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Digital frequency display for the Tram D201 radios.

nomadradio

Analog Retentive
Apr 3, 2005
6,913
11,004
698
Louisville, KY
www.nomadradio.com
A digital frequency display for the Tram D201 radios would be nice, but there's a problem. The only displays that fit the VFO dial window are LCD. Black dot-matrix numbers on a green backlighted background.

Customers don't like LCDs. Neither do I.

Tried it. It worked, but I didn't like it.

But every LED frequency display I can find, since the 1980s-era PDC256 is just too big to fit inside a window that's 2 and 1/8 inches wide.

The solution, of course is to roll your own. Never design and build what you can just buy. Especially if it comes from China for less money than you could ever hope to build one yourself. The SanJian Studio model PLJ-6LED frequency display has all the features you need, but one.


IT'S JUST TOO BLOODY BIG!

Solved this problem in the Siltronix VFO by removing the aluminum front panel and substituting one made from smoked plex.

6HBpuS.jpg


Can't do that with the D201.

Decided to meet the solution in the middle. The 6-digit counter/display with the too-large digits is just too cheap to resist, and it works just fine. I had pc boards made that accept two 3-digit displays that fit the D201 window and then removed the large digits from the Ebay counter. My board now "piggybacks" on the counter where the original digits mounted.

J3R8zr.jpg


Naturally the VFO tuning capacitor must come out to remove the white plastic dial. Just be sure to get the end-stop screw properly aligned with the capacitor shaft when it goes back in. A new smoked-plex window replaces the original. The right-most dial lamp socket gets removed (on the left in this pic) and the brown wire spliced to power the one behind this side of the meter.

1UWFtn.jpg


The input cable supplied has two insulated wires, one black and one red. Oddly enough the black wire is the signal input, and the red one is ground. The 40-channel D201A will require a shielded input lead 22 inches long, spliced as close to the display's input plug as possible. The shield does not get grounded to the top socket of the radio's crystal board, but gets grounded for RF only using a .001uf disc cap. The center lead has a 470-ohm 1/4-Watt resistor at the tapoff point, to prevent loading down the crystal board's output signal.

9kABS1.jpg


A mask made from black construction paper will block the glare from the radio's meter lamps, and black out the area around the digits.

B0VbE5.jpg


The power hookup is no big deal, so long as the radio's 14-Volt supply has another 150 mA of capacity, more or less. This radio has our upgraded BA-plus board in it, with a much-larger heat sink on the 14-Volt regulator. A 47-ohm 1-Watt resistor in line with the power tapoff makes life easier for the 5-Volt regulator on the PLJ6 counter board.

fvuaxi.jpg


Here's the final installation, ready to use.

MVjhME.jpg


Looks pretty legit from the outside, too.

4KmNUi.jpg


I'm getting close to selling this as a D-I-Y kit. Still need to come up with more-detailed instructions.
Also found that the placement of the two threaded studs inside the front panel above the windows is not exactly the same on every radio. Need to come up with a more-sophisticated mount bracket with slots instead of screw holes.

The question of the radio's 14-Volt power supply overheating is a real possibility. For now I'll just make a package deal of our improved BA board. Has a bigger heat sink on the 14-Volt regulator and won't break a sweat powering 6 LED digits.

Gettin' there.

73
 

that is badass.

i just love the look of LEDs in old radios.

how bad is the noise created by these buggers when it comes to the Tram?

I have had the best success running these counter boards at 8 volts and using the lowest brightness setting.
that level seems to match best with the stock channel LEDs in the radios ive done.
im using purple plex as i find that it knocks down the glare from the red LEDs just a bit more than the smoke plex i was using.

are you using 1/16" thick plexi? just curious.

i also use an electrolytic right at the power leads on the board like you did, but i've been using 1000uF.

can't remember whether or not i found that noise was still decreasing as i went up in cap value or if i just tried 1000uF first and just stuck with it.

boy that chassis doesn't give you much to work with when it comes to bracketing does it LOL.
LC
 
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We avoid the problem of receiver noise by using the chassis ground only for the power hookup. Probably don't need it, since the mount brackets already ground it to the chassis. The 47-ohm resistor in the positive power lead keeps noise from sneaking back "upstream" into the radio's regulated 14-Volt DC supply. Not shown is the upgraded BA board that powers it. Has a 3-terminal regulator in place of the original emitter-follower regulator circuit, and a heat sink with three times the surface area of the original. I suspect the factory-original regulator would run too hot powering six LED digits.


Using the disc capacitor for the input-coax ground breaks any potential ground-loops by blocking DC. The reactance of a .001 uf cap is low enough at the 21 MHz local-oscillator frequency to serve as an effective RF ground for the coax shield.
The new window is 1/8-inch plexiglass. If I want the thinner stock, I have to buy the whole 3-by-6 foot sheet. They'll cut what I want from the 1/8-inch material at a really reasonable price.


The counter board has a 47uf cap across the power input. Haven't needed to add filtering so long as I feed the power through that resistor. It drops between 4 and 5 Volts. Makes life easier on the display board's 5-Volt regulator.


I have discovered that the exact placement of the threaded studs for the panel-light sockets is not always the same. I should probably make a single bracket the width of the counter board with slots for the mounting holes. The two brackets you see are just parts we had on hand.


That part of the setup will need to be improved to make it a proper DIY kit.

73
 
When I added an external counter to my D201 I noticed when it was turned on, it generated noise in the receiver. Using a smaller value coupling cap to drive the counter reduced the noise but the counter stopped reading before the noise could be eliminated. Adding a one stage transistor buffer kept the counter reading at lower drive levels and removed my noise. If removing the drive signal to the counter stops the noise, it's not a shielding issue, it's a coupling issue. Check to see if it's the same thing I noticed.
 
The need for a buffer amp to drive a long coax cable is partly what prompted me to mount them inside the radio.

We had to do the same thing, and I threw the whole external-mounting idea overboard. The labor to mount it inside wasn't much different from putting it into an external enclosure.

Haven't had any counter-noise problems since using a disc cap to isolate the input-coax ground from the crystal-board ground.

73
 
Nomad have you found a seller for the freq counter that is fairly cheap. I use to buy them from China for about 3.00 each and now they are about 8.00 for them now from China. I may have over looked a seller that is less than 8.00.
 
I've been looking at this board and had a few questions about it. Does this board have a programmable IF offset that makes it compatible with many radios or is the offset fixed for specific model radios? Does it have the ability to do the SSB offset so it reads correct on the Tram in USB? I ask because I'm looking for a counter that I can add on to an older NC-183 receiver and the ability to control the offset is ideal here.
 
You can always get it close on one mode and just fine tune it by ear on usb. From my experiemces talking dx on the 27555 being on perfect on frequency is not importent, neither is alc for that mater.
 

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