Odd reverse swing problem

[techman]

Hello all!

I've been experiencing an odd issue with my mobile setup, and came here in the hopes that someone may be able to explain to me what is happening.

My mobile radio is a Uniden 520 (tuned and aligned by Sparky's). I use a D104-M6B microphone, and the radio is run into a Palomar 250 (Yellow face, class AB1). The antenna is a Larsen NMO27C on a Larsen trunk-lip mount.
The Palomar amp is wired directly to the battery with 10AWG wire, and has a short 10AWG ground to a seat bolt.

I attempted to measure the RMS power output of the amplifier using a Dosy 4001 meter. When I power off the amplifier and run the radio directly into the meter, I see about a 5.5 watt RMS deadkey with a small amount or forward swing. When I turn the amplifier on, I begin to see reverse RMS swing on the Dosy (no more than 10 watts reverse from deadkey). What puzzles me is that if I replace the antenna with a dummy load, I begin to see forward RMS swing on the meter, even with the amplifier on.

One other interesting point of note: I asked a friend about 2 miles away to watch his signal meter while I was transmitting with the amp turned on and he reports that I do have forward swing on his radio's meter.

My question then, is the following:
Given the situation, does it seem that there is indeed a problem with my equipment, or is the meter simply giving inaccurate measurements when connected to my antenna?

Any pointers are greatly appreciated. I just want to ensure that my setup is operating as efficiently as possible!

 

[SmackDown]

I'd add a larger ga. wire to that 10ga. about 6 inches outside the box. I'd get a 60 amp fuse put it inline and run both wires to the battery for starters.
Next time you key up as it is, feel the length of 10ga. and you'll understand why I made the suggestion.

3's

 

[MrSuburban]

Hello all!

I've been experiencing an odd issue with my mobile setup, and came here in the hopes that someone may be able to explain to me what is happening.

My mobile radio is a Uniden 520 (tuned and aligned by Sparky's). I use a D104-M6B microphone, and the radio is run into a Palomar 250 (Yellow face, class AB1). The antenna is a Larsen NMO27C on a Larsen trunk-lip mount.
The Palomar amp is wired directly to the battery with 10AWG wire, and has a short 10AWG ground to a seat bolt.

I attempted to measure the RMS power output of the amplifier using a Dosy 4001 meter. When I power off the amplifier and run the radio directly into the meter, I see about a 5.5 watt RMS deadkey with a small amount or forward swing. When I turn the amplifier on, I begin to see reverse RMS swing on the Dosy (no more than 10 watts reverse from deadkey). What puzzles me is that if I replace the antenna with a dummy load, I begin to see forward RMS swing on the meter, even with the amplifier on.

One other interesting point of note: I asked a friend about 2 miles away to watch his signal meter while I was transmitting with the amp turned on and he reports that I do have forward swing on his radio's meter.

My question then, is the following:
Given the situation, does it seem that there is indeed a problem with my equipment, or is the meter simply giving inaccurate measurements when connected to my antenna?

Any pointers are greatly appreciated. I just want to ensure that my setup is operating as efficiently as possible!

OK a couple of things your deadkey( when you talk no modulation) of radio sounds like it is too high for the amp which will make it backswing. Don't know why you see forward swing with dummy load but, Dosy's are a cheap meter personally i would not use one if you gave it to me. Secondly RMS is not the correct term you are reading avg power. I would try a different radio that you can adjust the deadkey to about 2-3 watts or turn that one down

 

[loosecannon]

dont run your negative wire all the way to the battery unless you think your car is all rusted up. if you have the negative wire going to a good chassis/frame grounding point; the vehicle will work better than a 10ga. wire any day.

you should have the positive wire going to the battery and a fuse (for fire protection!) should be added right at the battery connection.

you definitely have too high a deadkey for that amp, and i believe you are sending the amp into self oscillation which would account for the back swing and the different readings from the dummy load.

that amp wants about a 1.5 to 2 watt deadkey. no more.

you are putting 5.5 watts deadkey into it and sending it into oscillations.

if you have sparky do your work for you, tell him to lower the deadkey to 2 watts, but let it swing as high as it does now.
he can do that for you easily.

if you want to do it yourself, find a sticky thread on this forum called "need to lower deadkey to 2 watts".

LC

 

[9C1Driver]

Bingo, that 5.5 watt dead key input is whats causing the backwards swing. Do like the guys have suggested and it will be fine.

 

[Turbogus]

On my base rig, Cobra 142GTL (yeah, I know, it's an ancient P.O.S. as I've heard so often in these forums) :sneaky2: and a shop added a potentiometer to the side of the case so I could tune down the radio when using the brick. Unbeknownst to me when I bought this rig it had an updated extra wattage final. Learned the hard way as I overdrove the brick once, but luckily it was an easy repair.

 

[hotrod]

ya definately way too high deadkey also check your swr
on antenna with another meter [no dosy] or even better yet
a mfj 259. i say this cause when u used a dummy load you seen
forward power not reverse. and we all know a dummy load is a perfect
50 ohm load or sopposed to be. now i could be wrong and mayber i am
but really got me wondering when you put the dummy load on .imho
i think you should,ve seen same results with your antenna as you
did the dummy load.but definately the dead key is way too high
thats 1 issue

 

[hotrod]

On my base rig, Cobra 142GTL (yeah, I know, it's an ancient P.O.S. as I've heard so often in these forums) :sneaky2: and a shop added a potentiometer to the side of the case so I could tune down the radio when using the brick. Unbeknownst to me when I bought this rig it had an updated extra wattage final. Learned the hard way as I overdrove the brick once, but luckily it was an easy repair.

if you think your 142 is a P.O.S I will gladly take it off of your hands

 

[VA3ES]

[...]The antenna is a Larsen NMO27C on a Larsen trunk-lip mount.

Once you get your rig adjusted to a lower dk, you will want to change out your antenna. The Larsen NMO27 was designed for commercial low-band use. Typical use is logging companies, and other businesses in rural areas. The NMO27 is perfect for that as it's comparatively short (49" whip) and easy to maintain. The local land-mobile company doesn't want to change out that antenna every week.

What you want is an NMO30 coil, with a 64" whip. You can order this from any Larsen dealer. the coil is the NMO30 coil, the whip is the W640 whip. You might need the spring depending on your mounting situation: SPRING. These are all available in black or grey. The difference in the new antenna is astounding. I run an NMO30/64" whip combo, and I get amazing reports. The total length of the system is about 70", same as the Wilson 1000, and performs about the same.

For 10M use, order the NMO34 coil; same whip.