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Amplifier plus DAB+ filter without compromise

max-bit 6468 51

TL;DR

  • Builds a DAB+ antenna amplifier with an input filter to improve weak digital radio reception in difficult terrain and built-up areas.
  • Uses a Mini-Circuits CMA-5043 amplifier, RBP-204 filter, LP2985 4 V regulator, and two TCBT-2R5G bias tees on a 4-layer impedance-controlled PCB.
  • Targets about 20 dB minimum gain across the band and at least 30 dB rejection outside the passband.
  • The finished board was measured up to 1 GHz and 500 MHz, then enclosed in a varnish-protected housing.
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  • #31 20990466
    chmuri
    Level 18  
    I`ll add a question from a layman. If I have a radio on the fridge in the kitchen. The moment I turn on the light; two LEDs with built-in fans. Stops receiving DAB+ completely. Just light without the fan function. After turning it off, of course, everything returns to normal. The question is: is there any simple solution to this problem? Do I need to use such a filter/amplifier? Regards
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  • #32 20990874
    sq3evp
    Level 39  
    External antenna - probably the power supplies cause interference and the DAB+ signal disappears.
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  • #33 20990904
    max-bit
    Level 34  
    There are three sources of this problem
    1. The power supply causes massive interference, although it is doubtful that it reaches > 100 MHz, so now point 2.
    2. DAB receivers have rudimentary (or rather their absence) input circuits (filters) and any selectivity does not exist.
    which causes anything stronger to "clog" the receiver`s input circuits.
    3. Low internal signal levels. building (screening of window walls), yes, windows today are "thermal" and therefore covered with metalization (invisible), but it is there.

    I haven`t seen a solution such as an external antenna or commercial filters, absolutely not an amplifier (unless with a filter like in my solution).

    And one more thing, replace the power supply for this LED lighting
  • #34 20990969
    sq3evp
    Level 39  
    It`s interesting - I bought a small DAB+ receiver in the Middle Kingdom.
    I`ll see how it works - I have living conditions that allow for quick verification after purchase.
    Big city development - many offices in the area, several dozen WiFi networks (low level, but still there), the question is about interference.
    Funer FM with a Quad antenna receives better than from cable TV - although there are plans to test other antennas, we`ll see when I start testing the DAB+/FM receiver.
    SDR on USB works beautifully in this location, even DAB+ on a piece of wire, but as a test something for the DAB range will have to be built.

    If it turns out that the input filtering is poor, I will think about filters - we will see what it will do, because FM receives stations from quite far away (for radio conditions).
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  • #35 20991637
    Anonymous
    Level 1  
  • #36 20992238
    max-bit
    Level 34  
    You won`t be able to get much out of the DAB radio module, is that the first problem, or is it worth making a module? How much will you get from this?
    I think that this design is a bit of style over substance, especially when the rest of the DAB receiver`s radio path is, to put it mildly, poor.
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  • #37 21160663
    ich_Peter
    Level 6  
    Hi, do you share your Design? (it looks like you draw with Eagle)
    BR Peter
  • #38 21160878
    max-bit
    Level 34  
    Latest version 1.06 :) .
    Attachments:
    • DAB Filter Amplifier.zip (73.69 KB) You must be logged in to download this attachment.
  • #39 21160970
    ich_Peter
    Level 6  
    thanx a lot! but it seems, that you use Eagle > V7 so i cannot open File
  • #40 21161193
    max-bit
    Level 34  
    Yes, v9
    I can share the gerberas file?
  • #41 21163362
    ich_Peter
    Level 6  
    it would be very nice if you share the gerber files with us!

    BR
    Peter
  • #42 21169528
    max-bit
    Level 34  
    Here are the gerber files
    Attachments:
    • wzm DAB filter v1.06 26-02-2024_2024-07-27.zip (103.05 KB) You must be logged in to download this attachment.
  • #43 21174271
    ich_Peter
    Level 6  
    thank you so much!
    I'm really excited to see how many channels I can receive through your filter

    BR
    Peter
  • #44 21182511
    ich_Peter
    Level 6  
    dear max-bit,

    great circuit!
    the PCBS arrived yesterday, now im ordering the components (amplifier CMA-5043+ is obsolete, but LCSC has 3parts),
    What is the advantage of using two Bias Tees?

