Spectra to 902-928

[VE3TUH]

To all
I have converted 3 Spectra's to the ham band, full TX, and RX from 920-928. I used the silver paint on the VCO stub to lower the VCO freq, whoever thought of that, it was a great idea. Here is another trick you may want to try. The radio wants to TX 45mhz below the RX. When you move the RX and TA down to 920-928, the TX wants to go 45 mhz lower. To get around this, I reversed the AUX1 and AUX2 lines, on the RF board. I set my band limits in RSS to 920mhz. All TX freqs below 920 now will take advantage of this AUX mod, and keep the VCO locked. I dont think you can RX below 920 with the stock front end filter anyway, I noticed a real drop off in sensitivity below 920 mhz. Question, though. I can only get up to 10 conventional modes on these pigs. Anyway around this? If anyone has an MLM that will do more for them, I would be interested in looking at it. Good luck to all trying this!

[walt10]

If your MLM board is later that V5.xxx you should be able to stuff a 128 channel code plug into it. I have done this on a few.
Walt WB4LDS
900 MHz in Tucson
927.1875 PL 154.1
927.3125 DPL 606

[VE3TUH]

Hi Walt. Could you please send me a file with the codeplug data? I have tried several different MLM software versions, but with my codeplug data I cannot get around the 10 conventional limitations. My email is ve3tuh@rac.ca. With the Spectra's you have in the 900 mhz band are you using 5khz deviation, and did you swap out the narrow filters in the front end, or are you running narrowband on these units? I was wondering what to do about that issue, also.

[Bat Wing]

Full lock TX/RX from 902-928? Can you detail your procedure... just painting the VCO I was having VCO unlock when I did a test unit.

Bat

To all
I have converted 3 Spectra's to the ham band, full TX, and RX from 920-928.

[VE3TUH]

If you read the original post, RX lock from 928 to at least 920, will probably lock down to 915 but unusable anyway past 920 due to front end filtering. There is NOT full RX lock. The TX does lock, however, 928 to 902. With the band limits set in RSS at 920, from 928 to 920 you can program your radio to TX in talkaround mode. Below 920 program your TX frequency in TX mode. Reverse the AUX1 and AUX2 leads going to the VCO. Do this on the RF board, it is much easier to do the mod there. I cut the traces going to the AUX pins and reversed them. The AUX lead mod is only active in TX mode, and will allow you to TX from roughly 920 to 902.
eg. RX 927.33
TX 902.33
TA 927.33.
All will lock. The RX and TA lock was easy to obtain using the silver paint mod. The Aux mod allows the TX to work also. I fine tuned the lock window by using the resistor mod on the - line of the VCO, with the silver paint on the VCO stub, the resistor value I required was in the neighborhood of 1.5 mohms. Good luck, and let me know how it works for you. btw, I am still looking for a 900mhz codeplug file with more than 10 conventional channels...can you help?

[Bat Wing]

Ahhh... I was reading too fast and interpreted that sentence differently. It would have been an interesting feat if you did what I thought you did...

I haven't got any codeplugs that do more than 10 channels. But I will let you know if one shows up.

Thanks for the clarification, I will look up the purpose of the AUX lines in the service manual when I get back and see what your mod actually does.

Thanks,

Bat

[recurry]

Full lock TX/RX from 902-928? Can you detail your procedure... just painting the VCO I was having VCO unlock when I did a test unit.

Bat

I have developed a mod for the spectra's that allows full VCO lock across the band. As well you can get good sensitivity (around .22uv@12db SINAD) by modifying the preselector (front-end filter).

I have done at least 20 radios with this set of mods and it works great. One must remove the cover from the VCO, add 1 chip cap and and do some minor stripline modifications to the tuning stubs, then replace the can.

The Spectra is a REALLY great 900mhz hamband radio with this mod. I have a repeater that has been running with two spectra as the radios for 6 years now (same radios!).

When I get a chance I'll document it and send to you. I also did a patch for the Lab software 6 years ago. It is different than the one you have now. This one allows entry of any frequency.

Lastly, I'm the guy who did the mots6 mod for the MTX900 if that lends any credibility to me statements above.

Regards,
Ron Curry

[xmo]

I am sure your information will be appreciated.

What took you so long to find Batlabs? - Just kidding - we KNOW why - spending all that time with your Canon D30!

Does the WED in your call mean you shoot weddings?

73

[recurry]

I am sure your information will be appreciated.

What took you so long to find Batlabs? - Just kidding - we KNOW why - spending all that time with your Canon D30!

Does the WED in your call mean you shoot weddings?

73

Actually, I just tried the Spectra RSS mod the guys published here on BatLabs and it's far eaiser than mine. Mine involved patching about 20 locations where the check for an inband frequency was made so that it didn't care what frequency was entered. The mod here on Batlabs get's essentially the same results if you make the band ranges large enough and only takes about 20 minutes - very nice!

WRT the Spectra mod, as soon as I get time I"ll take some photos and send it to the Batlabs folks. I've started this project several times but never got it finished.

WRT to not showing up here for so long, well, I did all my 902mhz work back in '96/'97/ and early '98. Batlabs existed but not this forum. After putting up a 440, a couple of 1.2ghz, a LOT of research and work getting 900mhz Spectra's, MTX900's, and a 900mhz Micor repeater going I was pretty burned out. In '98 I started on a homebuilt helicopter project that took three years. I got it finished late last year and have since regained some interest in ham radio.

Anyway, that's the story.

Cheers,
Ron