Stabo 933/934 prs cb.

Ok, so I received my Loop antenna for 934mhz, looks to be well contructed but is pretty old, has never been assembled though.,

Also in the box was a brand new old stock stabo prs 933/934 radio, all in mint condition.
Looks to have been made around 1983 i think.
So After seeing what I had in the box, I assembled the power cord and microphone to the radio, checked the polarity to the power supply and switched on.
The first thing I noticed was I could not see the display, it didnt come on which isnt what should happen.
I could hear the static on receive but no display, the channel selection button did work as did the beeper.
I then thought I saw the vaguest wisp of smoke coming from the front of the set, immediately I switched off.
That was most concerning to me, so I decided to remove the covers and see if anything obvious stood out.
Its been probably 25 years or more since I had my nose inside anything electronic and these radios are fairly compact with a lot of smd components so I was a little concerned to say the least!
I couldnt see anything obvious on the pcb, no tracks burned, nothing shorted, the radio was keeping its secret.
Sniffing the pcb gave a clue, I could detect the smell of something that had become heated but not burned.
Hmmm, where to look?
Thankfully the circuit diagram I had sent from Stabo last week provided some help.
I had noticed that a small ceramic coated inductor appeared to be discoloured behind the front panel, so I looked at the location on the diagram.
Its connected to pin 1 of a transistor array which drives the display and from there it jumps off onto a 470 uf 10 volt electrolytic capacitor, the other side of which goes to ground.
Tracing backwards on the diagram, shows that the inductor is fed by an 8 volt line that comes directly from an AN 7808 voltage regulator.
Establishing that the regulator is the source of the power for the IC I turned my attention to the capacitor.
Using a needle type multimeter, set to ohms range of x10 I touched the leads and found a direct short. The diagram shows the capacitor in series to the power feed so it means the 8 volts is flowing directly to ground and turning the inductor into an electric heater.
A quick check of the capacitor in reverse showed the same result-shorted.
As you know, a quick and dirty check of electrolytics can be done using the charge/reverse charge method.
What I think has happened is over time the capacitor has broken down internally due to the electrolyte corroding the internal structure and allowing the short to occur.
Since the 8 volts has been directed to ground through the capaictor, it also means the transistor array has no voltage to drive the display, I do feel happy to have found the issue so quickly!

Im quite pleased with myself so far ( hopefully no other issues will be found) as its been a long time since I had anything to do with electronics of any kind.
I have ordered up a load of capacitors ( Rubycon from Japan) to replace all the other electrolytics inside the radio also. I shall also replace all the capaictors in the other Stabo radio too as its of a similar age.
I will report my findings when I have replaced the defective component!
Tomorrow, I may assemble the loop yagi and take a few pictures for you all. Smile


glad to read, that Stabo could send you the technical papers :-)

The capacitors may fallen dry after so long being unused.

schön zu sehen, dass STABO Dir helfen konnte.
Die Elektrolyt Kondensatoren könnten nach so langer Zeit, wo das Gerät nicht genutzt wurde, ausgetrocknet sein, dann passieren seltsame Dinge.

73 & 55 (Gruss)
Henning Gajek
CB: Bad Dürkheim 23 / Bravo Delta 23 / 13HN23
QRV seit 1977

Hello Henning, yes you are correct.

Ok, capacitors arrived very fast indeed so the first order of business was to release the suspect component from the board. Quite fiddly as its a through hole component but double sided with those little "vias" that join each side.
Using a very small tip and a desolder pump (not ideal, I need a proper desoldering station) I released it.
A quick check with the multimeter showed it was shorted.
I actually took it apart and after unwinding about 4 turns the short disappeared.
The new component went it easily and was soldered in position.
After clipping the front panel back on and checking nothing was amiss, like trapped wires etc, I held my breath as the power went on.
Neednt have worried, I had a fully operational display and best of all no smoke! Smile
Ive had a closer look at the diagram since and found another electrolytic thats even more critical than the failed item.
Its located on the 13.8volt feed directly from the switch and is again connected between the ground and power line, so if that ever shorts out its possibly going to destroy part of the pcb and let out lots of expensive magic smoke, so that capacitor will get changed along with all the others before I dare apply power again.
Heres a couple of pictures inside the radio, I didnt get a chance to assemble the antenna today unfortunately.

[Bild: MlyOftP.jpg]

[Bild: OlB0eY4.jpg]

[Bild: wxcfbMW.jpg]

The diagram shows the capacitor that failed on the left arrow, followed by the choke that heated up, then over on the right the voltage regulator and finally the capacitor thats connected to 13.8volts that might do some nasty damage if it ever goes the same way as the other one.

[Bild: C6s1klj.jpg]

Failed item.

[Bild: zLSN1kA.jpg]

Replaced item.

[Bild: mn2BJRD.jpg]

And it works!

[Bild: oiMZx0a.jpg]

Does anyone know how to find out what the individual codes are for these radios?

