'Quiet' VHF transmission problem with good VSWR readings

S

Sierrafox

New Member
Joined
23 Aug 2013
Messages
12
Visit site
Hi

First time poster looking for some help in diagnosing an odd VHF transmission problem with a new Standard Horizon GX1700E radio. Reception is perfect but when I broadcast on 1W or 25W, any receiving station (if they hear it) responds that the signal is extremely quiet. It seems to make no difference whether the signal is received by the boat next door or a mile out.

Initially I just assumed it was a problem with my installation. I purchased another aerial for the stern rail. Same symptoms. Then I purchased a neat cheap VSWR meter. It showed VSWR values of between 1.00 and 1.17, broadcasting on both 1W and 25W on both mast and stern aerials. The Tx power readings on the meter were around 0.5W on the 1W setting and 22.5W on the 25W setting. Apart from a suspiciously good VSWR reading of 1.00 (mast aerial on 1W), the transmission values seems fine to this amateur. This being so, I returned the set to the supplier. However, they returned it back stating that they found no problem. They did claim to check Tx, Rx and modulation, but made no mention of checking the microphone directly.

I was going to email the supplier and complain about their testing, as I can't see how my installation(s) could lead to a 'quiet' transmission. However, thought I would check here first to see if anyone had any suggestions? In case it matters, the hull is aluminium and the set is grounded to it. Also, no big drops in power supply voltage and it was tested once with the inverter off.

Thanks

Shane
 
I would suspect a microphone or modulation problem. From your description it is unlikely there is anything wrong with the installation.
 
Thanks Jiris. That was my understanding too. They said they checked modulation but didn't mention the microphone on the test report. I just wanted to check I wasn't missing anything obvious.
 
At risk of teaching granny to suck eggs... The microphone has built in noise cancellation, if you don't put your mouth to it just right it ought to ignore you. I think the manual says your mouth should be half an inch from the oval slot.
It's a very common vhf, maybe you could borrow someone else's to swap mics/anything else that can be swapped? Sending it back to the supplier with a note to say that an identical,one worked on your boat carries a shed load of weight.
 
Yes proximity to the mic makes a difference. A friend's wife tried to make a test transmission and held the mic several inches away. quiet transmission was cured by telling her to get up close
 
Thanks for the suggestions. I do remember speaking very loudly (and possibly closely) while testing to see if it made a difference, but it didn't seem to. I will try again and see how I get on.
 
Sorry, meant to add... unfortunately the mic is non-removable, without opening up the case and no doubt voiding the warranty. I agree it would be pretty conclusive though if a different mic worked. Seems like something the supplier should have tested when I sent it back.
 
Sierrafox said:
Hi

First time poster looking for some help in diagnosing an odd VHF transmission problem with a new Standard Horizon GX1700E radio. Reception is perfect but when I broadcast on 1W or 25W, any receiving station (if they hear it) responds that the signal is extremely quiet. It seems to make no difference whether the signal is received by the boat next door or a mile out.

Initially I just assumed it was a problem with my installation. I purchased another aerial for the stern rail. Same symptoms. Then I purchased a neat cheap VSWR meter. It showed VSWR values of between 1.00 and 1.17, broadcasting on both 1W and 25W on both mast and stern aerials. The Tx power readings on the meter were around 0.5W on the 1W setting and 22.5W on the 25W setting. Apart from a suspiciously good VSWR reading of 1.00 (mast aerial on 1W), the transmission values seems fine to this amateur. This being so, I returned the set to the supplier. However, they returned it back stating that they found no problem. They did claim to check Tx, Rx and modulation, but made no mention of checking the microphone directly.

I was going to email the supplier and complain about their testing, as I can't see how my installation(s) could lead to a 'quiet' transmission. However, thought I would check here first to see if anyone had any suggestions? In case it matters, the hull is aluminium and the set is grounded to it. Also, no big drops in power supply voltage and it was tested once with the inverter off.

