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Amplifier plus DAB+ filter without compromise

max-bit 6813 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  
    Posts: 299
    Help: 14
    Rate: 13
    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  
    Posts: 6542
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    Rate: 869
    External antenna - probably the power supplies cause interference and the DAB+ signal disappears.
  • #33 20990904
    max-bit
    Level 34  
    Posts: 4613
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    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  
    Posts: 6542
    Help: 219
    Rate: 869
    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).
  • #35 20991637
    Anonymous
    Level 1  
  • #36 20992238
    max-bit
    Level 34  
    Posts: 4613
    Help: 117
    Rate: 851
    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  
    Posts: 6
    Rate: 1
    Hi, do you share your Design? (it looks like you draw with Eagle)
    BR Peter
  • #38 21160878
    max-bit
    Level 34  
    Posts: 4613
    Help: 117
    Rate: 851
    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  
    Posts: 6
    Rate: 1
    thanx a lot! but it seems, that you use Eagle > V7 so i cannot open File
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  • #40 21161193
    max-bit
    Level 34  
    Posts: 4613
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    Yes, v9
    I can share the gerberas file?
  • #41 21163362
    ich_Peter
    Level 6  
    Posts: 6
    Rate: 1
    it would be very nice if you share the gerber files with us!

    BR
    Peter
  • #42 21169528
    max-bit
    Level 34  
    Posts: 4613
    Help: 117
    Rate: 851
    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.
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  • #43 21174271
    ich_Peter
    Level 6  
    Posts: 6
    Rate: 1
    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  
    Posts: 6
    Rate: 1
    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  
    Posts: 4613
    Help: 117
    Rate: 851
    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  
    Posts: 6542
    Help: 219
    Rate: 869
    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  
    Posts: 4613
    Help: 117
    Rate: 851
    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  
    Posts: 6
    Rate: 1
    LCSC is a chinese distributer (like TME)
  • #49 21183041
    sq3evp
    Level 39  
    Posts: 6542
    Help: 219
    Rate: 869
    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  
    Posts: 4613
    Help: 117
    Rate: 851
    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  
    Posts: 6542
    Help: 219
    Rate: 869
    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  
    Posts: 4
    Rate: 1
    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: With ~20 dB gain and the claim that "the parameters are quite good," this Mini-Circuits DAB+ preamp/filter targets hobbyists who need cleaner Band III reception than a bare single-chip receiver front end can deliver, especially where hills, weak front ends, and local interference cause dropouts. [#20980128]

Why it matters: DAB+ often fails because antenna, receiver front end, propagation, and local interference all interact, so a filtered preamplifier helps only when it fits the real bottleneck.

Option What the thread says Concrete figures
Bare DAB receiver Often uses a very simple single-chip front end with little or no input filtering "zero input filters" was the design complaint [#20980128]
This CMA-5043 + RBP-204 design Adds gain plus out-of-band filtering without tuning ~20 dB gain, min. 30 dB filtering outside band [#20980128]
Better antenna only Often the first improvement to try, especially at home Example suggestion: dedicated DAB antenna instead of X-300 compromise [#20985186]
DX-oriented tuned setup Can outperform a general Band III preamp for chasing distant muxes Approx. +40 dB with amp + narrow filter + amp chain [#20988426]

Key insight: This design improves DAB+ most when the receiver front end is weak or overloaded. It cannot defeat terrain blocking, poor indoor signal levels, or noisy LED power supplies by itself. [#20990904]

Quick Facts

  • The published design uses a Mini-Circuits CMA-5043 amplifier, RBP-204 band-pass filter, LP2985 4 V regulator, and two TCBT-2R5G Bias Tee blocks on a 4-layer PCB with controlled impedance. [#20980128]
  • The target electrical performance is ~20 dB minimum gain across Band III with minimum 30 dB rejection outside the band, aimed at cleaner DAB+ reception than a bare tuner input. [#20980128]
  • Power can come through the antenna connector over a 5 V to 12 V range, while the amplifier stage itself is stabilized to 4 V through the LP2985. [#20980128]
  • Approximate material cost reached 380 PLN without housing and time, while the stated total material cost was about 500 PLN. The largest line items were CMA 60 PLN, RBP 90 PLN, and TCBT 50 PLN ×2. [#21182885]
  • Home testing used an X-300 VHF antenna with about 35 m of half-inch feeder, and reported reception examples included 215.072 MHz, 211.648 MHz, and 206.352 MHz muxes around Kraków. [#20985163]

