Posts Tagged ‘Equipment’

An Easy HF Antenna

When radio amateurs get ready to put an HF station on the air, they often have questions about what antenna to use. The good news is that there are many options to choose from. The bad news is that there are too many options to choose from. It can be overwhelming. This post describes an antenna I just installed that is easy to put up and works well.

The ponderosa pine tree supports the endfed wire antenna.

Having 30-foot tall pine trees on our property, my usual approach for HF antennas is “wires in the trees.” I have several ropes strung up over these tall trees so that I can raise and lower wire antennas as needed. These ropes were installed using a slingshot to launch a fishing line over the top of the tree, and then pull up a lightweight rope.

The 9:1 UNUN provides the matching at the end of the wire antenna.

End Fed Long Wire

The antenna is the EFLW-1K from MyAntennas.com, which is an End Fed Long Wire Antenna. (This should not be confused with an End Fed Half Wave antenna.) This antenna is intentionally cut to not be a resonant length on any of the bands. The 9:1 UNUN transforms the high impedance at the end of the wire down to something closer to 50 ohms. The match is not perfect so an antenna tuner is required to cover all of the bands. MyAntennas offers this antenna with different lengths of wire, with longer wires required to support the lower HF bands. I purchased the 53-foot version but decided to shorten the wire. My interest is working 20 meters and higher and I wanted the antenna to be mostly vertical, so I shortened the wire to about 30 feet. The MyAntennas products are good but any 9:1 UNUN on the end of a wire will work.

An endfed antenna like this needs some kind of counterpoise to balance out the antenna operation. Many people have written about this and there are many different approaches. The MyAntenna UNUN has a connector intended to support adding a short length of counterpoise wire. A decent length of coaxial cable lying on the ground can function as this counterpoise and that’s what I decided to use. I have a 50-foot length of LMR 400 connected to this antenna, lying on the ground.

The B11ISO isolation transformer is inserted in line with the coaxial cable.

I also added an inline isolation transformer to minimize the common mode currents getting back to the transceiver. I don’t know that this is required but I had one available so I used it. The antenna has 50 feet of LMR coax to the inline transformer and then another 25 feet of RG-8X to the transceiver. The internal antenna tuner in my Icom IC-7610 handles this antenna quite well, tuning up on 20m, 17m, 15m, 12m and 10m. This means I can instantly switch between the bands and be ready to go.

I’ve been running SSB, FT8 and FT4 on this antenna, working many stations in all regions: Europe, Asia, Oceania, Africa, North and South America. Conditions are great and I keep telling newer folks: now is the time to be on HF! This basic antenna is a great way to get on the air and work some DX.

73 Bob K0NR

The post An Easy HF Antenna appeared first on The KØNR Radio Site.

Improved IC-705 SOTA/POTA station

This past year, Joyce/\K0JJW and I did quite a few Summits On The Air (SOTA) and Parks On The Air (POTA) activations, often as part of an RV camping trip. During this time, we made some improvements to our portable gear. For SOTA, we primarily use the VHF/UHF bands but we have been sprinkling in a bit more HF activity. For POTA, we often don’t have a Height Above Average Terrain advantage, so we definitely use the HF bands.

The ICOM IC-705 is a great backpack portable rig for SOTA and POTA.

Our main goal was to have a backpack portable station for SOTA and POTA that can cover HF through 70 cm, on the most popular bands/modes including CW, SSB, FM and FT8.

Using The IC-705

Bioenno Power Battery
This 4.5 Ah battery from Bioenno is a compact, lightweight battery for portable operating.

The Icom IC-705 is a great transceiver for covering most HF, VHF and UHF bands. With an external battery, the transceiver puts out 10 watts of RF power. (This is a bit less than the 50 watts from our Yaesu FT-90, which is our default choice for 2m and 70 cm SOTA.) We have accumulated a number of Lithium Iron Phosphate batteries from Bioenno. They are all set up with PowerPole connectors and are easily interchanged. See a previous post, My SOTA Battery Journey.