The manual states that its possible to selectively call a particular radio by its code but so far ive not found the code to do so... ?


the code has to be negotiated between the users before starting the conversation.

In Switzerland the Code "00000" was used as the CQ-Call-Code (Common Call-Code for all users)

There was a manufacturer offering a code cracking tool to identify the code of a private conversation with 00001 and 99999.


Der Code musste zwischen den Funkfreunden vor dem QSO verabredet werden.

In der Schweiz wurde der Code "00000" als CQ-Code (Allgemeiner Anruf) genutzt.

Es gab wohl ein Gerät, was unbekannte Codes (00001-99999) knacken und anzeigen konnte. Näheres weiß ich nicht.

73 & 55 (Gruss)
Henning Gajek
CB: Bad Dürkheim 23 / Bravo Delta 23 / 13HN23
QRV seit 1977

Hi there if you only want to repair the 933/934 Mhz radio for collection purposes, that's ok. I do not recommend operating, however, as this could be a costly hassle with the English regulatory authority, because it has long been forbidden to operate hob radio on the frequency. It is a real shame 933/934 would have been very enriching for us in Germany, because it is 100 times better than this neutered PMR446, Freentfunk149 Mhz and LPD 433/434 Mhz
73 de Peter

Übersetzung German

wenn du das 933/934 Mhz Funkgerät nur zu Samnelzwecke wieder Reparieren willst ist das ok.
Ein Betrieb empfehle ich dir jedoch keineswegs, das könnte kostspieligen Ärger mit der Englischen Regulierungsbehörde geben, weil es leider schon lange auf der Frequenz verboten ist Hobbfunk zu betreiben. Es ist wirklich schade 933/934hätte uns auch in Deutschland sehr bereichert, weil es 100 mal besser ist wie dieses kastrierte PMR446, Freentfunk149 Mhz und LPD 433/434 Mhz

73 de Peter

Funke im 11 Meter Band seit 1987
Geboren in Heidelberg   Exclamation

Thanks Peter, concerns duly noted. There are still users on 934 in england however, most are using yagis with horizontal polarisation which as you know impacts far less on the vertically polarised signals of the celltowers.

Thanks for the reply Henning.
As far as the manual goes it seems that the radios have their own unique identifaction codes, such as 45321 (5 digits) which when input into the radio means your/my radio will call with that code only to connect with the radio that has that code.
As far as I can see its a selective calling system but I cant see how you can actually aquire the codes from any other radio unless it identifies itself first...

The 00000 cq code does work however as Ive tried it on the other stabo and both do talk to each other and select their own channels as per the manual.

Hi there when I started with the CB radio in 1987 and a little later had read in relevant specialist books that there was an additional CB radio on 933/934 in the neighboring country of Switzerland, I found it very exciting. Since I am now half Swiss and have relatives in Switzerland, I thought that it would be possible to get a license there and on vacation in Switzerland also with the grandparents in addition to the 40 Cept CB radio channels on 933/934 should spark. Unfortunately, that's probably not the case. You had to have at least a second place of residence in Switzerland. Today, in my opinion, the G2 cell phone network is outdated. Henning maybe there is a possibility of a comeback from me. There are radios for 933/934 Mhz and at least 5 watts of output power, mobile devices with an antenna socket that you could also use as a base station, everything that you want on VHF, favors and is rather unlikely with PMR446 and Freenetfunk 149. 73 & 55 Peter


als ich 1987 mit dem CB Funk begann und ein wenig später auch in einschlägigen Fachbücher gelesen hatte, das es einen zusätzlichen CB Funk auf 933/934 im Nachbarland Schweiz gab, fand ich das ganz spannend. Da ich nun halb Schweizer bin und Verwandte in der Schweiz habe, dachte ich mir das es wohl möglich sei eine Konzession dort zu bekommen und in im Urlaub in der Schweiz auch bei den Großeltern zusätzlich zu den 40 Cept CB Funk Kanälen auf 933/934 auch funken dürfte. Leider ist dem wohl nicht so man musste einen zumindest zweit Wohnsitz in der Schweiz haben.
Heute ist nach meiner Meinung das G2 Handynetz eh veraltet Henning vielleicht besteht ja doch die Möglichkeit eines Comeback von mir aus könnte man dann auch auf das Nationale Freenet149 Mhz Verzichten.
Funkgeräte für 933/934 Mhz gibt es ja und immerhin 5 Watt Ausgangsleistung, Mobilgeräte mit Antennen Buchse, die man auch als Feststation nutzen könnte all das was man sich auf UKW doch wünscht, fodert und bei PMR446 und Freenetfunk 149 eher unwahrscheinlich ist.
73&55 Peter

Funke im 11 Meter Band seit 1987
Geboren in Heidelberg   Exclamation

I did a little experimenting the other night.

