Firestik MURS45 / Wouxon KG805M SWR

[fremont]

Used a fender mount (with NMO adapter and SS spring) to install Firestik MURS45 on truck.  Attached to Wouxon KG805M and used a Surecomm SW-33 meter.  Got reading of 19.9 SWR on "Blue" (154.570).  Would you chalk this up to "HTs give wacky readings*," lack of ground plane, etc?  (* I love Surecomm's instructions, e.g., hold vertical, place BOTH hands on meter then depress PTT...... feels like ham Twister.)

[WRAM370]

And just for some general information for other folks looking to use a similar antenna like the Firestik antenna you have, and are relatively new to radio operations...

-3/8x24 mounts are not ideal for VHF and UHF frequencies. They are fine for HF frequencies (like CB). That is why you don’t find a lot of V/Uhf antennas made with 3/8x24 studs.

-The instructions/recommendations you posted from We Are CB refer to using 18 feet of quality coax. That is a generalization commonly applied in the world of CB radio usage, but that is not really necessary, as you should only use as much coax as is needed from the radio to the antenna, but I understand not everyone is comfortable in cutting coax and soldering on connectors. It is a skill worth learning. 

-The NMO mount you are attaching to your vehicle is actually the best mount to use for V/Uhf, and there are many inexpensive VHF and UHF (and dual band) NMO antennas, so those would probably be better options for most people in these applications (MURS/GMRS). The PL type mount is also fine, and widely used in ham radio applications, but when we get to GMRS frequencies, the NMO is better.

-If you feel the need to have a spring on your antenna to endure strikes from tree limbs, etc., antenna companies like Larsen and others do make V/Uhf antennas with spring bases, that have been factored into the design for the operating frequencies.

-There is an antenna manufactured by Comet antenna (CA-2x4SR) which is designed to cover both MURS and GMRS (as well as the amateur 2m and 70cm bands), which is available in a PL (PL-259) mount or NMO mount.

-Proper grounding/bonding of an antenna system to a vehicle is an important component in the installation. Google “K0BG.com” for excellent info on mobile antenna installations  (that is K zero BG).

 

 

[wayoverthere]

14 minutes ago, WRAM370 said:

-If you feel the need to have a spring on your antenna to endure strikes from tree limbs, etc., antenna companies like Larsen and others do make V/Uhf antennas with spring bases, that have been factored into the design for the operating frequencies.

-There is an antenna manufactured by Comet antenna (CA-2x4SR) which is designed to cover both MURS and GMRS (as well as the amateur 2m and 70cm bands), which is available in a PL (PL-259) mount or NMO mount.

 

One small note on the 2x4sr: they don't come with a spring out of the package, but comet does offer a spring kit sized to replace the bottom bit of whip without affecting the tuning.

Haven't used mine on MURS, but it's done well for ham and gmrs.

[marcspaz]

For spring protection when offroad, I use the Comet SBB-1.  Its basically a taller rubber-ducky antenna good for 60w.  100% flexable and works great for MURS, 2m, 70cm, and GMRS.

 

[fremont]

First off, @marcspaz and @mbrun, I really appreciate the patience and help.  On the PL-259 end, I have continuity between shield and pin; same for outer nut and NMO center pin.  I didn't bother with removing the mount; new coax/NMO on order.  Thanks again.  (PS  Since this was a first for me--using a MM on coax--I did the three tests--pin-to-pin, shield-to-shield, shield-to-pin--on a new PL259/PL259 cable and it passed with no continuity on shield-to-pin.)

[fremont]

4 hours ago, WRAM370 said:

 

4 hours ago, WRAM370 said:

 

-The NMO mount you are attaching to your vehicle is actually the best mount to use for V/Uhf, and there are many inexpensive VHF and UHF (and dual band) NMO antennas, so those would probably be better options for most people in these applications (MURS/GMRS). The PL type mount is also fine, and widely used in ham radio applications, but when we get to GMRS frequencies, the NMO is better.

-If you feel the need to have a spring on your antenna to endure strikes from tree limbs, etc., antenna companies like Larsen and others do make V/Uhf antennas with spring bases, that have been factored into the design for the operating frequencies.

-There is an antenna manufactured by Comet antenna (CA-2x4SR) which is designed to cover both MURS and GMRS (as well as the amateur 2m and 70cm bands), which is available in a PL (PL-259) mount or NMO mount.

 

 

 

I understand now the issue of an add-on (vs. integral) spring.  What about a 3/8x24-to-NMO adapter (assuming the use of an antenna with a 3/8x24 base)?  Does its height play into the equation at all as far as increasing SWR?

 

 

[marcspaz]

Everything that adds height about the ground (in this case the mount itself) adds height/length to the antenna, thus impacting SWR.

[fremont]

Again, thanks to everyone who lended a hand.  Jeff Bezos dropped off a new coax and NMO mount.  Given the last few days, I first checked them with a MM and they were good to go.  Here are the SWRs using 1) Wouxon KG805M MURS and 2) TK-8180 (std; not H model) GMRS frequencies using SW-33 Surecomm.

KG805M to MURS45 with 3-4" SS antenna spring and 3/8x24 stud-to-NMO adapter:  1.44     Without spring (only stud-to-NMO adapter):  1.04

I first checked TK-8180 fwd power with dummy load:  4.2w Low; 25.0w High

TK-8180 to Tram 1181 dual band:  Ch 7 (Low) 1.01*  Ch 21 (High) 1.47

TK-8180 to Laird GMRS ghost:  Ch 7 (L) 1.01*    Ch 21 (H) 1.94

* Is "1.01" as low as the SW-33 will go?

 

Edited January 24, 2022 by fremont
KG not HG805M

[mbrun]

Looks like have made great improvement. Can’t speak to ‘1.01’ being as low as the 33 can go, but 1.00:1 is lowest theoretically possible value you could possibly achieve.

Looks like you are getting some good numbers now. Enjoy.


Michael
WRHS965
KE8PLM

[wayoverthere]

6 hours ago, fremont said:

* Is "1.01" as low as the SW-33 will go?

 

I'll try to poke at mine tonight, see what it shows with the dummy load. I know the sw102 is showing 1.04 with the new 60 watt rated dummy load, I think I remember the 5 watt showing 1:1...we'll see what i find.

edit: tested across both dummy loads (5 watt and 60 watt) and both meters (sw33 and sw102)...channels 1 and 21RP, on my kg805g.

sw33: 1.01 on the 5 watt, 1.26 on the 60 watt.

sw102: 1.05 on the 5 watt, 1.0 on the 60 watt

appears the sw33 does not display lower than 1.01, as far as i'm seeing.

Edited January 24, 2022 by wayoverthere
added test results