Marconi 2955A

[Biggenz]

I've used many radio communications test sets over the years and have just bought myself a Marconi 2955A, which incidentally I've never used before.

Not a problem as a test set is a test set right? Well I can't seem to work out how to select the ctcss tones on RX test. In the tones menu I'm expecting to see an option called ctcss or sub audible tones, but there's nothing of the kind. There are two sub menus, one for analogue and one for digital. The analog sub menu has 5 tone, dtmf etc. and the digital has dcs, pogsac etc.

How do I select the ctcss tones I want??

[Dickie]

The recommended (and only) way to do it is to set up the 2nd audio generator as the CTCSS tone.

[Biggenz]

I see. Thanks for that. Pretty simple if you think about it.

Do you know if there's any way to decode the ctcss in TX mode?

[Superscope]

I was going to say, I didn't think the 2955 had native CTCSS.

The later version of the 2955 did, can't remember the Model
Number off hand, might be the 2960.




Ian

[Dickie]

Originally Posted by Biggenz

Do you know if there's any way to decode the ctcss in TX mode?

I think the only way to do it is to do it using the mod. meter functions. Won't work if there's other modulation on at the same time, of course, unless one of the filters can be used.

[Biggenz]

Originally Posted by Superscope

The later version of the 2955 did, can't remember the Model
Number off hand, might be the 2960.

The 2945 is the model up and has native ctcss. Tbh I've never really been a fan of the Marconi test sets as they always feel slow and clunky.

I used to love working on the IFR 1200S - so snappy. In my old days as an engineer I used to repair tonnes of radios in such a short period of time using that.

[AC/HL]

IFR took over Marconi Instruments. In turn it was taken over by Aeroflex, which was then taken over by Cobham.

[TALKINGWITHPYE]

Hello from Dave, to read the transmitted ctcss select the low pass filter and you get the ctcss frequency on the display.

[Biggenz]

Turns out I bought a lemon. It works fine whilst it's busy warming up, but after around half an hour the transmit frequency starts drifting all over the place in TX mode.

I guess that's why you should never buy test equipment on the net!

[Radio Wrangler]

Might have been OK before transportation, but who knows, and nothing can be proven.

By TX mode do you mean when the test set is working as a sig gen? or do you mean when the radio under test is in TX mode?

Some modulation meters try to find the transmitter frequency automatically, and if you don't have a working transmitter connected up, will drift around aimlessly. Otherwise you are looking for a synthesiser fault. Not the end of the world and not impossible but they scare the pants off the uninitiated. Got the manuals?

David

[Dickie]

In "Tx Test" mode the 2955A will sweep around looking for a signal to lock on to. When it finds one it will display what it thinks is the Tx power, frequency, modulation, etc. With a marginal input the instrument might lock and then lose it, with random incorrect readings.

It is possible to manually input the expected Tx frequency, the instrument will then display what it thinks is the frequency offset between expected and measured.

Check the input power is within the spec. for the input in use.

[mole42uk]

It's also possible that the gold pcb interconnects in the lower region of the instrument might have become dirty or displaced when in transit. That happened to me once and I took apart all the lower boards, cleaned the contacts with 100% alcohol and it's been fine ever since.