In recent threads, the subject of auto mounted passive repeaters (an inside
antenna connected to an outside antenna) was discussed, and they were shown to
be pretty much ineffective because of losses. Continuing this discussion in a
slightly different tack, I am wondering how effective such a repeater would be
for a RF tight enclosure such as an RV that has very little leakage because of
screened windows and a metal body.

How would one estimate the amount of loss before the transmitted signal arrived
at the external antenna? Would multipath inside the vehicle affect the
transmitted signal?

This is just a mental exercise, as I have already run coax directly to the rig
from the outside antenna on my trailer.

TIA
--Wayne

On 15 Nov 2003 18:48:21 GMT, (WP20032) wrote:

This is just a mental exercise, as I have already run coax directly to the rig
from the outside antenna on my trailer.

Hi Wayne,

Speaking of the loss of passive repeating, compare that to the loss of
the shielded inclosure you are trying to transceive through. No doubt
the latter will overwhelm the former giving you a new appreciation to
the chestnut "can you hear me now?"

The losses of passive repeating are typically compared to the coupling
from your set to the inside antenna (this is the loss to be computed
as it is by far the greatest). Losses within the coupling between
antennas (if matched) are trivial in comparison. Further, when the
topic arises, the simple observation that you are sitting next to a
window that is extremely large (in terms of wavelength) dilute the
argument that the passive re-radiator is needed at all (and serves
only as placebo).

73's
Richard Clark, KB7QHC

On 15 Nov 2003 18:48:21 GMT, (WP20032) wrote:

In recent threads, the subject of auto mounted passive repeaters (an inside
antenna connected to an outside antenna) was discussed, and they were shown to
be pretty much ineffective because of losses. Continuing this discussion in a
slightly different tack, I am wondering how effective such a repeater would be
for a RF tight enclosure such as an RV that has very little leakage because of
screened windows and a metal body.

I tried it using a 5/8 mag mount in the center of the ceiling on my
shop. The interior is all barn metal with the doors also being metal.

I ran a shot lead to a collinear antenna on the roof. Results? I did
just as good next to the small window on the south side (repeater is
to the east). IOW, neither was worth the effort.

I set up the duobander in the ham shack TM-V7A to cross band (one
way) and then used the HT to transmit on the 440 band while listening
on the repeater output of 147.00. Now that worked just find.

Currently I have a station set up in the shop so using the HT from
there is no longer necessary.

Portions of the shop can be seen at the bottom of
http://www.rogerhalstead.com/boatanch.htm Although a much better over
all view is 4th from the top in
http://www.rogerhalstead.com/glasair2.htm

Ceiling and walls are the same material often used for the outside of
hangers, shops, and other out buildings. Doors are insulated metal.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

How would one estimate the amount of loss before the transmitted signal arrived
at the external antenna? Would multipath inside the vehicle affect the
transmitted signal?

This is just a mental exercise, as I have already run coax directly to the rig
from the outside antenna on my trailer.

TIA
--Wayne

This is just a mental exercise, as I have already run coax directly to the
rig
from the outside antenna on my trailer.

Hi Wayne,

Speaking of the loss of passive repeating, compare that to the loss of
the shielded inclosure you are trying to transceive through. No doubt
the latter will overwhelm the former giving you a new appreciation to
the chestnut "can you hear me now?"

The losses of passive repeating are typically compared to the coupling
from your set to the inside antenna (this is the loss to be computed
as it is by far the greatest). Losses within the coupling between
antennas (if matched) are trivial in comparison. Further, when the
topic arises, the simple observation that you are sitting next to a
window that is extremely large (in terms of wavelength) dilute the
argument that the passive re-radiator is needed at all (and serves
only as placebo).

73's
Richard Clark, KB7QHC

Richard--
The question came up in my mind because I was not able to hit a relatively
close repeater from inside the trailer. The windows are screened, but there
are some minor leak areas around the refridgerator vent, etc.

My question was directed at a theoretically RF tight container. In such a
case, how effective would the reradiator be....20 dB down....40 dB, etc. I am
not sure how this would be calculated in the relatively near field, with
reflections.

TIA
Wayne

On 16 Nov 2003 23:42:38 GMT, (WP20032) wrote:

My question was directed at a theoretically RF tight container. In such a
case, how effective would the reradiator be....20 dB down....40 dB, etc. I am
not sure how this would be calculated in the relatively near field, with
reflections.

TIA
Wayne

Hi Wayne,

Resonant cavities are RF tight containers, and they exhibit less than
1dB to several many. The lower values are a function of low loss
(very large resonators), the higher values are a function of either
high loss or poor coupling. No doubt when you have folks residing
within the "cavity" loss becomes an issue - and then add coupling loss
to boot. This says nothing as to the state if the cavity is resonant
or not.

If the radiating antenna is within less than a wavelength of the
pickup, you don't stand much chance of coming out with less than 3dB
loss. You may as well count on at least 20dB loss.

A low power, half duplex, cross band repeater would probably remove
all the presumptions and actually work. One half residing within a
shield would also cut down on annoying hits on a shared frequency.

73's
Richard Clark, KB7QHC