Maldol AL-500H VHF/UHF airband whip

[nanZor]

The Maldol AL-500H/HS whip is a thin, whippy dual-band duck for the VHF airband, and UHF milair band. Essentially, it provides a quarter wave on each band, with a small decoupling coil in the middle. It is available in both BNC and SMA versions.

While there are many other choices of improved antennas available, the one area where the Maldol shines above the rest if for what it doesn't do - namely it is a narrowly-tuned antenna with good rejection of the FM broadcast band.

This rejection may not be noticed by those in urban areas far away from FM broadcasters, or have radios with great bandpass filters. Strong FM broadcast signals don't always mean you will hear FM broadcasters in the airband(s). In my case, close to an FM broadcaster, it is as if someone turned my rf-gain down a little bit.

So I ran a test for FM rejection against the following antennas, using an Icom R6 with it's expanded S-meter:

Diamond SRH-77A
Diamond SRH320A
RS telescopic tuned to airband
OEM Uniden and RS ducks

For the test, I tuned to one of the offending FM broadcasters that overload my receiver. I attenuated the R6 so that I could actually detect a difference.

For the Diamonds and the telescopic, even with full attenuation, the FM broacaster pegged the meter. The OEM ducks were about 1/2 to 3/4 scale.

With the Maldol, the FM broadcaster varied from totally gone, to about a single flickering bar.

Recommendation: If you are in a metropolitan area, have a receiver with wide bandpass filters, or both, the Maldol comes highly recommended.

Even if you are not interested in the dual-band nature of the Maldol for milair, the FM broadcast rejection for the VHF airband makes it my top choice.

I am not sure why the Maldol is so narrowly tuned. I'm not going to cut it open to see if there are any additional tuning components inside the base. Perhaps the decoupling coil is making it narrow. I don't know. But the testing and my own listening with a variety of low-cost scanners tells me that the FM rejection is a welcome "feature".

 

[nanZor]

What about NOAA and pagers?

I forgot to mention that the narrowband nature of the Maldol attenuates these too.

Of course the venerable Diamond RH-77CA works GREAT here, so from an interference standpoint, this is not the best choice for airband if you are suffering from NOAA overload, or possibly pagers.

Know up front that if you run this test yourself, to see any difference on strong signals, you'll most likely have to attenuate the scanner first. The Maldol won't make a band disappear.

The objective is to try and attenuate out-of-band signals to the point where it won't affect your scanner's front end so much that it turns down the rf gain - making the offending station disappear completely is not always necessary.

Without any test gear, I can't get any sort of attenuation-slope figures for what is happening with the Maldol. AND, if your situation is bad enough, even the narrowband nature of the Maldol might not be enough.

What I can see for those who are just being totally crushed, is possibly trying a combination of say an AOR or PAR filter, in addition to a Maldol! Perhaps that will come in a later review...

 

[prcguy]

I have an AL-500H and believe the lump in the center of the whip is not a coil but a piece of solid plastic used as a dielectric junction to resonate a UHF frequency on the long VHF whip.
prcguy

 

[nanZor]

In the interest of science, I'll let you cut it apart.

The one reservation I have is really how effective is a very thin whip for the UHF milair side of things going to cope? Sure, it is resonant near 300 mhz (I think), but with a very thin whip I'd think that performance at the upper and lower ends of milair would suffer. Then again, this is just a short whip - photographers would just say to get a better signal with this, get closer!

I think to do it right for a milair duck, one would need something like a flat tape-measure type of antenna to get a wider bandwidth.

 

[prcguy]

I have several military mil air duckies, one is for the Motorola LST-5 series radio and its a braid covered spring about 1 1/4" dia and about 8" long. Another is for the Cincinnati Electronics HST-4 series and its a bendable spiral metal thing about 3/4" dia and 9" long. I can post pics if anyone is interested.

I'll patiently wait for you to cut your AL-500H apart and let us know if its a coil or solid plastic.
prcguy

In the interest of science, I'll let you cut it apart.

The one reservation I have is really how effective is a very thin whip for the UHF milair side of things going to cope? Sure, it is resonant near 300 mhz (I think), but with a very thin whip I'd think that performance at the upper and lower ends of milair would suffer. Then again, this is just a short whip - photographers would just say to get a better signal with this, get closer!

I think to do it right for a milair duck, one would need something like a flat tape-measure type of antenna to get a wider bandwidth.

 

[eorange]

I've had the RH77, SRH77, and the Maldol for many, many years. I use all of them in clear/intermod-loaded/questionable environments, all in the name of receiving VHF and UHF mil air across all regions of those bands.

Every time, they perform exactly the same; maybe a slight real or imagined advantage to the Diamond.

