kidphc
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Posts posted by kidphc
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Damn it. That was what I was looking for. I am looking for the lowest log?Here is a snap shot of my NanoVNA showing the resonance of the external GMRS at my home. The resonance can recognized by the sharp dip in the yellow LogMag trace. Since the impedance of the antenna (as depicted in the green smith chart) is also closely matched to the 50-ohm coax there is also a corresponding dip in the SWR. So this image shows that, in my case, the best SWR reading corresponds with the resonance of antenna.
So, in part, how can you view the resonance of an antenna independent of SWR? Use a NanoVNA, perform an S11 measurement with the instrument set to display the LogMag trace.
Hope this helps.
.
Michael
WRHS965
KE8PLM
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Its a Larsen NMO34 coil. Unfortunately, no information on capacitance. Might have to go old school and break out a mult-meter to measure it out. Thanks for the information it is a start.
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I remember back when I obtained my NanoVNA and was doing experiments with a simple 1/4 wave ground plane. It allowed me to not only see the resonance change as I trimmed the antenna down to size, but it also allowed me to observe the impact of length and descending angle of the ground plane radials had on the impedance of the antenna. Without it those factors are hidden mysteries.
Michael
WRHS965
KE8PLM
That kinda was the question to begin with. How to see resonance frequency not using SWR.
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If you are using the repeater memory slot. Which should be memory 15-22.
Then no worries with the frequencies it should automatically listen to 462.xxx and transmitting on input 467.xxx. Make sure it is the right frequency.
As far as your DCS codes that sound about right.
Program it and clunk away to see if you break the repeater's squelch.
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I have seen the video before and it was no help.
Michael thanks for the input. I guess this antenna coil combination wants to stay resonant at 28.59 or so. Uncut it seamed to be resonant at 29 mhz, with the swr at 1:1.7. Currently, it's 2.0 swr at the band edges and at 1:1.7swr at 28.450, 1:1.66 at 2.58.
I guess next step is to check the impedence values at those frequencies.
When the nmo30 and hamstick comes in about a week I will have to rerun the sweeps.
The 1:1.7 swr I started to think was due to the terrible ground plane interactions. Bending the antenna away from a pillar resulted in an swr that dropped a few hundreths.
I will never recommend a hood mount that close to the pillar as an even remotely acceptable mounting location. May have to get another mount that mounts the antenna closer to the center of the fender. Should be intresting to compare the two locations and their respective swr values.
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I have a nanovna ver h4.
Kinda why I am asking how you would look for the resonance. It certainly has way more ability then the user to do many functions at this point.
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That is one way. But a rigg expert will have to wait. Was hoping for something like with the nanovna like at lowest reactance and inductance.
Actually might have found something on those lines.
Basically, the lowest impedance value.
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This is the frequency where the capacitive and inductive reactances cancel each other out. At this point the antenna appears purely resistive, the resistance being a combination of the loss resistance and the radiation resistance.
Well kinda. For a pre-engiered antenna generally 1.5 swr is where the antenna is resonant. But an antenna can be resonant t frequency and have a really high swr say like 1:5, example folded dipoles.
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So building out my system for the truck. Finally, after a year of laziness I am building a center console (well the front half) to house a FTM400xdr and an Anytone at6666 10/12m radio (code for illegal cb radio for those that don't know). It will be used for 10m work as well.
STAY TUNED FOR A BUILDOUT POST.
So the antenna is mounted to the hood in front of the a pillar. Using a NMO34 with a 64" whip (10m) and a NMO30 with 64" whip(11m).This is going away. The whip is .100 and it flexes to 45 degrees above 30 mph and much more at 70. Incoming MFJ 10m hamstick. Should be tunable for both bands.
I was trying to hold to Marc's talk about every commercial antenna for 11m is too short even with a spring. SIDE NOTE: I DID FIND SOME ONE THAT MAKE CUSTOM EXTENDERS TO GET A 102" TO 115" OR SO.
Now back on track. The nmo34/30 combo the lowest I could get was a SWR of 1:1.6 or 1:1.7 with trimming. I gave up because the SWR started climbing back up. Lowest frequency for the 10m set up was 28.594 (VSWR OF 1:1.6). Just a hair away from the target of 28.400.
It started making me think of antenna resonance and how to calculate it.
So in order to find the resonant frequency of an antenna I am looking for an impedance of about 75 ohms purely resistive? This the value I gather for a dipole in free space.
So the question is how the hell do I find resonance of a custom, less then ¹/4 wave whip with a bottom loaded coil?
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Might have to go with a hood mount by the windshield with a s much antenna as you can get to clear the windshield and roof.
Outside of that you may be stuck with a mag mount.
