Attempt to move 403-433 Spectra to 440mhz

[ku4zs1]

The power amp, the back part of the Spectra chassis CAN be moved up to cover 440 thru 480. The RF board is the same in all 4 UHF ranges, as is the command board. The MLM may be able to be range changed.

The hard part is the Receiver frontend board, so far no one has 'moved' them. The VCO may go up to 440-468 with some surgery.

Quoted from Will

I am willing to try this modification. I found this http://www.batlabs.com/specvco.html and I am fairly confident that I can modify the VCO to bring it up (just add another cut at the appropriate location right? make the strip shorter)

What do I need to do to modify the PA to bring it up to 440?

As far as the receiver front end, does anyone know what the component level differences are between the 403-433 model and the Range 2 model? Can I not just swap out the components with different values, and then some retuning at the local Moto shop to fine tune it? I understand that no one has been successful on this step, and I may not be as well, but its worth a try eh?

Also, understand that I have absolutely no interest in having any coverage on anything other than 440mhz. If possible, I do have several business band repeaters that I have permission to use, and if they will work on them that would be great, but if not then 440mhz will make me happy.

[ku4zs1]

No one is going to touch this with a 10 foot low-band steel whip?

[Jim202]

To my knowledge, no one has found the secret of moving one of these low UHF splits into the ham band frequencies. I have tried along with many others. The VCO and programming is the main problem. This version of the Spectra just doesn't like it.

Jim

No one is going to touch this with a 10 foot low-band steel whip?

[BikerScout]

Now that would be a real Hat Trick.

[ku4zs1]

The VCO and programming is the main problem. Jim

Well, the VCO is actually the same for every one of the UHF radios from 403-482mhz, the only difference is the laser cut in the substrate in the VCO, right? I am sure that I can adjust that cut so the VCO will lock on 440mhz.

As for programming, from what I have seen, it will likely require removing the MLM board and probably unsoldering the two EPROMs (write once chips). I could replace the two EPROMs and burn them with a range 2 model number. (or can this all be done by bit bashing with the Lab RSS?)

[Hartley]

Hi,

You don't have to do any "tricks" to program a 403-430 Spectra out of band, just "adjust" your RSS with the "Batlabs hack" (look for it in the Spectra section). I pushed my "Range 1" up to 450 without any problems, tho you could take it to 512 if U want..

But the VCO is not as easy as you think - while they may all start the same, tweaking them upward in frequency is non-trivial - that substrate is tougher than U think! (forget a razor knife - won't touch it)

73 DE Hartley

[ku4zs1]

I did the RSS hack and now the RSS indicates that the radio is capable of 403-450mhz operation, but if I try to type in anything over 438mhz in a conventional mode, it complains about that being out of band.

How thick is the substrate? I would think that a small dremel tool would be able to dig thru it.

[Will]

The VCO substrate is ceramic, and you just need to cut the copper layer thru not the ceramic substrate. On some I worked on, I made a very narrow cut in the copper "stub". Too much and you CAN break the substrate.

A dremmel tool is a god choice with a fine burr cutter.

Also check the PIN shift commands, two of them, for proper settings at the new frequencies. The PIN shift commands come fom the Command board/MLM.

[Hartley]

Hi,

If it won't accept a freq over 438, you missed one of the band limits (they're in several places) - run thru it with your editor again (happened to me, too )

73 DE Hartley

[ku4zs1]

Hi,

If it won't accept a freq over 438, you missed one of the band limits (they're in several places) - run thru it with your editor again (happened to me, too )

73 DE Hartley

Thanks, Ill have to check that again.

If no one knows what the component differences are in the receiver front end for the range 1 and range 2, then what manual would that info be in? Can anyone tell me a part number for it?

Also, does anyone what modification needs to be done to the PA so that it will work properly on the higher freqs? Would this also be component value differences? Or is this more of a tuning difference?

[BikerScout]

So with all this info floating about, how hard would it be to go the Other Way? Moving a 480-512 Mhz radio down to the 440 Mhz range.
I assume the conductive ink pen method would work.

