SkyArrow 250 CB Radio

[Sparky67]

Hi all,

Not something I usually have on my bench, but today there is a SkyArrow 250 multimode CB radio sitting there. It has been modified with a UK / CEPT channel switch, there are 80 channels available in each of these bands. However it appears to be well off freq for the UK allocated band. In fact it’s way off freq for any band plan I can find!

Bit of a long shot, does anyone have a service manual, or even a circuit diagram for this radio please?

The pin-out for the 4-way mic socket would be useful too.

Many thanks.

Martin
G4NCE

[SiriusHardware]

A lot of these radios with almost made-up names have familiar chassis inside, if you can give us an idea of the likely age of the radio and show good overhead and track side views of the PCB we might be able to come up with something close.

[ortek_service]

The original 'odd +1.25kHz offset' channels (or -3.75kHz relative to original CEPT / FCC ones) was often made on the most-common built-in ROM PLL's by a slight adjustment of the 10.24MHz single reference frequency which resulted in the UK channels all being on slightly-different offsets as this also controlled the spacing, when divided down by 1024.
But as the spec's were quite generous on freq. accuracy, it allowed this PLL-manufacturer 'bodge' to work well enough for the original UK40 channels.

So if the mods are the common piggy-backing of a TC9119 (UK40) / TC9106 (CEPT/FCC) or LC7137 (UK40) / LC7132 (CEPT/FCC) PLL's, then the 10.24MHz reference crystal should ideally have an adjustment to pull it a bit for UK frequencies.
And if you've got an accurate frequency counter, then you could try measuring the 10.24MHz frequency to see what it is on each band - but with care, using a high impedance probe / measuring on drive-side of crystal oscillator , to not pull-it when measuring.

SSB transceivers, with more versatile PLL systems, had separate crystal down-mix oscillators that could be moved with the kHz shift control without affecting channel spacing. And usually a pre-set was added to move down by 3.75kHz which left adjustment a bit asymmetric on UK channels.

[SiriusHardware]

I had a quick look around for images of the set and for a multimode it's very small, so that suggests to me that it is not a 'classic' period model and won't contain any of the well known old Cybernet or Uniden multimode chassis.

Unfortunately with these more modern-era sets the service data can be difficult or near impossible to obtain - I did have a good search around but haven't been able to find anything.

[Techman]

Interesting!

I just had a look around on the net and found these:-

[Alistair D]

This site has many manuals but not your one. It may be worth a look to see if you can find something similar.

http://www.cbradio.nl/

Al

[SiriusHardware]

Well done Techman. Bit scruffy but a lot better than nothing.

[electronicskip]

There is a YouTube video of the Sky Arrow 250 in action , the quality is poor however and one of the comments after is someone also asking for a circuit diagram, that was posted 9 years ago and no one's replied.

I've never heard of the Sky Arrow CB before so afraid I can't help you with this one.

[Techman]

This could be the same radio from 9 or 10 years ago - it looks like it was doing the rounds back then, so possibly had a few fingers inside it since then. I've never seen or heard of one before, apparently it's the same as the Ferris and thought possibly to be made by same company as did the innards of the old Grandstand home base etc.

[electronicskip]

Originally Posted by Techman

This could be the same radio from 9 or 10 years ago - it looks like it was doing the rounds back then, so possibly had a few fingers inside it since then. I've never seen or heard of one before, apparently it's the same as the Ferris and thought possibly to be made by same company as did the innards of the old Grandstand home base etc.

It could well be the same unit.
There is some dialogue on one of the CB forums about the Skyarrow being an ultra rare unit , hence the lack of information.

[SiriusHardware]

Did anyone else notice that techman managed to find the diagrams in #5?

Techman, do you have a direct link to where you found them? The forum engine has crushed the images you posted to the point of near unreadability as usual.

[Techman]

Pity I didn't save a link to it. I think it was somewhere in the middle of a 7 page thread on the Transmission forum about 10 years ago - trust me, the originals weren't much/any better. There were pictures of the front of the radio, which was quite interesting to see.

[SiriusHardware]

I found it: This link places you at the start of the bit where the diagrams are posted.

https://www.transmission1.net/viewto...13958&start=80

The very last post in the thread has an attached .jpg which may be a better version of the schematic but I am not a member of that forum - only registered members can view it, I think. Anyone a member there?

Interesting that this actually does seem to be an old radio, although not one of the common ones. I've honestly never heard of them before now.