Given that, I prefer the Diamond because its not crazy floppy!

 

[nanZor]

I wish the Maldol was more stought, but I think that they are trying to eek out a very narrow bandwidth with it on VHF. I suspect something else is going on in the base, but I can't be sure unless I cut it open.

The overload from the FM broadcaster was noticed mostly on my PRO-106, and both of my clock-radio scanners - the Pro-136 and Uniden CRS370 (cheapest milair scanner I've run across!) I mean, it was usable, but until I played with some fm traps and whatnot, did I discover that I wasn't getting all the rf gain I should have. Then I re-evaluated the Maldol, and found out about it's narrow bandwidth.

In all honesty, I prefer the RH77CA if I don't have any issues as my all-rounder antenna, but around the neighborhood, I've got to use the Maldol.

 

[freqhunter]

As with eorange I have run both for several years. I am a huge Maldol fan. That being said I run the 77 most of the time for a couple reasons. First the performance difference between them is marginal. Second the 500 is far to long and delicate for everyday use. Especially when trying to be discreet in an airport. Watson also makes a air band antenna. It is 8" long and looks like a small version of the 77. It rocks for discreet work. Unfortunately I have worn the model number off the base.

 

[FrankJ]

How does the Watson air-band antenna compare to the Diamond RH77CA?

Yeah, I tried the Maldol years ago and was way too long for me! Same reception as the 77CA anyway....

 

[freqhunter]

The Watson does not perform as well as the 500 or 77. Given it's size though it works well.

 

[nanZor]

Yeah, I tried the Maldol years ago and was way too long for me! Same reception as the 77CA anyway....

Almost - except that the Maldol doesn't make as good as an FM broadcast antenna as does the 77CA.

I noted that the Maldol no longer appears at HRO, and it may have been discontinued. I'm not sure if the manufacturer has actually discontinued it, or HRO just stopped carrying it.

I think if you want one, now is the time...

 

[K2KOH]

I've used the Maldol 500...other than the antenna always flopping around I like it. It hears pretty well...

 

[RES51CUE]

what is sma version

 

[nanZor]

The sma version is the antenna connector type used. It differs from the standard BNC type - for instance most of the high-end Uniden handhelds use an sma connector. Recent Icom handhelds use the smaller sma type instead of BNC.

 

[sholt]

I have been on the forums a bit today in search of an antenna primarily for VHF air band monitoring, and I think this thread might be the one to help me make a decision.

I am between the RH77CA and was looking at the Watson W-901 (the airband antenna freqhunter mentioned above) though it sounds like performance wouldn't be amazing despite the convenient size.

The reason I have not been considering the Maldol is that it is apparently out of production. However, having seen this thread I am wondering if I should hunt down a used Maldol given how narrow band it is.

Some background:

I currently use a Grecom PSR-310 with either the stock rubber antenna or a radio shack telescopic antenna tuned to around 126MHz 1/4 wave. I don't seem to get a much better signal from the radio shack antenna. Better range, perhaps, but the signal-noise ratio is the main problem for me.

I live in San Francisco pretty much atop a hill facing south towards SFO. I am in an apartment with nowhere to put an outdoor antenna, hence my search for the best I can do with a whip/rubber/portable antenna.

O a good day my most distant low altitude signals are aircraft on finals at SFO communicating with TRACON prior to handing over to tower. Again, the main problem is the amount of noise making it difficult to hear the voice. Ideally I'd like to up the clarity of what I can receive, then as a bonus pick up more distant or obscured transmissions (I.e. SFO Tower).

Based on this, do you think I should try to track down the Maldol to really zone in on the frequencies I'm interested in while cutting off FM which may be causing trouble, or would you expect the RH77CA to do give me a good improvement? Or, as a last option, is my location likely just terrible and I should just wrap p warm and get on my roof?

Thank you for your help, sorry if this is a little long/newbie!

sholt

 

[nanZor]

...I currently use a Grecom PSR-310 with either the stock rubber antenna or a radio shack telescopic antenna tuned to around 126MHz 1/4 wave. I don't seem to get a much better signal from the radio shack antenna. Better range, perhaps, but the signal-noise ratio is the main problem for me.

One thing you can try is disabling/bypassing the low-band vhf coil and turning it into just a plain whip. With the coil inline and fully extended, it is resonant near 45 mhz. Fully extend the whip, and then push the element just above the coil down into the coil a bit until you feel some resistance - about a 1/4 inch or so. Then adjust the furthermost element if you like. This will bypass the coil as it makes contact with the internal fingers for bypassing.

I live in San Francisco pretty much atop a hill facing south towards SFO. I am in an apartment with nowhere to put an outdoor antenna, hence my search for the best I can do with a whip/rubber/portable antenna.

