[MRCA] Fwd: SCR-274N with B-24 Antenna

Tue Jun 3 08:58:59 EDT 2025

Grounds wires / long cointerpoises cannot be used due to tripping hazards
for pedestrian foot traffic at the event.

I thought a ground rod would suffice, but apparently not.

Depending upon where I will be setting up in the tent, I can try and run a
wire around the tent perimeter.
I'm not sure I can do that;  it depends.

That's one of the challenges I'm facing.  I will be in a congested area
with high foot traffic.  Antenna space is at a premium.

I originally wanted to put up a CFZ or Invented VEE with the ends going to
other tents, but ran into issues with that.
No ground radials needed for those.
My next choice was the 45 foot wire and ground rod -- hoping I can run the
end of the wire down the tent exterior etc.

Last choice -- backup plan.... is my 80M Shark Mobile Antenna on a cake pan
in the corner with a counterpoise....  that does work.

Mark K3MSB

On Tue, Jun 3, 2025 at 4:51 AM Christopher Bowne <aj1g at sbcglobal.net> wrote:

> I agree with Mike, you absolutely need to have a counterpoise to work the
> wire antenna against.  A quarter wave of wire will present a nominal 35 -50
> ohm impedance against a counterpoise such as a vehicle body or a few
> radials on the ground or elevated radials.’  I have successfully used
> nominal quarter wave wires run in various arrangements from slopers to an
> NVIS configuration with the entire nominal 65 feet of wire parallel to the
> ground and only a few feet above it, attached to the feed point of my
> mobile antenna mount on my Tacoma, using the truck body as the coonterpoise
> (with the mobile antenna removed of course.
>
> I wouldn’t get my shorts in a knot too much trying to use the Command Set
> antenna relay box ammeter for tuning, just use a simple SWR/wattmeter at
> the transmitter.
>
> Most of my mobile antenna installs get the best low SWR match with 500 or
> 1000 pf shunt capacity across the feed point, or alternatively a shunt coil
> of about 6-8 turns of No. 14 insulated wire close wound on a large
> prescription pill bottle.  Start with the antenna length on the long side
> for your operating frequency and prune to tune.
>
> Never tried operating a Command set into this arrangement with the Tacoma,
> but worked very well with my GRC-9 field set, also with my Icom 7100 mobile
> transceiver.
>
> Chris AJ1G
> Stonington CT
>
> Sent from my iPhone
>
> On Jun 2, 2025, at 22:27, B. Smith via MRCA <mrca at mailman.qth.net> wrote:
>
>  Use 3/4 pr 1  inch, PVC, wind turns on it with enamel wire till you get
> tired. Put in a couple of taps. Use it to feed your "random" wire.
> Z
> <coilK4CHE.jpg>
>
>
>
>
> On 6/2/2025 8:53 PM, Michael St. Angelo via MRCA wrote:
>
> Are you simulating the body of the aircraft with some radials?
>
> Mike N2MS
>
>
> On 06/02/2025 1:39 PM EDT J Mcvey via MRCA <mrca at mailman.qth.net> <mrca at mailman.qth.net> wrote:
>
>
> It should work with the cap in series with the antenna, plus a good amount of inductance.
> Failing that, try increasing/decreasing the wire length.
> Also, if you are going for the short wire antenna, do not use any coax in the mix-just wire.
>
> On Monday, June 2, 2025 at 12:53:29 PM EDT, Mark K3MSB <mark.k3msb at gmail.com> <mark.k3msb at gmail.com> wrote:
>
>
> Forwarding to this group......
>
>
> Hi Guys
>
> The estimated length for the Command Set antenna on a B-24 is about 45 feet taking into account the length inside the fuselage.
>
> I cannot get this work with my command set on 3885. No antenna current at all. Dosen't matter if I use the 200 pF cap on the antenna relay unit.
>
> I can use my 9:1 Balun and series capacitor, the output of which goes to an MFJ tuner connected to the 45 foot wire. I'm getting about 30W out with low Ip.
>
> Don't understand what I'm doing wrong with only the 45 foot wire.
>
> I can certainly do it this way at the airwhow this week, but I'd rather not have the MFJ box in line.
>
> 73 Mark K3MSB
>
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