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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 9th Oct 2003, 11:32 am   #1
Barnmead
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Default R1155B. Noise on one band.

I am having trouble with excessive noise on the 75-200 kHz band and
suspect the aerial coil L6 may have shorted turns. I have checked
through the wiring for the switch FSxr and all seems OK. The resistance
of this winding is 42 ohms though the figure given in the AP2548A is 57
ohms. I am reluctant to take the thing apart and rewind if there may be
variants on the design of the coils. (other coil resistances seem to be
about 5% low so I assume these are OK)

Can anyone shed some light for me?

Regards

Richard

Last edited by Station X; 27th Dec 2004 at 10:50 pm. Reason: Import
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Old 21st Jan 2004, 8:09 pm   #2
JHGibson
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Default Re: R1155B

Hi Richard, Did you get the noise problem sorted out yet? I measured L6 on my R1155a and it was 42 ohms also.
What is the nature of the noise, is it a hiss, or crackles or hum and does it persist with the aerial removed and the gain full up. Do you notice that frequency band noisy on other radios?
John.
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Old 21st Jan 2004, 9:54 pm   #3
Barnmead
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Default Re: R1155B

Hi John
Interesting that yours measures 42 ohms. Thanks for comments an measuring yours.

Responses to queries on the web elicited offers of spare coils and advice so I spent the best part of a day taking the coil apart and putting it back together. I removed the outer centre tapped DF winding and screen to find that the main winding is in 4 sections wound with Litz wire. It still measured 42 ohms, so I carefully scraped away the covering of the winding adjacent to one of the dividers with a view to determining which section was at fault and I found that the resistance had mysteriously increased! I must have exerted sufficient pressure to move the wires slightly. (Interesting 42X4/3=56?) I applied a little more melted wax and put all back together and it works!

I still found a lot of noise on bands 4 and 5. The IFs seemed to be lined up OK and I tweaked the trimmers at the HF end of each band and the dust cores at the LF ends. This made a marginal improvement.

The main culprit was a strong local station (in London) transmitting on 558 kHz and once I had reset the rejector filters for minimum output I noticed an improvement, though inserting series and parallel rejector circuits between the aerial connectors and the set seems to have solved the problem.

see my page http://www.richardsradios.co.uk/r1155b.html
I guess purists would not agree to the modifications I have made!

Regards

Richard

Last edited by Station X; 27th Dec 2004 at 10:51 pm.
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