Newbie With Sangean 909X

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Gecko10

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Just getting started and at the bottom of what seems to be a rather sharp learning curve. I am sure I will have many questions, so the first should probably be, is there a FAQ for this forum and if so I would appreciate it if someone could point me to it.

Next, for today at least, what antenna configuration are folks with the 909X having the best success with. So far I seemy to be having the best results with the wire antenna that came with the radI clipped to the whip. This seems to be better than the wire plugged into the antenna por of the radio.

Any suggestions or help would be greatly appreciated.
!!!
 

theleman

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I am also using outdoor wire antenna clipped into the tip of the whip on my 909X in black. It works great in pulling weak SSB ham signals.
 

majoco

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Now I don't know anything about the 909X, but many of the small portables have a high-impedance FET amplifier at the base of the whip antenna - this FET is very prone to going bang with static discharges making your radio totally deaf afterwards. It doesn't take much to pop the FET, just shuffling across a nylon carpet and touching the whip will do it. The reason why the external antenna socket seems to give poor results is that the FET amplifier is then bypassed - the radio is expecting a big outside antenna when that socket is used.
You may get away with it, but one day.....
 

ka3jjz

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It can happen if the antenna on the external jack gets zapped, too, and for similar reasons. That's why this is a real good idea to add to your antenna, no matter what you're using...

http://forums.radioreference.com/receive-antennas-below-30mhz/295299-great-first-timer-project.html

In fact this might be a good option if you want to use a connecting plug from the antenna that the little 3.5mm jack on the side of these radios won't fit. ..all you'd need is a single jumper from the other end of the box to the antenna jack, and you'd be good to go.

As to what to use - there are literally dozens of different antenna designs out there (and some we have linked in our wiki). Just don't go too long with the length - radios like this one are all prone to overload if you put too much antenna on it (the little box described above will help with this, to an extent).

Are you looking for something inside or outside (which would be much better)?

Note too that sometimes there's a little switch on the side to select the antenna port or the internal antenna. If there is, make sure the antenna switch is selecting the jack when you plug the antenna in

Mike
 

theleman

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Isn't that what RF gain / attenuator is for? Where signals are strong, or noise level is high, you turn the RF gain control down to minimum?
 

theleman

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The only reason that I use wire clipped into the whip is because the alligator clip off the wire doesn't fit into the 909x AM antenna socket. Anyhow both ways they work fine.
 

ka3jjz

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Isn't that what RF gain / attenuator is for? Where signals are strong, or noise level is high, you turn the RF gain control down to minimum?

Yes, but a fixed switched level doesn't allow for times when it might be too much - or not enough. With a bigger antenna, you might need more - hence the pot in the box.

Mike
 

majoco

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"RF gain control" and "Attenuator" are really two different things. An attenuator is good if you are troubled by a nearby BC band transmitter making false signals where they are not supposed to be (cross-modulation) - switching in a degree of attenuation will reduce the unwanted signal far more than the wanted one making it more readable. The RF gain can't do this as the damage has already been done in the early amplifier stages of the radio and reducing the gain in the IF amplifier can't correct it. RF gain is particularly useful in making SSB and CW more intelligible by matching the BFO against the signal level and by preventing the background noise coming up in between syllables or dit/dahs.
 

Boombox

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The 909x, like the Sangean 909 / DX-398 before it, has back to back diodes in between the external antenna jack / whip antenna and the first RF amp transistors in the radio. If you look at the schematic, the 909X has two diodes, back to back (the 909/398 has four diodes doing the same thing).

Won't take a lightning hit, obviously, but static electricity from your hand, or minor static charges off a wire probably won't kill it. I wouldn't use any portable with an outdoor wire without either a) being very careful or b) using external protection just because static charges in winter and lightning storms can be very damaging.

The RF gain control on the 909 is very useful (I have the DX-398), and it helps keep strong SSB from pumping (although on my 909 SSB never chirps, just pumps on strong CW or SSB), and the RF gain control also keeps some AM modulated broadcasts from pumping, as the AGC is fairly tight. It's a resistor working off the antenna input (It's not quite that simple, but basically that's what it is doing).

I would bet the RF gain on the 909X works the same. It looks like it's wired the same.

My guess is that with the 909X they didn't change that much next to the antenna circuits. i think most of the changes were later in the chain, especially the firmware. Looking at the schematic, the big changes were the AM IF chip used, the SiLabs chip used for FM & RDS. The AM circuitry looks extremely similar to the 909 schematics you can find online.
 

Boombox

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PS -- I recently took a second look at the 909X schematic. It looks like the SiLabs DSP chip does more than just decode FM and RDS. It seems to be in the MW/SW chain also.

How it actually works with the TA7640 analog IF chip I really don't understand. I think it's used to drive the SSB demodulation circuits, but I could be wrong. Maybe someone with more experience with schematics could look at the service manual and explain how the two chips work together.

Either way, the inclusion of the DSP chip may be a reason the 909X gets reviews saying it's an improvement over the 909. I've got a couple radios with the SiLabs chips in them -- they work really well.
 

theleman

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My 909x seems working best with outdoor wire antenna connected to the external antenna jack on SW SSB in conjunction with the RF control. It is so sensitive and quiet, picks out the weakest signals other radios cannot even know its there. Heard a lot of weak sub DX stations with the 909x recently.
 
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