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 Post subject: Question on B-T AM60-550A Modulator
PostPosted: Feb Wed 14, 2018 11:29 pm 
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Location: Tyngsborough, Massachusetts
A couple of weeks ago I picked up two Blonder Tongue AM60-550A Agile Modulators from EBay. I bought two because the price was good and I figured it would be good to have a backup. It was stated that they powered up but were otherwise untested, and that they could be returned if they didn't work. I tested them when I got them and they both worked.

The question I have has to do with using the DIP switches to set the frequency. On the switch setting cards that come with the units, all of the channels after 13 are cable channels. No settings are given for UHF broadcast channels. The 550A should be able to cover UHF channels 14 through 27. Now I realize that I could use their channels 65 through 78 and probably adjust the fine tuning to make up the difference but it would be nice to be able to tune them to the proper frequencies.

The specifications indicate that the units cover from 50 to 550 MHz in 0.25MHz steps, but there are no instructions for making the switch settings for frequencies other than those in the tables. I haven't been able to extrapolate from the tables.

Does anyone know the secret to setting these switches for frequencies not listed in the tables?

Jeff


Last edited by jeffs01879 on Feb Wed 14, 2018 11:55 pm, edited 1 time in total.

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Wed 14, 2018 11:52 pm 
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You had me going in circles for a bit. You asked about the AM60-550 in the title and I didn't realize that you said AM50-550 in the text. The AM60-550 doesn't use DIP switch programming.

Sorry, I could not find a manual for the AM50-550 and ran out of time to look.

If you could provide the table that might help.

Curtis Eickerman

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Wed 14, 2018 11:58 pm 
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Curtis,

Thanks for your response. The 50-550 in the text was in error. The thread title is correct. They are AM60-550A units. I have corrected the body of the test in the first post. These units do use DIP switches for setting the frequency.

Jeff


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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 12:09 am 
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Joined: Aug Wed 04, 2010 5:40 pm
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Location: Tyngsborough, Massachusetts
This link is to a manual that is the closest I found to my units. The switches and settings are the same. The switch settings are on pages 8 and 9 of the pdf.

https://manuals.solidsignal.com/AM-60-550.pdf

My units are stock number 59414.

Jeff


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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 12:12 am 
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I figured that out once. I will see if I can find the papers with the results. No guarantees.

It helps if you understand the binary counting used internally by computers. At one end of the switches (or maybe one up from the end) is a switch that makes a 0.25MHz change. The next switch makes a 0.5 MHz change. The next a 1.0 MHz change. The next a 2 MHz change. The next a 4. And so on. With that arrangement you can make any change you want to in 0.25MHz steps. I think that there is a switch or two that make small fudges for special cases.

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 12:39 am 
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It could be that if these units have tunable VSB filters (they probably do), there is a limitation in the range of these filters (there almost certainly is) and as a result to publish the possible range of the PLL section would be pointless.

There is usually more than one group of switch inputs to the PLL (not to mention the VSB filter) so to interpolate the switch numbers you'd need to know how many bits are used for the prescaler, the main counter and the VSB filter and where the boundaries occur. It's binary so not too hard to see the pattern once you realise it's not just one number.

I just saw Tom's answer and it's good!


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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 3:32 am 
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I found two different manuals that both said AM60-550. One had the display on the front with simple push button programming and the other has the dip switches.

Here is the DIP switch version and at the moment I am stumped as to which bits are doing what. https://manuals.solidsignal.com/AM-60-550.pdf

Here was the push button version (much nicer). https://www.dfcco.com/content/document/ ... ctions.pdf

Curtis Eickerman

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 4:14 am 
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Location: Tyngsborough, Massachusetts
Curtis,

I believe that the version with the pushbuttons is the newer "B" model. The one with the DIP switches is either the unlettered version or the "A" model. Mine are the "A" model.

I've not been able to make much sense of the switch configuration other than the left hand group of four switches controls the 12.5 or 25kHz offset for, I think, frequencies that fall in the aviation bands.

Jeff


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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Thu 15, 2018 4:57 am 
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Well, I can't find my notes. I will keep looking.

To give you a better idea of binary counting, I will give an example. I will use the numbers 0 and 1. You could think up and down instead.

00000 = 0
00001 = 1
00010 = 2
00011 = 3
00100 = 4
00101 = 5
00110 = 6
00111 = 7
01000 = 8
01001 = 9
01010 = 10
01011 = 11
01100 = 12
01101 = 13
01110 = 14
01111 = 15
10000 = 16
10001 = 17
10010 = 18
10011 = 19
10100 = 20
10101 = 21
10110 = 22
10111 = 23
11000 = 24
11001 = 25
11010 = 26
11011 = 27
11100 = 28
11101 = 29
11110 = 30
11111 = 31

There are 10 types of people in the world. Those who understand binary and those who don't. :)

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Fri 16, 2018 7:13 pm 
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Found it. This is a chart for the AP series modulators with notes as to which switches to use for the AM series modulators.

Attachment:
IMG_0784_adj.JPG
IMG_0784_adj.JPG [ 108.98 KiB | Viewed 803 times ]

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 Post subject: Re: Question on B-T AM60-550A Modulator
PostPosted: Feb Fri 16, 2018 8:19 pm 
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Joined: Aug Wed 04, 2010 5:40 pm
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Location: Tyngsborough, Massachusetts
Tom, that is what I was looking for, thanks.

Meanwhile I think I've started to figure out the switch settings, I'm familiar with the binary switch concept, but it took Tom's posting of the binary counting to prompt me to, rather than the normal descending order left to right, try to read the switch tables ascending from left to right, that is the left most switch represents 2^0, the second from left 2^1 up to 2^7 for the first group of 8 switches, and then the left most switch of the second group of 8 switches represents 2^8 and the right most switch represents 2^15.

When I set up a spreadsheet for the basic TV channels 2 through 6 and 7 through 13, I got a progression that increased by 6 from each channel to the next from channels 2 though 6, and from 7 through 13, except from channels 4 to 5 where the increase was 10 as it should be. The gap from channel 6 to channel 7 is 92, again as it should be. So these two sets of DIP switches seem to select the frequency in integral MHz. I think the the left hand group of 4 switches determines the fractions of MHz, but I'll have to relearn about fractional binary numbers before I can tackle that. But I have the information I was looking for.

Thanks Tom and everyone for the help.

Jeff


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