Depending on the shape of the trunk a lip mount on the side of the trunk. Similar to the link below.
https://hamradioschool.com/wp-content/uploads/2014/07/GetStarted-bands.jpg
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Nano vna is easy peezy. Not a turn on and good to go device. But close.The nano vna looks like something I don't want to mess with, regardless of price. I have a feeling OP was looking more towards the simpler end of the spectrum as well.
Buy it. Buy it... only if you are constantly tweeking or building antennas. The other swr meters you need to provide an input. Aka key up.
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You get close to a nanovna in price. Two different functions. For tuning I prefer the Nano Vna.I have this one:
https://www.amazon.com/dp/B075H8FDDR/ref=cm_sw_r_cp_apa_glt_fabc_094Z4EYM185PWC0QPRFA
But maybe wish I would have bought this one:
There are many many other examples. There's a thread on this board somewhere where people are trying to figure out the best reasonably priced one. I'm still watching that waiting for a consensus.
I just ordered an rs70 for the cb. For real-time monitoring. However, I wanted as a on the fly reference. The rs50 is the vhf/uhf version.
If it weren't a mobile install I would of done a swing needle.
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Just like gmrs is in the 70cm band.
You'll cover it in the tech study manual.
https://hamradioschool.com/wp-content/uploads/2014/07/GetStarted-bands.jpg
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They work the same. One just has the bridge setup for hf or vhf/uhf.
You can sometimes us a 11m cb swr meter for 10m. Really depends if it was designed for that range. A hf swr meter usually has no problem with 11m cb. Since most hf swr meters go up to at least 10m sometimes 6m.
You get what you pay for.
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Just remeber perfect SWR doesn't mean you have a resonant antenna.
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Depending on amount of metal, shapes etc. You get distortions in the radiation pattern.
Ground plane is important because it is the other half of an antenna. 1/2 and larger are marketed sometimes as no groundplane or non groundplane dependent. It is because at the 1/2 wave point the sinoid is partially complete and not reflected back into the ground plane.
As well as directionality of the antenna. You are shaping the radiation pattern based off the ground plane and its contiuity. Basically, you can get better recieve or nulls in the radiation pattern.
Take it all with a grain of salt. Because you may or may not perceive the differences.
In all any antenna is better then no antenna. The mobile install is already a compromised install.
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AM FM SSB 15/45/60 pep
Modding for final reliability
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Welp bit the bullet. $315.94 for radio and 3 year warranty. No shipping (prime) but the tax
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Yup. Talked to a local radio fantic ham. He said buy it stock with or w/o the warranty. If it blows up we can mod/fix it hopefully.Extended warranty
I think the blow ups are caused by people over driving it. Why? There is a video of a guy open keyingbit with high swr for hours (could be wrong) and it didn't blow up. So it has to be something else.
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Only thing I have heard as far as negatives are that it has the habit of blowing its final. Single stage from what I get. Looking at a modded one, upgrade final and regulator. Just not sure if it is worth x2 the cost.I'm considering the same radio for the same use. I think we had a QSO a month or so back
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Bueller...? lol
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Definetly do the tech and general at the same time. I wish I had alot of the material is the same.Tech for sure first, and will try for my general at the same time. I will get the books here soon to start studying.
For starters, it would just be VHF and UHF.
I did a quick search and it doesn't look like the application is a big deal for the FAA, so I will probably get that going anyway. It could still gain me a few feet even without the HAM ticket.
Be on the look out for silent key estates. Their families alot of times will just want their old towers removed, which they will tell you to take apart. Then you may get a taller tower using some of your and buddies time. As well as get some free antennas. Give you a chance to inspect their install as well.
If you get lucky your 20' section may attach to the one you just pulled down and you get more height.
Downside setting up the tower cost $$$. Just in quality cabling it adds up.
Either case, good luck. Have a feeling you'll be that "guy" in the area.
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Certain frequency can interact.
Spacing/distance can be partially resolved by having one vertical pointing upwards and the other facing downwards on a cross tee. With a 20' tower that can be an issue. Since some of the nicer vertical antennas can be in excess of 20' by themselves. Would be kinda funny if you were constantly kicking the tip of your upside down antenna. Well not really.
Grounding should be done at before the tower's foundation is poured
As far as the faa permit, I didn't think it was massively difficult. The installation of a beacon light is a requirement after a certain height, which sounds like you are at.
Which ham ticket where you shooting for?
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Pretty much. Had some what the same problem with my burb. The sunroof slid so far back it limited some options.
So even a mag mount might work better then a permanent install. Some options on your truck. But even then everything is going to be a compromise of sorts.
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Generally, a no ground plane antenna will work better then one requiring one and fabbing one.
A no ground plane antenna will work even better with some ground plane available.
I would do the 10". Make sure the rack has continutiy to the bed and cab. In which case make increase the available groundplane.
I would expect some radiation pattern biases due to proximity of other metal surfaces ie, cab, bed trunks and the bed.
Fox Delta
in Amateur Radio (Ham)
Posted
So here are my thoughts on the radio.