From: rohre (firstname.lastname@example.org)
Eric Rehm of Seattle and others may get help from my going down this road with
an R5 with the same construction as the R7, and prior to that a Hy Gain AVT-18,
and presently with a Gap Titan model. Along the way, I helped another ham with
a Gap Model VI or so.
Firstly, Eric if you still have the box, and the R7 is new. -- Why not have all
the bands with full bandwidth and at least some of 80M with the low sunspots?
To do that put a for sale sign on the R7 and get a Gap Titan model. (No Traps.)
I hope I don't offend you with that, but the R7 does not adverstise full
bandwidth on 40 even, and that has been the wonderful thing about the Titan. It
even covers more than 100 K Hz on 80M with 2:1 SWR up there at the edges. It is
1:1 over the whole of the other bands. The R5 we have experience with has not
done as well at working out to DX, and I have heard the traps frequently fail in
some cases, and am going to check the R5, which is at a friend's for bad traps,
as he has not been getting good results.
The other reason I advise that, is the base clamping arrangement of the R7. It
IS HARD to get the proper size pipe, to go up inside the bottom of the R7. Then
ALL that is holding it against winds are two set screws. What happens to knobs
after twisting for some time? The set screw loosens. Same for the R5 we put
up, it tipped over after awhile. That is why they now tell you to guy them.
Actually guying any vertical is a good idea if you have any winds ever at all.
You can get the nylon that is used for tieing up boats, and that is cheap at Wal
Mart Discount stores with 880 pound test rating. Now it will stretch, so a slip
knot or turnbuckle can be used to take up eventual slack. Mail order cos. have
kevlar, and other exotic non metal guy material. Go to a camping store too and
see what they have that stretches the least and resists sun.
Back to the poor design of the R7 mount and what to do about it. If you are
going to keep it, there is a way to fix it. Finally, a friend came up with
large u bolts to do away with going up inside the bottom of the vertical tube,
and instead just clamped the pipe to the outside of the vertical bottom tube.
Now, about roof mounting. As you describe, it is a bear to get strength on the
roof areas where the foot print of the mounting sits. Weather proofing will
always become unweatherproof, and be a constant maintenance item. DO NOT mount
to a 49 year old chimney, nor to a vent pipe. You have too much torque arm with
the length of the R7. What we did for the R5 can be done for the R7 or any
You can get steel water pipe, perhaps in salvage, in good condition. Or you can
get steel or aluminum conduit pipe. We used the compression fittings to join
two 10 Foot conduit pieces; but I would seek threaded conduit to do it again.
We set this in concrete at side of house near the peak of the gable. We used a
pipe strap arrangement at the trim board on the gable overhang to anchor the
upper pipe, and we extended it above the roof by the amount to clear the roof
peak. BTW, remember you have to hoist the vertical onto the top of this pipe,
so don't have it too tall above the roof peak that you can't do this from atop
the roof. The conduit type support is fine in the vertical condition; but NOT
strong enough to walk up with the vertical attached to it, nor will you likely
have room in a side yard.
Thus, with concrete holding the bottom of the vertical, and a clamp strap at the
edge of the roof line, we had a very sturdy arrangement to hold our vertical.
The R5, after we did away with the factory mounting scheme, has been adequately
sturdy, even without guys. You can buy a bag of sackcrete which is premix for
fence posts, and this is about 80 lbs. of concrete. You can dig a hole and then
just shovel in a few scoops at a time, and mix just enough water to make a stiff
mixture, this has more strength. Don't forget to set the pipe in the hole first
on some rocks or gravel at the bottom so water drains away from it. You could
also paint it before cementing like they do steel gas pipe. If it is
galvanized outside finish, you can cement it directly.
For any wood you use, if you decide to go to all the work and risk of the over
roof mounting of a tripod; use the pressure treated lumber that is for outdoor
use. It is a bear to saw, but it can be painted, and will withstand the
weather. Ordinary lumber, even red cedar like in fences will rot away in a
Most hams become dis-satisfied with any antenna over time, or time and weather
takes its toll. Therefore, I believe in putting antennas up in such a way that
does the least alteration to the house, and certainly in a way to not bring roof
problems or chimney problems on the house---because it is not permanent anyway!
Chimney mounts like you see at Radio Shack are good for just what you see on the
box---small VHF antennas. As someone else put it once, chimneys were designed
to let smoke out of the fireplace! The way old ones weather and the morter may
not be trustworthy, and the careless way modern ones have the morter applied,
makes me reluctant to trust one with any significant antenna, although I have
wanted to; it looks very risky.
In assembling your vertical sections, place a no-ox compound that is sold for
aluminum wiring from electrical supply stores, on the aluminum joints. This
will keep the antenna conducting as long as possible, and ease its dis-assembly
when you take it down to try another antenna. Aluminum untreated oxidizes
rapidly, even in a few minutes, but we can't see the initial result; later you
may see a white powder form. That is why it is usually stated to polish the
joints with a fine sandpaper or abrasive before assembly.
Hope these thoughts help you out! Use elevated radials by the way, at least
four. The ones that come on the R5 and R7 will be less efficient than quarter
wave ones you add yourself. That is the opinion of the Butternut Antenna
founder, Don Newcomb, and I agree that a good counterpoise is the best friend of
the vertical of any design. The radials can be insulated hook up wire stapled
along the edge of the roof, or run along the ridge. For the ridge or over roof
verticals, you can tie on to nylon line to keep them in tension, and nail an
anchor on the roof edge at the other side of the house. Three or four on an
elevated vertical are usually sufficient. They are usually computed with the
length equals 246 over frequency formula, which is 5% longer than a half a
Let us know how it turns out!
73, Stuart K5KVH
Search QRP-L Archives
QRP-L Archive |
[ 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 ]
This archive was generated by hypermail 2b29 on Fri Jun 02 2000 - 11:28:10 EDT