CB problems over the weekend

[silverbullet]

Over the course of the Surrey lanes day, my CB transmissions went from "Crystal clear" to "very faint" in the space of a few hours. Reception was good all the time. SWR before setting off checked at 1.7
The aerial didn't get dislodged or knocked back on the knuckle (bolted through in centre of caravelle roof) so where to start?
Could the set's TX circuitry be "going off" after a time? I'm no electronics expert.
PS it's a Midland 98 plus that I got from Neil

[Justavan]

When you say very faint do you mean going very quiet os shorter in range or distance.
If Audio failing some models of Midland CB had habit of fading away once they got on a bit.
A bugger of a fault to track down or a simple dry joint on the circuit board
If it is failing in distance it could just be the final drive transistors failing which are the two bolted on to the heat sink at the back of the circuit board.
If it is the power out put the transistors are easy to change and only cost a few quid from Maplans and usually just a Google away on "How To" .............

[silverbullet]

Thanks for that. The initial comments I got were "you're coming through loud and clear - really good" but as the morning went on it was a case of "is that you Ian? you're really faint, can hardly hear you etc."
I guessed that maybe as the unit warmed up and "soaked" a bit the TX power was falling off?

[lloyd]

Have you checked what SWR is now?

Simple way to determine if it's radio or antenna is to try your radio on another antenna or another radio on your antenna.

[silverbullet]

Good point. I'll plug in the SWR meter tonight and leave the set on for a while to see if there's any change in values.

[Simon Baxter]

knocked it down to .4w?
Earth braid on Coax touching the centre pole in the PL plugs?

[Justavan]

Yep, Si is right you should check the antenna and power switch first but if the antenna is at fault the damage will already have been done.
easy way to check the arial is put a test meter leads across the antenna whip to a good earth point and if you get any sign of a connection your antenna is shorted out.
The centre core of the co-axil cable must be well connected to the the arial without touching any earth points to the bodywork and the outer braided cable going to the arial must be earthed to the antenna mount and bodywork without touching the centre core of the cable.
It is VERY important that you have a proper earth for the Antenna to the bodywork as without one the CB unit will burn out or have very poor performance. (mag mounts work without being Earthed as such but thats another long explanation)
To check your antenna for maximum performance you need a Frequency Deviation meter for FM modulation as SWR meters are only measuring the Standing Wave Ratio for
Amplitude Modulation which was for the old AM Cb sets.
It does give you a ruff guide to set your antenna by using the SWR or better a Power meter but Frequency Deviation meters are what we should use but they were never marketed when FM CB's became legal and are like hens teeth to get your hands on one now.
Hope this helps as I'm just killing time on this subject as I'm stuck indoors due to ill health at the moment but feel free to ask.................

[syncrodoug]

Your arm wasn't getting tired so that the mic got progressively further away from your mouth as the day wore on?

[silverbullet]

Your arm wasn't getting tired so that the mic got progressively further away from your mouth as the day wore on?

It had crossed my mind that poor mic technique could be part of the problem...I didn't want to be bellowing down the thing or sounding all "bwah bwah mumble garble" like a BR platform announcement.
How close to get one's lips for optimum performance?

[v-lux]

How close to get one's lips for optimum performance?

Snigger..

[silverbullet]

A cheap gag but I just couldn't help myself...Ooh you are awful...