Lowband Syntor-x question

[n3chu]

Hi All, I have a Syntor-x lowband on 6 meters. I use it on 52.525 where the output is about 90 watt sand SWR is less that 1.5 to1. When I go down in the 51 mhz aria the radio puts out 125 watts and the SWR is a little over 2 to 1 and draws a bit more current. That seems backwards? Isnt the radio supposed to protect itself and cut back the output as the SWR goes up? I think I,d rather have it just the other way around? Antenna is a PD-128 monopole groundplane fed with about 60ft of andrews 1/2 in. hardline. I tuned the antenna at 52.525. thank you all. Am I out of the antennas bandwidth?. any answers appreciated. Davie n three c h u at atlanticbb.net

[kf4sqb]

What type of wattmeter are you using? Some really cheap ones are not 'directional', and can, in some instances, give you the sum of foward and reflected power instead of just foward power. If you're not using a Bird, Telewave, or something similiar, try to get your hands on one, and see if it tells you a different story. If you are already using a high-quality meter, I don't know what to tell you, unless it's simply a function of how the PA is tuned.

[n3chu]

The watt meter is a Bird 43(thats never been dropped) with a good slug.

[Will]

The PD 128 is not a broadband antenna, and from the SWR reading is not doing too well at 51 mHz. If I remember correctly the antenna is only rated at about 250kHz bandwidth.

You could try to lenthen the element just a little and see how the SWR does at the two points.

[n3chu]

Thanks for your input will, I know the antenna dosent like the SWR at 51 mhz but why dosent the transmitter cut back the power then? Cant get up to change the setting on the antenna so I,m stuck with it, but I dont move usually very far from 52.525 anyway so its no biggie.

[George]

What you are seeing is the end of the range of the output filter in the power amp. You are burning up the difference in power in the PA with less coming out to the directional coupler and since it's slightly out of tune, consumes less input current.

The X/X9000 low band power amp isn't that particular, unlike some radios, in that if you have an antenna and are making a decent attempt at tuning, it will throw power at it. If you have no antenna at all, then it's a different story.

I think you will find that the radio will perform better at 29.5 or 29.6 than up in 51/52 MHz. This is due to getting more range out of it in the lower frequencies because of the greater wavelength.

YMMV depending upon the vintage of the radio. It seems like the newer ones are better about stretching than the older metal labeled ones. At least that's been my experience and I have had several different installations.

George

[n3chu]

You are saying as I go from 52 to 51 I,m going back IN band where its designed to operate so the PA is getting more effecient?. It is putting out more power and drawing more current. Thank you George

[George]

Maybe efficency is not quite the best word. How about productive? The power amp is more productive in the range in which it's designed to operate.

When you get outside of that range, and yes, tis a broad range considering the 29.7 to 50 MHz area that it's covering, you are running into the filtering before and after amplification. I doubt that the devices used care about the frequencies as long as they are not outrageously outside of the area of design, but the filtering does care. As a result, the further you get out of range, due to input filtering, the less gets amplified, the less power consumed in the form of input current and the more gets eaten by the output filter network resulting in lower power out.

Pull the cover off your PA and it's all those chokes in those cans on the left side of the board. That's where a good chunk of power is getting converted to heat rather than leaving the radio in the form of RF energy.

The closer you get into range or into range results in more drive to the devices, more current consumed because of greater drive, the more power goes through the final filters and you end up with your 125 watts.

This isn't like using a range one MSF power amp in range two, such as up at 444.5 when the designed cutoff is supposed to be 430. (Or using the other extreme such as a range three PA at 444 when the cutoff is 470.) You can use it, but at your peril because you can certainly get drive into it, but the effiency due to the range of the splitter and combiner sections will result in greater current being consumed and eventual device failure. All of the tuning and filtering for that power amp is external to the amplifier and those circuits have ranges that can be adjusted or even totally replaced while the X/X9000 low band PA does not.

Does this make it clear?

I have gone through several low band X9000 drawer units to get ones that have good effiency for both 6 and 10m. When I find one I am satisfied with, I guard it because I am lazy and don't want to repeat the work.

George

[n3chu]

Yes pretty clear, the filter chokes in this pa is something I havent messed with only programmed the radio. I have spread chokes to get the output filter above 50 mhz on other radio like mitreks etc. Havent looked into the pa on the Syntor-x in a long time so can that be done to the output chokes without takeing them out?