not wide band.

satnipper
Posts: 1062
Joined: 03 Oct 2014 12:58
Location: Western Europe

Re: Where can you buy MuRata 80 kHz filters?

Post by satnipper » 03 Feb 2015 09:02

" isn't the Preamplifier is acting as a front end"

This is another way of expressing what I wrote - front end is the pre-selector/filtering function so only the band or frequency range that is desired is let through. However putting amplification in front of a dongle I can not see working. The main reason for pre-amplifying (as opposed to pre-selecting) is to compensate for transmission line losses.

regards

Stuart

Damien Read
Posts: 76
Joined: 17 Nov 2014 20:20

Re: Where can you buy MuRata 80 kHz filters?

Post by Damien Read » 03 Feb 2015 10:38

I would normally agree Stuart, as l did share your view, however practice has made me re think, when using my Elad.
It was only after reading John Faulkners comments on the Elad not being sensitive, that lead me to take a risk using the TGN PREAMPLIFIER, my issue was overload and not being sensitive.
So I agree, it shouldn't work, but it does.
I use the same approach running my Wellbrook, although l am so close to Droitwich, everything overloads, so I am forced to null and phase out.
Anyway, l'm going off subject, but it's an interesting subject, as you would expect overload.

satnipper
Posts: 1062
Joined: 03 Oct 2014 12:58
Location: Western Europe

Re: Where can you buy MuRata 80 kHz filters?

Post by satnipper » 03 Feb 2015 12:01

http://www.tgn-technology.de/shop2/prod ... d850a0c63b Is this the pre-amp in question?

You will notice that it states "No interference from strong local stations" and "High selective filter against interference" - it is this narrow-band filtering that cures the overload (you amplify noise you get more noise). One of these in front of a dongle would be worth trying if you turn the gain all the way down. 10 db might still be too much though. Does it still pass through the signal when no power is applied? If the pre-selection/filtering is passive it would improve the dongle performance.

FWIW I have no pre-amp on my Elad and it's fed by an FM5 with some very strong London nationals and locals. I do use an internal Fringe Electronics 3-way distribution amp to feed the Elad/FM+/XDR and Dongles. The sensitivity is the same as the FM+ and XDR.

regards

Stuart

Alex Cator
Posts: 648
Joined: 26 Dec 2014 14:53
Location: East Harling, Norfolk, England (QTH JO02LK)
Contact:

Re: Where can you buy MuRata 80 kHz filters?

Post by Alex Cator » 03 Feb 2015 12:48

satnipper wrote:However I would not have thought a Norfolk village would have such RF issues.
Norfolk is lucky, not to have a crowded band. By the way, I wish I was in a different bit of Norfolk, such as Great Yarmouth, or even Lowestoft, which is in Suffolk, but not far from the Norfolk border near Gorleston. Lowestoft has Tacolneston reception fine, even though it's not THAT strong in Lowestoft, as can be told by the times I've had Classic FM knocked out by VRT MNM during tropo (both 101.5). The band is not as crowded in that bit of Norfolk/Suffolk (Great Yarmouth and Waveney), as the western half of Norfolk is swamped by Cambridgeshire radio stations. That includes western areas of South Norfolk and Broadland districts, and all areas of Breckland district, and, to more of an extent, in the district of King's Lynn and West Norfolk. Areas such as King's Lynn and Downham Market are stated as in the coverage area of Heart (Peterborough) 102.7, as the coverage of that is so much better than SHC, in the far west of Norfolk. You can also have the choice of Tacolneston or Peterborough for BBC nationals and Classic FM, and I presume the DVB-T as well.
Tacolneston is very strong here in East Harling, hence the fact many of the ordinary radios in my house, get overload. Sometimes, you may hear BBC R3 on 95.1 while trying BBC Radio Norfolk from SHC. Assuming I may own a Korner 9.2 in the future, hopefully no overload will be present at 90 degrees from Tac. That will make software-defined radios so much nicer, not having to contend with Tac overload. The only problem is that 90 degrees from Tac (south-south-east, towards French/Belgian border) may have a degree of Kiss overload, from Ipswich on 106.4. An antenna phaser may reduce Kiss to a degree, as it's slightly weaker than Tacolneston. Strong enough, as the average youth in my village likes Kiss.
Home: Sony ST-SB920 (modified), Sony XDR-S10HDiP, Onkyo T-4970, Ford 5000 RDS, horizontal Triax FM3
Mobile: Ford Fiesta (Style, 2013) and Ford Focus (2012) car radios
Portable: Tecsun PL-390, Grundig G5 (2 x 110kHz), Etón G8

Damien Read
Posts: 76
Joined: 17 Nov 2014 20:20

Re: Where can you buy MuRata 80 kHz filters?

Post by Damien Read » 06 Feb 2015 00:36

Hi All,
I finally got my RTL dongle up and running tonight using SDR #.
Firstly to answer Stuart question, YES, the link is the same TGN PREAMPLIFIER that l have.
I must admit, I forgot how fiddly SDR # GUI is, but after 15 minutes, my memory kicked back in.
The good news, using my Blake FM8 beam and TGN is possible, thankfully this is down to being able to manually adjust the gain. This is really useful, and depending on which way my beam is pointing, you can ramp the gain up to give slightly better and lower noise floor than the Elad.
So in terms of sensitivity, it can match the Elad, but you have to play a bit with the gain.
In terms of selectivity, it's certainly no Elad or XDR, even though you can vary the BW, you end up listening in mono, as you have to use a pretty narrow settings, but let's put in reality, this was a on my local tx 104.60 BBC HW and 104.70 BBC Leicester, only a XDR and Elad have ever been able to do this from all the tuners l have owned. It's not a problem, as it only takes 300khz to get rid of the splash.
Alex, provided you have a pc, and like to play around, I think you would be crazy not to have a play with a RTL Dongle, it would also unlock so many other aspects of the radio bands, they are so cheap, you have everything to gain.

