Batboard

i have a w9 high power Astro Spectra that the rx dosent open til about 2.94 microvolts.i think specs are .2-.5 microvolts rx sensitvity. I have swapped out the vocon, rf, vco and reciver front end assembly. the other things the service manual talks about is the antenna switch on the pa board and the syntheizer. the syntheizer troubleshooting chart basically says to swap out the above boards. so that leaves me at the antenna switch. I have a communications monitor it is an older motorola R-2100C.
Can this monitor check for insertion loss? if it can, can someone instruct me on how to set it up for this type of test? if anybody can help or share some advice on this problem it would be greatly appricated. Thanks kt

What do you mean by "does not open until 2.94 uv"?
When it "opens" is it clea audio at that point? Is it a squelch setting issue? If you open the squelch (open noise), at what level do you start to hear audio?

In general, the Astro Spectra isn't very sensitive. It disappoints me quite often, In my case however, it has everything to do with the coarse squelch adjustment which cannot be lowered enough to be adequate... somewhere between 0 (open squelch) and 1 (squelch too tight) would work, but it cannot be adjusted other than the coarse 0-15 settings.

The analog spectra was another story. Some of my Analog spectra's squelches wouldn't close until around 8 or 9 on the 15 unit scale.

Long story short, check the squelch setting. If not that then just understand that the astro spectra doesn't work as good as the astro saber, analog spectra, or pretty much any other radio in terms of reception.

-Josh

The specs in the service manual aren't that bad, certainly along the same lines as the regular Spectra: 0.35-0.50uV for 12dB sinad or 20dB quieting. If you need microvolts to open the squelch, I'd say it's set way too tight.

If it opens at 00 but closes at 01, then you probably need to make a component adjustment to get it to close at a higher setting. I seem to recall there were a couple of "factory selected" values on the RF board which could have an effect on this.

With the appropriate connectors, you could measure the insertion loss of the antenna switch. It should be under 2dB.

Bob M.

sorry for the delayed response guys. here are the answers to some of your questions.

What do you mean by "does not open until 2.94 uv"?
When it "opens" is it clea audio at that point? Is it a squelch setting issue? If you open the squelch (open noise), at what level do you start to hear audio?

If the squelch is set at 0 when i hear clear audio tone from the speaker is at about 2.94 uv.

Bob can you give me some pointers on how to check for insertion loss on the antenna switch?

To do it right, you'd need some kind of cable that mates with the T-D female jack on the RX front end. Feed a signal from your sig gen into that jack and go for either a specific level of quieting, or breaking squelch at some point.

Then reconnect the normal antenna cable, feed your sig gen into the mini-UHF jack on the back of the radio, and see how much signal you need to get the same quieting or squelch opening. The difference between the two is the loss in the antenna switch.

Bob M.

Thanks for the info ill see if i can put something together and let you know.

The Astro Spectra RF board demodulates the IF signal into a digital bit stream which feeds the VoCon board. Audio and squelch take place between the VoCon and the command board. The regular Spectra RF board uses a different IF chip entirely and handles its own squelch.

It may be that the digital stream is getting through just fine at lower sensitivities, but the VoCon board won't pass audio (open squelch) until you get a really quiet signal.

When you feed in that 2.9uV signal, how quiet is it? Or is it sill quite noisy? In other words, if the receiver is making 20dB quieting at 0.5uV, it should be even quieter at 2.9uV if everything is working just fine. If, however, it's barely quieting the radio at 2.9uV and you aren't reaching 20dB quieting until a lot more, this would indicate a problem. Find how many uV it takes for 20dB quieting at the antenna jack and get back to us.

Bob M.

It was barely quieting at 2.7-2.8 and full quieting at 3.1 . i have an analog spectra here and swapped out pa boards. it is now breaking in at 1.1 uv and full quieting at 1.66 uv though its better its still not in spec. command board is the only one left.....