Originally they seem to have been multi mode but single band, in fact the diagram shows the use of a 'restricted' Sanyo LC7131 PLL which is dedicated to generating the 40 FCC / EU CEPT / 'Mid' band only. However there is a 'dodge' which can be employed to make that PLL generate a block of channels at frequencies +455KHz from the intended ones and with frequencies ending in '0' rather than 5, or 27.420 to 27.860, so perhaps this was the means by which this radio was 'persuaded' to -sort of- cover most of the UK frequencies, still with the occasional FCC frequency jumps and the foldback around channels 22-25. A degree of shift would then have been applied to shift those channels a further +1.25Khz for 'UK mode'. I have to say all of that would have been far too crude for my tastes.

The classic old multimodes at least had unrestricted PLLs making it possible to insert an EPROM to untangle the FCC order of channel steps into a straight set of ascending 10Khz steps, as the UK channel scheme required. This radio sounds like it would have been best left where it originally worked.

[Sparky67]

Thanks all. Yes, unfortunately the circuit above isn't great on the source Transmission1 forum and is a bit too indistinct to work from, so was hoping someone might have a better copy filed away somewhere. Also, is it me or do the mic socket connections not make too much sense?

If this is a not-too-popular name hopefully the attached images might throw some light on the chassis under a more popular badge?

The two yellow wires from the trimmer caps go to the UK / CEPT DPST switch on the rear panel.

Thanks again.

Martin
G4NCE

[SiriusHardware]

In the link I posted in #13 the radio also seems to come in the guise of the 'Ferris CB8000', another set I have unfortunately never heard of.
Might be worth searching for info under that brand / model as well.

As well as the wires from the 'band switch' to the trimmers are there also wires going from the other half of that switch to pin 20 of the LC7131 PLL?

Edit: Hang on, I see that one of the front panel switches originally has the function 'Hi/Lo band'. On the 'Hi' band what is the TX frequency on channels 1 and 40?

[SiriusHardware]

With regard to your microphone connections, see attached.

Of course there are no pin numbers marked on the socket on the diagram, so if it's not clear work it out like this:

Power off, meter on resistance, find which of the four pins has a very low resistance connection to the supply -Ve lead. That one is GND.

Power on, meter on volts, find which of the other pins has roughly 13.8V on it. That pin is PTT, take it to GND to put the radio into TX mode. The +13.8V is coming to this pin through the coil of the TX / RX switching relay, so don't worry about connecting it to GND, you won't short the supply out by doing so.

Of the remaining two pins on the socket, find the one which has nothing connected to it at all and ignore that one. The other remaining pin is microphone audio in. The transistor and the bundle of components including a preset to the right of that look as though they are a kind of audio ALC circuit. The transistor regulates the amount of microphone audio which is allowed to get through to the microphone amplifer IC, marked 'Audio IC' in pencil.

[SiriusHardware]

Another thing: It seems the original version of this radio was a made-for-USA market model - if you look at the Ferris CB8000 the mode switch has AM/LSB/USB and PA (No FM) and no channel hi/lo switch, so 40 channels, therefore a legitimate USA domestic model. (SSB has always been a permitted mode in the USA).

This variant we are looking at here (the radio and the diagram) seems to have FM incorporated but the pencilled information on the 'clarifier close-in' diagram refers to some downmix crystals which are on an off-circuit oscillator board, presumably. The images following the Ferris set show a fairly large and complicated daughterboard with two crystals on it, this no doubt incorporates whatever makes the radio into an 80-channel set. Unfortunately we don't seem to have the diagram for that downmix PCB.

[crackle]

Originally Posted by SiriusHardware

I found it: This link places you at the start of the bit where the diagrams are posted.

https://www.transmission1.net/viewto...13958&start=80

The very last post in the thread has an attached .jpg which may be a better version of the schematic but I am not a member of that forum - only registered members can view it, I think. Anyone a member there?

The image in the last post is a circuit containing a 7808 regulator wired to the clarifier circuit.
Mike

[SiriusHardware]

Thanks for that. Can I ask whether the set pictured in #14 is the actual set being looked at as it does not seem to have that large daughter board with the two crystals on it?

And again, what is the TX frequency on channels 1 and 40 of the 'high' channel mode?

[Sparky67]

I actually joined the forum to see that last image, which I (wrongly!) presumed was a legible copy of the cct...

The image in post 14 is the actual radio on my bench. I have now found time to check some Tx freqs on my test set. Results are:

‘UK’ channels
1 - 26.959
20 - 27.199
40 - 27.399
41 - 27.411
60 - 27.651
80 - 27.851

‘CEPT’ channels
1 - 26.965
20 - 27.205
40 - 27.405
41 - 27.415
60 - 27.655
80 - 27.855

All +/- 150Hz, measured with the radio out of its case. The 2955A isn’t locked to an external standard. The Rx is reasonably sensitive on FM on these freqs.

Also proved USB and LSB work with a the carrier produced by a 1kHz test tone reading as above on USB and 1kHz lower on LSB.

Cheers,

Martin