Re: Topband: antenna analyzers
I can now verify that the FA-VA5 does just fine on my 160 meter inverted-L. As an aside, we've had some rain here in Tucson lately and I've observed a decrease in the feedpoint Z of about 5 ohm due to increased ground conductivity. Welcome, but I know it's temporary. Wes N7WS On 10/12/2018 1:35 PM, Wes Stewart wrote: I can vouch for the AA-55 Zoom, although it is not without flaws. I live 5.9 miles from a 50KW BC station on 1550 kHz. On my 160-meter inverted-L they are 70 dB over S9 on a calibrated K3, that's 70 dB above -73 dBm or -3dBm. As long as I don't sweep through that frequency, the analyzer is unfazed. As an aside, I have yet to find a low cost SDR that will stand up to this. I had to return a RSP2 Pro that even with BC band filtering folded up like a cheap suitcase. My N2PK VNA works fine as does the DG8SAQ VNWA. I just last night finished building a DG5MK designed FA-VA5, which I suspect will do okay. It will run using the VNWA software too. Good thing, since so far, the standalone interface is wanting, but that could be my failing. (It's really tough to run an instrument this powerful with just three push buttons) Note that all of these are vector analyzers. Wes N7WS _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Gamma match success
On 10/15/2018 10:43 AM, Tree wrote: I replaced the variable cap with a home made cap using RG8. I had one Sometimes, capacitors made from coax are lossy. I modeled your coaxial capacitor using Simsmith (very easy to do) and the Q turns out to be 340, if I did it correctly. So the coaxial capacitor gets a clean bill of health and probably doesn't have anything to do with your broad bandwidth. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Gamma match success
Maybe someone can put together a web page with examples of successful gamma match configurations for towers. Here is what I found this weekend with my new tower. Tower height - 97 feet. Top loading - 10 foot mast and essentially a 34 foot 3" boom at 98 feet. This is my Steppir with all of the elements retracted. Gamma match - attached at 47 feet - made out of a piece of RG8 with the center/shield connected together. Spaced about 18 inches away from the tower. Capacitor value - something around 400 pf. Radials: Currently 11 radials - most are around 1/4 wavelength of slightly longer At first - I had an SWR around 2.3:1 around 2.3 MHz - but using my variable capacitor - increased the capacitance and quickly got to a perfect match around 1800 kHz. Guess there are not any AM broadcast stations near me as my MFJ-259B seemed quite happy. I replaced the variable cap with a home made cap using RG8. I had one laying around from a previous installation that looked "about right" (length was 10 feet or more) and special treatment at the end of the capacitor to keep it from flashing over (involving a larger ceramic guy insulator). This also yielded a perfect mach and I went with that. Testing with high power this morning didn't show any arcing and the matched was stable. The bandwidth seems very broad (maybe somewhat due to the low number of radials) - however, this does remind me of the first gamma match I did some 32 years ago on a different tower which might have a similar electrical length as this one. It gets up to about 2:1 at 2 MHz. We'll see what happens as I continue to add radials. Goal is to get to at least 40 eventually. The ground here is possible very good... totally clay - with no rocks to be found and lots of rain during the winter (57 inches average annual rainfall). The RX 4 square is physically up and will be QRV soon. Was able to get it a good distance from the TX antenna but still on top of the hilltop. Will appreciate any signal reports during the PreStew. This is the first time I have had an antenna like this on a hilltop and I am curious how it compares to being in the flats. I have a 600 foot drop-off over about a mile distance in the important directions. A quick CQ 5 minutes after sunrise this morning didn't yield any far away RBS spots other than VE6/VE7. Tree N6TR / K7RAT _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Beverage F/B using oscillator
Greg, I re-did the exercise at 470m distance from both ends of the beverage and the F/B has increased to 7db. I was tired to go further in a VERY muddy ground but I will test again at near-field edge (around 840m) when it gets drier. Thanks 73 Ash 3V8SF www.kf5eyy.info Message: 2 Date: Tue, 9 Oct 2018 22:57:54 +1300 From: Greg - ZL3IX To: topband@contesting.com Subject: Re: Topband: Beverage F/B using oscillator Message-ID: Content-Type: text/plain; charset=utf-8; format=flowed Hi Ashraf, The rule of thumb I use is 2D^2 /lambda, where D is the largest dimension of the antenna. So if your Bev is 320m long you need to be over a km away. If only 160m long you need to be 300 m away. 73, and I hope to work you one of these days at my SR. Greg, ZL3IX _ Topband Reflector Archives - http://www.contesting.com/_topband
