PCS-Electronics

We have this unit installed in a case (cybermax FM 150W) driving a 150 watt linear amp: broadcast warehouse.
we are going to use this transmtter arrangement to run a full power FM (licensed in USA) and need close to 65 watts ERP from the antenna (circular polarized) mounted on top of a mountain (antenna is Jampro single bay gives 46% out).

with 150 watts out, we would be fine; only lose about 4 watts in low loss transmission cable.
problem is we can never quite achieve output power of 150 watts; it's more like 120 or less.
Power amp has 28 volts at 7 amps going to it fine which it specifies..
MAX PRO 3 has 15 volts going to it which is also fine, but noticed it has been modified (has it's final transister T3 removed) to cut the driving power to amp; I understand, yes, this is necessary to keep it from frying 150 w Amp which takes only 1-4 watts drive.

I'm down to staring at the double sided MAX PRO 3 pcboard and have found the power is 12volts max going to transistor P/N BD135-16 which supplies voltage to the final transistor (T1) on the MAX PRO 3 which drives the 150 watt PA.

If I could find out details of how to re-install the pot that adjusted the output power (if that'll work) or get a schematic (I can draw one out eventually as it is fairly obvious what the chips are even with their numbers removed, but time is not on my side; winter is coming this month).

If I could raise the drive voltage to the final transistor manually up higher, similarly to what the LCD does, I may achieve 150 watts out. Yes, I've tweaked the tuning and all to max power out to 130 watts into a 50 ohm dummy thru a Bird wattmeter.

any detailed help would be appreciated; I could always cut the MAX PRO 3 etch and run a higher voltage in manually myself, but would rather not; plus I'm not sure of transister (FET?) ratings. this transmitter has survived fine on a test for weeks in the summer, but power is not up to FCC specs nor our liking.

Sounds like an ancient unit, probably 5-7 years old.

Possibly not even assembled and sold by us.

150W BW amps were a joke at the time, they could typically produce some
120-140W long-term safely. The sd1407 device used by bw was pushed way
over its specs.
Also some of the PSU units they sold with their amps were too weak at the time.
The max pro 3 you mention is old version that hasn't been selling for years.
Even the new version of MAX PRO 3+ is now obsolete and not available.

Stuff available today is superior in every way, there is just no comparison.
I guess its time for an upgrade?

yep, sounds like what you are saying is the case.

I wondered about the 150 watter Amp.

I've had to mess with it a bit to get it up in power and keep from overheating and generating spurious signals every 3.6 MHz all the way up and down the band; has no LPF in it either; finally got that solved with shielding.

I have no idea how old unit is; was given to us few years ago.

guess we'll limp along till we purchase a ungraded unit.

thanks

Well, when you decide just let me know, may be able to give you a bit of a rebate

Current models display output power and a number of other parameters.
300W model has 500W PSU, for example. Its all put together very neatly,
you'll like it.

ok, I appreciate the offer of a rebate.

I'll let you know.

I was wondering what you ment by gives 46%?
ERP is effective radiating Power. This is usually achived by the antenna gain, loss of coax. For example 125watts + Gain of antenna 0DB gain equals 21.0 DBW. Feedline loss Worst case senario 100mhz, loss on coax RG-8 is 1.6 DB loss per 100 feet. Total that. 21.0 DBW Minus 1.6DB loss equals 19.4 DBW. Convert it back to watts, equals88 to 89 watts ERP. If your antenna has any gain, factor it in, and your coax loss. If your running hardline you can cut DB loss in half and you'll probably have your 100watts erp. I am basing this on a repeater coordination paper I have. It has all the feedline loss info and Factors. Go to Southeast repeater Association, and find repeater coordination application. It's on page 2 of the app. 125= 21.0dbw+ 0DB Gain =21.0dbw -.60db loss = 20.4 DBW =102 Watts ERP

thank you for your lengthy reply.

to answer your question, I will start with what I said at the 1st: ".....(circular polarized) mounted on top of a mountain (antenna is Jampro single bay gives 46% out)."

the 46% efficiency comes from that type of antenna.
Based on a simple dipole antenna, a single bay (meaning "one" antenna) circular polarized antenna theoretically would have a "net" gain of 50%; i.e.- half the power in horiz; half the power in vertical plane.

So according to engineering specs, if one uses such antennas, they would have to run 2 times the power into it to get an ERP they wish. But of course nothing in nature seems to be 100% efficient, so such antennas have a lower rating ERP; mine has a 46% rating.

Other solution is to use a 2 bay (meaning 2 antennas) which will give very close to 100%; (i.e.- a power gain of 1) ERP of what is applied to them.

Here's an example of such specs here:
http://www.jampro.com/index.php?page=jlcp-fm

here is an "excellent" and lengthy discussion on using such antennas:
http://www.ccbroadcasters.com/Equipment-antennas.htm

yes, we understand about loss of cable: we are using LMR400 coax which offers low loss, but for FCC purposes, we take the max. loss afforded us for a transmission line which of course would subtract from the transmitter input power in figuring what comes the end feeding the antenna.
here's a nice "online" site which automatically figures cable loss for most types (RG8, LMR400, etc.) if you scroll down:
http://www.ocarc.ca/coax.htm

Thanks again.