Spectra UHF 110W... PA Input Drive?

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sat May 27, 2006 9:34 pm

How much drive (in watts) does a Spectra 110W PA need?
Thank you!

kcbooboo · Post by **kcbooboo** » Sun May 28, 2006 3:47 am

The drive comes directly from the VCO board and is the same no matter what output power level the radio operates at. The VCO block diagram indicates +16dBm typical (that's 40mW).

The 40w PA block diagram calls for 20mW. The writeup for the PA says you should see 30mW, and if not, troubleshoot the VCO.

Bob M.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun May 28, 2006 1:18 pm

What line on that 12-position/10-pin connector to the PA do I bring high or low to make it key up, without using any of the logic inside the radio?

Also, what kind of connector is that from the PA to the VCO? (the one labeled with green heatshrink that says "TX".) Is there any chance of getting an adapter from that to a more conventional RF connector?

kcbooboo · Post by **kcbooboo** » Sun May 28, 2006 1:40 pm

Here's the info for the 45w UHF PA for doing functional testing:

transmit: keyed 9.4v=9.4, 9.6v=9.6, control voltage=increase until power equals 46w or 10.0v max (DO NOT EXCEED 10.0V), power in=30mw, A+=13.0

receive: keyed 9.4v=0, 9.6v=9.6, control voltage=0, power in=0mw, A+=13.0

In other words, you need all the DC voltages and some input power.

The schematic and the test procedure show a 12-pin connector, with the odd numbers on one long side and the even ones on the other. The board x-ray view shows 12 positions but only 10 numbers, and they go clockwise and skip the missing pins. Leave it to Motorola to screw up connector pin numbering; the Spectra is full of that.

The block diagram calls it a Taiko-Denki. It's the same small coaxial pin plug that's also used on MaxTracs, Radiuses, and GM300s, to attach the PA to the RF board. I have seen them on the web, but they require a specialized crimping tool. You could order a short cable for a MaxTrac PA that already has one on it, then add your own connector to the other end. I bought two last year to rebuild some MaxTracs and I think they cost about $5 each. None of the cables are specified in the detailed service manual.

Bob M.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun May 28, 2006 5:58 pm

OK...

Here is what I'm getting from the pins powered up:

1. 0V
2. 0V
3. 13.7V
4. 0V
5. 13.7V
6. 1.25V
7. NO CONNECTION
8. 0V
9. 13.7V
10. 4.18V
11. 13.7V
12. NO CONNECTION

I think something's messed up, because I'm only getting 4.18 from the 9.6V pin.

kcbooboo · Post by **kcbooboo** » Mon May 29, 2006 3:35 am

Send me an e-mail address (via PM) and I'll scan a couple of pages and send them to you.

I can't tell from your pin numbers what's what, as my manual says pins 1 & 8 are missing. But you certainly should have +9.6VDC on one pin, coming from the command board. Let me know which command board you have and I'll copy part of the regulator circuit as well.

I suspect these are the voltages in RECEIVE mode.

Do you have any kind of service manual, or are you flying blind here?

Bob M.

GlennD · Post by **GlennD** » Mon May 29, 2006 6:48 am

The 10 Mfd 50V Electrolitic cap on the command board leaks and corrodes the power control trace that runs next to it. When this happens you will have no, low, or erratic power depending on how severe the damage is.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Mon May 29, 2006 11:29 am

I don't have a command board at all.

I'm trying to feed another exciter into the PA, and make the PA power up. This radio had all of it's other componants stolen from it.

I'm feeding it 12 volts on the main radio power connector, and that is all.