Cushcraft R7. Hi just got this ant,what is the best hight to mount this at. The Cushcraft manual it explicitly states 'The R7 should not be attached to a ground.
R7 Vertical..Maintenance and Repair The Cushcraft R5 and R7 verticals are favourites of mine, ever since Alex EI6AG, my friend and 'Elmer' for many years, gave me a present of a set of faulty R7 traps.It was fun to repair the traps, and then 'homebrew' the rest of the antenna, including the matching box. Many thanks to Joe Reisert W1JR, whose advice helped me get it up and running. Thanks also to Dave Moore EI4BZ, who allowed me to dissect his R5 'Black Box' in the name of Science..!
I like the idea of the 1/2 w/l radiator, as against the usual 1/4 w/l fed against ground. My 'homebrew' version works extremely well, and I use it as my 'standby' and 'reference' antenna. (Circuit diagram of the matchbox) There are a few problems which arise from time to time in older units. especially in wet and windy areas. or close to the Sea. Varying, or high SWR on one or two bands. This isusually caused by bad connections on the trap clamping arms. They should be carefully loosened, moved aside, and the contact area cleaned with steel wool. When clean, the area should be greased with Vaseline, or one of those dissimilar metal contact greases used by the electrical power utilities. Cushcraft R7 Antenna ManualIf this treatment doesn't work, and you still have high SWR one band, Then you have a .. Faulty trap. ![]() Traps usually go faulty because the heatshrink seal on the trap fails, and water gets inside the coaxial 'trombone' capacitors on the traps. If the insideof the tube gets wet, this changes the dielectric constant of the capacitor, and the value of the capacitor changes, thus moving the resonant frequency of the trap. You will find that the SWR minimum point has moved, and normal adjustment will not bring it back on frequency. If this situation is not corrected, eventually the capacitor will short out, especially if you're running high power. Running high power into a bad SWR can eventually destroy the matching unit.!!!! More on that later.. To repair the trap, you must carefully note the length that the capacitor 'rod' extends out of the 'Tube'. The rod can slide in and out of the tube, and is one plate of the capacitor, so you need to get it back the way it was before you dismantled it..! Carefully dismantle this capacitor. Dry and clean all of the components, and reassemble. Re-seal the tube with 'self-amalgamating' tape. All should now be well again.. If the insulator tubing is badly damaged, you should go to Gerry VE6LB's page. He has a great method of repairing traps using Hot Melt Glue. When you see the original damaged trap, you'll be amazed that it could ever be fixed. Well done Gerry! If you have high SWR on ALL bands, then you probably have a Faulty Matching Unit. A - Matching capacitors. These are a pair of 86pF in series, to give an actual value of 40/50pF. These can, and do go open-circuit. Replace them with a single HIGH CURRENTtype (doorknob) of 50pF if you can. ( I use three 15pF caps in parallel)
D - Make sure that all hardware connections are clean and secure
( Pic of my homebrew R7 matchbox. Not as pretty as the commercial one, but works just as well! ) Take a look at the brilliant rebuild job that Darren G0WCW did on a wrecked R5 Match box. It's now working perfectly again.
Oct 22, 2012 Its what Sabian said except you have to make the changes using the Adobe Reader program. Open Adobe Reader; Go to Choose Choose Choose Choose Choose Under Toolbars and Extension look for Adobe PDF Reader. Click on it & Disable on the right hand corner. Hit closeOK& OK. Open Adobe Reader or Adobe Acrobat. Open the Edit Preferences. Menu from the menu bar or use the keyboard shortcut Ctrl + K to get there even quicker. From the left pane, select Internet. In the Web Browser Options, uncheck the box next to Display PDF in browser. Choose the OK button to save and exit the settings window. Mar 03, 2017 How To Disable PDF Reader in Microsoft Edge. Open Control panel and go to Control PanelProgramsDefault ProgramsSet Associations. Find the line starting with '.pdf' in the table and click the Change program button. In the next dialog, select an. Adobe reader free download.
Measure your trap frequencies.
It's a good idea to take a note of your trap's frequencies, in case you need to repair one in the future.
I measured my traps under the following conditions.
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Disconnect Each trap unit from the rest of the antenna.
My measurements were taken with the trap unit resting on a large cardboard box, well away from all metallic objects.
I used my MFJ 259 analyser with a piece of insulated wire , configured as a single loop around the end of the coil on the trap assembly.
Vary the frequency on the MFJ until a strong dip is seen.
Cushcraft Antenna Manuals
Now move the single turn link away from the end of the coil, while retuning for the dip, until a very shallow dip (least loading on the trap) is seen, and take note of the frequency read out.
Make sure that you do not touch any part of the trap while taking the reading.
These readings, though not strictly accurate because of the loading effect of the attached tubing and hardware, are very useful.
Make a note of your readings for each band, and keep them safe. If, in the future, you need to readjust a trap, then you can set it to the original reading.
I obtained the following readings from my R7..
TV1 10m 26.5 mHz
TV2 15m 20.05
TV4 20m 12.85
You can see from these readings, how the hardware loads the traps, and gives a lower frequency reading than the actual.
Ken KA1VMR, who was very helpful to me, told me that Cushcraft, when making these traps, used a Signal generator and oscilloscope to set up the traps on the following frequencies.
TV1 10m 28 mHz
TV2 15m 21.2
Cushcraft R5 Specs
TV4 20m 14.47
R7 AntennaAny manuals that you may require for these antennae are available in .PDF format from the Cushcraft website . Comments are closed.
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