Arguably the biggest weakness of the IC-705 is the lack of an internal antenna tuner for the HF bands. Of course, you can operate without a tuner by making sure your antenna is always 50 ohms. I find that limiting, especially under portable conditions where the antenna configuration might be compromised. Also, some common end-fed antennas that cover multiple bands are not a good match for all bands. There are external automatic antenna tuners available for the IC-705, so initially those looked like a good solution. Then I remembered that I had a small MFJ-902 Travel Tuner that could do the job. The MFJ-902 is a classic T-network with two variable capacitors and one variable inductor. I gave it a try and was impressed with how easy it was to tune using the SWR meter of the IC-705. This thing is simple and it works.

The MFJ-902 Travel Tuner is a simple T-network antenna tuner.

The rear panel of the tuner has two SO-239 connectors, one for the transceiver and one for the antenna. I put a BNC adapter onto the transceiver port and used a short BNC cable to connect to the IC-705.

The rear panel of the Travel Tuner, with an SO-239-to-BNC adapter installed.
A typical picnic table setup using the IC-705 with the MFJ-902 tuner.

The Travel Tuner is compact and not very heavy, so it works out well for backpack portable use. It can handle up to 150 watts, which is overkill for the IC-705 but it may come in handy when used with a higher power transceiver. Still, I am on the lookout for an even more compact (probably lower power) manual antenna tuner.

A typical end-fed half-wave wire antenna for 15 meters.

We have collected a variety of HF antennas, focused mostly on 20 meters and higher. These are typically end-fed, including single-band half-wave designs as well as multiband random-length antennas. These are used in the classic SOTA configuration with one end of the wire supported by a lightweight fishing pole and the coax connection on the ground, fed by a 25-foot length of RG-8X coaxial cable.

FT8 Solution

With the popularity of FT8 on the HF bands as well as 6 meters, I figured we should include that mode in our portable kit. My first thought was to use a compact Windows computer running the standard WSJT-X software. Ultimately, I chose the SDR Control app for the Apple iPad (by Marcus/DL8MRE), which supports specific Icom radios. The iPad connects to the IC-705 via its WiFi connection, which simplifies the connection/cabling challenge. The SDR Control app does cost $49.99, so it is not your inexpensive iOS app but I have found it to be worth the price. Because this app is focused only on iOS and certain Icom radios, it is well-tuned to be a no-fuss solution. I am currently using the app only for FT8 but it has other features and modes for me to explore.

The portable station for FT8, running SDR Control on an iPad.

The Powerwerx PWRbox is shown in the photo above, which we often use for operating POTA. (This box is a bit heavy for hiking.) The PWRbox holds a 20 Ah battery as described here. Also shown in the photo is a handy little stand for the IC-705, the NEEWER Folding Z Flex Tilt Head. It does a great job of holding and stabilizing the radio at a variety of angles. (Hat tip to Kyle/KD0TRD.) It is also a little heavy for backpack portable, so it usually gets left behind on a hike.

The Maxpedition bottle holder case works well with the IC-705.

For a protective case for the IC-705, we use the Maxpedition 12-Inch X 5-Inch Bottle Holder. I’ve seen other IC-705 users recommend it and OH8STN mentioned it on his blog. At first glance, the case seems a bit large but this provides enough room inside to stow a small Bioenno battery and other accessories. The side pouch is a good place for storing the microphone and power cord.

Wrap Up

This post shares some new equipment configurations we are using for SOTA and POTA, mostly focused on the IC-705. I really like that radio for portable ops as it is the best solution for operating HF through UHF. The SDR Control software on an iPad has also turned out to be a win for us.

What are you using for your portable station?
Do you have any tips or other operating ideas?

73 Bob K0NR

The post Improved IC-705 SOTA/POTA station appeared first on The KØNR Radio Site.