Sounds good, although you may be getting some FM broadcast desense/overload affecting vhf air.

Based on this, do you think I should try to track down the Maldol to really zone in on the frequencies I'm interested in while cutting off FM which may be causing trouble, or would you expect the RH77CA to do give me a good improvement? Or, as a last option, is my location likely just terrible and I should just wrap p warm and get on my roof?

The RH77CA is good, although it is resonant near 152 mhz (as measured on a Comet analyzer) or so for vhf low. For vhf airband, I find that standard 2M amateur whips a little better - although one could say we are splitting hairs for rx-only. One thing the Maldol has(had) was good FM broadcast attenuation. The loading coil really got very reactive off frequency helping this aspect. So does the Diamond SRH320A, which I really like as a substitute for the Maldol - at least on vhf airband - note - this is an sma mount.

The Maldol is great being dual-band for civil and milair - although milair bandwidth is tough to cover with just a thin wire. The oft-overlooked feature is the fm broadcast attenuation. The RH77 is not as good in this respect, lacking a loading coil to go way reactive on FM.

Before spending any cash, try just bypassing the coil on the RS telescopic first, and perhaps tweaking the last element. If that doesn't work, it may be time to either go for something like a "VHF Airblade" for a temporary/indoor/deck mount from DPD:

http://www.dpdproductions.com/page_vhf_air.html

Or, as you said, it may be time to go on the roof with something more permanent..

 

[sholt]

Thank you for the prompt and thorough reply, hertzian!

I tried bypassing the low-band vhf coil and it seems to have helped in terms of clarity of voice on some frequencies, based on a quick listen this morning before work. I'll try to get some more time in to see how much of an improvement it has made.

Thank you for the recommendation of the SRH320A - I might try to find somewhere with a good return policy to see if it helps if the radio shack coil trick isn't sufficient.

I have had my eye on the DPDP Airblade for a month or so now, but it has been hard to find reviews of it from more than one person. I may write to them directly with my situation and see if they can make a good call as to how much their product could/would help.

Then there's always VHF air band filters to try out too.. maybe I'll just start putting a little hobby money aside each month

Thanks again!

sholt

 

[nanZor]

...I tried bypassing the low-band vhf coil and it seems to have helped in terms of clarity of voice on some frequencies, based on a quick listen this morning before work...

Ok, we're getting somewhere now. With the coil shorted out, if you had FM broadcast or even NOAA wx overload, the problem would be even more severe. Since you have improved reception on some airband frequencies, I think we can rule out desense / overload.

Thank you for the recommendation of the SRH320A - I might try to find somewhere with a good return policy to see if it helps if the radio shack coil trick isn't sufficient.

Going from the shorted-coil RS whip to the 320A won't improve things now. In fact, it may even be a little worse than what is now a standard telescopic. Save your money, as no flexible antenna will produce a fantastically better signal.

I have had my eye on the DPDP Airblade for a month or so now, but it has been hard to find reviews of it from more than one person. I may write to them directly with my situation and see if they can make a good call as to how much their product could/would help.

That is an end-fed half-wave, which WOULD make a noticeable difference. But it would be hard to say if it would be enough for your situation. Personally, a quality-built airband-specific half-wave antenna like the DPD is where I'd put my efforts first as a baseline reference.

Then there's always VHF air band filters to try out too.. maybe I'll just start putting a little hobby money aside each month

With desense/overload ruled out, you can now save even more money without them. I think the best bet now would be to use the RS telescopic with the coil shorted out, and try to scout out locations where the signal is strongest / least noise. You may have to go up on the ladder or roof (BE SAFE). You can now get an idea if you could use an antenna that is better than essentially a quarter-wave telescopic. Also, you may have in-band noise sources that need to be hunted down. My latest capture in that area was a huge multi-LED bulb, that while quiet on HF, was a huge noise source from 30-300 mhz.

 

[sholt]

Great knowledge, thank you for clearing up what affects what.

I can get on my roof safely so I'll try that out. There is a sun chair up there so I'm sure I'm not the only one who has found access ;-)

If you'd be interested, perhaps we could work together on some flow charts in future? It might be useful for other relative beginners to visualize how you troubleshoot / the process you take to evaluate a situation and a really good asset for radioreference.com users?

 

[nanZor]

Well, we're not out of the woods yet. Take a trip to that rooftop deck-chair, short the RS whip coil out, and then test with your attenuator in and out of line. If the signals are better with the attenuator on, we've got some overload conditions in that new location.

A flow chart is a good idea, although I think other members here would be much better at it than I am. I have a tendency to be too verbose and redundant, verbose and redundant.