Receiving 2 Meter from a distance question

[jclh]

Greetings,

Brand new to Ham Radio, so new I'm not even licensed yet (I have broadcast turned off so I can't even drop the radio and PTT by accident ) but I'm working on that!

Right now I'm interested in receiving 2 meter from as far away as I can because I'm interested in monitoring SkyWarn repeaters from distant counties.

National Weather Service Fort Worth can monitor and broadcast to a 42 county area in North Texas from Tarrant County (Beach and 820 for those wanting to look it up on a map) so I know it is possible to go a distance (although I know I probably won't be able to go that far because I don't have as many resources as the government).

I am in Plano (SW Collin county) and I have an N9TAX antenna that I've mounted on a PVC pipe 20' in the air. I don't plan on this being a permanent setup - I'm just trying to test different scenarios. With this I've been able to receive at most the next county over (approx 30 miles).

My current goal is to get from Plano to Decatur (Wise county) about 65 miles away, or Weatherford (Parker county) about 80 miles away.

From my limited research, it seems I have 3 general variables to play with: antenna height, antenna gain(or quality), or an antenna pre-amp.

My least favorite of these is height - due to city permits and cost. I did, however, read about someone that put a magnetic mobile antenna on one of their roof vents which would get me up to almost 30'... but what would the extra 10' buy me? Also, I have an aversion to getting up on the roof (and ladders in general).

Antenna quality I would be willing to spend up to about $100... but how low can I realistically keep it?

Antenna pre-amp is the biggest unknown to me right now... would a pre-amp help on the *receive* side (such as a Radio Shack HTA-20 2M preamp)? If a preamp is a viable option, what is the best value out there (cost vs. performance)?

Thanks for the help!
I'll post my callsign once I have one

[AC5PS]

Those NWS broadcasts stations do have big mouths but 80 miles will be pushing it. VHF is line-of-sight and that is 75 miles so by theory receiving a good signal may be difficult. But during tropospheric ducting it will be possible.
I don’t think a pre-amp does any good on FM.

[brandon lind]

There are many situations where VHF can exceed line of sight. Tropospheric ducting as mentioned by AC5PS is one propagation mode, but what might be more effective for what you are trying to do is to focus on tropospheric scattering (troposcatter). Tropospheric ducting and weather related inversions (such as radiation inversions, evaporation inversions along marine boundaries, aiming along the back edge of a cold front, land breezes off the ocean or great lakes along shore lines, or mountain breezes like the Chinook wind) are fairly unreliable as they change with weather conditions (but can be very exciting). The best thing is to focus on troposcatter as it is the most persistent of the beyond line-of-sight propagation modes. For the most effective scattering, you should try to aim your antennas main lobe at the region of the atmosphere that is common to both antennas up to a height of 6 miles at the midpoint between the 2 stations. You will likely want to use a yagi antenna. You might get lucky and find one for 100 dollars, but you will also need a coax cable. Coax is very lossy at VHF, so radio shack stuff isn’t going to cut it. Your best bet is to buy some decent coax (LMR-400 might run around a dollar a foot, but well worth it) and just build the antenna. Tuning the antenna might be tricky as you do not have the ability to transmit and thus cannot check SWR or field strength. I would recommend seeking out your local ham club, sitting in on a meeting, and see if anyone would be willing to help you with the tuning.

EDIT: The ARRL Antenna book states that the most important factors are receiver sensitivity and coax line loss. Get those as good as possible before worrying about the rest. The book also states that the gain given by heights of 0-30 feet are nearly 0dB but once you get to around 50 feet, you can add about 4dB. An interesting thing to notice in the Antenna book is the graph showing the path loss at VHF. The path loss rises rapidly out to about 75 miles, then levels off at around 180 to 190dB for about 150 miles more. Trouble is, most hams are a few dB under that requirement, so if you focus on receiver sensitivity and spend a little money on your station, you will be able to reliably break that 75 mile “rule of thumb”. One thing to remember with pre-amplifiers is that you are also amplifying the noise floor, the signal to noise ratio stays the same. This means that if the signal coming in from your antenna is right down there with the noise, the amp isn't going to help you much. This is another benefit of a directional antenna like a yagi, it receives less signal (noise included) from the other directions.

[N4AAB]

I don't know if this will help or not. I tried my Western Mountain dsp filter on my 2m base station/portable. It didn't seem to do much for the noise floor. I have the previous version than the one they are currently making.

Is there a dsp filter for 2m ?

[brandon lind]

I don't know if this will help or not. I tried my Western Mountain dsp filter on my 2m base station/portable. It didn't seem to do much for the noise floor. I have the previous version than the one they are currently making.

Is there a dsp filter for 2m ?

I think the trouble with noise is the noise that occurs on frequency. The radios do a good job filtering off frequency signals, but no amount of filtering will remove the noise on a particular frequency if it is that frequency you wish to pass.

[N4AAB]

My dsp filter cleans up what I can hear on hf. The filter isn't a notch filter, but one that filters out the noise floor. The dial can be turned too far, or not far enough. I have found it to be very useful for my HF QSOs.

[brandon lind]

My dsp filter cleans up what I can hear on hf. The filter isn't a notch filter, but one that filters out the noise floor. The dial can be turned too far, or not far enough. I have found it to be very useful for my HF QSOs.

I dont think it does anything to the noise floor of the incoming signal, it works with what comes out of the audio jack after the radio processes it.

