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Hi all, 

some of you will know that for a wee while, I have been amongst the wiring on my TR4.

Almost all finished, buy now the cb doesn't work.

Think I might have inadvertantly tried to transmit with the antenna disconnected, think this is Kaput?

John.

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I doubt it John. Does it do anything, ie hissing sounds, lights / displays coming on ? if not check any fuses, wiring etc.

If nothing obvious I can take a look for you if you like (I used to "dabble" in CB sets a few decades ago) (nuf said)

Bob

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It is generally considered bad news to transmit without the antenna disconnected. i think they sell dummy loads to connect when testing without being connected to an antenna. So if you did transmit with it disconnected you might well have damaged it.

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It depends on whether the transistors in the output stage can withstand much over-voltage. The antenna acts as a matched load to absorb the transmitter output power. Without that load there is nowhere for the power to go so it reflects back into the output stage and in worst case can double the voltage on the transistors.  If the manufacturer was working down to a price and specified ones which are only just good enough for correct conditions, they might break down. 

That is the reason for adjusting the antenna length for minimum voltage standing wave ratio (VSWR). At anything other than 1:1 matching there is a proportion of the power being reflected back and this has to be dissipated in the output stage. 

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Agreed, but worst case would be O/P tansistor needing to be replaced, a fairly simple job.

John, does it still receive messages from others ?

Bob

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Thanks Guys, 

and Bob thanks for the offer to have a look.

I'm away from home just now, so it will be early next week, before I can check if it still receives.

Annoying, 

a) cause it was my stupidity, and 

b) It lives in a dedicated slot in my H frame, so simply buying an other is not the preferred option.

Be in touch.

John.

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Have faith in Bob.

Last year I got hold of a lovely Radiomobile car radio. However it suffered from age and the tuner transistors (AF117)  were duff.

It took NASA to find out why AF117 went duff like this)

Bob volunteered his help. It took him all of a day to sort it out (probably an hour or so)  He is an asset to the forum.

 

Roge

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3 hours ago, RogerH said:

 

Bob volunteered his help. It took him all of a day to sort it out (probably an hour or so)  He is an asset to the forum.

 

Roge

Agreed. 
he helped me out with steering stops on what is now a championship class winning car. 
thanks Bob

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