This is weird

[roadrage]

Set up: Galaxy 95t2 with the output impedence matched for amp, TNT 600HD, Dosey TR1000, 102" antenna on a hustler ball mount, spring, and 1" riser at the top of the front bedrail, directly behind the center of the cab on a Silverado 2500HD. Entire truck has been bonded with tinned copper straps. Using Times Microwave LMR 200 coax.

With the amp off my radio and external meter (mounted after amp) both read 1.5:1 across the 11M band with the amp off and radio at full power (50W dead key).

Power turned down on the radio with the amp on so the amp is dead keying 150W out. External meter reads 1.25:1. I have seen and heard of many people have SWR reading increase after the amp is turned on. This is the first time seeing or hearing of a decrease. Curious


Not that I'm complaining, lol

 

[RatsoW8]

The increase in RF might cause a slightly off reading on that precision Dosey meter. Either way it goes that's not enough of a difference to give it a second thought. Meter readings are relative to begin with anyway and considering how you have the antenna mounted you're golden!

 

[psycho]

Dosy meters are OK for reading peak but are not good for checking swr.

 

[space cowboy]

I had that with my 102 off the decklid. I forget what it was barefoot, but it was quite a bit better with my boomer 400 on. there was a definite reading barefoot, with dropped the movement to the width of the needle.
after the decklid gave out I drilled a hole in the bumper and it was the same for both.

 

[roadrage]

That Galaxy is the only one that this happens on. Every other radio sees a slight increase in SWR. I have noticed that a change SWR between the amp and antenna is relative and opposite the SWR between the radio and amp. I checked this after reading a thread by the DB. I hooked a tuner up between the radio and amp. I drop the SWR flat and the SWR between the amp and antenna rose. If I de-tune for higher SWR between the radio and amp, the SWR dropped between the amp and antenna.
I just got the Galaxy back from Bells CB and he told me that he did something to the output impedance of the radio to run with the amp. My SWR between the radio and amp was 1:1 before repair. And between amp and antenna was 1.8:1. Now I am seeing 1.5 between radio and amp and 1.3 between amp and antenna. I am pretty happy with that. Both are safe readings and the pills seem happy and cool.

Hey psycho, don't you have that reversed? Without a powered active peak circuit, they suck at reading peak. I only bought the Dosy because it was what I could afford at the time. I don't trust the peak readings at all. Sometimes I think it is reading high and sometimes I think it is reading low. I hope to get a true peak meter in the near future. I hear good things about the Daiwa 801HP.

 

[Shockwave]

You can bet something is going on with the MOSFET finals in that Galaxy causing this. The other radios probably show a lower VSWR when the amp is off than the Galaxy too.

When you detune the match between the radio and amp, this causes the output power of the amp to drop. If you don't turn up the calibrate control on the meter, it could give you the false impression the VSWR has dropped.

It is also very possible to have a 1:1 match between the radio and amplifier while having the same match between the amp and the antenna. What you're noticing is abnormal especially if you have recalibrated the VSWR meter after the amp.

 

[roadrage]

The Galaxy I have doesn't use mosfets finals. It has 2 2290s. I am happy to see 1.25:1 out of the amp. I'm ok with 1.5:1 out of the radio to the amp. I did calibrate the meter between readings. I'm not changing anything in the system with the exception of installing a low pass filter between radio and amp.

 

[W5LZ]

That low pass filter can cause an SWR change too. Shouldn't be a large one, but it can mean a small one.
- 'Doc

 

[Shockwave]

You'll probably find the transistors driving the Toshiba's are low grade MOSFET's. With solid stage RF stages, problems with signal in one stage can easily pass right through to the next. Although, this one does not seem serious. If the change in VSWR was much greater, I'd be worried.

 

[roadrage]

That low pass filter can cause an SWR change too. Shouldn't be a large one, but it can mean a small one.
- 'Doc

Yes. But I get a break in the squelch on my scanner at 155.310 MHz when if I key up on ch 26.
The radio has been out to repair 4 times between two different shops. It was explained what I am seeing on my scanner, and saw no spurs or harmonics on either of their scopes. I am sure it is just a proximity issue. The antennas are only about 2' apart. But I still want to do all I can to make sure my signal is clean. I don't need to be driving by a police car and have "501 state of Maine" coming in their squad car.

You'll probably find the transistors driving the Toshiba's are low grade MOSFET's. With solid stage RF stages, problems with signal in one stage can easily pass right through to the next. Although, this one does not seem serious. If the change in VSWR was much greater, I'd be worried.

I'm not too worried, but I still keep a close eye on things. Thanks for the tip.

 

[Shockwave]

Yes. But I get a break in the squelch on my scanner at 155.310 MHz when if I key up on ch 26.
The radio has been out to repair 4 times between two different shops. It was explained what I am seeing on my scanner, and saw no spurs or harmonics on either of their scopes. I am sure it is just a proximity issue. The antennas are only about 2' apart. But I still want to do all I can to make sure my signal is clean. I don't need to be driving by a police car and have "501 state of Maine" coming in their squad car.

155.310 divided by 27.265 is 5.69. That tells me there is no harmonic relation between these two frequencies and the low pass filter on the CB should do little to help.

On the other hand, a high pass filter inline with the scanner antenna is much more likely to help reduce the interference. You're probably just overloading the wide band front end in the scanner. This filter should cut the HF RF hitting the scanner front end by at least 60 db.

If you use the scanner below the cutoff frequency of the typical high pass filter, consider making a 27 MHz. trap for the scanners antenna input.

 

[roadrage]

155.310 divided by 27.265 is 5.69. That tells me there is no harmonic relation between these two frequencies and the low pass filter on the CB should do little to help.

On the other hand, a high pass filter inline with the scanner antenna is much more likely to help reduce the interference. You're probably just overloading the wide band front end in the scanner. This filter should cut the HF RF hitting the scanner front end by at least 60 db.

Thanks, I'll give it a try. Like I said, I am pretty sure it is a proximity issue. That is a bunch of power and not a lot of room between antennas. I am just really anal about transmitting a clean signal. I preach it all the time and don't want to be hypocritical, lol.

 

[roadrage]

155.310 divided by 27.265 is 5.69. That tells me there is no harmonic relation between these two frequencies and the low pass filter on the CB should do little to help.

On the other hand, a high pass filter inline with the scanner antenna is much more likely to help reduce the interference. You're probably just overloading the wide band front end in the scanner. This filter should cut the HF RF hitting the scanner front end by at least 60 db.

If you use the scanner below the cutoff frequency of the typical high pass filter, consider making a 27 MHz. trap for the scanners antenna input.

I took a drive last week, to go to camp. I was about 30 miles out of town, in the woods. My Galaxy radio (ch 26) was no longer interfering with the 155.310 scanner/radio. Even with my amp on, I didn't get as much as a flutter on the S-meter. On my way back, I got a few miles from town and gave it a try. I keyed up on 26 and got signal on the 155.310 again.

I was up to camp again today and was curious if it was a fluke. Same thing. No effect from the Galaxy to the 2M I use as a scanner until I got close to town.

I believe the police are using a repeater. Budget cuts in town eliminated our local PD dispatch. Dispatch is now run through Bangor, the nearest city, 65 miles away. Could that have something to do with it? For whatever reason, I get away from town a few miles and suddenly there is no bleed over. I don't know if it is related, but I do notice that when I get within about 1/2 mile from the police station (also next door to the fire station) my CB gets S-7 of static. Even my truck's stereo loses reception and only gets static. Any thoughts?