How does the Mini-Circuits CMA-5043 + RBP-204 DAB+ amplifier/filter improve reception compared with a bare DAB receiver front end?

It improves reception by adding gain and real input filtering before the receiver. The design targets about 20 dB minimum gain across DAB Band III and at least 30 dB suppression outside the band. That matters because the thread describes many DAB receivers as single-chip designs with little or no input filtering, so strong unwanted signals can overload them. In practice, this preamp helps weak or interference-prone receivers more than strong, selective tuners. [#20980128]

Why does DAB+ reception drop out completely behind hills or in valleys when FM radio still plays with acceptable quality?

DAB+ drops out because Band III at 174–230 MHz behaves much more like line-of-sight reception, and digital decoding has a cliff effect. The thread notes that one large hill can wipe out the mux, while FM often remains usable with noise. FM degrades gradually, but DAB+ either decodes or goes silent. That makes valleys, mountain shadows, and blocked routes much more obvious during mobile listening near Kraków. [#20980128]

What is a Bias Tee, and why were two Mini-Circuits TCBT-2R5G blocks used in this DAB+ amplifier design?

"Bias Tee" is an RF power-injection network that combines DC and RF on one coax path, while keeping the DC supply separated from RF circuitry. In this design, two TCBT-2R5G blocks handle remote powering through the antenna connector and then feed stable DC to the amplifier section. The author later explained that the dual Bias Tee arrangement supports the power option and allows a 5–12 V supply range via the antenna connector. [#21182768]

What is tropospheric ducting (tropo/ducts), and how can it affect long-distance DAB+ reception tests?

"Tropospheric ducting" is a propagation effect in the lower atmosphere that carries VHF signals unusually far, often beyond normal terrain-limited range. In the thread, long-distance receptions were explicitly linked to a passing tropo event, with comments like "There will be ducts :)" That means test results during such weather can overstate the amplifier’s everyday benefit, especially for distant DAB muxes that are normally marginal. [#20985263]

How can I power this DAB+ preamplifier through the antenna connector from 5 V to 12 V without damaging the CMA-5043 stage?

Power it through the coax and regulate it down before the amplifier. The design accepts 5–12 V at the antenna connector, then uses an LP2985 4 V regulator to feed the active stage. The thread also mentions Option 2 as an extra capacitor to reduce regulator self-noise and Option 3 as a Zener diode for overvoltage protection when another stabilizer is used. That setup protects the RF stage from raw supply voltage. [#20980128]

Which matters more for DAB+ reception: a better antenna, a filtered preamplifier, or the sensitivity/selectivity of the receiver itself?

The antenna matters first, the receiver front end matters next, and the preamplifier helps only when it fixes a clear weakness. Several replies insisted that the antenna is the main issue, especially at home, while the author argued that many DAB receivers have overly simple front ends. The thread supports both views: a good antenna improves signal capture, but a filtered preamp can rescue weak or overloaded receivers. Receiver quality still sets the final limit. [#20980375]

What are the practical advantages of using a ready-made Mini-Circuits RBP-204 band-pass filter instead of building a custom DAB Band III filter?

A ready-made RBP-204 gives predictable performance without extra tuning work. The author chose it because the filter was already available, universal, and resistant to changing interference conditions. He rejected traps for individual interferers because local QRM sources can change, and he said the chosen filter’s parameters were already good enough, while better filters cost significantly more. That makes an off-the-shelf Band III filter practical for repeatable builds. [#20982899]

How much does it cost to build this DAB+ amplifier with CMA-5043, RBP-204, TCBT-2R5G parts, sockets, and PCB, and are there cheaper alternatives?

