Is there a modification that can add a 10k slide switch to a Cobra 29 and or a Cobra 25? I haven't been able to scare one up on the net. Thanks in advance. RF
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Cobra 25/29 10k slide help.
- Thread starter Radio Face
- Start date
This is listed for a 29 GTL, but it looks as if it should work for a 29 LTD.
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I saw a curious trio of mods over the years.
One was based on the "Expo kits" of old.
1) a 15.350 crystal oscillator injected as per the Expo instructions.
This just shifted everything down 10Kc
2) Switch the 10.240 reference with a 10.233333~ . this accomplishes the same thing. This also skews the channel spacing a bit.
3) change the varactor with a more aggressive one and pull on the reference crystal.
I guess you were just wanting to get to the alphas, correct ?
I prefer the first as #2 skews the channel spacing
#3 packs most of the tuning range to one end of a potentiometer and makes tuning very touchy
One was based on the "Expo kits" of old.
1) a 15.350 crystal oscillator injected as per the Expo instructions.
This just shifted everything down 10Kc
2) Switch the 10.240 reference with a 10.233333~ . this accomplishes the same thing. This also skews the channel spacing a bit.
3) change the varactor with a more aggressive one and pull on the reference crystal.
I guess you were just wanting to get to the alphas, correct ?
I prefer the first as #2 skews the channel spacing
#3 packs most of the tuning range to one end of a potentiometer and makes tuning very touchy
Won't this destroy the 455khz 2nd RX IF?
I think one correct way to accomplish this is to build a 5.12 mhz oscillator and replace the signal from the pll going into L19. Then pull that with a varactor. 10khz slide is easy to achieve with this method. I found pulling a crystal 10khz is hard to do but when using this method it's not necessary to pull the crystal 10 khz because of the tripling action of L19.
It's also possible to get another band of 40 channels with the addition of a 10.695 TX oscillator using the stock pll. This addition also makes the radio compatible with the Galaxy FC-347 or cheap China made PLJ series freq counters.
The "second" set of freqs will be 5khz off but it doesn't matter because of the slider.
This is for the 29 and not the 25.
Best to all
I think one correct way to accomplish this is to build a 5.12 mhz oscillator and replace the signal from the pll going into L19. Then pull that with a varactor. 10khz slide is easy to achieve with this method. I found pulling a crystal 10khz is hard to do but when using this method it's not necessary to pull the crystal 10 khz because of the tripling action of L19.
It's also possible to get another band of 40 channels with the addition of a 10.695 TX oscillator using the stock pll. This addition also makes the radio compatible with the Galaxy FC-347 or cheap China made PLJ series freq counters.
The "second" set of freqs will be 5khz off but it doesn't matter because of the slider.
This is for the 29 and not the 25.
Best to all
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10.240 / 1024 = 10 (Kc)
1014 / 2 = 512
5.12 x 3 = 15.360
.91 + 15.360 + 10.695 = 26.965
10.695 - 10.240 = .455
If you shift the 5.12 x 3 (15.360) signal of course what is presented to the filter will move . 5.116666667×3=15.350000001, 15.350000001+.91+10.695=26.955000001, then the filter "sees" is 15.350000001-10.695=4.655000001.
If you pull on the 10.240 reference it actually works a bit better because the 5.12 is derived from the 10.240 then multiplied by 3 to get 15.360 , the difference is still an issue, 10.2333333 / 2=5.11665 ×3 =15.34995 =5.11665.
Or the more common Murata
Plenty of room for warpage. In any case it's not ideal. A kluge of course would be to warp the 10.695 along with either the 15.360 or 10.240.
These analog solutions are all just that , analog solutions to a digital problem.
The ideal method is to do away with the rom locked PLL . That is a discussion for another day save for one thought. It is far more economical to just use a radio/PLL that can be modified.