KB1HQS Arrow Antenna Mods

Stuart/KB1HQS has been experimenting with various modifications of the Arrow II antennas. Recently, he put together a video of the various mods, well done and interesting:

Ultimate Arrow Antenna Modifications

I am a big fan of the Arrow II style antennas for VHF SOTA. Initially, I used the dualband 2m/70cm antenna for satellite work as well as mountaintop activity. This started before SOTA was even a thing, as I hiked in the Colorado mountains and made radio contacts just for fun. These days, we normally carry the 2m-only version of the antenna, with split boom and 3 elements. My personal seamstress (Joyce/K0JJW) worked up a really nice rollup case for it. Sometimes, we’ll take along a separate 5-element 70 cm Yagi, which can remain fully-assembled and strapped onto my pack.

K0NR operating 2m FM from a summit using the Arrow II 3-element Yagi antenna.

All antennas are a compromise between cost, size, weight, performance, convenience and durability. I have found that the 3-element Yagi from Arrow fits my needs really well. I have not been motivated to modify it. The Arrow antenna has a gain of about 6 dBd and is 37.5 inches long. We handhold the antenna and that is about as big/long as I’d like to hold. I am still in search of a higher-gain antenna for those special situations when I know that a few more dB of gain could make a difference. I’ve not really found anything I like. A longer boom would likely require a mast and, therefore, a guy system, which adds more weight and complexity.

Antennas are a never-ending source of options and experimentation, so go out and try something new.

73 Bob K0NR

The post KB1HQS Arrow Antenna Mods appeared first on The KØNR Radio Site.

Checking Out The KT-WP12 Transceiver

I’ve been interested in the idea of a microphone-centric radio and wrote about it here: How About a Mic-Centric Mobile Transceiver? Shortly thereafter, I discovered that QYT has introduced a VHF/UHF ham rig that has the display and controls in the microphone (Model KT-WP12).

You may want to watch the video by Tech Minds, which does a good job of introducing the radio.

I was very keen on trying this radio out, so I purchased one, paying about $110.

On the Bench

First, I did some bench tests to check the basic performance of the radio. The receiver sensitivity, transmit frequency and FM deviation all looked very good. The one specification that was disappointing was the RF power output. On the 2m band, the output power was 20.6 W, while the 70cm band was 15 W. The specification for the radio is 25 W. The power was measured using an HP 8920A RF Communications Test

I’ve noticed this on other radios from Chinese manufacturers: the basic specs of the radio check out, except the RF power level is low.

User Interface

As you might expect, cramming all of the controls into the microphone is a challenging user interface design. I spend quite a bit of time playing with the radio at home before actually using it on the air. Overall, I found the user interface to be acceptable, but several areas that should be improved.

QYT relies on the menu system to provide control of many of the settings. This is similar to the various Chinese handhelds where you push the MENU button to access the menus, followed by UP/DOWN to sequence through the menus, followed by MENU to access the specific setting. Then the UP/DOWN buttons choose the value of the setting and another push on MENU to accept it. The volume control setting is buried in this menu system, which seems like a poor choice. Fortunately, Mick/M0VMK pointed out that the volume can also be set by enabling the monitor feature (big button on the top of the mic) and hitting UP/DOWN.

The portable SOTA station with Bioenno battery.

This design depends too much on the menu system. A few user-defined buttons would be a real help. This radio could benefit from a serious redesign using User-Centered Design.

This radio has one receiver but allows for three independent frequencies to be displayed simultaneously. There is a scanning mode that tries to emulate a multi-receiver radio. This too is all too common with the Chinese radios…somehow they have it in their heads that this adds value for the user. My experience is that it mostly confuses the user. Most users would be better served with a single frequency display, supplemented with dual-watch and scanning capability.

You probably won’t be surprised that the user manual is terrible, also common with Chinese manufacturers, but this one is particularly bad. Same with the programming software…it mostly works (I had a few crashes) but it is poorly written.