Thanks

Shane
Click to expand...

It’s hard to diagnose without the “subject on the operating table” but these are the most common issues
Low Modulation: low recovered audio at the receiver means the transmitter was not modulated very much. This could be due to a defective microphone, poor microphone technique, or low microphone gain in the transmitter.

Garbled Modulation: if the transmitter antenna is too close to the transmitter, the radio signal can interfere with the transmitter. This usually results in garbled modulation. Repeat the check on 1-WATT power and see if the modulation sounds better. If the modulation is clear at 1-Watt and garbled at 25-watt, your transmitter is too close to the antenna.

No Modulation: lack of any audio modulation is usually a broken microphone, a bad connector, or a broken wire in the cord.
Weak Signal (not weak modulation): the transmitter output is below 20 to 25-watts due to malfunction of the transmitter, poor antenna, poor transmission line.
I can’t see anything besides these that could cause the receiving station to barely hear you.
 
Thanks GregOddity. I will check my microphone technique and any difference between 1W and 25W. If it's any of the other problems, then it's back to the supplier. The set was originally tested with the antenna at the top of a 14m mast, so I'm guessing it is unlikely to be antenna proximity, but worth a try. The VSWR meter states 22.5W for power transmitted so I'm guessing it is not a weak signal. However, that figure may be derived in a way I don't understand.

I'm still a little suspicious of my ground plane connection, as I have an aluminium hull, which obviously is an extremely good conductor for any electrical leaks. I do have an isolation transformer and galvanic isolator for the 240v though.
 
Sierrafox said:
I was going to email the supplier and complain about their testing, as I can't see how my installation(s) could lead to a 'quiet' transmission. However, thought I would check here first to see if anyone had any suggestions?
Click to expand...
I've always found Standard Horizon to be very helpful, a chat with them before sending it back would probably be worthwhile.

As mentioned above, the instructions do say that it's a noise cancelling microphone (page 28) and needs to be within 1/2 inch (1.3cm) from your mouth. That's a lot closer than I would instinctively hold the microphone........
I guess a noise cancelling mike will have very low gain so as to reduce background noise and rely on a strong (close) input.

It's almost certainly not a antenna or transmission problem per-se, IMHO it's likely to be something to so with low modulation caused by microphone gain (or lack of it)
 
Sierrafox said:
Thanks GregOddity. I will check my microphone technique and any difference between 1W and 25W. If it's any of the other problems, then it's back to the supplier. The set was originally tested with the antenna at the top of a 14m mast, so I'm guessing it is unlikely to be antenna proximity, but worth a try. The VSWR meter states 22.5W for power transmitted so I'm guessing it is not a weak signal. However, that figure may be derived in a way I don't understand.

I'm still a little suspicious of my ground plane connection, as I have an aluminium hull, which obviously is an extremely good conductor for any electrical leaks. I do have an isolation transformer and galvanic isolator for the 240v though.
Click to expand...

The aluminium hull can be a problem with grounding and depending what cables you are using. I’ve had problems with cables that are sold to a high standard and still the shielding left lots to be desired and gave issues and kinks until we changed them for new ones. You can also have some faraday effect with the smaller stern antenna, but my money is on the modulation and the microphone gain.
You may also need to check your fuse boxes and make sure all the terminals are well clean. As someone pointed out on a different thread, there is a peak of power as you press the mic and if your fuse or connector’s are not in their prime it will lead to arcing and problems.

Afterthought,
I don’t really think it’s to do with the hull. You describe a pretty good install and although you may have issues with grounding I fail to see how that could influence the power output of your radio unless you had a short. And that you would notice. Having a power loss is a more realistic scenario and that could be a fuse or a bad connection and when you press the mic the power surge arcs and creates loads of resistance that will affect your modulation. Oxidation is the scourge of modern electronics. Very small surfaces of contact, easier to wipe out in aggressive environments.
Having said that I still think mic gain and positioning to be something you need to test, especially on a noise suppressing mic. Aviation mics are like that, you talk 3cm away from the mic and a whisper comes out the other end of the string.
 