Bryan

[ku4zs1]

I think you will have similar trouble moving a spectra that far down as it is to move one as far up as I plan to. I bought the detailed service manual for the spectra and plan to move my 403-433 to 440 ham I see it as a four part process, though the details I do not know yet:

1) Cut the stub in the VCO shorter so it locks on higher frequencies (reliably)

2) Modify the RX front end (plan to compare component values between the two ranges and swapping those that are different)

3) Modify the PA to run on 440 (no idea what this will involve yet, it might be similar to step 2)

4) Hex edit rss so the spectra will program to higher freqs

*maybe* 5) Have local moto shop realign rf sections to maximize performance.

[camcam990]

The rec front end modification might not be to difficult, I have a spectra front end here part number hre6001a, There is a five pole helical ceramic filter on the under side, now if you look real close at this filter you will notice that there are oblong rings cut around each of the poles. and on one edge there is an area that has been removed. From what I can tell this is where the filter gets tunned for the various band splits. It looks like all that might need to be done is to remove a very small amount from each of these poles. To do this in a proper manner would require a network analyzer. It would not be to difficult to connect this filter up and do a sweep and adjust from there. The plated material/metal can be removed with a dremmel tool and a small carbide or diamond bit. I would suspect that only a small amount from each poll would need to be removed. By removing this metal the frequency should start to move up. After looking at a couple of spectras here it looks like some of the parts are interchangeable?????? so replacing components might not be needed???/
feel free to pm me and we can talk some more. I going to fireup my hp network analyzer and start doing some investigation

[mancow]

The rec front end modification might not be to difficult, I have a spectra front end here part number hre6001a, There is a five pole helical ceramic filter on the under side, now if you look real close at this filter you will notice that there are oblong rings cut around each of the poles. and on one edge there is an area that has been removed. From what I can tell this is where the filter gets tunned for the various band splits. It looks like all that might need to be done is to remove a very small amount from each of these poles. To do this in a proper manner would require a network analyzer. It would not be to difficult to connect this filter up and do a sweep and adjust from there. The plated material/metal can be removed with a dremmel tool and a small carbide or diamond bit. I would suspect that only a small amount from each poll would need to be removed. By removing this metal the frequency should start to move up. After looking at a couple of spectras here it looks like some of the parts are interchangeable?????? so replacing components might not be needed???/
feel free to pm me and we can talk some more. I going to fireup my hp network analyzer and start doing some investigation

To what degree, if any could testing be done with a regular service monitor (tracking generator)? What does a network analyzer exactly do? I've seen them on ebay for incredible prices but never was sure.

mancow

[ku4zs1]

Here is a picture of the helical filter. Also, in the second pic, it looks like there is some more laser cutting (like used on the VCO). There are three spots underneath the metal shield that appears to be more laser cutting for tuning. I took a picture of one of them.

[camcam990]

Hello, this filter in the picture looks like mine, there is more material removed from the one in the picture then on mine. This looks like the tunning points for the filter. Now the use of the network analyzer would help greatly. The fiter can be swept thru a range of frequencys and the bandpass and cutoff points can be observered. This filter from what we already know will work from about 400 to 430 mhz range. As you go higher in frequency the filter response will start to roll off and not pass any signals. With the filter connected to the network analyzer, you would then start to remove small amounts of metal and watch the filter response. The input and output ports are connected to the network analyser. It is looking like only a small amount of metal removal is necessary. Be carefull on the input and output ports, these are most likely 50 ohm and if you remove to much material the impedence will shift. You donot want that. I am working on mine and will update when I get more information. Thanks Kurt WK7Q

[ku4zs1]

I looked at the parts list in my service manual and it lists the exact same parts for the Range 3 and Range 4 receiver front end boards with only one part difference, the helical filter.

The PA board does have some component differences between the Range 3 and Range 4 versions though. I don't have the parts list for the Range 2 model, but I can just part swap it for Range 3 and that should be close enough.

There is also an injection filter which is laser cut, directly under that metal shield on the top of the receiver front end board.

The injection filter is a printed pattern on the substrate which is laser-tuned at the factory. The insertion loss of this filter is about 3db.

The injection filter is tuned to pass frequencies from 559 to 592 MHz for Range 3 or 592 to 622 for Range 4.

