SWR on DB20-G

[Newb]

I have a DB20-G, a Browning BR-450 mag mount and am using a Workman Mod.104 SWR/Power meter. I am on my second intermediate antenna rod section trying to get my SWR below 1.75:1. Any suggestions. When the SWR gets below 2:1, I take off 1/16 inch at a time.  When I get below 1.75:1 another 1/16 inch puts me back to 2:1.

Any suggestions?

[FrostyFruits]

Where is the antenna mounted? Are you cutting the bottom section or the top section? What frequency are you trying to tune for? Are you in a vehicle or on a power supply?

[Newb]

In the center of the cab on a full size crewcab pickup. The instruction say to cut the bottom section.  467.6000.  In the vehicle.

[SteveShannon]

That may just be the best you can achieve with that combination of antenna, mount, and feed line. 
Did you check to see what the SWR was at the original designed frequency?

[Newb]

The antenna didn't have any doc on designed freq out of the box. The as supplied SWR out of the box was 5:1.  ?The antenna is a 5/8 over 5/8. Can the top section be trimmed or will the screw with the gain?

[SteveShannon]

26 minutes ago, Newb said:

The antenna didn't have any doc on designed freq out of the box. The as supplied SWR out of the box was 5:1.  ?The antenna is a 5/8 over 5/8. Can the top section be trimmed or will the screw with the gain?

Everything affects everything with antennas. I have no idea if the top can be trimmed. I would stop at 1.75:1 and live with it for a while to see how well it works. 

[wayoverthere]

1 hour ago, Newb said:

The antenna didn't have any doc on designed freq out of the box.

Btwr lists it as pretuned for 450-470.  With it starting out that bad on 467.(anything),  it makes me wonder if it was really bad to start with, if there's something up with the feed line, or the meter.

Do you have a dummy load to check the meter with? Failing that, or along with, I'd be tempted to grab a 450-470 rated 1/4 wave and see what that reports. They're only around $10, and may be good to have for limited clearance situations.

[FrostyFruits]

Is your feed line pinched through a door? Do you have the radio pos and neg hooked up to battery? Are you testing with doors open or closed? Engine running or off? 

[Newb]

wayoverthere, Just now got a dummy load coming for UHF.  Will pickup a 1/4 wave to try.

FrostyFruits, The feed line is running through the rear cab window which is down far enough to get the PL259 trough. This is a new radio and a new truck. The radio came with a lighter plug so for now that's how it's running. If this radio works for me I will put Anderson Power Poles on it and attach it to the master feed in the cab.  The ground system in GM trucks after 1999 is not good to attach directly to the battery, too much alternator interference because the alternator feed goes to the battery.  Doors closed engine running.  This isn't my first rodeo with antennas, just my first one with UHF.

[Newb]

Found this on eBay. I would be using the upper table, no spring, and a dimension between 11 and 1/4 and 11 and 9/16.  I'm at 11 and 3/4. If I cut 1/16 off, I am almost at 2 SWR. I already have an intermediate rod at 11 and 9/16 that gives an SWR of above 2.

[wayoverthere]

30 minutes ago, Newb said:

Found this on eBay. I would be using the upper table, no spring, and a dimension between 11 and 1/4 and 11 and 9/16.  I'm at 11 and 3/4. If I cut 1/16 off, I am almost at 2 SWR. I already have an intermediate rod at 11 and 9/16 that gives an SWR of above 2.

It's hard to tell, but the model number at the top of the chart looks like it ends in a 3, leading me to think it's intended for a different model (possibly with different length above the phasing coil or in the base).

Also did some googling and had zero luck turning up a cutting chart for the br-450

[SteveShannon]

If you’re trying for perfection, you’re fighting a losing battle.  Raising the antenna might affect impedance and thus SWR.  Lowering the antenna might affect impedance and thus SWR.  The size of your ground plane will affect SWR.  The length of your feedline can affect SWR. The length of the element isn’t the only variable.

You can even have near perfect SWR and still have an antenna that nobody can hear.  SWR is important. High SWR is to be avoided because of the power that’s reflected back into your transmitter, but 1.75 isn’t high SWR. 

[Newb]

I thank you guys for all the help! This is a GREAT forum for help. I will check my Workman meter as soon as my dummy load arrives. I'm still looking for Browning cutting specs for my Model BR-450.  Hope this entire convo helps someone else also. Appreciate all your help!  3's from WRQD330!

[Newb]

So I found the box that the antenna shipped in from Amazon. In the bottom corner stuck to a tail on the shipping tape was a plastic bag with a business card from the vendor AND a trim card!  I have marked the freqs I am looking for and all the info for the antenna I have.  It looks the same as the one I found on eBay except it has my model #.  It doesn't make any difference but it does verify the specs.