Last edited:
Great suggestions all, thanks. Seems to be a consensus around the mic, either gain or technique. As there is no mic gain control, my test will have to be around technique. Agree that the distance from the mic is not intuitive. If after testing with the correct distance it still doesn't work, I will have a talk with Standard Horizon.

Greg, I did test for a voltage drop on the power feed into the radio when transmitting at 25W. It dropped to about 12.3V which I presume is not excessive (I think the inverter/charger was on trickle mode at the time). Also, I'm guessing the fact that the VSWR meter is showing a transmitted power of 22.5W would seem to indicate the power is getting to the antenna. However, I don't understand the mechanics of this and perhaps the power is there but the signal has been corrupted by resistance.

There didn't seem to be any oxidation when I first wired the radio up, but I agree oxidation is a scourge. Frankly, I can't understand why my fuseboard doesn't have seals and grommets.
 
Sierrafox said:
Great suggestions all, thanks. Seems to be a consensus around the mic, either gain or technique. As there is no mic gain control, my test will have to be around technique. Agree that the distance from the mic is not intuitive. If after testing with the correct distance it still doesn't work, I will have a talk with Standard Horizon.

Greg, I did test for a voltage drop on the power feed into the radio when transmitting at 25W. It dropped to about 12.3V which I presume is not excessive (I think the inverter/charger was on trickle mode at the time). Also, I'm guessing the fact that the VSWR meter is showing a transmitted power of 22.5W would seem to indicate the power is getting to the antenna. However, I don't understand the mechanics of this and perhaps the power is there but the signal has been corrupted by resistance.

There didn't seem to be any oxidation when I first wired the radio up, but I agree oxidation is a scourge. Frankly, I can't understand why my fuseboard doesn't have seals and grommets.
Click to expand...

