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Power change...explain why?

The Jerk

Active Member
May 6, 2008
647
58
38
Reading, PA
Here's the deal...I ended up with a Fatboy 5-pill. Installed it a couple weeks ago using a DX959 (DTB-tuned), RG-8 coax, and a 102" whip (SWR 1.1:1). I was getting between 100 and 125 dead key and 400 to 450 watts of swing (using a Dosy meter)...which I thought was about ideal.

Saturday I changed the setup slightly, I wanted to step back to a simpler radio (I hardly ever use SSB on the 959 because of the way the amp switches to SSB delay) and a different mounting location (front console to floor) because of a child's car seat.

I installed a PC76 (DTB-tuned) with a piece of Mini-8 to the amp, RG-8 to the meter, and RG-8 to the antenna. Barefoot, the PC76 shows less overall watts than the DX959 (by about half)...but the PC76 will get over 650 watts from a 100 to 120 watt dead key (as shown on the Dosy). There is NO swing kit in the PC76. I actually had to pull my intended meter from the setup (an Aries A-460) because its only rated for 500 watts (although it would read the 650 watts?).

What caused the change in swing? I see the only variable being the addition of a piece of Mini-8 between the radio and amp, and the radio?? Everything else is the same (the RG-8 is the same pieces I used with the 959, just rerouted). What is especially confusing is the fact the 959 shows more barefoot watts than the PC76...even when both are dialed into 100 watts on the amp.

Would this be a difference between a MosFet in the DX959 and a 1969 final in the PC76?
 

Here's what I'm seeing with the Aries A460 (before I pulled it from line, I actually did check the output to see what the DX959 was doing so I had a baseline for the PC76):

* DX959 with Mosfet - DK/swing 3.1/11.4 watts yielded approximately 100/400 output.

* PC76 with 1969 final - DK/swing 2.9/7.6 watts yields approximately 100/600+ output.

Again, I pulled the Aries because it is supposedly only rated for 500 watts.

:confused:
 
What was the input swr with each radio into amp? Possibly one is better matched. Meaning the impedance between the 2 matches better. Could be one is a harmonic turd.
 
I feel another SWR/ coax discusion coming on, wake me when it's over.


I thought the same thing, but...

The DX959 is now in front of a TS350HDV using a roof mounted Wilson 5000. And I'm experiencing the same thing...the DX959 shows more watts than the Uniden Grant it replaced, but the Grant gets more watts from the amp. Both radios were/are tuned by DTB, and the coax is all Belden RG-8X (I did not change any coax this time).

The Grant is doing 1.25 watts and swinging almost 5 watts...the DX959 is doing almost 2 watts and swinging to just over 10 watts. The Grant is a fixed output where the DX959 is variable, but the Grant will do about 50 watts and swing to over 200 watts where as I have the DX959 doing a dead key of almost 75 watts and it barely swings 200 watts (most times it appears to be around 175). And don't get me wrong, I'm not worried about the difference between the two setups, this is just simply observation.

In short a 1969 doing 1.25/5=50/200+ where a mosfet doing 2/10=75/200-. The SWR before and after are the same too...1.0:1 barefoot to 1.4:1 under power. This is using an Aries A460 SWR/watt meter...which are reported to be pretty decent.
 
It could be that the 76 and the grant are type accepted. And the 959 is not. Meaning more of your power could be on frequency. Just speculation though.
 
And more observations...

Took the truck out for the first time since installing the 76 and meter. I have several aftermarket gauges that monitor various things like pyro, oil pressure, trans temp, etc. Several would "go wild" when I would key the DX959 with the amp on. Now, only two react when I key the 76, and those don't react nearly as wildly as before.

I'm getting really good reports too, go figure.

I was under the impression the 959 was a type-accepted radio??
 
Here's the deal...I ended up with a Fatboy 5-pill. Installed it a couple weeks ago using a DX959 (DTB-tuned), RG-8 coax, and a 102" whip (SWR 1.1:1). I was getting between 100 and 125 dead key and 400 to 450 watts of swing (using a Dosy meter)...which I thought was about ideal.

Saturday I changed the setup slightly, I wanted to step back to a simpler radio (I hardly ever use SSB on the 959 because of the way the amp switches to SSB delay) and a different mounting location (front console to floor) because of a child's car seat.

I installed a PC76 (DTB-tuned) with a piece of Mini-8 to the amp, RG-8 to the meter, and RG-8 to the antenna. Barefoot, the PC76 shows less overall watts than the DX959 (by about half)...but the PC76 will get over 650 watts from a 100 to 120 watt dead key (as shown on the Dosy). There is NO swing kit in the PC76. I actually had to pull my intended meter from the setup (an Aries A-460) because its only rated for 500 watts (although it would read the 650 watts?).

What caused the change in swing? I see the only variable being the addition of a piece of Mini-8 between the radio and amp, and the radio?? Everything else is the same (the RG-8 is the same pieces I used with the 959, just rerouted). What is especially confusing is the fact the 959 shows more barefoot watts than the PC76...even when both are dialed into 100 watts on the amp.

Would this be a difference between a MosFet in the DX959 and a 1969 final in the PC76?
sounds like another case of pep confusion!sounds like the galaxy has higher dead key and the 76 has more modulation so your probably picking up modulation, reflected power or spurious emissions as pep power which is inaccurate.test it in average or rms and it will probably look a bit better.if you have any way of checking the modulation between the two the 76 will probably be higher.unless you have a scope i would forget about the pep crap.
 
Unfortunately, I don't have access to a dummy load...so that's not an option.

However, my Dosy does show "AM modulation", although I'm not 100% sure how accurate it is since it won't "set" at the 100% scale. It probably does provide a baseline...and using it as a baseline, the PC76 is showing a lot more modulation than the DX959, although still under that 100% modulation mark. Keep in mind, both of these radios were tuned by DTB, limiters are intact.

I guess my next question is, should I be concerned by the swing since that seems to be a little more than the capability of four 2879s (based on responses I have read on this forum)? I believe I would be in the 14 to 14.5VDC range based on what I have seen in the past from this charging system. But we are still talking more than 150 watt per device?

I do get good reports...
 
Unfortunately, I don't have access to a dummy load...so that's not an option.

However, my Dosy does show "AM modulation", although I'm not 100% sure how accurate it is since it won't "set" at the 100% scale. It probably does provide a baseline...and using it as a baseline, the PC76 is showing a lot more modulation than the DX959, although still under that 100% modulation mark. Keep in mind, both of these radios were tuned by DTB, limiters are intact.

I guess my next question is, should I be concerned by the swing since that seems to be a little more than the capability of four 2879s (based on responses I have read on this forum)? I believe I would be in the 14 to 14.5VDC range based on what I have seen in the past from this charging system. But we are still talking more than 150 watt per device?

I do get good reports...
did you test it on average power?or was that pep.
 

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