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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 2022, 23:04 3 3,626 on 1/2/22
VHF/UHF FM Voice? Dec 17th 2020, 22:17 4 6,592 on 31/12/20
My first radio- Gifted to me... RS HTX-202 Oct 11th 2020, 22:57 3 5,406 on 16/10/20

Latest Posts

Topic Author Posted On
Gasoline/LPG generator for use with a radio trailer KI7GJG on 3/6/23
I would suggest a PM (permanent magnet) excited generator. They are less affected by fluctuating inductive loads. This would also reduce the likelihood of RF interference.
The field excited generator might introduce RF into the output, as well.
I learned this from using a field excited generator to power through a UPS. The inductive load of the UPS switching in and out set up an oscillation, causing the UPS to switch online/offline/online....
Antenna to Tower separation distance dan_spence@me.com on 16/4/23
Is your Yagi polarized vertically or horizontally? If horizontally, the mutual induction from the vertical to the horizontal Yagi antennas shouldn't be a issue.
End fed questions Tscott78738 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?

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