On The Air (SOTA)

I was very interested in trying out this radio for Summits On The Air (SOTA) use. The idea is that the radio can be stuffed into a fanny pack, with the microphone, speaker, display, and controls in your hand.

The QYT radio stuffed into a fanny pack.

The basic concept of holding everything in the palm of my hand worked out quite well. The display was visible in bright sunlight, the speaker audio was clear, and the microphone worked great. I made a number of SOTA contacts and received good signal reports. I held the microphone in one hand and pointed the 3-element Yagi antenna with the other hand. (Joyce/K0JJW assisted with logging and we took turns working the SOTA chasers.)

As soon as I fired up the radio, I heard interference on the 2m band, not very strong but noticable. It sounded like it was coming from an FM broadcast station. Pointing the Yagi antenna in the direction of the FM station on the adjacent mountain seemed to confirm the source. I did not hear any interference on the 70cm band. I’ve operated from this SOTA summit before and have not noticed any interference with other equipment, including Yaesu handhelds. Also, I switched to my Yaesu FT-90 and the broadcast station was not heard. As various people have suspected, this indicates that the receiver in the QYT is not very robust in terms of rejecting off-channel signals. Of course, this is an anecdotal report, not based on bench measurements.

Bob/K0NR on a SOTA summit with the KT-WP12 in a fanny pack.

I also encountered an anomaly where after my transmission, the radio did not revert back to receive quickly. There was a few seconds where no audio was coming out of the transceiver. This caused me to miss a few responses to my CQ call. This issue requires some additional investigation. It may have just been operator error on my part. However, I suspect that the radio was probably locking onto another frequency but I am not sure (see previous comments about the three frequency scanning mode). So file this issue under “stay tuned for more information.”

Note that I did not use the radio very much on repeaters, focusing on SOTA simplex operating with no transmit offset or CTCSS.

Conclusion

On the positive side, I really like the microphone-centric approach that this radio uses. The user interface can be improved but it is good enough.

The two big limitations of this radio are 1) low RF power output and 2) weak off-channel receiver performance. Now you might say that the RF power is not off by that much but my interest is having a SOTA radio that greatly exceeds the power of a typical 5 W handheld. On the 70 cm band, this radio only put out 15 W, so only 4.7 dB better than a handheld. The poor receiver performance will tend be an issue on summits that have radio installations nearby. In some cases, this can completely prevent a VHF SOTA activation.

I will probably use this radio again for SOTA activations but I’ll be bringing along a backup rig, just in case.

The post Checking Out The KT-WP12 Transceiver appeared first on The KØNR Radio Site.

Power Box for Bioenno Battery

When operating portable, I use Lithium Iron Phosphate batteries from Bioenno. Most of my portable operating is for Summits On The Air (SOTA) and I wrote about it here:

My SOTA Battery Journey

For POTA activations, I purchased a larger, 20 Ah Bioenno battery and use it to power a Yaesu FT-991 (and other radios). This battery has worked out really well. It is a bit large for backpack portable and weighs 5.4 pounds, but I have taken it along on a few SOTA activations.

Powerwerx PWRbox

I decided the battery could use a case to protect it while being tossed around in the back of the Jeep. Powerwerx has a really good battery box that includes a digital voltage readout, automotive (“cigarette lighter”) socket, dual PowerPole plugs and high-current binding posts.

The Powerwerx PWRbox

Initially, I did not think I needed the extra gizmos, and I did not want to take up more space with the battery system. Later, I figured that I could always pull the battery out of the box and use it in its original form.

The top of the battery box, with the connector covers open.

The power switch is handy for turning on/off the battery power and the digital voltmeter provides a simple view of the battery condition. Most of the time, I use the PowerPole connectors to connect up my radios but occasionally the automotive socket comes in handy.

The 20 Ah Bioenno battery sits inside the box with plenty of room to spare.