From what you say, it sounds like its working. Those values are what I would expect. The mechanics of it all is a TAD of a whiff more complicated to explain.
But don’t read too much into the VSWR meter, it’s not a very precise instrument. And it’s a complex field to try and explain in plain English.
But despair not. Good o’ll Larry Butler (@W4CSC) has explained it all in simpler words then I could muster. So with a nod to a great brain and hopping he’s enjoying his retirement here are some of his words.
And I quote :
> I've seen many posters talk about antennas and know lots of boaters
> with antenna troubles and no clue how to see how it's doing, way up
> there, so thought I'd stick my neck into the guillotine and give some
> basic instructions on what an SWR meter is, what it does, and what it
> means after you learn how to use it. This will be all about VHF
> marine band, but is the same for any frequency the meter is made for.
>
> FIRST, let me say not all SWR meters are suitable for VHF marine band
> use. The reason for this has to do with the directional coupler, the
> part that senses power going this way and power going that way built
> into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
> out of its design range and its directional coupler is too long. Put
> using a CB SWR meter out of your mind. It's not a good reading. A
> ham radio VHF SWR meter IS acceptable as its range is usually from 140
> to 170 Mhz, which includes our VHF marine band. Most boaters will get
> the little white Shakespeare VHF power and SWR meter from Waste Marine
> or some other overpricing boat shop so that's what I'll use for my
> example.
>
> These little passive SWR meters use the RF power of your radio to
> power the meter and require no batteries or power source. One guy I
> know got no reading and through the meter had dead batteries in it.
> There aren't any. His transmitter power amp was kaput....no output.
>
> THE CONTROLS.
>
> The controls on it are quite simple. There's a switch that switches
> from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
> switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
> jack plugged into a 50 ohm dummy load like the guys at the factory did
> to calibrate it. Depending on the position of the meter in the line
> of a defective antenna system, it might read way low or it might peg
> on 1 watt. Consider it fairly accurate if the SWR of the antenna is
> quite low (below 1.5 to 1)
>
> So, What's SWR??.....
>
> SWR (pronounced as three letters, unless you're on CB where it's
> called "swur" for some reason noone knows) means Standing Wave Ratio.
> The keyword there is RATIO, a measurement of the peak voltage found on
> the transmission line in one place, compared to the minimum (trough?)
> voltage found 1/4 wavelength from that peak in either direction.
> These peaks and valleys are caused by reflections of an imperfect or
> off-tuned antenna, bad connectors, kinked transmission lines bent too
> sharply and a lot of just poor luck. You can watch these waves out by
> the seawall. If you toss a rock into the water (transmitter) it
> creates waves that expand out in all directions. When the wave
> bounces off the seawall, watch what happens. The wave coming in from
> the stone bounce off the REFLECTIVE seawall and go BACK towards the
> transmitter, a "reflected power" that wasn't absorbed by the wall. As
> the reflected waves pass through the incoming waves that haven't
> reflected, yet, notice how there is a wave that doesn't move.....a
> Standing Wave that has PEAK positions that stand still a set distance
> from TROUGH positions, that also stand still.
>
> The same exact thing is going on in your antenna system, every time
> you press that button. In electronics, there are two simple devices
> that STORE electrons....capacitors that charge (electrostatically) and
> inductors that store energy (magnetically). If you doubt this, go out
> and pull the spark plug wire off a running Seagull outboard to test
> this theory....we'll wait. Ah, I see you're back? Why do you look so
> "shocked"? Did it work?
>
> A perfect RF transmission system perfectly transfers the power from
> the transmitter to the perfect antenna, which radiates all the power
> the transmitter put out into the air, blasting all the recievers with
> your fantastic signal so they can hear your pleas for help. These
> systems do not exist. The antenna is never tuned to your channel,
> only close to your channel (we hope) and the transmission line is that
> cheap white crap from Wasted Marine or RatShack, not rigid coaxial
> line used by broadcast stations, made to exacting standards. To keep
> it short, the line and antenna have "reactance", like that wall. And
> it's that reactance (inductance and capacitance) that cause anomolies
> that make reflections, like that wall.
>
> What can we do? How can we measure how bad it is?...............
>
> Most marine antennas are sealed up and "pretuned" for open areas. Not
> much we can do to "tune" them to the middle of the band. I like old
> Metz antennas, made by an old ham company, just because I can trim
> that element for best results. It's tunable. That fishing pole of a
> fiberglass antenna is actually a little, specially bent wire embedded
> inside fiberglass to keep it straight (and disintegrate reliably in
> sunshine so you can replace it, often). "Pruning" the tunable antenna
> requires us to measure SWR at different frequencies so we can center
> its curve up on the band we want for best results.
>
> What "curve"??
>
> An antenna "resonates", where the inductance balances out the
> capacitance and acts like a radiating resistive load, over a fairly
> large range of frequencies, not just one. Lucky for us.....it can be
> made to pass channel 1 and channel 72, fairly reliably, without
> retuning like you have to do to change channels on the HF SSB antenna.
> The curve looks kinda like this:
> | * *
> SWR| * *
> | * *
> | *
> Frequency>>
>
> If we center the best (lowest) SWR up in the middle of the band, it
> will have an acceptable SWR (low) on channels on the bottom and top we
> want, and are allowed to use. Part of the testing, we will test
> different channels across the marine band to get an idea of what YOUR
> plot would look like.
>
> So, how do we measure SWR??.............
>
> For the little meter to measure the antenna, it has to be located
> INLINE with the RF power, between the transmitter and antenna.
> IDEALLY, we'd like to adjust the antenna with the SWR meter located
> between the transmission line, antenna end, and the antenna's coax
