ARRL

Login Help

KJ7WUZ

Joined: Tue, Mar 31st 2020, 15:11 Roles: N/A Moderates: N/A

Latest Topics

Topic Created Posts Views Last Activity
Stacking verticals on single mast. Jan 31st, 23:04 3 1,031 on 1/2/22
VHF/UHF FM Voice? Dec 17th 2020, 22:17 4 3,646 on 31/12/20
My first radio- Gifted to me... RS HTX-202 Oct 11th 2020, 22:57 3 2,636 on 16/10/20

Latest Posts

Topic Author Posted On
End fed questions tscott on 5/3/22
I am purchasing a 5W QRP radio kit for 40m recently featured in the Feb 2022 QST review column. I am a newly licensed Tech that wants to learn and use CW for portable operation. Would an EFHW be the antenna for this?

Should I attempt a homebrew EFHW or just go with say, a Par EndFedz 40?

I fear the Par may not be long enough, designed for the 40m band and the CW segment I am allowed to operate in is the very lower end of the band. (i have used a Par EndFedz SWL to listen for years and love it).

Thank you, and 73
Dave KJ7WUZ
Stacking verticals on single mast. KJ7WUZ on 1/2/22
Thank you, W1VT and noted! I will look into the diplexers and check used market for a source. I will post my results after trying the solutions provided.
Stacking verticals on single mast. KJ7WUZ on 31/1/22
Landed my Technician ticket 9 months ago.

Comet CX-333 (VUF/UHF) antenna at top of mast.

Comet CA-712EFC (GMRS) antenna mounted directly below and tip 12 feet below the ground plane of the CX-333.

I have researched the topic and found that UHF separation of antennas should be minimum of 10 feet, radiation center to radiation center. BUT... the references are for dipole antennas.

The antennas I am using are high gain (6-9dBi) collinear, hence I was thinking of putting at least 10 feet between ENDS of the antennas.

I am concerned that the lower antenna will induce common mode current onto the outer surface of the shield of the feedline to the upper antenna due to close proximity and mutual inductance. Is this a possibility?

The same documents show horizontal separation would need to be around 10x greater, which on my small lot is not feasible (not to mention the expense and loss to get the feedlines the length needed.

I have not yet found a high-Q low-pass filter, and probably won't be able to since the UHF radio reaches 450MHz and the GMRS starts at 462.550MHz.

Can this be mitigated by using ferrite bead chokes of the proper mix at the upper antenna and perhaps just below the ground plane of the lower antenna? Or am I trying to locate the "Holy Grail" with this?
Newbie - Antenna Mast, Antennas, etc KY4RWW on 31/1/22
I have tried vertically stacking a Comet CX-333 VHF/UHF and Comet CA-712EFC (GMRS) antennas on a mast following the suggestions of multiple documents. The documents seem to be geared toward folded dipole or dipole antennas, however. What I failed to consider is that my antennas are actually collinear antennas. The separation distance is different from the dipoles, in that the collinears are stacked 1/2 (or 1/4) waves and radiate along the entire 10ft length. With the antennas 10 ft center-center the GMRS radio below the VHF/UHF causes the VHF/UHF radio to open squelch when it transmits. I am trying the separation of 10 feet from end to end between them rather than center to center. The other consideration may be the creation of common mode current in the upper vertical antenna's coax shield by the lower antenna when it radiates (transmits). I will be trying ferrite common mode chokes around the upper antenna's coax at the antenna and just below the ground plane of the lower antenna. If this doesn't work the separate masts it is. I have not been able to find a low-pass filter commercially available with a sharp enough Q to filter the GMRS out of the UHF antenna system.
Stupid question about braided shield K7RRD on 31/1/22
W1VT has given the methodology I have used in the past. I suppose a dental pick may also serve.

Back to Top

EXPLORE ARRL

Instragram     Facebook     Twitter     YouTube     LinkedIn