I would assume that a small amount more of the three stubs of the injection filter would also need to be trimmed off to bring the frequency up.

[ku4zs1]

Can the helical filter be tuned by desoldering it and using a signal gen with some receiver, like a handheld? Inject a low level signal so its noisy on the handheld and slowing eat away at the metal "inside" the rings until the signal has very low loss?

Every day I am wishing that I had not gotten rid of that Heathkit signal gen Though I dont think it did 440mhz anyway.

[camcam990]

Hello again, IN order to tune this filter correctly you need a network analyzer, or a spectrum analyzer with a tracking generator. The reason for this is that this filter is a BANDPASS FILTER, that means it will only pass frequencys for which the filter is adjusted for, now you are working with a range of frequencys, this current filter is set up to pass 403 to 433 mhz, so this filters band pass is about 30 mhz wide, using a signal generator you are only going to adjust to maybe one frequency, which means that this filter will then be peaked instead of being a true bandpass filter, I suspect that you will not be able to do this and most likely trash the filter during the process, the whole issue is to try and move this filter up in frequency by about 10 mhz to set it in the middle of the 440 ham band, now the other item to consider is that this filter will roll off after a certain frequency range and that is normal, this is where the network analyzer comes into use, Thsi filter is soldered to the metal plate and removing it will most likely crack the ceramic circuit on the other side. I get back to you later, have to leave work

[ku4zs1]

Have you made any progress with this yet? I asked on the board what a replacement ceramic filter would be, and it was $60! That pretty much knocks that out of the question. Only options left are to try to retune the one in there, or find a suitable replacement.

I looked around Mouser.com trying to find something similar that could possibly replace the one that is in there. I didn't have much luck, but I also had a hard time making alot of sense of the descriptions of the parts though. Do you know of any possible cheap replacement parts that could just replace the ceramic filter that is in there? There must be a cheap way around this.

[N4KVE]

I was pretty much in the same boat as you. I ended up buying a UHF motorcycle Spectra because it's the only Spectra that is made for 438-470 MHZ. Found it on Fleabay, & it works GREAT. No tricks required. Good luck. GARY N4KVE

[techie]

I found a range 2 spectra a few years ago that I think came from the canadian market.. not a motorcycle unit. D34KXA7JA7AK.. 30 watts.

[deznetwork]

Has anyone been able to get the 403's up to 440?

I have 2 110 watt'rs that have been under my desk, I have been thinking about taking a stab at it.

D

[George]

Your best bet when dealing with this is to get a range two mobile and transfer its guts to the 110 mobile. Watch for them on Ebay, they are around occasionaly.

You will then have all the important pieces in one place. After that, you can shorten up the paths in the power amp to move it up and regain some efficency.

This makes it easy. You can always get a range three and do the same thing and maybe have better results.

Trying to reengineer the VCO and front end on a range one is not worth the effort. I would concentrate efforts on moving a range three down a bit.

George

[spectragod]

Starting with a range 3 is much easier. I tried modding the vco's on my range 1's, I have a couple left if anyone would like them to experiment with.

SG

[wa6jbd]

I realize this is an old thread, but I've been unable to find anything more current on the subject. I am currently attempting to convert a range 1 Spectra to the ham band with some success. The VCO is the easy part, the RSS was only a little more challenging. For those wanting to attempt it, I used a Dremmel with a diamond tip to cut off about a 1/4" of the microstrip on the VCO. Best to do it in small slices so you don't over shoot. I ended up with a VCO that maintains lock across 440-450. Easy enough... Now, my question is, has anybody been able to figure out what's required to get full performance across the band? I'm seeing rx sensitivity falling above 445, but it's useable. Above 449 or so, it's deteriorated to 10 uv. TX goes away completely around 448, but that's not a real problem here - it still works on the input side of the pair. Has anyone had any success with these beyond replacing the entire front end?

Mel - WA6JBD

[Will]

Mel,

Did you spread out the coils in the low pass/harmonic filter on the PA?. There are a couple of caps that change on the two transistors, the driver and final. Also did you trim off a very little of the oval shape on the ends of the helical resonators on the receiver mixer board?

