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 Post subject: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 5:25 am 
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Location: Weimar, Texas
I haven't asked a dumb question since the last time :) so here goes. I have a pretty nice HP RF signal generator back home (950 miles away) but no plans (or room) to bring it here. I have a Rigol DG4102 Arbitrary Waveform Generator here (not RF signal generator). I also have the Precision Apparatus E-200C that I restored a number of years back. Which would you use for alignment and / or troubleshooting?

I have a Silvertone farm radio that I'm trying to get out of... I mean finish restoring and return to a friend. It may just need an alignment. It will pick up some a shortwave station and some local AM stations with no antenna other than what I have curled up.I'm not sure about dial accuracy. I just got it to sing and I haven't tried to restring it yet.

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 5:43 am 
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The Rigol will probably have a cleaner signal and be more accurate on frequency. You may have to add an external divider to reduce the level to the uV range to get the detector level low enough.

The PACO will do fine.

Use whatever you want. It is not high precision alignment.

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 7:37 am 
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If nothing else, just do it by ear, using a weak but non-fading station.

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 9:53 am 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
Minimum requirements: must be capable of outputting an output-level-adjustable, audio-tone-modulated (AM) sinusoidal wave at the following frequencies:
- IF filter frequency (typically 455 kHz)
- Low end of standard broadcast band (550 kHz)
- High end of standard broadcast band (1600 kHz)
- Middle of shortwave band (10 MHz) (some procedures spec low end/high end shortwave-band frequencies as is traditional with the broadcast band)

Whichever RF generator that you have at your disposal that will meet the above requirements will be satisfactory.


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 1:14 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
lorenz200w wrote:
Minimum requirements: must be capable of outputting an output-level-adjustable, audio-tone-modulated (AM) sinusoidal wave at the following frequencies:
- IF filter frequency (typically 455 kHz)
- Low end of standard broadcast band (550 kHz)
- High end of standard broadcast band (1600 kHz)
- Middle of shortwave band (10 MHz) (some procedures spec low end/high end shortwave-band frequencies as is traditional with the broadcast band)

Whichever RF generator that you have at your disposal that will meet the above requirements will be satisfactory.


The Rigol isn't an RF sig gen so that's out. It works good on guitar amps though :) The E-200C was probably one of my better test equipment restorations so I'll use it and a good frequency counter. As was already said, it's not a precision alignment.

The only info I have on the radio is from Riders so not much to go on. Are there any AM SW stations left in the 11-12 MHz or 15Mhz bands? It sounds like there are some SSB stations (maybe just distorted AM?)

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 1:51 pm 
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Mike6158 wrote:
The Rigol isn't an RF sig gen so that's out.


That's just not so.

The Rigol is just probably fine for what you want to do. The biggest issue that I found with my function generator is their ability to reduce the output signal low enough to do RF/IF alignment. Otherwise .... a signal is a signal is a signal ... and all you're looking for is a modulated or unmodulated sine wave, depending on what you use to read the result.

To reduce the output, use an inductive coupling to your set and reduce the coupling to reduce the signal strength.

I've been using a function generator for about 15 years. It works just fine for RF/IF alignments. The guys who are deep into comm sets probably wouldn't use it ..... you're doing as basic a set as can be had.


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 2:47 pm 
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Location: Near Brandon, Iowa
Mike6158 wrote:
Are there any AM SW stations left in the 11-12 MHz or 15Mhz bands? It sounds like there are some SSB stations (maybe just distorted AM?)


There are, but you may not be able to receive them. Much depends on your geographical location, adjacent terrain, time of day/season and your antenna (or lack thereof). While there aren't wall-to-wall stations like I remember there being from my teenage SWL days (50 years ago) there seem to be plenty still active.


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 3:16 pm 
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Location: Lexington, KY USA
I don't think anyone pointed out that if you use an unmodulated RF signal, such as the one from a function generator, you will need to monitor the AVC voltage at the detector, instead of the audio at the speaker.

Ted

Later Edit: I should have looked up the Rigol unit before posting. It will in fact provide an AM signal. Also FM. Also frequency sweeps.

Probably cooks dinner and washes-up, as well. I want one!

There are still advantages to monitoring the AVC signal while aligning a set. And if your generator does lack modulation, this can work well.

http://www.saelig.com/product/dg4102.htm


Last edited by Usually Lurking on Apr Wed 08, 2020 3:18 am, edited 1 time in total.

