FM Cobra 29LTD finally hits the streets.

[nomadradio]

Yes, the FM-capable Cobra 29LTD is making the rounds. It's not the "classic" radio on the inside. But at least it's not a totally-surface mount beast.

Yet.

But the pc board looks pretty sparsely populated between the channel selector at the lower-right, and the transmitter power stages at the lower-left.

The two tiny green pc boards standing up from the main pcb now contain a lot of the stuff that used to take up this half of the old radio's pc board. Looks as if it has a separate frequency synthesizer each for transmit and receive.

The one with the metal shield cover is the transmit module.
The old 40-click channel selector is gone. Uses an encoder. The black glob on the channel selector board covers what's called a "Chip On Board" microcontroller, handling the encoder, driving the LED digits, and feeding frequency clock/data bits to the frequency synthesizers.

At least the RF final and driver transistors are old school. Both are bipolar. And the jumper wire where your carrier control gets wired in is the same. Except now it's called "JP36".

It's not a totally surface-mount nightmare.

Yet.

Oh, and about that "FM" thing. You press the channel knob. When it goes 'click' you get FM, and another click takes you back to AM.

73

 

[NZ8N]

New Cobra 29 Am/Fm

New Cobra 29 Am Fm for the American market. Finally at last. https://delboyonline.blogspot.com/2023/01/new-cobra-29-ltd-amfm-for-us.html?m=1

www.worldwidedx.com

Cobra 29 LTD Classic & Chrome FM Radios are Here

Cobra 29 LTD Classic & Chrome FM Radios are Here Well, that’s a little anticlimactic. It’s the same radio, feature wise, except FM. Push the channel selector for FM. Hope it’s ok, I’m quoting NZ8N from another post about the 29LX —————— NZ8N [begin quote] The PLL in this latest generation...

www.worldwidedx.com

Any mods for the new Cobra 29 Classic am/fm yet

Just got it today to play with on fm only. 73

www.worldwidedx.com

https://fccid.io/BBO29LT01/Internal-Photos/Internal-Photos-6305096

I got mine in Feb. straight from Cedar Electronics (Cobra Chicago) through Amazon.

The board with the metal cover is the "PLL" board, using a Beken BK4802P chip to generate the frequencies needed to run the radio. It outputs the 27MHz TX frequencies direct, and then in RX, outputs Hi Side Injection Frequencies, offset by 10.695, so Ch01 is 37.660, through Ch40 at 38.100. It is I2C serial programmed.

Why Quotes around the "PLL" ? The Beken BK4802 is actually a 2 way FM transceiver chip designed for Walkie Talkies, , with RX and TX subsections, which the RX functions are never used in this instance. The radio uses only the TX mode and output of the chip to go direct to the frequencies needed to put it on channel. Also, FM modulation, going through VR7, goes into the BK chip.

BK4802-Beken Corporation

BekenCorporation (SSE: 603068) was founded in December 2004 by a technical team from Silicon Valley of the United States. Focusing on intelligent transportation and intelligent home application. Beken is a well-known enterprise in the field of wireless connection chip design for the Internet of...

www.bekencorp.com

1. Band 1 - 24MHz~32MHz
3. Band 2 - 35MHz~57MHz
2. Band 3 - 128MHz~170MHz
4. Band 4 - 384MHz~512MHz
5. Half-duplex transceiver chip
6. On-chip FM Mod/De-mod
7. On-chip 10dBm RF Power Amplifier
8. 2.5V~3.3V Supply Voltage
9. I2C Interface

In the Cobra 29AM/FM, the "PLL" chip itself can transmit from 24 to 32 MHz, and there is no TX bandpass filtering, so the TX coils from the TX buffer on through, would be the only limiting factor, no TX Mixer chip and coils like previous generations of 29 radios.
RX is using Band 2, which if the lowest RX mixer frequency 35 MHz is used, the RX can go down to 24.305. Assuming broad-bandedness.

This "PLL" board (29LTD VCO-2) is also used in the new 2nd gen 29LX radios.

Cobra 29LX Changed Again

I started a thread back in Sept of 2021 about the Cobra 29LX being surface mount technology. Like other manufactures, Cobra has been hit and miss with inventory and I recently was able to grab a couple dozen of the 29LX. Not knowing what to expect, I opened one up and what I found was a...

www.worldwidedx.com

The second daughterboard is the FM detector, which also passes the AM 2nd IF to the AM 455KHz section. This part of the board and setup looks similar to the 29LX-EU.

http://www.servicedocs.com/artikelen/9500257280001.pdf

When in FM mode, there is a shorting line (Orange wire, RSW pad) that disables the last AM IF amplifier transistor, same as in the 1st gen LX, when in Weather receive.

https://cbtricks.org/radios/cobra/29_lx_le/graphics/cobra_29lxle_sch.pdf

All other subsections and components, part numbers and values are the same as the 29LTD-Classic generation of radios. The RX sections, (except for the FM board), Voltage regulation and TX section, TX switching, (mostly) match.

 

[Shadetree Mechanic]

Wow, that FM chip sounds like we need to hook some switches to it.