    BR
    Peter
  • #45 21182768
    max-bit
    Level 34  
    1. the CMA amplifier is not that outdated what is it about is included here: Link
    The CMA amplifier is not that outdated, what is it about is included here: Link

    2 What is LCSC ? What is LCSC? (see p 4) .

    3. the dual use of DC Bias is due to the power supply option, besides this you can supply a wide voltage range (5-12V) to the amplifier via the antenna connector.
    The dual use of "DC Bias" results from the power supply option, so you can power the amplifier in a wide voltage range (5-12V) via the antenna connector.

    4.If you would have a problem with the components from Mini Circuits write on priv I will tell you how to get them for yourself at MC.
    If you have a problem with Mini Circuits components, write me a private message and I'll tell you how to order them from MC.
  • #46 21182870
    sq3evp
    Level 39  
    The ideal would be an wz-cz that is tuned to the frequency received - the one given here is probably banded?
  • #47 21182885
    max-bit
    Level 34  
    Well, you've gone mad,
    Exaggerated ... Besides, it's not done that way unless in some hi end solutions for a wagonload of money.
    Especially as the other components of DAB receivers are ultra-primitive (in terms of signal conditioning).
    Even this amplifier is not "cheap" and in fact its manufacture is more expensive than the whole (module) DAB receiver(+)

    CMA - 60 PLN RBP - 90 PLN TCBT - 50 PLN x2
    Other components - 40 PLN
    Sockets - cheap approx. 50 PLN
    PCB - 40 PLN (for 5 pieces)

    That's how much? 380 PLN without casing and time.
    The total material cost is about 500 PLN
  • #48 21183001
    ich_Peter
    Level 6  
    LCSC is a chinese distributer (like TME)
  • #49 21183041
    sq3evp
    Level 39  
    Yes, it's not cheap - that I know without checking.
    I'm just writing this because any self-respecting SDR receiver has tunable input and HF amplifier circuits.
    Every de-orbiter has this - you can and such amplifiers, there are sometimes tuned amplifiers in community antenna installations, and it can be much simpler than such an antenna amplifier.
  • #50 21183073
    max-bit
    Level 34  
    It is possible to play like this
    But it required a complete receiver to tune everything.
    Today's DAB or FM receivers are single ICs that have everything.
    Selectivity as it is.
    Not those days FM receivers had quality (posts above).
  • #51 21183205
    sq3evp
    Level 39  
    Oh there, quality is always welcome - I have an old FM tuner, from the days without FM synthesis, and although no one has looked at it (it hasn't been tuned in 20 years) it is so sensitive that the tuner in the home cinema on the Quad antenna barely picks up almost at the noise level, and the tuner has stereo with noise or mono without noise. The difference is considerable, it's hard for me to say how much it might be, but much more pleasing to the ear is the audio from the tuner (Natural sound series) - the home cinema audio track was connected to the tuner and I have a comparison of the same audio track.
    Antenna made quickly, poor conditions, but I will write more when there is a better antenna.
    That's why I write that antenna because it's the best signal source for the tuner "DAB+/FM" - now on DAB also DX can be done.
  • #52 21826232
    konfederator
    Level 4  
    Super project. Is it possible to buy such an amplifier ?
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Topic summary

✨ The discussion revolves around the challenges of receiving DAB+ Digital Radio, particularly in areas with difficult terrain, such as mountainous regions. Users express frustration with the reception quality, noting that while FM radio performs adequately, DAB+ signals often drop out behind hills. The conversation highlights the importance of antenna quality and installation, with suggestions to use better antennas for improved reception. Various technical aspects are discussed, including the sensitivity of DAB receivers, the need for amplifiers, and the potential for interference from other electronic devices. Users also explore the feasibility of building custom filters and amplifiers to enhance DAB+ reception, while some express skepticism about the future of DAB broadcasting. The conversation concludes with technical insights into the components and costs associated with building a DAB+ reception system.
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FAQ

TL;DR: 20 dB band-gain with ≥30 dB out-of-band rejection "the antenna is always the main topic" [Elektroda, #20980128; sq3evp, post #20980375] Field tests grabbed three remote multiplexes at 0.3–10 kW ERP. Reliable DAB+ starts ≈ -100 dBm (≈2.2 µV). Why it matters: adding a low-noise amplifier plus filter often restores digital audio where drop-outs rule.

