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Author Topic: Transceiver "sees" signal generator input But no Air RF  (Read 410 times)

K1KIM

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Transceiver "sees" signal generator input But no Air RF
« on: July 09, 2022, 07:00:48 AM »

The receiver on my radio, IC-551D, sees the input from my signal generator but receives no transmitted signals by "air"

Receiver is deaf with nothing but an S-0 noise on all modes through the band.

I've tried three different antennas and though I can hear the local transmissions on my 991, nothing heard on the 551D.

Andy thoughts?
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W7CXC

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #1 on: July 09, 2022, 07:08:29 AM »

What level does it take to hear the sig gen?
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W1VT

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #2 on: July 09, 2022, 07:27:22 AM »

Bad cable or coax adapter.
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K1KIM

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #3 on: July 09, 2022, 08:14:08 AM »

Bad cable or coax adapter.

Not the problem. Those familiar with the radio know there is a RCA jumper in the rear between the Receiver  Input and the Receiver Antenna Output.  There is a dead short on the SO-239 antenna IN when this jumper is in place. However, the output power and SWR are good into a dummy load.

Since my signal generator is out on loan, I used the MFJ 259B attenuated by 83dB to produce a S9 +20 meter reading on the radio.
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W7CXC

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #4 on: July 09, 2022, 09:25:56 AM »

Was this a test?
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AC2EU

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #5 on: July 09, 2022, 10:07:49 AM »

Bad cable or coax adapter.

Not the problem. Those familiar with the radio know there is a RCA jumper in the rear between the Receiver  Input and the Receiver Antenna Output.  There is a dead short on the SO-239 antenna IN when this jumper is in place. However, the output power and SWR are good into a dummy load.

Since my signal generator is out on loan, I used the MFJ 259B attenuated by 83dB to produce a S9 +20 meter reading on the radio.

If it was a dead short, how did the signal generator work?
Something is wrong with this picture...   :-\

K1KIM

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #6 on: July 09, 2022, 11:57:54 AM »

Bad cable or coax adapter.

Not the problem. Those familiar with the radio know there is a RCA jumper in the rear between the Receiver  Input and the Receiver Antenna Output.  There is a dead short on the SO-239 antenna IN when this jumper is in place. However, the output power and SWR are good into a dummy load.

Since my signal generator is out on loan, I used the MFJ 259B attenuated by 83dB to produce a S9 +20 meter reading on the radio.

If it was a dead short, how did the signal generator work?
Something is wrong with this picture...   :-\


It's an odd arrangement inside the radio with a receive relay. It's all in the service manual, but too hard for me to explain. Whatever that is supposed to do, it's not doing.
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N4ATS

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #7 on: July 09, 2022, 12:46:51 PM »

Its a choke (inductor) , its not s short.  Your typical hand held meter is about 20 KHZ or so , thus you appear to read a "short" across it because of very low frequency, However at at higher frequencies, it is open, so RF will pass thru it...
« Last Edit: July 09, 2022, 12:53:37 PM by N4ATS »
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W7CXC

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #8 on: July 09, 2022, 01:46:18 PM »

I have gotten mixed up like that from time to time... so RF will pass thru it...NOT  :)
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AC2EU

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #9 on: July 09, 2022, 04:05:08 PM »

I think this thread needs a "reset"
I still don't understand how the generator gets a signal through but the antenna doesn't.
Do you have the generator cranked to max output or something?

The radio show turn up just as deaf for the generator as the antenna. ( If it's really deaf)

K1KIM

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #10 on: July 09, 2022, 05:55:43 PM »

I think this thread needs a "reset"
I still don't understand how the generator gets a signal through but the antenna doesn't.
Do you have the generator cranked to max output or something?

The radio show turn up just as deaf for the generator as the antenna. ( If it's really deaf)

I don't believe that is always true.  I have a FR-101R receiver that has an internal signal generator and both the Internal and my external signal generator both show on the receiver but both radios are "deaf" to hearing audio. Speakers are fine and S meter moves.
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AC2EU

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #11 on: July 09, 2022, 07:34:54 PM »

I think this thread needs a "reset"
I still don't understand how the generator gets a signal through but the antenna doesn't.
Do you have the generator cranked to max output or something?

The radio show turn up just as deaf for the generator as the antenna. ( If it's really deaf)

I don't believe that is always true.  I have a FR-101R receiver that has an internal signal generator and both the Internal and my external signal generator both show on the receiver but both radios are "deaf" to hearing audio. Speakers are fine and S meter moves.

So far all of this is talked about in very vague terms. Specifics are where it's at.
How much input for what response in the radio?  Ideally if you pump in -73 Dbm, the audio should be very loud and the s-meter should show S-9 ( however , you can't always depend on S-meters!).
The real "hearing test" test is at the low input sensitivity.

So, what exactly was the input and what did the s-meter show?
Also, does the FT101 have an RF or audio problem?, they can fail independently...
The internal generator is introduced at more or less the same point as the antenna. It should produce a substantial s-meter reading.

If your radio can hear -110 Dbm or so, it should work fine on an antenna. If not, your antenna or whatever is in between has a problem.

W9IQ

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #12 on: July 10, 2022, 04:27:55 AM »

The receiver on my radio, IC-551D, sees the input from my signal generator but receives no transmitted signals by "air"

Receiver is deaf with nothing but an S-0 noise on all modes through the band.

I've tried three different antennas and though I can hear the local transmissions on my 991, nothing heard on the 551D.

Andy thoughts?

Andy,

Had the radio worked properly for you in the past and this is a new problem?

Have you checked the position of the RF gain control (the ring concentric to the AF gain control)?

Since you reference S-0 noise, do you have the squelch control fully CCW?

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N4ATS

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #13 on: July 10, 2022, 07:39:57 AM »

Also...

"The receiver on my radio, IC-551D, sees the input from my signal generator but receives no transmitted signals by "air"

Unless you have a really good RF Signal Generator with a good step attenuator, what amplitude are you injecting to hear it? Typically RX is around -110 for decent SNR to be able to hear it. If your generator is pumping in 5 or 10 dB , of course you will hear it even if the preamps are dead. "air" signals are roughly -90 ish depending on the distance.
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AI5BC

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Re: Transceiver "sees" signal generator input But no Air RF
« Reply #14 on: July 10, 2022, 08:31:54 AM »

Sounds normal to me. Like ham forums and radios, both are crocodiles, all mouth and no ears.
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