Anyone Up for some HooDoo? Voodoo this...

[Bow]

I run 10 meter mobile... and mostly talk to W5udx (Gregg) when I am out and about town, or coming home from work onm the weekdays...
my 10 meter rig is basically a glorified CB- It Is A RoadPro Titan II RSPY-485.

It was sold under several names with either single final transister for 4 W AM or 12 Watts SSB, or there was a dual final version that would do 10 watts AM or 25 Watts SSB , it was commonly know as a Radio Shack HTX-10 or the current production Magnum 257.

Mine is the 4 watt AM/12 Watt SSB version. and on the Stock microphone, with no linear amplifier behind it, the audio looks like this (Thanks W5UDX for the Scope):



Not Pretty, not Voodoo.. Not Even a Little...
... but keep in mind, this is a CB based radio... (4-10?)

OK.. The schematic for the radio is here:

RSPY-485 Schematic

Anyone got any ideas for some modifications to give it a bit more low-end?

Keeping in mind that this is a Mobile rig...

Problem #2

I run a RM-italy KL-300P amplifier behind this radio.
W5UDX noticed that the radio, with the amplifier on sounds very compressed and has a raspy, midrange audio quality to it, but with the amp off, it is normal, for a radio of this caliber...
Gregg scoped my audio with teh amplifier ON and it has a low-end cut off of about 500 Hz and goes up from there to about 5000Hz.

The Amp Schematic is here:

http://www.rmitaly.com/download/manuals ... el_310.pdf

How can the amplifer cause an upward audio shift?


EDIT.. Correct Radio Schematic found....

[Voodoo Guru]

Hmmmm....
Thats a good Question.
We'll look at the schematic when we get some free time (HA!) and see if theres anything we can do for the lows.

[Bow]

Swap some bypass caps maybe?

I don't think running a Condensor in my truck is feasible, but I am willing to gut a Audio Techniques dynamic mic for the element to drop in a hand mic application...

I also have an old Stereo EQ with the 40 booster on it...

If I could unhook the booster portion, I maybe able to use the EQ side of it...



Let me know what the Voodoo Gooroos think!!!!

I pulled the suspect amplifier out and replaced it with TUBE power, a Lafayette HA-270... 2x 6JS6's BABY!

...and I also installed a Radio Shack Dynamic mic on it (CB Style), as a couple people said that teh stock electret sounded "Narrow"

When the weather is working with us, i will see if W5UDX can give me an Audio update report...

[Voodoo Guru]

We listened to the audio clip Greg sent us....YUK!
Wow that is pinched.
Almost Sounds like the element is stuck in the Mic.
Looking at the schematic, its a condenser though.
Maybe trying the different mic will help.
Looking at the schematic it looks like there are a few caps that could be changed in the mic circuit to improve the low frequency response.
Need to spend more time looking at it to be sure.
Thats a rare commodity here lately....time...
Guess the amplifier could change your audio if it is not linear.
Would be interested to know what Greg thinks of the audio difference between amps.
Let us know the differences in the mic and amps swaps.

[Bow]

I talked with Gregg last night on the ride home.

I used an HA-270 (tube Amp!) and a Dynamic Mic Replacement, still communications style mic, but not an Electret like the stock unit...

He said that the audio sounded "Better", as in not and compressed and "crunchy"/distorted as it was with the old amp, but it was still all above 450-500 hz... That lead us to believe the radio is the limiting factor...


When you get a chance, I would like to know what you think as far as caps to swap and possible values to swap in.

Thanks Mike... I'm a learning as we go!

[Bow]

I found the Service Manual for teh Radio Shack version of this radio, the HTX-10.
http://www.repeater-builder.com/radio-s ... manual.pdf

I am trying to find the Carrier Set Point adjustment.. anyone see it?

I was going to try with Mike W5CUL was talking about in the other thread...

[w5cul]

Bow,

Do you have any schematics for this rig that are more readable than the ones in the service manual? Judging by what I have seen thus far, that radio can is capable of 250hz to 5Khz in transmit bandwidth. The question is how to adjust or modify it such that you blow past the 250Hz limit and get it down around to 50hz on the low end. I see where you can adjust it up to the 5K limit. Did you see the advertised skirts for this thing; ~60db at +/- 20Khz? If I didn't read that wrong, then that is one sloppy filter when compared to todays standards. Anyways, I would need to see a better schematic for the rig in order to go any further with this one.

[w5cul]

Bow,

By the way, where were you last night? Me and Greg were talking on the Saltgrass Network till about 11pm. It seems like a good alternative when 75M is in the toilete.

[Bow]

Thanks for looking Mike.

No, I wasn't on last night, I was busy doing school/home stuff.

tonight is a radio night though... I'll be on somewhere...

Here is a better schematic.
http://service.alan-germany.de/Amateurf ... ircuit.pdf

I swapped the C173 out to a .22uf to try and let more low end through, but Greg couldn't hear any difference.

[w5cul]

Bow,

I will look it over when I get home. I wouldn't try and swap out anymore components just yet. I think the setting of low end and the high end is a function of the crystal alignment procedures within the service manual, at least that is what I gather at this point. So if I am right, you would have to align the corresponding crystal/oscillator for 250Hz, the lowest it can go per the manual. After that, then I would think that any component changes would become audiably noticeable. Probably the reason why Greg did not notice anything in your low end after the cap change.