[motorola_otaku]

For those wanting to attempt it, I used a Dremmel with a diamond tip to cut off about a 1/4" of the microstrip on the VCO. Best to do it in small slices so you don't over shoot. I ended up with a VCO that maintains lock across 440-450.

What did you use to de-solder the shield? Or did you work through the "window?"

[wa6jbd]

I haven't tried any of those suggestions yet, Will, but that leads me in the right direction. Thanks! I'll post here with my final results.

motorola_otaku - I just worked through the 'window'. It's a tight squeeze, especially trying to maintain visibility of the work, but it seemed easier than disassembling the vco and taking the cover off. Once I was done cutting, I used canned air to spray out the dust and debris. Doing it this way, it wasn't too much trouble to plug the vco back in, and see where it was. It took several cuts to get it in the desired range.

[altaphon]

There seem to be a lot of Spectras out there now on 450-470. We're looking for some in 420 for links. Anyone having some that haven't been hacked and would like to work out a trade, let me know. WA6NMF

[Will]

Altaphon,

PM me, we could work out a swap to 403-430 for you.

[wa6jbd]

Will, I took your advice on how to tune the rx filters, taking a Dremmel tool to the oval ends of the resonators. Success! I ended up having to take most of the material off each of the resonators. I temporarily soldered RG174 coax to the input and output pads, then connected the coaxes to the network analyzer and started cutting while watching the trace. I ended up with a receiver front end with .5 uv sensitivity (no preamp) across 440-450. As I previously stated, TX is fine on the low end of the band, and I don't need talkaround on the 448-449 channels, so my range 1 conversion is complete. Thanks for your help.

To everyone else, if you want to take the time and trouble, those range 1 Spectras *DO* go up to the ham band.

[wa6jbd]

Update to this...

I've converted a couple more Spectras from range 1 to the ham band, and have photographed the process and written up an article with the intention of having it posted. What I've found is that these things are relatively easy, IF you have the necessary gear to retune the filter. That's a big if, because not everyone has access to sweep gear of some sort. Over all, the receiver seems to be the issue, and the vco. I started with the vco mod mentioned above, then retuning the filter, which is a but tedious. The transmitter on two additional units completed put out rated power from 440 - 450, so I haven't found it necessary to play with the harmonic filter. A realignment of the power and current limit settings seems to have solved the drop off above 448 that I previously mentioned on the first radio I converted - perhaps less than optimal, but it's been trouble free.

If Bob will contact me off line, I'd like to resume the article discussions we had back in December.

[wa6jbd]

More info on this...

Because of several requests received, I've created and posted a temporary web page detailing how I converted range 1 Spectras to ham band use.

http://mysite.verizon.net/res8teuc/Rang ... ver1.1.htm

This website will be there temporarily, until I decide what to do with it, if anything.

Now, something else interesting that's occurred. I have been corresponding with another user on this board, who followed my instructions and ended up with a VCO that doesn't lock. I've converted several successfully with the process detailed on the web page above, so I'm pretty confident in the process. In an e-mail received today, he indicated that he bit banged the radio to alter the range to range 2 so that it could be programmed. I need to confirm that's what he actually did...

Coincidentally, a radio that I converted for a friend a month or two ago has come up with the same problem. And there seems to be a common thread. Both radios were bit banged into thinking they were range 2 radios - one, AFTER it had been successfully programmed with a modified version of RSS that allows the out of band frequencies. In the case of my friends radio, the display indicated out of lock. Loading the old codeplug that I created with the modified RSS cleared his problem, and the radio now works fine from 440-450. He had wanted to program some new frequencies, and rather than hack the RSS band limits, he attempted to convince the radio that it's a range 2. In both cases, the radio and RSS apparently accepted the new frequencies while programming, but seem to cause issues with VCO locking. It remains to be seen if that's actually the case with my e-mail correspondent's radio.

I can't vouch for the process used to bitbang either radio, but I find it interesting that the two cases that I know of where a radio was altered in the MLM to think it's a range 2, and then the vco modified, they have failed to function. If anyone chooses to try my method of conversion, I'd suggest that you modify the RSS instead to allow out of band programming.