http://www.microwavers.org/scatterpoint ... t_1303.pdf
Just wondering if anyone else has any experience with modifying and using these for DATV? Also wondering which other amplifiers might be available/suitable for use when Es'hail-2 is activated.
thanks and 73
Unfortunately, while good, that article missed out a lot of the information that was available at the time. There seemed to be a rush to publish quickly rather than checking what was out there already, which was a lot, including schematics.
I wrote an article on modifying these using an Arduino Nano to provide diagnostics and protection.
However, these amplifiers are for 2.1 GHz and going to 2.3 GHz, without modification of the RF matching was already pushing it. Going up to 2.4GHz is maybe pushing too far, untested. That does not mean it won't work, but it is likely to work a lot better with some retuning. The good news is they run off -48V so you can use a standard telecoms supply, but also the internal system is 28V which might be better as the existing PSU is a limiting factor for CW output. If you want to operate well backed off for DATV, its fine as it is. I also have a spare in my garage.
Meanwhile, there are other options - Stealth Microwave do a range of highly linear amplifiers and people will be very familiar with the 20W 3.4GHz units with the purple heatsinks that were widely available surplus a year or two ago. So available I remember the box containing 2 of them, with PSUs were going for £5 to £10 at Didcot last year. There were also 50W units but these were much rarer.
Anyway, they also made identical looking amplifiers covering 2.4 GHz. The trick to identification is to understand the model number - e.g. SM3437-43 is an amplifier covering 3.4-3.7GHz at 43 dBm (20W). The SM2325-47 covers 2.3-2.5GHz at 47 dBm (50W) and there is a 44dBm (25W) model. They do appear, from time to time at Rallies and on Ebay.
This forum does not allow PDFs to be uploaded but google SM2325-47 should come up with the info.
There are quite a few other options but I would try to modify your Andrew PA first.
Does anyone have any idea as to whether this would make a good candidate for Es'hail-2? If so, what sort of o/p power do you think I could realistically get out of it for TV modes?
An RF board (no PSU etc) was given to me at the local club on Wednesday evening, quite out of the blue. I had seen SP1303 but not your later details in 1305, so many thanks.
I understand the RF board needs 28V and 9V? I'm assuming the spade terminal on the board should be connected to 28V but is that +28 or -28?
Someone else had it on a shelf? Nice present.
The board on its own needs the heatsink, if not attached there may be a reason, so I would check the FETs before investing a lot of time. The original PSU limits the output but it would have been fine for DATV as that's usually well backed off. Several people removed them so you might find a spare.
The 28V and 9V PSU should be easy enough, but pay attention to sequencing the 9V first in case it is driving any gate supplies (don't remember). The supply is positive with respect to ground. The maximum rating of the circulator should not be exceeded. These boards produced about 30W and some parts are sized accordingly. People have got 100W+ easily, but usually SSB/CW duty cycle, not PSK. It should be linear enough for DATV at 30W - try it and see..
Many thanks for the advice. The circulator is missing (has been bypassed by a short length of 50 ohm bendable coax), The early stages have been bypassed by coax going directly to the driver stage and the 0 ohm links near the bias pot pads have been removed so whoever originally had the board must have read your SP articles but gone no further since no pots have been fitted. Presumably I could get an initial idea of the health of the driver and PA transistors by powering up with, say, 12V rather than 28V and also applying 9V for the bias (via individual 1K pots as intended)?