I may have screwed up!

[bigloudvtwin]

Ok a couple questions. I'm a total rookie and tend to leap before I look or (in this case read). I built both of these yagi's. 70 cm and 2 meters. My reasoning for building 2 instead of a single dual band was good band coverage for each. My MFJ bridge confirms the 2 meter one has nice flat swr across the band and my FT857D (I don't have a UHF annylizer) shows nice swr range for the 70 cm one.
First...should I have put a balun at feed point for both of these?
Second....They are exactly 24" apart on the mast, is the 70 cm beam on top interfering with the 2 meter radiation pattern?
The 2 meter antenna is fed with LMR 400 (direct fed)
and the 70 cm antenna is fed with RG8x (direct fed as well)
Obviously they are on a rotator and approx. 32' up.
Thanks ahead of time from a stubborn rookie.
73
KG7GUM

 

[Captain Kilowatt]

That spacing may cause a little interaction but not likely much. You say they are direct fed but I see what appears to be a gamma match on the 2m yagi. Direct feed is simply splitting the coax and connecting the ends to the driver element. If that is a gamma match then you do not want a balun. Usually at UHF a balun will introduce more losses than any impedance matching device.

 

[bigloudvtwin]

That spacing may cause a little interaction but not likely much. You say they are direct fed but I see what appears to be a gamma match on the 2m yagi. Direct feed is simply splitting the coax and connecting the ends to the driver element. If that is a gamma match then you do not want a balun. Usually at UHF a balun will introduce more losses than any impedance matching device.

Ok thanks CK. Yes the 2 meter yagi has a gamma match. The 70 cm is as You say direct fed. I can't seem to reach anyone via the repeaters I'm picking up. Of course my radio is only showing at most s3 when I in on the signals with the rotator. I also might not be programming my radio correctly. I wish I had an "Elmer". {Cry_river}

 

[Captain Kilowatt]

Repeaters? :blink: You need vertical polarity for those. You are seeing around 25 dB loss by having your antennas horizontal. I thought you were setting them up for 2m/70cm SSB or such. That mode uses horizontal antennas but FM into repeaters uses vertical. HUGE difference in signal when you are the wrong polarity. That S-3 would be S-9++ if you flipped those antennas to vertical. Also you may not have the proper access tones programed if those repeaters require them.

 

[Road Squawker]

(edit).... I can't seem to reach anyone via the repeaters I'm picking up... I wish I had an "Elmer". {Cry_river}

well, you are losing a LOT of signal (both ways) due to X polarization to a vertical repeater antenna.

can you actually "open" the repeaters receiver? in other words,.. do you have the proper PL tone/offset?

 

[Road Squawker]

Repeaters? :blink: You need vertical polarity....

Dayum,..... we "doubled" on both issues**Jump_im**

 

[bigloudvtwin]

Repeaters? :blink: You need vertical polarity for those. You are seeing around 25 dB loss by having your antennas horizontal. I thought you were setting them up for 2m/70cm SSB or such. That mode uses horizontal antennas but FM into repeaters uses vertical. HUGE difference in signal when you are the wrong polarity. That S-3 would be S-9++ if you flipped those antennas to vertical. Also you may not have the proper access tones programed if those repeaters require them.

Ha! Thank you very much! I'm dragging both of those down today and flipping em. Yes I am sending the tones to open up the repeaters (I'm pretty sure). I look them up on the internet or My radio searches for the tone for me and let's me know when it hits. You've been a big help. I am joining the local club (MCARC) so I should have local help soon!

 

[bigloudvtwin]

Dayum,..... we "doubled" on both issues**Jump_im**

Thanks Got it! Double!

 

[KC9Q]

Capt,

I think the 'direct feed' implied that there are two coax runs: LMR-400 for the 2-Meter, and RG-8X for the UHF antenna.