> connector. Obviously, sometimes, this is not practical for a simple
> test. However, the further you are from the antenna, back down the
> transmission line, the less the reading is about the antenna SWR and
> the more the reading is about the cable losing the signal (attenuation
> and leakage) and the reactivity of the cable, itself. If we measure
> the SWR at the antenna end, the SWR we measure is only about the
> antenna. If we measure it where it's easy, at the radio, the reading
> is about the antenna AND the cable, so you can't tell which is at
> fault if it sucks.
>
> OK, let's assume you're like me, hate heights, weigh too much to haul
> up on a winch with less than 6 strong arms on a winch handle and the
> bos'n's chair might not like the load, anyways. So, we'll measure the
> antenna at the radio end, at least until we find it's all screwed up.
> Disconnect the antenna from the radio, with the radio off so you don't
> inadvertently transmit into an open which might do harm to the
> transmitter.
>
> Now you need a "coax jumper" that didn't come with the meter. Radio
> Shack has them, so get one that's just long enough to hook the meter's
> RADIO port to the radio so we can still read it and switch the
> controls. If you'd like to MOUNT the meter on your panel, buy two
> right-angle UHF 90 degree adapters so we can mount the meter on the
> front of the panel and the L-shaped connectors will go back through
> the panel to connect the cables to. That would let you see power
> output every time you keyed the VHF so you'd be SURE it was
> transmitting, instead of calling out for a radio check so often. I
> leave them in SWR to watch the antenna, here.
>
> Hook the antenna to the antenna jack and the jumper between the Radio
> jack and the radio. Turn on the radio and tune it to a commercial
> channel not monitored by the DEA or USCG around 40-something. Put the
> meter's little switch in the REFERENCE or SET position and turn the
> set control all the way to the left, to keep from pegging the meter.
> Test at FULL POWER so you can see if something up there is arcing at
> FULL POWER (the meter jumps up in SWR if it is).
>
> Key the transmitter and don't talk into the mic. Turn up the SET level
> "volume" control until the meter reads FULL SCALE, all the way to the
> SET mark. This sets the reference level of the meter to the power
> coming out of the radio "under these conditions". Once set to full
> scale, flip the switch to SWR and pray it drops all the way to 1 on
> the SWR scale (no reflected power) indicating I was a liar and there
> IS a perfect antenna system.....Read the pseudo-accurate meter SWR
> scale. 1 is the left edge (1:1 standing waves - there aren't any
> standing waves because the antenna is perfect). The next mark up is
> probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
> Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
> marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
> mic before the cops start looking for you.
>
> What does this mean??
>
> Here's the relative power levels of the major points.
>
> 1.0 SWR....no reflected power....all 25W is going out on the air
> 1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
> out and noone notices anything because you couldn't measure 4% out of
> the lab.
> 2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
> goes out on the air and STILL noone notices anything unless they are
> magicians.
> 3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
> goes out on the air. Someone comparing this antenna with your perfect
> antenna just notices a little movement in his S-meter on the other end
> if you're weak. 3.0 and above is considered "bad SWR" and something
> needs to be fixed.
>
>
>
> CB myths........
> 1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
> they get this from? ANTENNA MANUFACTURERS selling new antennas,
> that's where. They made millions from this myth. Wanna see a real
> broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
> http://www.wzpxtv.com/wzpxtransmitter.htm
> This a real readout of a powerful +megawatt TV transmitter from WZPX
> on Channel 44 (with a nice new digital TV transmitter, too!) The
> software company puts it on the net. SWR tonight on the
> beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
> really high at these power levels. On your boat, it's not. You don't
> have thousands of watts coming back down the pipes at you!
>
> Ok, now always turn the SET control back to the left before unhooking
> the meter or changing channels. Do it now.....
>
> Ok, make the same measurements on a few channels (not 16, 22A please)
> across the marine band. Record your SWR results and make a crude
> chart of them plotting SWR measured against channel (frequency) number
> like I did above.
>
> Is the lowest SWR near the middle of the channel numbers? No? Does
> the curve at least have a low point (dip) inside the marine band?
> Yes, but the dip is around Channel 3 and SWR is much higher at Channel
> 72 (why they could hear you on 16 but not 72 way off). The antenna is
> tuned too LOW. If it's tunable, we need to shorten the element to
> raise the resonant frequency. If 1 is high SWR and 72 is low, we need
> to lengthen the antenna element. Ideal is a curve with its low point
> somewhere in the middle of the band with less than 2:1 SWR on any
> channel. The curve shows you where the antenna tuning is and how
> broadbanded (how many channels will it radiate well).
>
> If you measure this curve up at the antenna before all that cable
> attenuates the SWR reading, it will simply be much more pronounced
> because the cable attenuates power up as well as it does power down
> the mast....making our reading weaker by a bit. AS you can see,
> tuning an antenna ISN'T rocket science. If the channels you use are
> all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
> If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
> CABLE OR THE MEASUREMENT, because every antenna has a curve.
>
> Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
> trim the antenna the way it shows in the instructions......
>
> You all should be able to measure SWR just fine with the little
> meters, now, and have a vague idea of what it means.
>
> Please leave the classroom quietly so's not to wake the four students
> in the back row we lost. (Class quietly leaves, instructor slips out
> and puts lights out with them still asleep. One once slept right
> through lunch....(c
>
>
>
> Larry W4CSC
>
> "Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"


