Amplifier plus DAB+ filter without compromise

max-bit 26 Feb 2024 22:54 51 6813 Cool? (+22)

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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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As I have been receiving DAB+ Digital Radio for a long time, I am also struggling with reception efficiency, even though the assumptions of the DAB radio specification (DAB+) were to ensure not only digital quality, but also ensure effective reception even in difficult conditions.
Unfortunately, the assumptions were "slightly" different from reality, as I often travel by car and I have a DAB+ receiver in the car, which means that I know "how it is".
And while the reception of regular VHF radio is not difficult even in mountainous or foothill areas (around Krakow), unfortunately for the reception of DAB+ radio, the first large hill that covers the transmitter quickly causes the signal to disappear. Unfortunately, the operating frequency range (174-230 MHz) means that the range is basically optical and while close (~ 20 km from the transmitter) in built-up areas is rather (but not always) problem-free, the further away the worse.
Another issue is the weak input circuits of DAB receivers, they are as simplified as possible, and the receivers are most often single-chip with zero input filters, which also limits the receiving capacity of the receivers.
So I assumed the construction of an amplifier for a DAB receiver with an input filter system, the minimum gain of such a system in the entire band is ~20 dB with filtering outside the min. 30 dB.
I didn`t make any compromises here - the elements I used were Mini-Circuits circuits and filters.
The system used is CMA-5043, and the filter is RBP-204, the system is powered from the output and can be supplied from 5 V to 12 V, and the LP2985 4 V stabilizer system is used, additionally two blocks are used Bias Tee - TCBT-2R5G elements for receiving DC voltage and then applying a stable voltage to the amplifier system.
The system can be directly powered from the antenna output (voltage range 4-5 V) (OPTION 1),
OPTION 2 is an additional capacitor that reduces the self-noise of the LP2985 stabilizer, OPTION 3 is an additional Zener diode that can be used to protect against too high voltage (when using another stabilizer).
The board was designed as 4-layer (wave impedance).

Diagram:

Schematic of a low noise amplifier with a filter for DAB+ radio.

Printed circuit board in 2 views:

View of the designed DAB+ amplifier on a PCB in schematic form.

View of the printed circuit board of a DAB receiver amplifier with Mini-Circuits components.

Render view:

PCB of DAB amplifier with mounted components in a sealed enclosure.

DAB+ amplifier circuit with components mounted on a printed circuit board.

Views of the completed board with installed elements:

Printed circuit board of a DAB amplifier with mounted components.

Green PCB of a DAB+ amplifier with mounted components and connectors.

DAB receiver amplifier PCB with mounted components.

DAB+ amplifier mounted on a green circuit board in a metal case.

DAB+ amplifier with filter in a housing labeled with input and output signs.

Measurement results of the completed system:

In the range up to 1 GHz:

In the range up to 500 MHz:

Graph showing the characteristic of an amplifier for DAB+ radio reception.

Finally, the amplifier looks like this (the housing was encapsulated by protecting it with varnish):

DAB+ amplifier with 170-240 MHz filter in casing.

About Author

max-bit wrote 4613 posts with rating 851 , helped 117 times. Live in city Kraków. Been with us since 2007 year.

Comments

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sq3evp 27 Feb 2024 08:22

You don`t write anything about the antenna - maybe there is a fault in the antenna installation? The amplifier looks interesting, but the antenna is always the main topic to solve, the amplifier comes... [Read more]

max-bit 27 Feb 2024 09:17

Well, I don`t write anything about the antenna because the antenna has nothing to do with it. The antenna installations are different in the car - this is the original, in the other locations these are... [Read more]

sq3evp 27 Feb 2024 09:38

Just because it t mean it`s ok. Often it is an antenna that is not fully matched (some quarter, too short for FM and too long for DAB), and an amplifier is used. I know that you can also receive on the... [Read more]

max-bit 27 Feb 2024 09:52

The amplifier is not intended for a car radio, so I mainly use sulfur in the radio :) This is for stationary/field reception testing. FM is surprisingly able to receive on a piece of wire even in "difficult"... [Read more]

slaw0 27 Feb 2024 12:29

And I guess it`s better. Someone will still think about giving up the analogue. [Read more]

rosomak19 27 Feb 2024 12:40

With the stations that are placed on the multiplex (at least in my case), it will certainly die. There`s nothing to listen to there. [Read more]

max-bit 27 Feb 2024 21:08

There were ideas to turn off FM, as far as I remember, it was turned off in Norway Link 1 Link 2 [Read more]

Anonymous 27 Feb 2024 21:43

Out of curiosity, I would like to ask what influenced the choice of ready-made solutions - especially the filter? From what you show, you have the knowledge and resources to make a bandpass filter yourself. ... [Read more]

BANANvanDYK 27 Feb 2024 23:19

If it m not surprised. As for DAB+ reception in the field, it`s unfortunately a lottery. For example, in Chełmno I can currently receive two multiplexes on a regular antenna: Solec Kujawski (approx.... [Read more]

max-bit 28 Feb 2024 17:01

And why should I do something when something is ready? I used it (this filter is both easy and not easy to make) The airwaves are full of sources of interference. Using traps for a given frequency makes... [Read more]

sq3evp 29 Feb 2024 11:48

I found a table which shows that the signal level for the subscriber sockets (it can be assumed that the signal levels from the receiver`s antenna) for DAB is at least 28µV, and for FM stereo it is at... [Read more]

max-bit 29 Feb 2024 12:19

Sorry, what are you writing about? What subscriber sockets? Moreover, I would like to know what the 28 uV level means in the DAB signal? (I suggest you familiarize yourself with the structure of the... [Read more]

sq3evp 29 Feb 2024 12:33

This is the signal level for the subscriber socket - it is something you have in the wall and you connect a tuner to it (in short). This is the minimum signal level required by the DAB+ standard - meters... [Read more]

max-bit 29 Feb 2024 12:47

By the way, what does an FM/DAB tuner look like today? Well, let`s take a look at the tuner for about PLN 2,000 https://obrazki.elektroda.pl/5595594400_1709206720_bigthumb.jpg we also have a specific... [Read more]

rosomak19 29 Feb 2024 13:10

DAB, like DVB-T2, has no intermediate states, as in the analog signal - it receives, but there is a bit of noise, or there is no stereo. Here it either receives and decodes, or there is nothing. [Read more]

max-bit 29 Feb 2024 13:12

And that`s a bit of a problem. Even though there was some noise in FM, it just dies here, which is irritating. [Read more]

sq3evp 29 Feb 2024 14:15

This is the specificity of the digital signal. This is the direction the world is heading. [Read more]

max-bit 29 Feb 2024 21:48

First tests Kraków QTH: KO00AC02 Reception was trouble-free (other weaker stations) - I omitted local or very strong stations. MUX Świety Krzyż 215.072 MHz (ERP 10 kW) - Emitel MUX Prehyba - Szczawnica... [Read more]

sq3evp 01 Mar 2024 07:55

And what signal levels? What antenna? In the car? [Read more]

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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