I used some of the plastic packing material that came with the box to hold the battery in place. A little bit of cutting with a sharp knife produced a good fit. There is enough room above the battery for the Bioenno charger, so it makes for a nice kit. The charger connects to the original charging plug on the battery.

The wiring underneath the lid of the box.

As expected, Powerwerx did a good job of wiring up the various components and included fuses in both the positive and negative cables. The box is big enough to hold a 40 Ah battery and I am tempted to upgrade it for larger capacity, but the 20 Ah battery has been sufficient, so far.

I’ve used this battery box for multiple POTA activations and a few other situations when I just needed to power up a radio at home. It works great. The voltmeter gives me a quick check of the battery status and the PowerPole connectors make for easy hookup.

The PWRbox costs $109.99, battery not included.

73 Bob K0NR

The post Power Box for Bioenno Battery appeared first on The KØNR Radio Site.

One Radio To Rule Them All (Ham, GMRS, FRS, MURS)?

The common Baofeng UV-5R can transmit and receive on a wide range of frequencies…but not necessarily within FCC rules.

From time to time, the question is raised about using radio equipment in multiple radio services. One common example is a licensed radio amateur that wants one radio to cover the Family Radio Service (FRS), General Mobile Radio Service (GMRS), and the 2m/70cm ham bands. Some people also want the Multi-Use Radio Service (MURS)…or maybe even marine VHF or aircraft VHF. The thinking goes that if one radio can transmit and receive on all these frequencies and that person is authorized to use those frequencies, then one radio can do it all.

This seems like a reasonable objective but the problem is that the FCC has a few rules and regulations that come into play.  This leads to an important note: I am writing about the FCC rules and regs here…you may choose to ignore them but that’s on you.

Part 97: Amateur Radio Service

First, the good news. The Amateur Radio Service, governed by FCC Part 97, has very few restrictions on the type of equipment you can use. Heck,  you can build a transceiver from parts and put it on the air. So the ham rules are not going to be a major limitation.

Part 95: FRS, GMRS and MURS

FRS, GMRS, and MURS radios are governed by FCC Part 95.  Section 95.591 says this about FRS radios:

§ 95.591 Sales of FRS combination radios prohibited.

Effective September 30, 2019, no person shall sell or offer for sale hand-held portable radio equipment capable of operating under this subpart (FRS) and under any other licensed or licensed-by-rule radio services in this chapter (devices may be authorized under this subpart with part 15 unlicensed equipment authorizations).

Section 95.1761 says this about GMRS transmitters:

(c) No GMRS transmitter will be certified for use in the GMRS if it is equipped with a frequency capability not listed in § 95.1763, unless such transmitter is also certified for use in another radio service for which the frequency is authorized and for which certification is also required. No GMRS transmitter will be certified for use in the GMRS if it is equipped with the capabilities to operate in services that do not require equipment certification, such as the Amateur Radio Service. All frequency determining circuitry (including crystals) and programming controls in each GMRS transmitter must be internal to the transmitter and must not be accessible from the exterior of the transmitter operating panel or from the exterior of the transmitter enclosure.

(d) Effective December 27, 2017, the Commission will no longer issue a grant of equipment authorization for hand-held portable unit transmitter types under both this subpart (GMRS) and subpart B of this part (FRS).

The Midland MXT400 is a typical GMRS mobile transceiver.

Similarly, MURS radios have this restriction (Part 95.2761):

(c) A grant of equipment certification will not be issued for MURS transmitters capable of operating under both this subpart (MURS) and under any other subparts of this chapter (except part 15).

The FCC is saying (requiring) that FRS, GMRS and MURS radios must work on their designated frequencies and nothing else. At one time, it was legal to sell a combination FRS/GMRS radio but the FCC has specifically removed that option. Part 95.1761 seems to leave an opening for a GMRS radio that is also certified for use in another radio service, but that is a very thin opening and it specifically excludes the Amateur Radio Service.