1014 / 2 = 512
5.12 x 3 = 15.360
.91 + 15.360 + 10.695 = 26.965
10.695 - 10.240 = .455
I'm guessing you don't completely understand the problem.
If you shift the 5.12 x 3 (15.360) signal of course what is presented to the filter will move . 5.116666667×3=15.350000001, 15.350000001+.91+10.695=26.955000001, then the filter "sees" is 15.350000001-10.695=4.655000001.
If you pull on the 10.240 reference it actually works a bit better because the 5.12 is derived from the 10.240 then multiplied by 3 to get 15.360 , the difference is still an issue, 10.2333333 / 2=5.11665 ×3 =15.34995 =5.11665.
Okay Let's see why any of this works...
Or the more common Murata
Plenty of room for warpage. In any case it's not ideal. A kluge of course would be to warp the 10.695 along with either the 15.360 or 10.240.
These analog solutions are all just that , analog solutions to a digital problem.
The ideal method is to do away with the rom locked PLL . That is a discussion for another day save for one thought. It is far more economical to just use a radio/PLL that can be modified.
I agree with you, Mr. Kopcicle, you the real way is to dump the 2816.
.91 is the RX n-code
So for TX it would be (Stock 5.12m * 3)
15.360 +1.365 (Ch1 TX PLL Downmix) + 10.240 = 26.965
RX
15.360+.91 = 16.270
26.695 - 16.270 = 10.695
10.695 -10.240 = 455
Using a frequency of 5.11665
Indeed the TX freq would be 26.955
5.11655*3 + 1.365 = 16.71495
16.71495 + 10.240 = 26.95495
For RX however,
5.11655*3+.91 = 16.25995
26.965 - 16.25995 = 10.705
10.705 - 10.240 = .46505
I'm running a 5.00m oscillator and it seems to work. Here is my math on the 29 PLL.
My freq range is 26.605 - 27.505 using the stock PLL and slider.
29 Downmix inputs are .91 - 1.35 for RX and 1.365 - 1.805 for TX.
TX
5 *3 =15
15+1.365 (TX PLL Downmix) = 16.365
16.365 + 10.240 (TX IF) = 26.605
RX
26.605 - 15.91 (RX PLL Downmix ) = 10.695
10.695-10.240 =.455
So Ch2 on my radio is 26.615
I want to get to 26.605 via the slider.
Using the oscillator method
RX N-code = .92
5.00 m oscillator
To find Required trippler frequency to slide down 10kc (Ch2 to Ch1)
26.605 - .92 (ncode for RX) = 25.685
25.685 - 10.695 = 14.99
14.99 / 3 = 4.9967
Check RX:
26.605 - (4.9967 *3 +.92) = 10.6949
10.6949 - 10.240 = .4549khz <== close enough
Check TX
(4.9967 * 3 + 1.375) + 10.240 = 26.605
I would need to adjust the 5.00 to 4.9967 to get 26.605 using n-code .92
Same for TX using TX ncode 1.375 (TX PLL Downmix Ch2) and still keep the
10.695/ 455khz RX IF's right on. Also keeping the channel spacing at the standard 10k.
4.9967*3+1.375 +10.240 = 26.6051 <== (My Ch 1 but the set would be on Ch2)
Best Regards to you, Kopcicle
There is no 10.695 oscillator in the 29 only 10.240. The 10.695 is generated for RX by shifting the n-code down and mixing that with the incoming 27m
.91 is the RX n-code
So for TX it would be (Stock 5.12m * 3)
15.360 +1.365 (Ch1 TX PLL Downmix) + 10.240 = 26.965
RX
15.360+.91 = 16.270
26.695 - 16.270 = 10.695
10.695 -10.240 = 455
Using a frequency of 5.11665
Indeed the TX freq would be 26.955
5.11655*3 + 1.365 = 16.71495
16.71495 + 10.240 = 26.95495
For RX however,
5.11655*3+.91 = 16.25995
26.965 - 16.25995 = 10.705
10.705 - 10.240 = .46505
I'm running a 5.00m oscillator and it seems to work. Here is my math on the 29 PLL.