With the delta connected to the co linear on Ch20 my noise floor here is around 3 bars, sometimes momentarily goes to 5 but most generally on 3.
Ch40 is usually 1 to 2 bars so much quieter.
The co-linear antennas fed by a length of westflex103 so I decided to see what would happen using a length of RG8 to connect inline.
I found a big drop off in received signal for only around 8 feet of RG8 and it shows just how sensitive things are at this frequency.

So if youre going to put an antenna its imperative to use the proper cable or else youre just killing the signal strength.
PL259 are no good you have to use N types.
It surprised me to see such a short length do so much damage actually!

Having aquired a decent swr meter for the job I tested out the co-linear.
Currently it is reading at around 1.5:1. swr.
Straight out of the box its pretty well on the money.

The yagi took a bit of messing to get the coax onto as its like trying to fit an angry snake onto the end of the N connector, the cables very stiff indeed.
Eventually after getting the yagi to sit and behave itself I found that the swr was 1.2:1.
Im very happy with that.
Swinging it around I could isolate the local noise sources from the towers on the band so at least I now can point it away from them to listen for potential voice traffic.

I will definitely fit the yagi to a tripod and take it to the hills and see what I can hear from afar...if anything! Smile

Hallo / Hello,

QRZ-934 schrieb

Da das Cybernet-Delta (= 934 MHz-Funkgerät) mit dem Co-Linear auf UK-Ch20 verbunden ist, beträgt mein Rauschpegel hier etwa 3 Balken, manchmal geht er kurzzeitig auf 5, aber im Allgemeinen auf 3.
Ch40 ist normalerweise 1 bis 2 Balken so viel leiser.
Die kolinearen Antennen werden von einer Länge von "Westflex103" gespeist, daher beschloss ich, zu sehen, was bei einer Länge von RG8 für die Inline-Verbindung passieren würde.
Ich fand einen großen Abfall des empfangenen Signals bei nur etwa 8 Fuß (ca. 2,40m) RG8 und das zeigt, wie empfindlich die Dinge bei dieser Frequenz sind.

Wenn Sie also eine Antenne einsetzen wollen, ist es unbedingt notwendig, das richtige Kabel zu verwenden, sonst töten Sie nur die Signalstärke.
PL259-Stecker sind nicht gut, Sie müssen N-Typen verwenden.
Es hat mich überrascht, dass eine so kurze Länge tatsächlich so viel Schaden anrichtet!

Nachdem ich mir ein gutes Schwingungsmessgerät für diese Aufgabe angeschafft hatte, testete ich das kolinear.
Zur Zeit beträgt die Anzeige etwa 1,5:1. swr.
Direkt aus der Schachtel heraus ist es ziemlich gut auf dem Geld.

Die Yagi musste ein wenig verwirrt werden, um den Koax anzuschließen, da es so aussieht, als ob man versucht hätte, eine wütende Schlange auf das Ende des N-Steckers zu setzen, wobei die Kabel in der Tat sehr steif sind.
Nachdem ich die Yagi schließlich dazu gebracht hatte, sich zu setzen und sich zu benehmen, stellte ich fest, dass der Swr 1,2:1 war.
Damit bin ich sehr zufrieden.
Durch das Herumschwenken konnte ich die lokalen Geräuschquellen von den Türmen auf dem Band isolieren, so dass ich es zumindest jetzt von ihnen wegzeigen kann, um auf möglichen Sprachverkehr zu lauschen.

Ich werde die Yagi auf jeden Fall auf ein Stativ montieren und sie in die Hügel mitnehmen und sehen, was ich aus der Ferne höre... wenn überhaupt! smiley

Ja 900 MHz ist eine ziemlich schwierige Frequenz. Deswegen glaubten damals auch viele, dass CB-Funk auf 900 MHz der "Tod" des CB-Funks gewesen wäre und waren dagegen.

Viele CB-Hersteller waren dagegen, weil sie schnell gemerkt haben, dass man eine gewisse Qualität braucht, damit es funktioniert.

In der Schweiz hat sich gezeigt, dass es doch geht :-)

Mobiltelefone mit GSM-Standard auf 900 MHz haben gezeigt, dass es doch geht und heute funkt die 5G-Technik bereits auf 3500 MHz (3,5 GHz)

english version:

Yes, indeed. 900 MHz is a little bit complicated to handle with.

Therefore many CBers believed that CB-Radio on 900 MHz would be the death of CB because of poor distance-range and were against it.

Many CB-Importers/Manufacturers were against it, as they knew, you need a minimum kind of quality to keep it working.

In Switzerland the CBers of SCBO-Organisation showed, that it works

Mobile GSM phones on 900 MHz show it, too.

Today 5G is using 3,500 MHz Frequency which is much more higher than 900.

73 & 55 (Gruss)
Henning Gajek
CB: Bad Dürkheim 23 / Bravo Delta 23 / 13HN23
QRV seit 1977

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