That dsp is working with the audio as it is coming out of the headphone or speaker jack on the radio and is simply cleaning the audio down to what is expected to come out of the rig given voice or cw. It might get rid of the hiss and clicks and pops and lightning sounds, but that is on an AM radio. 2m is FM and all the audio is extrapolated from frequency content. 2m FM is also not as susceptible to the sources of the RF noise on HF and the signals are processed and delivered to the speaker differently.

signal to noise ratio is a problem to deal with well before anything hits the audio out jack... we are talking about the radios ability to detect the signal amongst the noise, not how well what is detected sounds coming out of the speaker

[jclh]

Thank you @brandon lind and @AC5PS!

You have given me some new topics to research and learn about: Tropospheric Ducting/Scattering and Receiver Sensitivity... I didn't even know those were things

When speaking of receiver sensitivity, what is the metric one looks for (i.e. I learned antenna sensitivity is measured in dB) and is a high sensitivity radio generally cost prohibitive?

Take care!

[5B4AJB]

If you're thinking of installing a pre-amp, go for a masthead type, otherwise you'll just be amplifying the noise picked up by the coax.

A good masthead preamp on VHF/UHF/SHF might mean the difference between copy and noise, but as AC5PS stated, 80 miles is pushing it (for 2m at least) - try it! most of amateur radio is experimentation!

[edit] build one! see if you can find plans for G0MRF's "new" one...

[brandon lind]

When speaking of receiver sensitivity, what is the metric one looks for (i.e. I learned antenna sensitivity is measured in dB) and is a high sensitivity radio generally cost prohibitive?

Signal to noise ratio, more commonly measured as signal to noise and distortion or SINAD is the ratio of the combined signal + noise + distortion power level to the combined noise + distortion power level. This is usually expressed in dB. The formula is SINAD in dB = 10*log(signal+noise+distortion/noise+distortion) when signals measured as power. If voltages are measured, the 10 is changed to a 20 in the formula.

EDIT: receiver sensitivity is the voltage level necessary at a specific sinad that can be detected, usually listed in microvolts

W2AEW has an excellent video that should make it amazingly easy to understand.
https://www.youtube.com/watch?v=sBqjNLB6HuM

[N4AAB]

I asked one of the other hams in my club, and he said the way to reduce noise on 2m was to go digital.

[brandon lind]

I asked one of the other hams in my club, and he said the way to reduce noise on 2m was to go digital.

There is nothing to show that the skywarn signals mentioned in the original post are even on a digital system. This post is about increasing the likelihood of hearing pre-existing signals (that are likely analog anyhow), not how two individuals can share a higher quality QSO. You are throwing ideas out there that are irrelevant to what he wants to achieve.

EDIT: the easiest way to monitor all those repeaters is to download a police scanner app. How those work is someone writes the app then pays people all over the country to stream signals received on their scanners onto the internet and into the app. I can pick up our local club repeater anywhere there is internet access from a simple app downloaded from google play (albeit a few seconds delayed).

[N4AAB]

I was commenting that that is the only way to reduce noise on 2m.

[paulears]

This is a weird topic! The critical things for VHF reception and/or transmission is simply the TX output power, minus the path loss - end to end - and then the sensitivity and noise performance of the receiver. All the usual things like height, antenna type, cable loss, preamps etc etc just help the maths. You also need to factor in the critical bits, like polarisation for example. This is why you see people with 60ft wind up towers, 16 element beams, masthead preamps, and higher output powers and of course rotators. So many newcomers forget that beams focus the energy and performance into one direction and spend their VHF and UHF radio life trying to squeeze more distance from an omni. It doesn't work. By the way - going digital doesn't reduce noise, it stops you hearing it. A noisy FM signal can be 'picked out' when the same signal strength on a digital signal produces zero. Don't forget that digital just performs differently. Instead of gradually getting hissier as signal drops, digital modes carry on working, then in a very sudden manner, they chop, then mute and that is that. Digital is better in apparent noise performance when signals are modest too strong. They're rubbish when strength is poor, because all of a sudden, it just stops.

So if you live on a hill, then a small antenna on your roof may give you 65 miles from another point, also on a hill. If you live in a 100ft dip, with a 60ft tower, it won't!

When I was first licensed I had a vertically and horizontally polarised 8 element beam. Getting close to 10dB gain and my antenna height was around 40ft, in the clear, on high ground. My practical limit to access repeaters was that I could access and use a repeater 45 mile distant. My nearby police and fire repeater mast could do the same distance to their control room. Similar path, similar results. My current house is next to where the Police mast used to be. With a vertical, I cannot hear the 45 mile distant repeater at all.

[AndyG0CCX]

I started in 1984 as G1ICE with 25w on 2m, running into a 'Slim Jim' for vertical and a 16 element parabeam for horizontal. But I was on the side of a hill that went steeply up 100' just yards from my house. Zilch in that direction, great in the others! When I moved here, I had a good take off in all directions, using just a 6 element horizontal beam and a vertical collinear. I could work GB3SN (about 50 miles) comfortably on FM most times but that's about the limit. Of course, with a bit of a 'lift', I was able to work Eire, Scotland, Italy and the West of England on SSB and/or FM. So you add that factor in too. FWIW my trusty Mutek 144SLNA pre-amp was in the shack rather than on the mast, and is still going strong after 35 years.