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 5:49 pm 
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Joined: Jan Sat 16, 2016 4:15 pm
Posts: 85
What used to be called a "function generator" has evolved into today's "waveform generator"

These instruments use DDS and arbitrary generation techniques and typically have 50 ohm calibrated outputs from 1 millivolt P-P up to several volts - a much better range than an old service grade "RF" signal generator. These units typically have two channels and the second can modulate the first.

If you have an instrument that can put an accurate frequency from DC to 100 MHz, modulated any way you want, at a calibrated level, into 50 ohms, it may not be sold as an "RF" generator but probably meets a lot of RF needs.

The Rigol DG4102 is an excellent example. Spend some time getting acquainted with the capabilities of one of these generators and I bet you never go back to an old service grade generator (unless for nostalgia)


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 9:17 pm 
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Location: SoCal, 91387
Mike6158 wrote:
Are there any AM SW stations left in the 11-12 MHz or 15Mhz bands? It sounds like there are some SSB stations (maybe just distorted AM?)

Quote:
WWV is a shortwave radio station, located near Fort Collins, Colorado. It is best known for its continuous time signal broadcasts begun in 1945, and is also used to establish official United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, and 20 MHz.

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Tue 07, 2020 9:33 pm 
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Location: Sanford Fla 32771 (USA)
Quote:
The Rigol DG4102 is an excellent example. Spend some time getting acquainted with the capabilities of one of these generators and I bet you never go back to an old service grade generator (unless for nostalgia)

Agreed, my Siglent SDG1025 is a synthized waveform generator but is outstanding as a signal generator.
Below is sweep of a 455Khz transformer. I think your Rigol will outperform any vintage generator.


Attachments:
1st_IF.JPG
1st_IF.JPG [ 94.88 KiB | Viewed 475 times ]

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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Wed 08, 2020 2:32 am 
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Location: Larose, LA, USA
Attachment:
20200407_200746.jpg
20200407_200746.jpg [ 670.67 KiB | Viewed 449 times ]

Better results than this gives, for sure!

Phil


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Wed 08, 2020 2:50 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2090
Location: Weimar, Texas
I forgot WWV was on 15 MHz. I usually catch it on 10MHz. I've been listening to it since I was a kid (70's).

Usually Lurking wrote:
I don't think anyone pointed out that if you use an unmodulated RF signal, such as the one from a function generator, you will need to monitor the AVC voltage at the detector, instead of the audio at the speaker.

Ted


Nope but I'll keep that in mind

xmo wrote:
What used to be called a "function generator" has evolved into today's "waveform generator"

These instruments use DDS and arbitrary generation techniques and typically have 50 ohm calibrated outputs from 1 millivolt P-P up to several volts - a much better range than an old service grade "RF" signal generator. These units typically have two channels and the second can modulate the first.

If you have an instrument that can put an accurate frequency from DC to 100 MHz, modulated any way you want, at a calibrated level, into 50 ohms, it may not be sold as an "RF" generator but probably meets a lot of RF needs.

The Rigol DG4102 is an excellent example. Spend some time getting acquainted with the capabilities of one of these generators and I bet you never go back to an old service grade generator (unless for nostalgia)


That's good to know. I usually use a homebrew RMA antenna. I say usually... it's been about two years since I've done an alignment and that was an FM alignment. My E200-C should still be spot on but I think I'll play with the Rigol since that's what I bought it for.

pauls.ironhorse wrote:
Quote:
The Rigol DG4102 is an excellent example. Spend some time getting acquainted with the capabilities of one of these generators and I bet you never go back to an old service grade generator (unless for nostalgia)

Agreed, my Siglent SDG1025 is a synthized waveform generator but is outstanding as a signal generator.
Below is sweep of a 455Khz transformer. I think your Rigol will outperform any vintage generator.


Nice!

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It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Wed 08, 2020 4:18 am 
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Joined: Dec Sat 28, 2019 4:18 pm
Posts: 291
Location: Corinth, TX
Mike6158 wrote:

The only info I have on the radio is from Riders so not much to go on. Are there any AM SW stations left in the 11-12 MHz or 15Mhz bands? It sounds like there are some SSB stations (maybe just distorted AM?)


You may be able to use WWV at 10 or 15 MHz.

John


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 Post subject: Re: Sig Gen for aligning a farm radio
PostPosted: Apr Wed 08, 2020 6:51 am 
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Location: Lincoln City, OR 97367
My suggestion for aligning Farm Radios:

Attachment:
Farm Radio Signal Generator.jpg
Farm Radio Signal Generator.jpg [ 61.25 KiB | Viewed 412 times ]


:D

Regards,

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