Now, why would the FCC put these restrictions in the regulations? The answer is pretty simple: these radio services are intended to be used by everyday, non-technical folks. The radios need to be simple to use and not include the capability to wander off onto any old frequency. Hence, the rules lock down the frequencies that the radios can use.

(As a side note, this regulatory approach is good for amateur radio. Imagine if FRS radios had Channel 30 set up to transmit on 146.52 MHz, with a note in the manual that says “only use this channel if you have an amateur radio license.” We would have a crapton of unlicensed operating on 2 meters.)

Part 90: Private Land Mobile Radio Services

Part 90 regulates a broad range of land mobile radio, including public service, police/fire, search and rescue, forestry, utilities, and businesses. Licensing is very specific under Part 90. A radio license will specify a particular set of frequencies allowed, specific power levels and emission types, and even the allowed operating location of the radios.

Radios designed for Part 90 are usually programmed by a radio tech to operate only those specific frequencies that a licensee is authorized to use. This results in a relatively simple operating set up with the user just selecting from the preset channels on the radio. Part 90 radios normally cover a wide range of frequencies so that the manufacturer and the radio shop can sell one radio model to any licensed user.

In many cases, these Part 90 radios cover the adjacent amateur bands, such as 2m and 70cm. (For example, the Anytone AT-D878UV is Part 90 certified and covers 140-174 MHz and 400-480 MHz.)   So this does open up the possibility of using a Part 90 radio under a Part 90 license and using it on the ham bands. A typical scenario is when a Search and Rescue member has a Part 90 radio set up to use the S&R frequency as well as the 2m/70cm amateur bands. The key to this is starting with a radio that is Part 90 certified and then programming it for the amateur band.  Of course, you need to be authorized to use the Part 90 frequency and have an amateur radio license.

Getting Creative on Radio Configuration

A few years ago, Anytone Tech tried to market the TERMN-8R VHF/UHF radio as legal for the ham bands, GMRS, MURS and Part 90 use.  An early review of this radio is here on the PD0AC blog. Basically, the radio had three distinct operating modes: GMRS, MURS, and Commercial/Normal. Initially, the FCC approved the radio but later took a closer look and canceled the authorization. The TERMN-8R is still available but without the three modes. It is marketed as a Part 90 radio that also does the amateur bands.

The Anytone TERMN-8R handheld transceiver.

I recently became aware of the Anytone AT-779UV which is sold in the USA as a Part 95 GMRS radio. However, using the programming software, the radio can be configured to cover the 2m and 70cm amateur bands or a much broader range of frequencies (136-174 & 400-470 MHz). If you change the radio configuration to operate on the ham bands (or wider), the radio is no longer Part 95 certified. The configuration via software takes some knowledge and effort so it is not a mode that you can easily switch back and forth. It is really no different than other software-programmable radios.

 

 

 

Wrap It Up

So there you go, your dream of One Radio To Rule Them All (FRS, GMRS, MURS, and the 2m/70cm ham bands) is not going to happen. At least not legally. You can configure a radio to do this…but it will not meet FCC regulations.  However, you can configure a Part 90 radio to operate legally on Part 90 frequencies and on the amateur bands.

The post One Radio To Rule Them All (Ham, GMRS, FRS, MURS)? appeared first on The KØNR Radio Site.

A Decibel Is Still A Decibel

When discussing signal levels and power output, hams like to say things like:

Using higher power isn’t important because it only gives you one additional S unit

and

You’ll lose some power in the coax but you won’t even notice a few dB

These statements are often true and at the same time may be completely wrong. I’ve noticed that radio amateurs pushing the limits of their station pay close attention to every decibel they gain or lose. This is especially true at VHF/UHF frequencies where signals may be weak. A dB here, a dB there, the next thing you know it adds up to something big!