[wayoverthere]

15 minutes ago, Newb said:

So I found the box that the antenna shipped in from Amazon. In the bottom corner stuck to a tail on the shipping tape was a plastic bag with a business card from the vendor AND a trim card!  I have marked the freqs I am looking for and all the info for the antenna I have.  It looks the same as the one I found on eBay except it has my model #.  It doesn't make any difference but it does verify the specs.

Good find! And yeah, while it differs a little at the ends, it agrees where you're aiming (465). Will be interesting to see what the numbers look like with the dummy load, too.

[Newb]

The dummy load has shipped and should be delivered tomorrow. I'll keep you informed.

[FrostyFruits]

8 hours ago, Newb said:

wayoverthere, Just now got a dummy load coming for UHF.  Will pickup a 1/4 wave to try.

FrostyFruits, The feed line is running through the rear cab window which is down far enough to get the PL259 trough. This is a new radio and a new truck. The radio came with a lighter plug so for now that's how it's running. If this radio works for me I will put Anderson Power Poles on it and attach it to the master feed in the cab.  The ground system in GM trucks after 1999 is not good to attach directly to the battery, too much alternator interference because the alternator feed goes to the battery.  Doors closed engine running.  This isn't my first rodeo with antennas, just my first one with UHF.

Just checking, gotta get all the details when trying to help. It's amazing what a small issue will cause. Do you have anyone close with a radio you can throw the antenna on or use their antenna?

[Newb]

I live in a small town so I haven't talked to anyone yet. Don't know anyone in town with GMRS but am watching for antennas. Good thought!  I was hesitant to transmit with a 1.7 because I have seen talk in other forums about roasting radios with SWR of 2.  I'm used to CB where 1:1 is no uncommon for me.  I my check it out today with a proper radio check call.

[Newb]

The dummy load arrive. The SWR meter shows 1.3:1 with the dummy load.  I would say the Workman meter is at fault.  So instead of 1.75:1, I would say I'm looking at 1.45:1 if the error is linear.  Haven't been able to find anyone in my area to talk to on the radio for a radio check.  We are expecting strong storms in the area this afternoon so I'm not sure how successful I will be in talking to anyone.  The 1/4 wave antenna should be here tomorrow.

[wayoverthere]

32 minutes ago, Newb said:

The dummy load arrive. The SWR meter shows 1.3:1 with the dummy load.  I would say the Workman meter is at fault.  So instead of 1.75:1, I would say I'm looking at 1.45:1 if the error is linear.  Haven't been able to find anyone in my area to talk to on the radio for a radio check.  We are expecting strong storms in the area this afternoon so I'm not sure how successful I will be in talking to anyone.  The 1/4 wave antenna should be here tomorrow.

Yeah, very good sign the meter is off, as a dummy load should basically be at or very close to 1:1 swr. Does it have an option for calibration?

[Newb]

The meter is analog so I will have to look for a calibration hole in the case.

[SteveShannon]

Here’s the instructions for that Workman 104:

[Newb]

Excellent. The access hole in the rear of the meter was for the wattage. I opened the box and found a capacitor with long leads soldiered to the input (radio) side that was bent at a right angle.  With the dummy load attached, and the meter set to infinity on the forward setting of the switch, move the switch to SWR and bent the cap until the needle just barely moved.  Switched back to set position and was still at infinity. Reattached the antenna to the meter and checked for infinity.  Switched to SWR and the reflected number on the meter with the antenna was 1.2:1 ON 467.625 slightly less on 462.625.  I think I'm good.  I saw 18 watts which I think I question from a 20 watt radio. I think my next investment is a better meter.

[wayoverthere]

17 minutes ago, Newb said:

Excellent. The access hole in the rear of the meter was for the wattage. I opened the box and found a capacitor with long leads soldiered to the input (radio) side that was bent at a right angle.  With the dummy load attached, and the meter set to infinity on the forward setting of the switch, move the switch to SWR and bent the cap until the needle just barely moved.  Switched back to set position and was still at infinity. Reattached the antenna to the meter and checked for infinity.  Switched to SWR and the reflected number on the meter with the antenna was 1.2:1 ON 467.625 slightly less on 462.625.  I think I'm good.  I saw 18 watts which I think I question from a 20 watt radio. I think my next investment is a better meter.

progress  

power wise, that's about par for these radios, and it lines up with what myself and others have seen from the same model, or its anytone twin (at779uv).

[Newb]

Again, Thanks for the help!  Greatly appreciated! 3s from WRQD330.

[donniefitz2]

The power you're getting is the same as what both of mine read. The radio puts out 18 watts on 467 and 462. It puts out more at lower UHF frequencies (20 watts mostly) and 25 on most VHF frequencies.