The stated material cost is about 500 PLN total, or roughly 380 PLN before housing and labor. The breakdown given later was CMA 60 PLN, RBP 90 PLN, TCBT 50 PLN each, other components 40 PLN, sockets about 50 PLN, and PCB 40 PLN for 5 pieces. Cheaper alternatives exist, but the author’s design goal was no compromise, so he used Mini-Circuits parts rather than budget RF blocks. [#21182885]

In a home setup, how should I test this amplifier with an X-300 antenna and a 35 m half-inch feeder to judge real DAB+ improvement?

Use an A/B test on the same muxes and the same feeder. 1. Connect the X-300 and ~35 m half-inch feeder directly to the receiver and note which muxes decode reliably. 2. Insert the amplifier at the antenna side and repeat the same channels, such as 215.072 MHz, 211.648 MHz, and 206.352 MHz. 3. Repeat on a normal day, not only during tropo, because special propagation can exaggerate gains. That isolates the amplifier’s real contribution. [#20985163]

What does DAB+ receiver sensitivity like -100 dBm or -80 dBm actually mean in practice, and how does it relate to µV at a 75 Ω input?

It means the minimum RF input level a receiver claims it can handle under its test conditions. The thread cites one DAB tuner at -100 dBm and another at -80 dBm, then converts -100 dBm to about 2.2 µV at 75 Ω. The key practical point is that sensitivity numbers alone do not guarantee good reception, because DAB+ also depends on multiplex structure, front-end overload behavior, and whether the receiver loses decode abruptly near threshold. [#20984040]

How does DAB+ audio quality compare with the same station streamed over the Internet?

The thread does not provide a finished listening comparison, so there is no confirmed winner here. One poster asked whether the DAB+ audio matched the Internet version, but no measurement or listening report followed. The safest takeaway is that this discussion focused on RF reception, not codec or stream quality, so you should compare the same station yourself with stable signal conditions before drawing conclusions. [#20987518]

What can I do when LED lights or their power supplies completely wipe out DAB+ reception on a kitchen radio?

First replace the LED power supply and move the radio to a stronger-signal location or an external antenna. The thread gives three likely causes: noisy LED electronics, weak DAB receiver input filtering, and low indoor signal level caused by wall and window screening. The author explicitly said not to use a plain amplifier in that case. A filtered solution may help, but only after you remove the interference source and improve signal pickup. [#20990904]

Could a tunable narrow-band filter or a directional DAB antenna work better than a wideband Band III amplifier/filter for DAB DX?

Yes, for DAB DX a narrow-band tuned chain and a directional antenna can work better than a general Band III preamp. The thread suggests a sequence of broad amplifier/filter, then narrow-band tunable filter, then another amplifier for roughly +40 dB total gain with tighter selectivity. It also mentions directional antennas and rotating masts in existing DAB DX practice. The trade-off is complexity, scanning inconvenience, and higher cost. [#20988426]

How can I open or use the shared Eagle v9 design files if I only have an older Eagle version, and when are Gerber files enough?

If your Eagle version cannot open v9 files, ask for Gerbers and build from those. That exact problem appeared in the thread: an older Eagle user could not open the project, and the author replied that the files were created in Eagle v9 and offered Gerber files instead. Gerbers are enough when you only need PCB fabrication, but not when you want to edit the schematic or board layout. [#21161193]

Where can I buy a finished version of this DAB+ amplifier/filter, or how can I source obsolete-looking parts like the Mini-Circuits CMA-5043 today?

The thread does not show a finished commercial version for sale, but it does show workable sourcing paths for parts. A later builder reported that LCSC still had 3 pieces of the CMA-5043+, and the author replied that the part was not truly obsolete and offered private help for ordering Mini-Circuits components directly. So the practical route is DIY assembly from shared Gerbers and sourced parts, not a ready-made retail module. [#21182768]
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