Astro Spectra VRS-EP S SPlit, possible lower than 450?

[W1HVN]

Can an S Split VRS-EP for an Astro Spectra be programmed lower than 450 into the Amateur 440-450 range?

[matt_tjaden]

I know the one I have is crystal controled. From what I found it is basicly an EXPO radio inside, so a crystal for and EXPO should work.

[Mike B]

The RF circuit boards on the Expo and RNet radios are the same. The audio circuit boards and housings are different. The VRS-EP is supposed to use the RNet radio. The older VRS (not the EP) used either the Expo or RNet radios. These are all crystal controlled narrow frequency range radios. Many components (capacitors and coils, etc.) have different values for different frequency sub-ranges. You have to manually tune these radios to your frequency. These are definitely old school radios.

The published factory frequency ranges for the RF circuit boards were 403 to 430 MHz and 450 to 470 MHz. The receiver uses two crystals. Different sub-ranges in the Rx frequency would switch the 455 KHz IF injection crystal between high and low (these were only one of two 44.545 or 45.455 MHz crystal frequencies). Including the Tx crystal, means you need to change either 2 or possibly 3 crystals to change the RNet operating frequency.

The Expo RF board had published frequency ranges from 406 to 420 MHz and 450 to 512 MHz. It appears Motorola never meant to operate these in the 440 to 450 MHz frequency range. It will take some custom component value changes and custom tuning to get these into the 440 to 450 MHz frequency range. However, since the VRS portable radio is only for very short range operation, the RNet Rx specifications do not have to be optimized or meet factory specifications.

If you start with a RNet radio operating in the low 450 MHz range, the custom modifications should be allot simpler. If you stay just below 450 MHz you should not need to make any component changes other than the crystals.

The VRS circuit board has a built in Rx bandpass filter between the RNet radio and VRS antenna connector. It should not be a problem, but you should be aware of it.

The RNet radio manual part number is 6880901Z35. This manual is a must for making "custom" operating frequency changes. A UHF Expo manual would also work. At least this is through hole circuit board technology, so it is easier to work on, but it may be harder to find parts.

[W1HVN]

That is great info. Thanks. I will find something that has no local bearing on freq use in the area just below 450. Will need to get new crystals. Performance is not critical, but being close to 450 is key. I imagine the bandpass doesn't steepen until further into the band than 449.5 and up. I will go as high as possible without causing local interference to anyone with using low power on the VRS (<1W) and a quarter wave antenna.

If anyone has the manual, I'd love to at least get crystal replacement info.

Thanks much.