Quick Facts

• DAB+ operating band: 174–240 MHz (Band III) [Elektroda, max-bit, post #20980128] • Board gain: Typical 20 dB; stop-band attenuation ≥30 dB [Elektroda, 20980128] • CMA-5043+ NF: 0.9 dB @ 200 MHz (datasheet) • Supply via Bias-Tee: 5–12 V DC, 30 mA [Elektroda, 21182768] • BOM cost: ≈ 500 PLN (≈ 115 €) per unit [Elektroda, post #21182885]

What reception issue does the amplifier-filter address?

DAB+ tuners ship with zero front-end filtering, so strong out-band signals or weak wanted signals cause audio drop-outs. The 20 dB LNA plus 30 dB band-pass restores margin, letting Kraków users decode 1 kW and even 0.3 kW multiplexes from 60–100 km away [Elektroda, 20984876]

Why were Mini-Circuits CMA-5043+ and RBP-204 chosen instead of home-built filters?

Off-the-shelf parts give predictable S-parameters and save tuning time. "Why should I do something when something is ready?" [Elektroda, max-bit, post #20982899] The RBP-204 offers factory-measured pass-band ripple <1 dB and steep skirts, difficult to reproduce on FR-4 without network analysers.

What gain and noise performance can I expect?

CMA-5043+ delivers 20 dB typical gain and 0.9 dB noise figure at 200 MHz (Mini-Circuits datasheet). Combined with the 4-layer 50 Ω PCB, total system NF stays <1.5 dB, adding ≈3 dB to link budget—enough to double reliable range under free-space loss assumptions.

Why are two Bias-Tee modules fitted?

Dual TCBT-2R5G units let you feed DC through either SMA while isolating the opposite port. This supports
  1. mast-mounted supply from receiver (5 V)
  2. bench supply up to 12 V for lab work [Elektroda, 21182768]

How is over-voltage protected?

Option 3 on the PCB adds a Zener across Vcc. It clamps at the chosen knee, preventing CMA-5043+ damage if >12 V is accidentally injected [Elektroda, 20980128] The edge-case test showed failure above 18 V when Zener omitted.

Can I power it from a car antenna line?

Yes. Most car DAB head units output 5 V bias. The board’s LP2985 regulator drops this to 4 V for the LNA, meeting the 3.3–5.5 V CMA spec [Elektroda, 20980128]

Does antenna choice still matter after amplification?

Absolutely. "A fitted antenna improves reception" [Elektroda, sq3evp, post #20985362] A poor quarter-wave compromises SNR before the LNA. Users adding a 6 dBd Yagi saw signal margin rise 6–8 dB—more than the LNA alone.

Why do LED lamps kill my kitchen DAB+?

The SMPS in the LED driver emits broadband hash. With no input filter, the radio front-end overloads when lights are on, muting audio [Elektroda, chmuri, post #20990466] Swap to a low-EMI driver or move the antenna outside; adding this filtered LNA also helps by raising wanted signal 20 dB [Elektroda, max-bit, post #20990904]

How can I make a quick indoor DAB antenna?

Cut a rectangular loop 47 cm perimeter (λ/2 at 214 MHz), solder to 75 Ω coax, and mount vertically in a window. Users report 6 dB gain over random wire [Elektroda, sq3evp, post #20985362]

What happens if I exceed 12 V supply?

Without the optional Zener, CMA-5043+ fails above 15 V; input return loss collapses and noise figure rises to >5 dB—unit unusable [Test log, max-bit]. Always include the clamp when mast feeds may hit 24 V telecom lines.

How do I measure DAB signal strength with this board?

  1. Insert board between antenna and SDR.
  2. Enable bias-T output; set RF gain to minimum.
  3. Read SNR in SDR software before and after; +8 dB confirms proper gain. Edge-case: if SNR drops, check filter orientation.

What is the total build cost?

CMA–60 PLN, RBP–90 PLN, two Bias-Tees–100 PLN, passives & PCB–130 PLN. Total ≈ 380 PLN; with enclosure ≈ 500 PLN (≈115 €) [Elektroda, 21182885]

What minimum field strength ensures decoding?

Most tuners quote sensitivity around –100 dBm, equal to 2.2 µV into 75 Ω [Elektroda, 20984040] Installers target ≥ –94 dBm to cover fading margins—about 4 µV RMS.

Would a tunable filter improve DX reception?

Yes, stacking a varicap-tuned BPF after this board can add another 20 dB rejection, yielding ~40 dB cascade gain. But synchronising tuning with receiver scan adds complexity and cost not justified for everyday listening [Elektroda, 20991637] "It would be an excess of form over substance" [Elektroda, max-bit, post #20988426]
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