Something else to take into account: Bigloud, you are feeding the 144 MHz antenna with a lower loss cable than the UHF antenna. If anything the UHF antenna should have the LMR-400 and the 2-Meter have the RG-8X. Actually, they should both use LMR-400. if possible

Did you use LMR-400 directly to the 2-Meter antenna? Concern is: LMR-400 uses a solid center conductor that will stress and break over time with repeated rotations with the rotor. There should be a 6 ft jumper of coax with a stranded center conductor (i.e. RG-213/U or LMR-400UF) to allow for antenna rotation.

Just something to think about.

73,
Mike

 

[bigloudvtwin]

Repeaters? :blink: You need vertical polarity for those. You are seeing around 25 dB loss by having your antennas horizontal. I thought you were setting them up for 2m/70cm SSB or such. That mode uses horizontal antennas but FM into repeaters uses vertical. HUGE difference in signal when you are the wrong polarity. That S-3 would be S-9++ if you flipped those antennas to vertical. Also you may not have the proper access tones programed if those repeaters require them.

Flipped em both. Made a contact immediately on the local repeater. RX went from s2-3 to s8-9. Bad thing is... now my swr is way up on both antennas! I had them down below 1.5:1 in the middle of the bands. Now Im lucky to be below 2:1. I can't believe this! :angry:

 

[bigloudvtwin]

Repeaters? :blink: You need vertical polarity for those. You are seeing around 25 dB loss by having your antennas horizontal. I thought you were setting them up for 2m/70cm SSB or such. That mode uses horizontal antennas but FM into repeaters uses vertical. HUGE difference in signal when you are the wrong polarity. That S-3 would be S-9++ if you flipped those antennas to vertical. Also you may not have the proper access tones programed if those repeaters require them.

Made contact on 2 meters as soon as I flipped the antennas. Things are looking up. Kinda. Now my swr is way up on both antennas! Darn it. I had them tuned well before. I'm assuming it is the metal mast they are bolted to. it is not grounded but probably acting as a giant reflector element? This is driving me crazy.

 

[Moleculo]

Bad thing is... now my swr is way up on both antennas! I had them down below 1.5:1 in the middle of the bands. Now Im lucky to be below 2:1. I can't believe this! :angry:

If your mast is metal, you're going to interfere with both the radiation pattern and probably the SWR of both antennas. Swap out at least the part of the masts that goes directly through the yagis with some fiberglass mast and you should see improved results.

 

[Captain Kilowatt]

I haven't been able to follow this thread too closely as I am on my phone at work (I'm out of here in 40 minutes. YEAH!) but yeah, the metal mast will mess with things for sure. I guess I misread which coax was going to which antenna but I agree. Get the lower loss cable on the 70cm antenna and use something flexible around the rotator.

 

[GnG8d]

No bigger than they are, I would put a horizontal boom on the mast, and then one of the vertical yagis on each end of that boom. Stacked verticals per say.

 

[bigloudvtwin]

Capt,

I think the 'direct feed' implied that there are two coax runs: LMR-400 for the 2-Meter, and RG-8X for the UHF antenna.

Something else to take into account: Bigloud, you are feeding the 144 MHz antenna with a lower loss cable than the UHF antenna. If anything the UHF antenna should have the LMR-400 and the 2-Meter have the RG-8X. Actually, they should both use LMR-400. if possible

Did you use LMR-400 directly to the 2-Meter antenna? Concern is: LMR-400 uses a solid center conductor that will stress and break over time with repeated rotations with the rotor. There should be a 6 ft jumper of coax with a stranded center conductor (i.e. RG-213/U or LMR-400UF) to allow for antenna rotation.

Just something to think about.

73,
Mike

Thanks mike. Yes I know the lower loss cable should go to the higher loss freq antenna but, it wouldn't reach. LOL This whole conglomeration is completely temporary for experimental purposes and because I can't shell out the $ for the mast I want at the moment. I think I'm gonna have to go to wal mart and buy a rake or some tool with a F. Glass handle! My problem is I knew that damn metal mast was gonna present issues and I still did it anyways! Ain't it fun being a man?!!