If it’s a wave and has a frequency, Larry is your man. Electronics Tech/ metrologist USN.
 
It certainly sounds like a modulation problem either mic or the way it is used. I have an old VHF set here that is similar and I have tried different mic etc but it is only a spare. I suggest get a hand held and a helper to check loudness of modulation. Also get the helper to use the mic and you listen. Is it louder if you shout? Mic is usually held side on to the mouth so you don't spit into it but with mic aperture (usually centre front of top part) as close to lips as possible. olewill
 
Sierrafox said:
Sorry, meant to add... unfortunately the mic is non-removable, without opening up the case and no doubt voiding the warranty. I agree it would be pretty conclusive though if a different mic worked. Seems like something the supplier should have tested when I sent it back.
Click to expand...
If you think there may be something wrong with the mic, why don't you borrow/buy/nick a RAM3 which will give you another microphone?
 
Greg (and by extension Larry!)
As you said, complicated but well explained, to the point that even I understand... mostly. My VSWR meter (a Surecom Sw-102) doesn't have the Reference or Set position to test against, but otherwise I can try the tests. What stood out in particular was that my power readings seem to require a dummy load to test against. That would indicate that my power readings might be suspect. However, they are oddly accurate with a reading of 22.5W for the 25W setting versus a reading of 0.5W for 1W.


Olewill and Findus
Thanks, but a RAM3 microphone is about 2/3 the price of an entire new set. I also don't know anyone in this marina and am just passing through. A handheld sounds like an excellent idea though. It would seem to be the best way to test both loudness and technique, and if I get one with an external antenna fitting, it will help determine whether the set or my installation is at fault. Not to mention it is very useful anyway as both backup and for the dinghy.
 
Good to know. Will have to add it to my growing list of VHF accessories!
Handheld arrived today and mast is getting stepped on Thursday, so should get to the bottom of it soon. Will add to this thread when I have the answer.... even if it is just not holding the damn mic close enough.
Thanks for the help. Hope the sailing and looking at boats (a delight of its own) was fun.
Shane
 
Sierrafox said:
Good to know. Will have to add it to my growing list of VHF accessories!
Handheld arrived today and mast is getting stepped on Thursday, so should get to the bottom of it soon. Will add to this thread when I have the answer.... even if it is just not holding the damn mic close enough.
Thanks for the help. Hope the sailing and looking at boats (a delight of its own) was fun.
Shane
Click to expand...

No worries, I hope you get it sorted. I’m going to install a new radio and antenna and wiring, mast is coming down on Wednesday. (crossing my fingers)
I bought a new boat :cool:
Greg
 
You must log in or register to reply here.

Share this page

Top