Damien

k6sti
Posts: 63
Joined: 20 Oct 2014 17:27

Re: Where can you buy MuRata 80 kHz filters?

Post by k6sti » 07 Feb 2015 14:58

Do cascades of these very narrow filters really improve intelligibility when DXing? I've never tried them myself, but from many experiments I've done with wider substitute IF filters, I'd be cautious.

I've found that I can cascade a pair of 110s with a pair of wider filters, such as 250s, with no audible loss of fidelity. A pair of 110s and a 150 also works fine. Measured distortion increases greatly, but despite trying many times under controlled conditions, I've never been able to hear it.

There is one exception. When multipath is present, the 110s audibly increase raucous multipath distortion. Narrow filters introduce large variation in group delay across the IF passband. Evidently this exaggerates multipath distortion, which can be thought of as adding a gross amount of group delay itself. Note that many signals that have propagated a long distance may have multipath, particularly Es signals. Multipath can be as much of an issue for DXing as for high-fidelity FM listening.

I have tried cascading three 110s as a narrow filter. Much of the time it sounded OK. But there were occasional ticks and pops, frequent enough that the filter was unusable. This illustrates another point. When something goes wrong with FM reception, it almost always occurs at maximum deviation. FM is a highly nonlinear process. Tricks that work at low deviation can fall apart suddenly as deviation increases. Very narrow filters exhibit this kind of deviation-dependent behavior.

Any filter narrower than twice the deviation will cause the signal to attenuate or disappear on deviation peaks. You can see the effects here:

http://ham-radio.com/k6sti/mn.htm

Digital IF filters can be successfully narrowed much more readily than can analog IFs using ceramic filters. FIR digital filters with symmetrical coefficients, the kind used for digital IFs, have no group delay variation and introduce no distortion due to that effect. They also have much steeper roll-off than analog filters. The Sony XDR-F1HD and its cousins uses a time-varying IF filter. It rapidly swaps among 16 filters with bandwidths from 55 to 315 kHz depending on adjacent-channel interference and deviation. Filter swapping is done in way that introduces no switching artifacts. The narrowest filters provide threshold extension during periods of low deviation that eliminates the high-amplitude clicks and pops conventional FM systems exhibit at low signal levels.

If you have had good experience with strings of 80 and 110 filters, you're all set. But if you're trying them for the first time, it might pay to run some careful checks to compare actual reception audio with that for wider filters. In addition to adjacent-channel rejection, listen closely for modulation trashed so much that it's no longer intelligible. This kind of comparison may not be easy to make because you really should switch filter sets in the same tuner. Too many things can differ and go wrong if you use two tuners, even of the same model.

Good luck!

Brian

Damien Read
Posts: 76
Joined: 17 Nov 2014 20:20

Re: Where can you buy MuRata 80 kHz filters?

Post by Damien Read » 09 Feb 2015 14:18

Some great points Brian, just slipping filters into a board is easy to say, but practice is another thing.
When l changed my Sony 920 with 110khz, everything went fine.
I tried the same to a Technics , and the unit was terrible, so l had to run with 150khz.
When you look at the cost, time and effort, it's no wonder SDR is slowly making the old tuner obsolete. Of course for Hi fi that's a different matter.

Damien

k6sti
Posts: 63
Joined: 20 Oct 2014 17:27

Re: Where can you buy MuRata 80 kHz filters?

Post by k6sti » 10 Feb 2015 01:03

Well, I carefully select ceramic filters and then align the IF and the rest of the tuner with instruments. I have put pairs of 110s in every tuner I've restored for the last several years. So far I haven't had a problem. I live between L.A.and San Diego and every 200-kHz channel is occupied. Even with a directional antenna I need good selectivity. A pair of 150s just isn't enough in some cases.

I forgot to mention that I wrote a filter optimizer for the Sony XDR-F1HD. You can design one or more filters and then use Konrad Kosmatka's program to upload them to the tuner in place of the stock filters. My original intent was to create filters with about the same passband width but much lower stopband response. I was able to do this, but when Konrad tried them, he heard no advantage. Evidently the phase noise of the Sony local oscillator swamps any improvement in stopband level. Still, transition bands are narrower and you can design a filter of any bandwidth to experiment and see just how narrow you can go. Performance will be far better than any combination of ceramic filters in an analog IF. You can replace all 16 of the Sony filters and use them as Sony intended, with automatic switching. Or you can use one filter for a fixed bandwidth. Konrad's software allows either option. The filter optimizer is a DOS program, but it runs fine in Windows XP, and presumably in Windows 7 with the optional XP thing. The program requires a CPU with SSE4.1 vector instructions, but that includes just about everything made in the last half-dozen or so years. The program and instructions are here:

http://ham-radio.com/k6sti/XDR.ZIP

Brian

Post Reply

Return to “Receivers”