Definitions

First, let’s make sure we have a few definitions right. The decibel (dB) is defined as the ratio of two power levels:

dB = 10 log (P2/P1)

One decibel corresponds to a 26% increase in power level. A well-known rule of thumb is that doubling the power corresponds to a 3 dB increase. Similarly, chopping the power in half drops the signal level by 3 dB.  A 10 times increase in power is 10 dB. (Voltage can also be used to calculate decibel relationships but to keep it simple, I’ll just use power.)

The S Unit is normally defined as a 6-dB change in signal level, which is a factor of 4 in power. (Your S meter may or may not actually follow this rule but that is a topic for another day.)

Power Level

Let’s compare a few different power levels to get a feel for how decibels and S units behave. Let’s use a 5 watt QRP level as our reference power. If we crank up the power to 100 watts, we  have 10 log (100/5) = 13 dB increase in power level. This is slightly more than two S units (2 x 6 dB), so we would expect the S meter on the other end to read 2 units higher.

Now suppose we kick in our linear amplifier to produce a 1 kilowatt RF signal. This power level is 10 log (1000/5) = 23 dB higher than the 5 watt signal, or roughly four S units.

Now if our QRP signal was a solid S9 to start with, adding another 23 dB on top of it may not be that significant. The station can be heard at S9 or can be heard even louder at S9 + 23 dB. Except when there’s a pile of stations all calling that rare DX…then the loudest station tends to be heard. Crafty operating skill and good luck may overcome the power difference.

But consider the other extreme. Our QRP station is being heard right at the noise floor on the receive end. The two stations are struggling to complete the contact and the propagation path degrades by 2 dB. Now the QRP station is below the noise and uncopyable. We increase our power to 100 watts and gain 2 S units…still not very strong but the ability to receive the signal improves dramatically. Crank it up to 1000 watts and you gain another couple of S units and the copy is quite good. The key point is that changes in signal level matter most at the margin, when you can just barely copy the signal. (By the way, there is nothing wrong with running QRP…many ops enjoy the challenge of making contacts with low power.)

At the receiver, our ability to recover the signal is determined by the signal-to-noise ratio (SNR). A higher noise floor at the receiver means it will be more difficult to hear the signal coming in. The type of modulation being used may also make a big difference. Good old CW and the WSJT modes use a narrower bandwidth and will get through when wider-band modulation (SSB, FM) fails. In all cases, a stronger signal works better.

Antennas

Antenna systems also increase our signal level…and they do it for both transmit and receive. I recently did some comparisons of VHF antennas from a SOTA summit. My 2m Yagi antenna has 6 dB of gain (referenced to a dipole) and my comparisons showed that the performance of this antenna was good enough to pull some signals out of the noise to be solid copy. This occurred when the other station’s signal was right at the noise floor (using my lower gain antennas) such that the 6 dB improvement had a significant impact.

Sometimes hams will say that VHF is just line-of-sight propagation and that the signal level doesn’t matter much. This is partially true but often we are stretching for contacts beyond line-of-sight. Take a look at this article: The Myth of VHF Line-Of-Sight. This is another case where we are operating on the margin and every dB matters.

Feedline loss can cause us to lose decibels, which impacts both transmit and receive performance. If your coaxial cable is short, then the losses may be negligible. Increasing cable length and increasing frequency produce more loss. For example, 100 feet of RG-8X has only 1.1 dB of loss at 10 MHz. Increase the frequency to 146 MHz and the loss jumps to 4.5 dB, using the Times Microwave cable calculator. That means 50 watts of power at the transmitter turns into 17.7 watts at the other end of the cable. Using LMR-400 coax reduces the attenuation to 1.5 dB.

Summary

You can choose to ignore small changes in your signal level. A dB here or there may not make a big difference with casual ham radio operating. But these losses tend to add up and may become significant. Most importantly, just a few dB may be the critical difference between making a radio contact or not, when operating at the margin.

The post A Decibel Is Still A Decibel appeared first on The KØNR Radio Site.


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