My freq range is 26.605 - 27.505 using the stock PLL and slider.
29 Downmix inputs are .91 - 1.35 for RX and 1.365 - 1.805 for TX.
TX
5 *3 =15
15+1.365 (TX PLL Downmix) = 16.365
16.365 + 10.240 (TX IF) = 26.605
RX
26.605 - 15.91 (RX PLL Downmix ) = 10.695
10.695-10.240 =.455
So Ch2 on my radio is 26.615
I want to get to 26.605 via the slider.
Using the oscillator method
RX N-code = .92
5.00 m oscillator
To find Required trippler frequency to slide down 10kc (Ch2 to Ch1)
26.605 - .92 (ncode for RX) = 25.685
25.685 - 10.695 = 14.99
14.99 / 3 = 4.9967
Check RX:
26.605 - (4.9967 *3 +.92) = 10.6949
10.6949 - 10.240 = .4549khz <== close enough
Check TX
(4.9967 * 3 + 1.375) + 10.240 = 26.605
I would need to adjust the 5.00 to 4.9967 to get 26.605 using n-code .92
Same for TX using TX ncode 1.375 (TX PLL Downmix Ch2) and still keep the
10.695/ 455khz RX IF's right on. Also keeping the channel spacing at the standard 10k.
4.9967*3+1.375 +10.240 = 26.6051 <== (My Ch 1 but the set would be on Ch2)
Best Regards to you, Kopcicle
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One mod from a year back on T1 for the cobra 29, gives low 40, high 40, 5kc shifter switch and 10kc shifter switch with $20 worth of ebay parts.
https://www.transmission1.net/viewtopic.php?f=53&t=56500
https://www.transmission1.net/viewtopic.php?f=53&t=56500
I tried that 5351/328 combination. I read the same post and asked for a copy of the software but no one ever got back to me so I just made a VFO. I tried running at 5 mhz using the trippler coil, and at around 15mhz.
With the rotary encoder the operation is more fun than 10kc/5kc. Using the switches still gives me the "limited" feel. If you wanted to get on the UK bands the stock configuration from T1 won't get you quite there.
I also coupled the 5351 with a .01uF cap and not directly as the schematic shows on transmission 1.
This project was ended several months ago. On a side note using the 5351 with the Cobra 25 would give it all the freqs one wanted although the software would need to be rewritten and a TX/RX control signal would need to be added.
Best to all.
With the rotary encoder the operation is more fun than 10kc/5kc. Using the switches still gives me the "limited" feel. If you wanted to get on the UK bands the stock configuration from T1 won't get you quite there.
I also coupled the 5351 with a .01uF cap and not directly as the schematic shows on transmission 1.
This project was ended several months ago. On a side note using the 5351 with the Cobra 25 would give it all the freqs one wanted although the software would need to be rewritten and a TX/RX control signal would need to be added.
Best to all.
Down here back in the late 80's and the 90's we would cut a trace on the board from the crystal to ??? and add a 6 - 80 pf trimmer cap ???? across the cut to get the full 10 Khz slide with a flip of a switch, I can't get the caps anymore but I'm getting close to it....I need to find out which other pin to solder the dang thing.... I put in close to a thousand of those sliders over a 14 year period....Maybe more we used to order them by the hundred lot bag....
In a radio that has only one quartz crystal, (the 10.24 MHz) there is a problem using that crystal to 'tweak' the frequency coverage.
That crystal sets the difference between the PLL's transmit and receive frequency. Pulling that crystal enough to matter will provide you with a choice. Make the radio transmit on frequency --OR-- receive on frequency.
Choose one.
73
That crystal sets the difference between the PLL's transmit and receive frequency. Pulling that crystal enough to matter will provide you with a choice. Make the radio transmit on frequency --OR-- receive on frequency.
Choose one.
73